US20190350728A1

Movatterモバイル変換

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Publication number: US20190350728A1
Application number: US16/437,546
Authority: US
Inventors: Nicholas van der Walt; Jonathan Nielsen
Original assignee: Orthalign Inc
Current assignee: Orthalign Inc
Priority date: 2015-02-20
Filing date: 2019-06-11
Publication date: 2019-11-21
Also published as: US10363149B2; US11020245B2; JP2018506361A; JP2021087853A; CA3011960A1; AU2016219992B2; JP2023059904A; US20210315716A1; US20250017745A1; US12376972B2; EP3258860A4; US20220313455A1; JP6850256B2; WO2016134168A1; AU2016219992A1; US20180193171A1; US20160242934A1; EP3258860A1; JP7227289B2

Abstract

A hip joint navigation system is provided that includes a base having at least one channel disposed therethrough for receiving a pin for mounting the base to the pelvis. A mount feature is disposed on a top surface. A registration jig is configured to couple with the base and to engage anatomical landmarks. In some aspects, a patient specific jig system for hip replacement is provided including an engagement surface formed to closely mate to acetabular bone contours of a specific patient and a registration feature configured to be in a pre-determined orientation relative to an acetabulum the patient when the jig is coupled with acetabular bone contours of the specific patient. In other aspects, methods of using the systems are provided.

Description

BACKGROUND OF THE INVENTIONField of the Invention

This application is directed to the field of hip replacement, and particularly to surgical tools and methods for guiding the preparation of the bones in connection therewith.

Description of the Related Art

Hip replacement surgery is common and getting more common by the year. One persistent issue with hip replacement is the relatively high incidence of poor placement of the cup and ball components of the prosthetic hip joint. For example, the cup is optimally placed in a specific alignment with a plane including a rim of the acetabulum of the pelvis. For several reasons an unacceptably high percentage of patients have the cup of the artificial hip joint out of alignment with this plane.

Unfortunately, misalignment can lead to dislocation of the hip as soon as within one year of the implantation procedure. This is particularly problematic because recovery from a hip procedure can take many months. Patients undergoing a revision so soon after the initial implantation will certainly be dissatisfied with their care, being subject to addition redundant surgery. Of course, all surgery carries some degree of risk. These poor outcomes are unsatisfactory for patients and surgeons and are inefficient for the healthcare system as a whole.

Also, in cup placement in total hip arthroplasty, the inclination and anteversion angles are with respect to the Anterior Pelvic Plane (defined as a plane created by the two anterior superior iliac spines (ASIS) and the pubic symphysis). While these anatomical features are visible/palpable while the patient is in a supine position, the majority of total hip replacements are accomplished via a posterolateral approach with the patient in some variation of a lateral position, in which most of these landmarks are not accessible or visible. Historically, navigation for posterior approach hip replacement has been accomplished by registering the anatomical features of the Anterior Pelvic Plane with the patient first in a supine position and, once this plane is recorded by the navigation computer, moving the patient to a lateral position in order to perform hip surgery—with navigation performed with respect to the directly registered Anterior Pelvic Plane. This approach to hip navigation is sub-optimal for surgical workflow because the extra movement of the patient from supine to lateral position takes more surgeon and staff time and requires breaking sterility and re-draping. This is one of the key reasons why hip navigation has failed to be adopted by most of the market.

Additionally, altered leg length is a common patient complaint arising from hip replacement surgery and has been a common cause of medical malpractice lawsuits that arise from hip replacement. Because part of the hip replacement procedure requires precise measurements of patient leg length and joint off-set that are frequently difficult to visualize utilizing conventional instrumentation, there are opportunities to improve the surgeon's performance of these measurements using computer technology.

SUMMARY OF THE INVENTION

There is a need for improved systems and methods for providing for proper alignment of hip components with a patient's anatomy during a hip replacement procedure. This can involve modular systems with low profile components. This can involve a camera component designed to read a length measurement. This can involve techniques for measuring leg length and joint offset. This can involve techniques for locating one or more points on a fixed femur tracker.

In some embodiments, a hip joint navigation system is provided. The hip joint navigation system can include a base comprising at least one channel disposed therethrough for receiving a pin for mounting the base to the pelvis and a mount feature disposed on a top surface. The hip joint navigation system can include a registration jig configured to couple with the base and to engage anatomical landmarks.

In some embodiments, a femur jig is provided. The femur jig can include a base configured to securely couple with a proximal aspect of a femur. The femur jig can include a reference frame member configured to be disposed above the base having a plurality of reference frame targets. In some embodiments, the base has at least one aperture therethrough configured to receive threaded pins to secure the base to the femur. In some embodiments, the member is removably mountable to the base and comprises an elongate upright member and an angled portion configures to be oriented generally along the long axis of the femur. In some embodiments, the base is configured to be attached to the proximal femur within an incision prior to dislocation of the hip. In some embodiments, the reference frame member is accessible by a reference probe coupled with the pelvis in use.

In some embodiments, a sensor unit for orthopedic navigation is provided. The sensor unit can include a housing having an elongate structure. The sensor unit can include an inertial sensor disposed at least partially disposed within the housing. The sensor unit can include a camera at least partially disposed within the housing, the camera oriented transverse to a longitudinal axis of the housing. In one embodiment, the sensor unit has a transparent area on a side surface thereof.

The sensor unit with a camera disposed in the housing can be combined with one or more other components in one or more systems. A system that includes the sensor unit can be coupled with a jig that includes a coupler that holds the sensor unit fixed relative to a device to be observed by the camera. The sensor unit can be oriented with its width or height extending along an extendable probe. The jig can include a sliding bearing for allowing the probe to be moved along a range and while being moved to pass through a viewing area toward which the camera is directed. The probe can include a binary code or other symbol that the camera can read. In another system the sensor unit is coupled with a user interface device. The user interface device can be located inside the surgical field in use. The user interface device can be coupled with a jig configured to mount to a bone, e.g., a pelvis, in use.

In some embodiments, a method of orthopedic navigation is provided. The method can include the step of detecting the orientation or positioning of a probe using inertial sensor. The method can include the step of detecting the extension of a probe using a camera. In some embodiments, the camera is positioned directly above the probe.

In some embodiments, a patient specific jig system for hip replacement is provided. The patient specific jig system can include an engagement surface formed to closely mate to acetabular bone contours of a specific patient. The patient specific jig system can include a registration feature configured to be in a pre-determined orientation relative to an acetabulum the patient when the jig is coupled with acetabular bone contours of the specific patient.

The patient specific jig system can include an anatomical engagement portion. The patient specific jig system can include a registration portion disposed laterally of the anatomical engagement portion such that the registration portion is disposed in a zone outside the acetabular rim. The patient specific jig system can include a registration channel extending from an anterior surface of the registration portion toward a posterior surface of the registration portion.

The patient specific jig system can include a mount base configured to be coupled with the pelvis adjacent to the acetabulum but spaced apart from a closest portion of the jig when the engagement surface is in engagement with acetabular bone contours. The patient specific jig system can include an inertial sensor device. In some embodiments, the registration feature comprises a recess extending from an exposed face of the jig. The patient specific jig system can include a channel extending posteriorly from an anterior side of the jig, the channel configured to receive a mounting pin of a navigation system. The patient specific jig system can include at least two channels extending posteriorly from an anterior side of the jig, the channel configured to receive a mounting pin of a navigation system. In some embodiments, the channels are disposed at an orientation related to a plane of the acetabulum.

In some embodiments, a patient specific method is provided. The method can include the step of coupling a patient specific jig to a rim of the acetabulum. The method can include the step of registering the orientation of a proxy for the plane of the acetabular rim using an inertial sensor device coupled with the patient specific jig. The method can include the step of removing the patient specific jig from the acetabulum. The method can include the step of orienting an acetabular shell in the acetabulum using an impactor and an inertial sensor device, wherein during orienting, inertial data from the inertial sensor device is used to confirm a proper orientation of the acetabular shell.

The method can include the step of mounting an articulated member to the pelvis and coupling the laser projecting device to the articulated member. In some embodiments, the articulated member comprises a ball joint. The method can include the step of articulating the laser projecting device to direct the laser light onto a portion of a foot of the leg. The method can include the step of locking the articulating member into a fixed configuration and maintaining the fixed configuration from at least step projecting a laser light onto the leg to illuminate a portion of the leg away from the hip joint to step projecting the laser light onto the leg and/or foot to confirm orientation of the femur relative to the pelvis. In some embodiments, recording comprises marking three points on the surface of the leg and foot coincident with the laser light. In some embodiments, recording comprises capturing a photographic image of the laser light and the leg and/or foot. In some embodiments, registering the portion of the proximal femur comprises registering the femur at the greater trochanter. In some embodiments, the step of projecting the laser light onto the leg and/or foot to confirm orientation of the femur relative to the pelvis includes recreating the recorded position by lining up the incidence of light with the leg and or foot. The method can include the step of constraining the motion of the foot relative to the lower in leg in at least one of step of recording the position of incidence of the laser light and projecting the laser light onto the leg and/or foot to confirm orientation of the femur relative to the pelvis. In some embodiments, the laser projecting device is disposed in a housing including an inertial measurement unit.

In some embodiments, a method of performing a hip joint replacement procedure is provided. The method can include the step of mounting a laser projecting device to the pelvis adjacent to the hip joint. The method can include the step of registering a portion of the proximal femur adjacent to the hip joint. The method can include the step of projecting laser light from the laser projecting device onto the leg and/or foot to confirm correspondence between pre-operative orientation of the femur and pelvis and the post-operative orientation of the femur and pelvis. The method can include the step of registering the portion of the proximal femur adjacent to the hip joint to confirm leg length and/or off-set.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages are described below with reference to the drawings, which are intended to illustrate but not to limit the inventions. In the drawings, like reference characters denote corresponding features consistently throughout similar embodiments.

FIG. 1 is a perspective view of a hip navigation system applied to a patient illustrating a measurement of leg length and/or joint offset after implantation of the prosthetic hip joint.

FIG. 2 is an image of hip anatomy illustrating some examples of anatomical landmarks that can be used in a method of navigating a hip prosthesis with the navigation system ofFIG. 1.

FIG. 3 shows a navigation base assembly coupled with a first anatomical landmark, in this case the ilium on the pelvis of the patient.

FIG. 4 is a perspective view illustrating first and second orientation detecting devices coupled with the base ofFIG. 3.

FIG. 5 is a perspective view of the navigating system, illustrating one technique for synchronizing a plurality of orientation and/or position detecting devices of the navigating system ofFIG. 1.

FIG. 6 is a perspective view of the navigation system ofFIG. 1 coupled with the pelvis and illustrating a step of registering a landmark of a femur prior to resecting the femur.

FIG. 7 shows the anatomy after the femoral head has been resected and an optional step of synchronizing a plurality of inertial sensors of the navigation system.

FIG. 8 illustrates a step of registering an anatomical landmark disposed about the acetabular rim on the pelvis.

FIG. 9 illustrates a step of registering another anatomical landmark disposed about the acetabular rim of the pelvis.

FIG. 10 illustrates initial placement of an impactor in the acetabulum.

FIG. 11 illustrates a hip prosthesis placement system, including an inertial sensing device.

FIGS. 11A-11C illustrate an embodiment of an impactor assembly.

FIG. 12 illustrates a step of navigating placement of a cup portion of an artificial hip joint.

FIG. 13 is a perspective view of another embodiment of a hip navigation system.

FIG. 14 is a detail view of portion of the system ofFIG. 13, with a camera recording linear position of a registration arm.

FIG. 15 shows a variation of the embodiment ofFIGS. 13 and 14 in which rotational orientation and linear position can be acquired by a camera viewing a radial scale.

FIG. 16 is an exploded view of an assembly showing a tilt/rotation mechanism adapted to enable a camera to track at least one rotational position.

FIGS. 17-17C-2 illustrate modified systems configured for navigating a posterior approach hip replacement procedure.

FIG. 18 is a perspective view of a hip navigation system applied to a patient.

FIG. 19 is a perspective view of a fixation pin of the system ofFIG. 18.

FIG. 20A-20H illustrate various view of embodiments of a fixation base ofFIG. 18.

FIG. 21A-21G illustrate various view of embodiments of a first assembly ofFIG. 18.

FIG. 22A-22F illustrate various view of embodiments of a second assembly ofFIG. 18.

FIG. 23A-23C illustrate various view of embodiments of an orientation sensing device ofFIG. 18.

FIG. 24A-24B illustrate various view of embodiments of a femur tracker ofFIG. 18.

FIGS. 25A-25C are views of a hip navigation system applied to a patient.

FIG. 26A-26C illustrate various view of embodiments of a fixation base ofFIG. 25A.

FIG. 27A-28C illustrate various view of embodiments of a femur tracker ofFIG. 25C.

FIG. 29 is a pre-operative x-ray.

FIG. 30 illustrates pre-operative positioning of a patient for a posterior approach technique.

FIG. 31 illustrates a configuration of the system ofFIG. 18.

FIG. 32 illustrates anatomical landmarks registered during some embodiments.

FIG. 33 illustrates a first set of points on the rim of the shell.

FIGS. 34-38 illustrate a hip navigation system configured for anterior approach hip replacement procedures, and various aspects of such procedures.

FIG. 39 illustrates the positioning of the system ofFIG. 18 in an anterior approach.

FIGS. 40-42 illustrate the positioning of another hip navigation system in an anterior approach.

FIGS. 43-52 illustrate various aspects of methods involving patient-specific positioning jigs.

FIGS. 53-60 illustrate various aspects of methods involving patient-specific positioning jigs.

FIGS. 61A-63 illustrate various aspects of methods involving patient-specific positioning jigs.

FIG. 64 illustrates methods for defining a patient-specific safe zone in a hip placement procedure.

FIG. 65 is an embodiment of a system for close range optical tracking.

FIGS. 66-67 illustrate various anatomical landmarks that can be used in various methods involving navigating with landmarks.

FIG. 68 is a pre-operative image that can be used to enhance alignment in a hip procedure by providing patient specific data.

FIGS. 69 and 70 are views of a hip procedure navigation system applied to a pelvis in a posterior approach.

FIGS. 71 and 72 are view of the hip procedure navigation system ofFIG. 69-70 modified and applied to a pelvis in an anterior approach.

FIGS. 73-73A illustrate a first embodiment of pin securement devices.

FIGS. 74-74B illustrate a second embodiment of pin securement devices.

FIGS. 75-75B illustrate a third embodiment of pin securement devices.

FIGS. 76-80 illustrate a modular system with an optical component.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A variety of systems and methods are discussed below that can be used to improve outcomes for patients by increasing the likelihood of proper placement of a hip joint. These systems can be focused on inertial navigation techniques, close range optical navigation, or a combination of inertial and optical navigation.

I. Hip Navigation Using Inertial Sensors

Systems and methods described below can improve prosthetic hip joint placement using navigation in connection with referencing anatomical landmarks, incorporating preoperative custom fit jigs based on imaging, and a combination of pre-operative imaging and landmark referencing. These hip procedures generally guide a prosthetic hip to an orientation within the acetabulum that minimizes the chance of dislocation due to impingement of the femoral neck on the cup or on bones around the acetabulum or other reasons related to suboptimal orientation of the prosthetic. Various techniques leverage population averages of proper placement while others are amenable to patient specific refinements. Also various techniques for registering and confirming the position and/or orientation of the femur pre- and post-implantation are discussed herein, which are useful to control leg length and joint offset at the end of the procedure.

A. Navigation Using Inertial Sensors and Jigs for Referencing Anatomical Landmarks with Posterior Approach

Most hip replacement procedures presently are performed from a posterior approach. In this approach, the patient is positioned on his/her side and the anterior pelvic plane is oriented vertically, e.g., perpendicular to the plane of the table on which the patient is positioned. Most surgeons performing hip replacement are very familiar with this approach and will immediately recognize the benefit of enhanced certainty about the orientation of the relevant anatomy when the patient is in this position.

1. Posterior Approach: Systems with an Orientation Sensing Device Coupled to a Probe

FIGS. 1 and 4 show ahip navigation system100 adapted to navigate a hip joint procedure with reference to anatomical landmarks without requiring, but not necessarily excluding, pre-operative imaging or other inputs apart from those discussed below. Thesystem100 is shown mounted on a pelvis in a posterior approach inFIG. 1.FIG. 4 shows an early phase of a procedure prior to the joint being dislocated but after the system10 is mounted to the pelvis.FIG. 1 shows a late phase of some variations of techniques for which thesystem100 is adapted. As discussed further below, such variations involve registering the femur prior to and after the joint is replaced to confirm an aspect of the relative position and/or orientation of the femur, e.g., leg length, joint offset, and rotational orientation of the femoral neck.

Thesystem100 includes aregistration jig104, analignment assembly108 and alandmark acquisition assembly112. Thealignment assembly108 is rigidly connected to the hip in the illustrated configuration so that motion of the hip cause corresponding motion of sensor(s) in theassembly108 as discussed below. Sensing this motion enables thesystem100 to eliminate movement of the patient as a source of error in the navigation. Thelandmark acquisition assembly112 provides a full range of controlled motion and sensor(s) that are able to track the motion, in concert with sensor(s) in theassembly108. Additional details of systems, devices, sensors, and methods are set forth in U.S. Pat. No. 8,118,815; US US2010/0076505; and U.S. Pat. No. 8,057,479 which are all incorporated by reference herein in their entireties for all purposes. The sensors in

assemblies

108,112 preferably transfer data among themselves and in some cases with external devices and monitors wirelessly, using Bluetooth, Wifi® or other standard wireless telemetry protocol.

Theregistration jig104 includes afixation cannula124 that has a distal end that can be advanced to a pelvic bone at an anatomical location or landmark or other selected location. In the illustrated technique, thecannula124 is secured by a pin132 (seeFIG. 3) that is driven into the ilium on the pelvis through thecannula124. Adistal end128 of thepin132 is shown inFIG. 1.

As discussed further below, thecannula124 can be coupled with other bones in other techniques with a posterior approach. For example, thecannula124 can be coupled with the ischium or the pubis in other techniques. In some techniques, thecannula124 is mounted to a pelvic bone but not at a landmark. Thehip navigation system450 discussed below in connection withFIG. 17-17C-2 can be used such that thefixation member466 is coupled at a point superior to the superior-most point on the acetabular rim. In a specific technique, themember466 is about 10 mm above the superior-most point on the acetabular rim. In such techniques, three or more anatomical landmarks disposed about the acetabulum can be acquired, as discussed below. When thecannula124 is coupled with a landmark, only two additional landmarks are acquired in some embodiments as discussed below. In another variation, a clamp can be used to couple with a bone without requiring that thepin132 be driven through thecannula124 into the bone. For example, if the bone is thinner in the region where thesystem100 is to be anchored, placing the pin may be disadvantageous.FIG. 2 shows a region where a clamp may be used beneath the point “A” on the ischium. One reason for mounting or clamping thecannula124 away from the landmarks is that the landmarks may not be visible or accessible before dislocating the hip joint. If the clinician wishes to use thesystem100 to reference the femur (as discussed below), it may be required to mount or clamp thecannula124 away from the landmarks.

FIG. 1 illustrates a step toward the end of a navigated hip joint implant procedure discussed in detail below. Some of the preceding steps involve removing the to-be-replaced joint, navigating the hip joint, preparing the implant location for the artificial joint, and placing the joint, as elaborated below. As discussed further below,FIG. 1 illustrates a technique for confirming that these steps were properly performed.

FIG. 2 shows some of the anatomy that is relevant to various methods and systems herein. In some embodiments, thenavigation system100 is configured to locate a relevant anatomical feature to aid in proper placement of a prosthetic hip joint. For example, a plane can be located using thesystem100 that includes at least a portion of a patient's acetabular rim. In practice, the acetabular rim may be uneven due to development of ostephytes. So, in the context of this application locating the anatomical plane can be an approximation of the actual topography, for example an estimate of the plane, a plane including a substantial fraction, e.g., a majority of the surface of the acetabular rim, or some other manner of estimating a relevant anatomical feature. Preferably the anatomical landmark being located is used to confirm accurate placement of at least the cup and preferably the complete artificial hip joint.

FIG. 2 also shows an example of anatomical landmarks that can be used to approximate the acetabular rim or another plane relevant anatomical landmark. In many patients the acetabular rim is not well defined, due to injury, advanced stages of arthritis or other conditions. Accordingly, approximating the acetabular rim for these patients includes calculating in the system100 a plane that references but may not include most or any of the actual acetabular rim. The plane that is defined is located near the rim but more importantly has a known anteversion and abduction angle relative to the anterior pelvic plane. For example, three points can be used to estimate the plane of the acetabular rim. In one technique, some or all of the points illustrated inFIG. 2 are used.

As illustrated byFIG. 2, three landmarks are defined at “A”, “B”, and “H”. The landmark “H” is located on the ilium at a location that is spaced away from the rim by an amount sufficient to avoid irregular bony growth due to injury, advanced stages of arthritis or other conditions, for example 1 cm superior to the most superior point on the acetabular rim. The landmarks “A” and “B” can be located on the ischium and pubis respectively and can be similarly spaced from the rim to avoid damaged/diseased areas. Each of these landmarks preferably is close enough to the rim, however, to be within the standard open area, e.g., the area exposed by the surgical cut down. Other landmarks that could be used include: anterior insertion point of trans-acetabular ligament to the ischium, mid-point of the inferior aspect of the acetabular notch, the anterior superior iliac spine, anterior inferior iliac spine, convergence of the acetabulum and anterior inferior iliac spine, as well as the other landmarks illustrate onFIGS. 66 and 67. In the techniques discussed below all of the ilium, the pubis, and the ischium are used to locate the acetabular rim. Thenavigation system100 has one or more processors that receive(s) data and determines the relative position of these (or other) anatomical landmarks from these points. The data can be generated by inertial sensors, as discussed elsewhere herein, or other types of sensors. Preferably the sensors are small enough to be mounted on or in handheld housings or embedded in the instruments. Thenavigation system100 preferably also has a memory device to at least temporarily store the position of these points or relevant orientation data.

FIG. 3 shows further details of theregistration jig104 and further aspects of methods of navigating an artificial hip joint. A proximal end of thepin132 is coupled with or disposed above aplatform136 that is configured to couple with thealignment assembly108 and/or thelandmark acquisition assembly112. As shown inFIG. 1, theplatform136 can be connected to both of thealignment assembly108 and thelandmark acquisition assembly112 at the same time. Theplatform136 comprises a rigid bar fixed to the proximal end of thepin132 and/or thecannula124 in the illustrated embodiment. Theplatform136 includes a plurality of mount features140A,140B, e.g., a mount feature on each of two lateral ends144A,144B of the platform. Themount feature140A is configured to permit non-rotational attachment to thealignment assembly108.

FIG. 3 illustrates that theregistration jig104 is configured to be used in left and right hip procedures, for example having adedicated mount feature140A for each hip. Preferably themount feature140A provides a post spaced away from the joint being treated so that thealignment assembly108 can be mounted as far away from the hip joint as possible.FIG. 5 shows thealignment assembly108 on this post and another post exposed. The exposed post is not used during the procedure on the hip joint illustrated inFIG. 5. However, if the other hip of the patient is being treated, theplatform136 is in the opposite orientation and the posted exposed inFIG. 5 will be coupled with thealignment assembly108. Stated another way, a longitudinal axis of theplatform136 extends between two mount posts, each of which can be dedicated to a hip on one side of the medial-lateral mid-plane of the patient.

Themount feature140B enables rotational mounting of thelandmark acquisition assembly112. For example, themount feature140B can include a pivotally mountedjig148 that projects upward to a free end that is adapted to mate with an orientation sensing device as discussed below. The joint148 permits a registration arm, such as theelongate member224 discussed below to be tilted downward to touch landmarks at different elevations.

In one technique, theregistration jig104 is preassembled and is driven into a suitable anatomical landmark, such as the ilium. In other techniques, an anchor jig can be mounted off-set from a landmark to be acquired. The ilium will have been previously identified by conventional means, such as by X-ray examination, palpation, or by making an incision and visually inspecting the pelvis. In one technique, thecannula124, thepin132, and theplatform136 are separable so that the pin can be placed and theplatform136 coupled to the pin at a later time. Thecannula124 can be coupled with other landmarks in some variations.

FIG. 4 illustrates further steps of various techniques. For example, thealignment assembly108 can be coupled with themount feature140A. In one embodiment, thealignment assembly108 includes arigid extension160 that is adapted to be mounted detachably to themount feature140A. Theextension160 has afirst end164 and asecond end168. Thesecond end168 is detachably mountable to asurgical orientation device172 that detects orientation and rotation of thedevice172 relative to a reference frame. Theorientation device172 preferably comprises at least one sourceless sensor, such as an accelerometer, a gyroscope, or a combination of these sensors and other sensors. In one preferred embodiment, the orientation device includes a three axis accelerometer to detect orientation relative to gravity and a plurality of gyroscopes to detect rotation. Other sensors could be used in various modifications. Examples of specific sensor combinations include Analog Devices ADIS 16445 and Invensense MPU-6050 or MPU-9150 among others. In some approaches, theorientation device172 can be disposable and so the sensors preferably are less expensive sensors. Sensors on thelandmark acquisition assembly112 may be reusable in some configurations and thus may incorporate more expensive, more rugged or more accurate sensors.

Thefirst end164 of the detachable extension provides several functions. Thefirst end164 has a device to engage themount140A in a secure but releasable manner. The engagement between theextension160 and theplatform136 minimizes or prevents relative movement therebetween to avoid any mechanical relative movement during navigation procedures so that movement of theorientation device172 corresponds to movement of the hip. Thefirst end164 also has a docking device that, as discussed further below, provides a stable and controlled manner to position thelandmark acquisition assembly112 relative to theorientation device172.

FIG. 4 also illustrates that thelandmark acquisition assembly112 can be securely coupled to theplatform136, e.g., at themount140B. In one embodiment, thelandmark acquisition assembly112 includes agimbaled jig200 and anorientation sensing device204. Thejig200 includes acoupler208 for detachably coupling with themount feature140B of theplatform136. Thecoupler208 is pivotally connected to a slidingsupport212. The slidingsupport212 includes a slot that permits slideable extension of anelongate member224. The slideable extension permits a range of motion of adistal end228 of the elongate member to facilitate acquiring a plurality of landmarks that are different distances from the attachment location of thecannula124, as discussed further below. In other words, thedistal end228 can be extended away from the axis of the slidingsupport212 or can be retracted to a position closer to the axis of the slidingsupport212.

FIGS. 4 and 6 illustrate the moveability of thelandmark acquisition assembly112 relative to theplatform136 between two positions. InFIG. 4, theelongate member224 is swung about an axis that may be parallel to a longitudinal axis of thecannula124 to move thedistal end228 away from thefirst end164 of theextension160. This is a moving configuration of thegimbaled jig200. In addition to rotation enabled by the pivotal coupling between thecoupler208 and slidingsupport212, the pivotally mounted joint148 can enable theelongate member224 to pivot about an axis that is not parallel to the axis of thecannula124. The axis of rotation of the joint148 can be perpendicular to the axis of rotation of the slidingsupport212. This rotatability enables thedistal end228 of theelongate member224 to pivot down to contact anatomical landmarks, as discussed above. Additionally, the slideability of theelongate member224 within the slidingsupport212, discussed above, enables thedistal end228 to move to reach anatomical landmarks in the same plane but closer to or farther from the distal end of thecannula124 orpin132.FIG. 6 shows thedistal end228 of theelongate member224 positioned closer to theplatform136 for referencing landmarks at higher elevation or closer positions, e.g. on the lateral side of the femur.

FIG. 4 also shows that thedistal end228 can include an angled length that enables theelongate member224 to avoid minor irregularities in height adjacent to the anatomical landmarks being registered. Such irregularities may be normal anatomy, osteophytes or irregular bone growth of various types.

FIG. 5 illustrates a parkedconfiguration260 of thelandmark acquisition assembly112. In particular, a portion of theelongate member224 is moved into alatch262 disposed at thefirst end164 of theupright extension160. The parkedconfiguration260 enables thenavigation system100 to manage errors that can compound in some inertial sensors. For example, in one embodiment, gyroscopic sensors in theorientation device172 and in theorientation sensing device204 can be synchronized when a stable and known orientation is detected and one or more of the gyroscopes, e.g., the gyroscope in thedevice204, can be zeroed after that condition is met. Further techniques employing the parkedconfiguration260 will be discussed further below. As discussed below in connection with thesystem450, some jigs have a registration point adjacent to the distal end of the anchor jig or bone connection site. Thesystem450 is capable of accurately acquiring landmarks based on only accelerometers operating in thedevice204 in one mode. In such a mode, a registration feature can provide an analogous function to the parked configuration, e.g., to enhance accuracy of the sensing devices in the system.

Another example of a parked configuration of thesystem100 can be provided. For example, the parked configuration advantageously includes the ability to stably position and hold the

devices

172,204 for substantially no relative movement. In one approach, theorientation sensing device204 is mounted on therigid extension160. Other arrangements could include a mounting post on theplatform136 adjacent to therigid extension160.

Where error management is less an issue, the parkedconfiguration260 can still be useful in that it prevents unwanted swinging or other movement in the surgical field.

In one basic method, the jigs discussed above are connected to the pelvic bone, thesystem100 is put into the parkedconfiguration260, and the sensors are initialized. The initializing can include synchronizing at least two sensors. In some cases, the initializing can include zeroing one or more sensors. In this context, “zeroing” is a broad term that includes any method of eliminating accumulated error in the system, including any form of resetting of the sensors, and/or confirming in one device that the data from the other device is reliable for at least a fixed period.

FIG. 6 illustrates an optional step of acquiring a landmark of a femur in connection with a hip replacement procedure. The hip is positioned in a neutral flexion/abduction position. Thelandmark acquisition assembly112 is in a withdrawnconfiguration266 with theelongate member224 moved, such as by sliding in the slidingsupport212, to accommodate the relatively short distance from theplatform136 and a landmark of the proximal femur. In one technique the tip of thedistal end228 is brought into contact with a part of the greater trochanter or elsewhere on the proximal femur. After the landmark is found and/or contacted, the clinician can make a mark Fm on the femur, such as a bovie mark, a pen mark, a stitch or other durable indication. Once the tip of thedistal end228 is in contact with the desired landmark, thenavigation system100 processes data from and stores the orientation of one or more sensor(s) in theorientation sensing device204. Additionally, in some embodiments, theelongate member224 is provided with ascale226 indicating position of the tip of theelongate member224, e.g., relative to thecannula124 or some other relevant fixed feature of the patient or thesystem100. By providing thescale226 to be read by the clinician, the system is made simple and cost effective.

After the optional step illustrated inFIG. 6, the proximal femur can be resected to remove the natural ball thereon.

FIG. 7 illustrates that in one advantageous technique, the user returns thesystem100 to the parkedconfiguration260. This step may be optional depending on the sensor(s) and the timing of the resecting of the femur. In this position, the sensor(s) in the

orientation devices

172,204 can be initialized again, e.g., zeroed. As discussed above, this is one technique for minimizing accumulation of error in some inertial sensors. By providing this optional step, less costly sensors can be used enabling thesystem100 to deliver highly accurate hip replacement while helping to manage cost for the patient, medical provider and healthcare system generally.

FIG. 8 illustrates a firstextended configuration264 provided in a step after the resecting of the proximal femur in which a second anatomical landmark is acquired or referenced. In particular, theelongate member224 can be extended and can be rotated by the

jigs

148,200 to be in contact with any suitable landmark. In one technique, contact is made between thedistal end228 and the ischium. To provide maximum accuracy, this contact may be provided within a short period, e.g., within about 20 seconds of being disengaged from the parkedconfiguration260. Once contact is made, thesystem100 is configured to store the orientation of thesensing device204. In one configuration, the orientation is stored after a button or other indirect means is pressed on theorientation device172. In addition to acquiring the orientation, a position value is input to the system. For example, thescale226 on theelongate member224 can be read by the user and the value of the scale input into the system. In one technique where thescale226 is read and input by the user, theorientation device172 has a user interface with an input device for inputting such variables. As can be seen in the drawings, thescale226 can in fact be two different scales, one for each of the retractedconfiguration266 and theextended configuration264. Alternatively, thescale226 can extend the entire length of theelongate member224 to provide a greater range of positions that can be read by the clinician or by the system as inFIGS. 13 and 14.

Theextended configuration264 is one in which thedistal end228 of theelongate member224 is adapted to touch an anatomical landmark located between the medial cephalad-caudal plane of the patient and the acetabulum of the pelvis.

Depending on the sensors used and the timing of landmark acquiring step ofFIG. 8, the user may return thesystem100 to the parkedconfiguration260 and also may initialize, e.g., zero, thesystem100 again.

FIG. 9 illustrates a secondextended configuration272 provided in a step after the resecting of the proximal femur in which a third anatomical landmark is acquired or referenced. The third anatomical landmark can be acquired before the second anatomical landmark in some techniques. In the second extended configuration thedistal end228 of theelongate member224 moved to contact a landmark, such as the pubis. To provide maximum accuracy, this contact may be provided within a short period, e.g., within about 20 seconds of being disengaged from the parkedconfiguration260. Once contact is made, thesystem100 can store the orientation of thesensing device204. The orientation can be stored by pushing a button or other user interface device. In some techniques orientation and position are input into the system. For example, thescale226 on theelongate member224 can be read by the user and the value of the scale input into the system. In one technique where the scale is read and input by the user, theorientation device172 has an input device, such as a user interface for inputting such variables.

Theextended configuration272 is one in which thedistal end228 of theelongate member224 is adapted to touch an anatomical landmark located anteriorly of the acetabulum.

Once landmarks have been acquired, thesystem100 can determine the bearing of three landmarks including that of the attachment location of thecannula124, if the pin is attached to a relevant landmark. The system can calculate the orientation of theorientation device172 relative the plane containing these three (or in other methods another group of three or more) landmarks. From this, a variety of post processing can be performed. For example, the orientation (anteversion and/or abduction) can be adjusted based on the known mean orientation of the plane containing these three (or another three or more, if used) landmarks from the pelvic anatomic reference planes.

One variant of thesystem100 enables a user to select between multiple sets of landmarks for use in the above calculations. The method discussed above exploits the use of three points that are off of the acetabular rim. These points are less impacted by local prominences at the rim that may be due to disease or deformity. Thus, they have a lower likelihood of requiring intra-operative improvisation. On the other hand, another set of landmarks can be selected where the rim is free of deformities, which might be confirmed pre-operatively. For example, two or three points can be selected on the acetabular rim for landmark acquisition. The on-rim landmarks are advantageous in that they are easier to access through a smaller incision. For example, on-rim points can include the center of the posterior insertion of the transacetabular ligament, the center of the anterior insertion of the transacetabular ligament and the most superior point on the rim. A group of anatomical landmarks including one or more extra-acetabular landmarks can include the ilium (where theregistration jig104 or other anchor member can be inserted), the lowest point of the acetabular sulcus of the ischium, and the prominence of the superior pelvis ramus.

Some techniques involve referencing a fourth point. The fourth point can be used in connection with some forms of patient specific registration. The fourth point can be extra-acetabular or can be disposed on the acetabular rim. An example of an acetabular landmark is the acetabular notch. Other landmarks are discussed herein, for example in connection withFIGS. 34 and 35.

The posterior approach systems are advantageously configured to allow intra-operative selection between on-rim and off-rim points. For example, if the rim looks free of deformities pre-operatively but when exposed presents differently, the surgeon can select an off-rim landmark set.

Several techniques for enhancing the accuracy of the relationship between the sensed landmarks and the location of calculated anatomical features, such as the anterior pelvic plane or angle of the acetabulum can be employed. For example, user input can be collected indicating whether the hip being treated is on the left or the right side of the patient and whether the patient is male or female. A more refined estimation of the model can be provided based on a characterization of a study group. For example, hip joints of a group of 30 or more patients can be studied to identify the correspondence between a feature that can be accessed in one approach and an anatomical feature of more surgical relevance that cannot. A group of subjects can be studied for any number of demographic characteristics such as gender, age, weight, height or any other variable in a relevant population. For those sub-groups, a correlation or transformation between a measured parameter and a parameter that cannot be measured but is desirable to know can be generated. Once such a correlation or transformation is established, transforming a measured feature into the unmeasurable but useful to have feature can be achieved by operating software on a processor. The software can be programmed to calculate one or two angles, e.g., inclination and anteversion based on a registered pelvic plane, such as a proxy acetabular plane. Such a system can be used to generate in real time the angles of a free hand instrument relative to the anatomy, e.g., relative to an acetabulum in placing a hip socket component.

Additionally, data from the use of pre-operative imaging or positioning (discussed below) can be used to enhance the accuracy of these calculations. Thus, the posterior approach systems preferably are configured to take user input directly by actuating buttons on theorientation device172 or by connecting an auxiliary data storage device, such as a flash memory device, to the system or by any means of other communication with the system, including wifi connection, Bluetooth, Internet connection among others.

In some techniques, the posterior approach systems described herein are adapted to determine, monitor, and confirm proper leg length and joint offset outcome in a hip replacement. For example, thesystem100 can calculate and store components of a leg length metric, e.g., a vector along the superior-inferior axis (leg length) and/or along the medial-lateral axis (offset). In one approach, thedevice172 has a display that indicates when the femur is in the same position pre- and post-operatively. For example, it can indicate “0” meaning no displacement causing a leg length change and “0” indicating no movement of the femur farther away from the cephalad-caudal mid-plane of the patient pre- and post-operatively. For enhanced accuracy, a plurality of points, e.g., three points, can be marked acquired and/or marked on the femur. The points can be spaced apart by an amount sufficient to provide increased accuracy. These three points can be used to confirm proper placement of the femur in abduction, rotation, and flexion.

One enhancement involves referencing the femoral neck to assure that after implanting the hip joint, the femur is positioned properly rotationally. For example, it may be desired to make sure that a feature of the femur like the greater trochanter resides in the same rotational orientation relative to an axis extending through the center of rotation of the femoral head and perpendicular to the plane of the acetabulum. To assure a substantially unchanged rotation orientation post-implantation, thesystem100 can record one or more, e.g., three points on the femoral neck pre- and post-implantation. Three points that would be convenient from either the posterior approach or the anterior approach (discussed below in connection withFIGS. 18-24B) are the greater trochanter, lesser trochanter and the insertion of the obdurator externus.

The foregoing are some steps that can be used to determine and store a variety of parameters useful in a navigated hip procedures. After some or all of these steps have been performed, in one embodiment, the acetabulum can be prepared for receiving a cup. For example, the acetabulum can be reamed in a conventional manner. In some embodiments, the reamer can be coupled with an orientation device containing an inertial sensor to guide the reaming process. This is discussed in some detail in US2010/0076505, published march25,2010 which is incorporated by reference herein in its entirety for this purpose and for all disclosure therein generally.

FIG. 10 shows that after reaming, animpactor300 may be used to place a cup of an artificial hip joint. The impactor handle304 may be positioned in the approximate correct orientation, e.g., with a longitudinal axis of the impactor being disposed perpendicular to the plane navigated above or a plane determined based on the navigated plane.FIG. 10 shows that this initial placement can be done while thesystem100 is in thepark configuration260. Theimpactor300 can be substantially aligned at this time, based on visual inspection. As part of the step illustrated inFIG. 10 or shortly thereafter, the sensors can be initialized, e.g., zeroed as discussed above.

FIG. 11 shows that in a subsequent step theorientation sensing device204 can be undocked from the proximal end230 of theelongate member224 and thereafter docked to theimpactor300. Preferably this step is performed while theimpactor300 is in place on the hip, close the proper alignment. In another embodiment, a third sensing device similar to thesensing device204 be coupled with, e.g., pre-attached to, the impactor and the data collected above transferred to the third device. Theimpactor300 andsensing device204 comprise a cup orientation navigation assembly. Preferably theimpactor300 has acylindrical shell312 that is moveable relative to aninner shaft316 of thehandle304. The shell has adocking device320 that can receive the docking device of the sendingdevice204. The moveability of theshell312 helps to isolate thesensing device204 from the forces that are transmitted through theimpactor300. These forces are applied by a mallet or other device for forcibly moving the cup into position. By providing at least some force isolation between theshell312 and the sensing device, impact on the sensors in thesensing device204 can be reduced. Excessive force being applied to thesensing device204 can put thedevice204 out of service, for example until synched with thedevice172.

FIG. 11A illustrates a further embodiment of animpactor300A in which the movement of ashell312A is cushioned by a plurality of

spring members

340,344 which are configured to absorb at lease some of the shock of the impact on theimpactor300A. Theimpactor300A also is configured to be modified to suit any of a plurality of hip prostheses. For example, a plurality oftip components348 can be provided in a kit where each tip component is attachable to and detachable from a distal end of theshaft316A of theimpactor300A.

FIGS. 11B-C show more detail of distal features of theimpactor300A. In particular, thetip component348 is removable from ashaft316A of theimpactor300A.FIG. 11C shows that thetip component348 can have arecess352 formed on the proximal side thereof and anengagement device356 formed on the distal side thereof. Therecess352 can comprises a plurality offlats350A corresponding to a plurality offlats350B on the distal end of theshaft316A. The flats permit proximal-distal sliding of therecess352 over the distal end of theshaft316A. Preferably a detent device or other mechanism is provided between thetip component348 and theshaft316A so that the component does not fall off the shaft. The flats prevent thetip components348 from rotating relative to theshaft316A. Theengagement device356 comprises threads in one embodiment so that thecup360 of the prosthetic hip can be screwed onto the distal end of thetip component348. The sliding engagement of thetip component348 on theshaft316A is important because theimpactor300A is intended to be used with hip prostheses of a variety of manufacturers. Often thecup360 will have a hole pattern for securing the cup to the prepared acetabulum that is unique to the manufacturer and that is dictated by the anatomy. The flats enable many discrete alternate relative angular positions of the tip component348 (and hence the cup360) to theshaft316A. A plurality of flutes or elongateaxial ridges364 on the outer surface of thetip component348 enable the user to securely grasp the tip component for mounting and dismounting the tip component on theshaft316A.

FIG. 12 shows the cup orientation placement navigation assembly ofFIGS. 11A-C adjacent to the anatomy. This figure also illustrates a free-hand navigation configuration274, in which at least the

orientation devices

172,204 are capable of six degrees of motion relative to each other. Any of the variations ofFIG. 11A-11C could be substituted in the illustration. In particular, thehandle304 is oriented as desired. In one embodiment, thesystem100 displays in real time the angle of the cup relative to the navigated plane, which was acquired as discussed above. Angles that can be displayed include any one or more of anteversion and abduction for example. Preferably the clinician can confirm the position of the cup within a short fixed time, such as within about 20 seconds. In one embodiment, the angles displayed can be adjusted by about 40 degrees abduction and 20 degrees anteversion. These angles are not critical, but they relate to the range of motion of the leg. It is preferred to be close to these angles because motion in abduction and anteversion extends on either side of these angles. It is believed that the systems discussed herein can increase the percentage of patients in a “safe zone” close to these angles, typically described as within 10 degrees of these angles. In contrast, studies show that conventional techniques yield close to 50% of patients outside the “safe zone.”

Depending on the sensors and the timing of cup placement step ofFIG. 12, the user may mount thesensing device204 on theelongate member224 again and may return thesystem100 to the parkedconfiguration260 and also may initialize or zero thesystem100.

Thesystem100 can be configured to provide a pre- and/or post-operative estimation of an angle relative to the angle of the table. In the posterior approach, the patient is placed on his/her side. In this approach, there is more chance for the patient's position to shift intra-operatively. In one embodiment, an alignment rod can be coupled with thesensing device204 and aligned with the plane of the table. The orientation of thesensing device204 when so aligned is recorded in the system. Later in the procedure, one or more angles is calculated and displayed to the user based on the assumption that the pelvis has not moved. At such later stages, the orientation of thesensing device204 can be confirmed again relative to the table to provide information about whether the patient has moved. If significant movement has occurred, such that any assumptions of no movement are violated, some or all of the landmark acquisition steps can be repeated. Alternatively, the movement of the pelvis can be tracked by the sensing device and corrected for. The manner of incorporating the table orientation with landmark acquisition is discussed in greater detail below.

The user will have placed the artificial ball of the replacement hip join in the proximal femur and thereafter can place the ball in the cup, which was properly oriented using the techniques discussed above.

FIG. 1 shows that thereafter, the user can optionally confirm orientation and/or leg length using thesystem100. The leg with the artificial hip joint assembled is placed in a neutral flexion and/or abduction and/or rotation position. Theacquisition assembly112 can be placed in the retractedconfiguration266. Thedistal end228 of theelongate member224 can be brought into contact with a landmark, which may be the same landmark acquired inFIG. 6. Once contact is made with this landmark (e.g., the bovie mark), the orientation of thesensing device204 is determined by thesystem100. Also, the distance indicated on thescale226 of theelongate member224 is input into the system in any of the manners discussed above (e.g., manual or sensed). Thesystem100 can thereafter calculate components of vectors along the S-I axis (leg length) or M-L axis (offset).

Once leg length and offset are determined post-operatively, they can be compared the pre-operative measurements (FIG. 6) to let the surgeon know if any adjustments should be made before completing the hip replacement surgery.

FIGS. 13 and 14 show other embodiments of ahip navigation system400 that can include any of the features discussed above. In addition, thesystem400 includes a free-hand sensor mount404 that can be used to mount afreehand orientation device204A in one configuration. Thefreehand orientation device204A preferably includes inertial sensors, similar to those hereinbefore described. Thedevice204A preferably also includes acamera412. The field of view is illustrated by the cone projecting downwardly from the base of thefreehand orientation device204A.FIG. 14 shows that the field of view includes awindow418 in a slidingsupport420. Thewindow418 enables thescale226 to be viewed therethrough.

Because hip replacement procedures involve an open surgical field with a substantial amount of exposed tissue and blood the line of sight thecamera412 to the scales can become obstructed. In one embodiment, a hood is provided above thewindow418. The hood keeps most of the blood and tissue out of the space where the camera views the scales. Additionally, a scrubber component, e.g., a thin rubber member, can be provided above the

scales

226,226A (discussed below) to prevent this tissue or fluids from entering into the field of view laterally.

One advantage of thesystem400 is that thecamera412 can automatically process the image captured through thewindow418 and thereby determine the position of theelongate member224 relative to the slidingsupport420. A further advantage of this is to eliminate one step from the navigation process, e.g., to eliminate the need to enter the linear dimension into thesystem400. Eliminating the step can reduce time and/or personnel in the operating room. Also, thecamera412 can be configured to read a much higher resolution than can be read by a clinician. This can provide greater accuracy in the system overall. Not only that, but he camera can be configured to make fewer or no errors in reading the position, which can improve outcomes overall. For example, miniature cameras can produce data in JPEG or other image format that a processor in one or both the

orientation devices

172,204A can process to extract the linear position of theelongate member224.

A further modified embodiment is described inFIG. 15, which shows anarcuate scale226A that can be positioned on a structure beneath theelongate member224, e.g., on a structure beneath theorientation device204A that is rotationally fixed relative to an axis extending out of the page.FIG. 16 shows one configuration with this arrangement. Apivot440 enables the slidingsupport420 to rotate about an axis extending upward on the page. Although thepivot440 is fixed about this upward extending axis, it can rotate about apivot444. Awindow418A in theelongate member224 enables the camera to see through the support to view thescale226A disposed on an arcuate or disk shaped feature of thepivot440. Thescale226A can be read by thecamera412 or a second camera to provide accurate determination of the rotational position of theelongate member224. This can enable one of the sensors in theorientation device204A to be eliminated or inactivated. In another embodiment, camera date derived from thescale226A can be used to confirm the data from sensors in theorientation device204A. Preferably thescale226A has markings over a range of from about 15 to about 90 degrees, for example, between about 30 and about 60 degrees, e.g., at least between about 40 and about 50 degrees.

2. Posterior Approach: Systems Adapted for Accelerometer Sensitivity

FIGS. 17-17C2 illustrate further embodiments. Asystem450 is adapted for navigating a hip procedure from a posterior approach. Thesystem450 includes ananchor jig454, analignment system458, and alandmark acquisition assembly462. The components may be similar in some respects to those discussed above, and such descriptions are incorporated with this embodiment where consistent.

Thejig454 includes ahollow fixation member466 and aplatform468 for coupling a plurality of devices to the pelvis. The platform has a generally T-shaped configuration including afirst portion468A coupled with the proximal end of thefixation member466 and asecond portion468B disposed transversely to thefirst portion468A. Thefirst portion468A provides a support for acradle476 discussed further below. Thesecond portion468B can include a plurality ofdocking devices469 for coupling directly or indirectly with theorientation device172. The T-shaped configuration provides the advantage that thedocking devices469 can be disposed father away from the surgical site than is the case with thesystem100. This reduces any intrusion of theorientation device172 into the working field.

In some cases, thefixation member466 provides adequate stability in anchoring thesystem450 to the pelvis. In other situations, thejig454 can be coupled with the pelvis from thesecond portion468B. For example, aslot470 can be formed in thesecond portion468B on one or both sides of location where thefirst portion468A extends from thesecond portion468B. Theslots470 can extend from a lateral edge of thesecond portion468B toward location where thefirst portion468A extends from thesecond portion468B. Theslots470 can include a plurality ofchannels471 configured to receive fixation pins (e.g., Steinmann pins) that can be advanced into the pelvis. Thechannels471 extend generally parallel to thefixation member466. The fixation pins can be securely connected to thesecond portion468B in thechannels471 by aclamp device472. The clamp device can include a screw configured to draw the portions of thesecond portion468B on either sides of theslot470 toward each other and thus to create large frictional forces on the pins in theslots471.

Theslots470 preferably are aligned such that a plane extends along both of theslots470 along their length. Because theslots470 are long and slender this plane can be readily visualized in an X-ray image. It is preferred that thejig454 be aligned to the pelvis such that the plane extending along theslots470 is perpendicular to an axis of the patient (e.g., the intersection of the medial lateral plane and the transverse mid-plane of the patient). This feature provides a convenient way to visually confirm proper positioning of thejig454 in one embodiment.

Thefixation member466 includes aregistration feature473 and afoot474 adjacent to a distal end thereof and acoupling475 adjacent to the proximal end thereof for connecting to theplatform468. Thefoot474 includes a plurality of spaced apart spikes extending from a distal end thereof capable of preventing or limiting rotation of thejig454 when thefixation member466 is connected to the pelvis.FIG. 17 shows that securing thejig462 to the pelvis can include positioning a pin or other bone engaging device through thefixation member466. The pin and spikes extending from thefoot474 can provide three or more points of contact with the pelvis providing secure mounting of thejig462.

Thecoupling475 generally secures theplatform468 to thefixation member466. In some embodiment, thecoupling475 has a rotational capability that enables the platform to be positioned at selective locations about the longitudinal axis of thepin466, for example to enable theplatform468 to be initially positioned in the correct orientation or to be moved during or after the procedure to make space for other surgical devices. One arrangement provides matching splines that extend parallel to the longitudinal axis of thefixation member466. This arrangement would permit splines on an upper portion of thecoupling475 to be disengaged from splines on a lower portion of thecoupling475. When disengaged, theplatform468 and the upper portion of thecoupling475 can be rotated relative to the lower portion of thecoupling475. The splines can thereafter be re-engaged.

Thejig454 also preferably includes acradle476 that can be used to hold aprobe arm477. Thecradle476 includes a U-shaped recess having a width between two upright members that is about equal to the width of anarm477 of thelandmark acquisition system462.FIG. 17 shows theprobe arm477 in a parked configuration as discussed above. If thesensor204 operates with components that are prone to accumulated error sources, the parked configuration can be used to eliminate such error. As discussed above, thesystem450 can be configured such that the position and/or orientation of thesensor204 relative to theorientation device172 is known. Thus, when thearm477 is in thecradle476 any accumulated error of components of thesensor204 can be eliminated.

Thecradle476 can provide other convenient functions even if the sensing devices in thesensor204 are not subject to sources of accumulated error. As discussed elsewhere herein, for confirmation of accuracy of the system or to provide a simplified reference frame not requiring landmark acquisition, it may be desirable at some point of the procedure to use theprobe arm477 and thesensor204 to estimate the plane of the surgical table upon which the patient is resting. If, as discussed above, the plane intersecting theslots470 is oriented perpendicular to the axis of the patient when thejig454 is mounted to the pelvis, the cradle will be parallel to the axis of the patient. If thefixation member466 is oriented vertically, thearm477 will be parallel to the plane of the table when in thecradle476. Thesystem450 can thus use the plane of the table as a reference frame for guiding the placement of the cup without registering landmarks. Or, the plane of the table can be used in combination with registering the anatomy about the acetabular rim, as discussed above, to increase the accuracy of navigating the cup.

Thecradle476 also provides a convenient home position that keeps thearm477 stationary and out of the way of other surgical instruments.FIG. 17A illustrates theprobe arm477 withdrawn from thecradle476 and free to move into contact with landmarks.

Thejig454 also includes apivot feature478 that is disposed horizontally.FIG. 17B shows that thepivot feature478 includes twohorizontal apertures480. One of theapertures480 is formed in the same structure forming thecradle476 but at an elevation below thecradle476. Theother aperture480 formed between thecradle476 and a projection of thefixation member466.FIG. 17A shows that theprobe arm477 is connected to thepivot feature478 by ashaft482 that extends through the apertures. A movement device is provided between theshaft482 and thearm477 to enable a distal tip of the arm to be rotated about perpendicular axes and to be advanced linearly relative to thestationary jig454. One axis of rotation A of the movement device is disposed parallel to and at an elevation above theplatform468. Another axis of rotation B is disposed generally perpendicular to the axis A. Sliding of thearm477 is enabled by a snug but sliding fit of the arm in a housing C. By orienting the axis A in this manner, the sensitivity of accelerometers in thesensor204 to small angular motions references points about the acetabulum is heighted or maximized. This can enable landmark acquisition with thesystem450 based solely on accelerometers, which advantageously are not subject to accumulated error, which can simplify the landmark acquisition process.

Theregistration feature473 is a convenient way to enhance the accuracy of thesensor204. In particular, in one variation of the method discussed above, a distal tip of theprobe arm477 is brought into contact with theregistration feature473. In one embodiment, theregistration feature473 is a notch configured to receive and temporarily retain the tip. Thereafter, the user can interact with theorientation device172 to initialize accelerometers within thesensor204. Thereafter the points to be acquired can be sequentially contacted and the orientation and position of thesensor204 can be sequentially recorded in thesystem450. Because the accelerometers are initialized close to the points to be acquired, accuracy of the reading is enhanced as the angular error resulting from an error in the scale factor of the accelerometers is minimized due to the small arc from the registration feature. For example, thejig454 is configured to enable thelandmark acquisition assembly458 to reach all points to be registered by moving less than about 45 degrees from an initial or home position in some embodiments. In other embodiments, thejig454 is configured to enable thelandmark acquisition assembly458 to reach all points to be registered by moving less than about 25 degrees from the initial position. In other embodiments, thejig454 is configured to enable thelandmark acquisition assembly458 to reach all points to be registered by moving less than about 15 degrees from the initial position.

Thejig454 also is configured to interact well with the soft tissue that is disposed around the surgical site in the posterior approach. In this approach, an incision is made in soft tissue that is kept as small as possible. In one approach, thefixation member466 is positioned at the end of the incision. Where the incision is made as minimal as possible, thejig454 can also function as a retractor. The T-shaped configuration is particularly well suited for this function because thefirst portion468A of theplatform468 can be received between the middle and ring fingers of the user with thesecond portion468B in the palm of the hand. With thefoot474 gripping the pelvis, thejig454 can be tilted from theplatform468 away from the hip joint to retract the tissue away.

FIGS. 17C-1 and 17C-2 illustrate further embodiments of aposterior approach jig454A having a mountingdevice488 disposed adjacent to the distal end of afixation member466A, which is otherwise similar to thefixation member466. Thefixation member466A includes atubular body490 coupled with thefixation member466A, which in this embodiment acts as a primary fixation member. Thetubular body490 extends along a lumen that is angled relative to the lumen of thefixation member466A. The lumen in thetubular body490 is configured to accept afixation pin492 that can be driven into the bone, as illustrated inFIG. 17C-2 at an oblique angle. Thefixation pin492 supplements the fixation provided by thefixation member466A. Thefixation pin492 can be used in conjunction with the optional long pin(s) extending through thechannels471, e.g., into the ilium or as a substitute for that option. Thefixation pin492 has the advantage of not requiring any additional holes in the skin because it is located within the primary incision made to access the joint in the procedure. Thefixation pin492 can be threaded to engage the bone in one embodiment. In some embodiments, alocking device494 can be provided to secure thepin492 in the lumen of thetubular body490. A set screw is one example of alocking device494 that can be used. Thelocking device494 enables thefixation pin492 to be headless, which avoids issues with screw threads stripping the hole in the bone into which thepin492 is inserted.

3. Posterior Approach: Workflow Considerations

As noted above, a workflow problem arises in typical hip replacement procedures in that anatomical features that can be more easily references are unavailable in the traditional posterior approach for operating on the joint.

By performing a CT-based study of a large number of human pelvises, the assignee of this application has been able to calculate a population-based average relationship between multiple planes created by various points in, on or around the acetabulum that are accessible during posterior approach hip replacement (each plane, an “Acetabular Plane”), and the Anterior Pelvic Plane. One of the key features of posterior hip navigation for some embodiments disclosed herein is the ability of a module, e.g., software incorporated into a processor, which may be on a computer, or one or both of theorientation device172 andsensor204, to calculate a transformation from one reference frame to another. As described in more detail elsewhere herein, several points are referenced in, on or around the acetabulum and from these points a proxy Acetabular Plane is calculated.

Next, in certain embodiments described herein a module operable to process an algorithm, e.g., by executing software in one or both of theorientation device172 andsensor204 alone or with a separate computer, is able to calculate a transformation from the proxy Acetabular Plane to Anterior Pelvic Plane. The approach indirectly registers the Anterior Pelvic Plane without requiring a direct supine registration and subsequent patient movement and re-draping necessary in standard navigation. A module in certain embodiments described herein is then able to provide the user real time navigation data of the orientation of a hip instrument (e.g., the

impactors

300,300A) with respect to the Anterior Pelvic Plane.

In certain systems described herein, a further advantage is that the systems are able to implement the plane transformation algorithm to calculate an Anterior Pelvic Plane from one of any number of proxy Acetabular Planes that the surgeon chooses to register. This enables the surgeon to have greater flexibility in Acetabular Plane landmark selection to take into account the quality or accessibility of certain landmarks. For example, in cases of minimal deformity around the acetabular rim, the surgeon may choose to register landmarks around the rim, which are easily accessible. In cases where there is great deformity or high presence of osteophytes on the acetabular rim, the surgeon may instead choose to register an Acetabular Plane based on extra-acetabular landmarks (or described as “off-rim” elsewhere herein) outside of the rim that are unaffected by disease or prior hip replacement surgery.

Examples of anatomical landmarks that may be used to create a proxy Acetabular Plane and that are shown inFIG. 2 include but are not limited to:

Extra-acetabular landmarks (Ischiumillium/Pubis)

- (A) The lowest point of the acetabular sulcus of the ischium
- (B) The prominence of the superior pubic ramus
- (G) The confluence of the anterior inferior iliac spine (AIIS) and the outer border of the acetabular rim

Acetabular Rim Landmarks

- (E) The center of the anterior insertion of the trans-acetabular ligament
- (F) The center of the posterior insertion of the trans-acetabular ligament
- (H) The most superior point of the acetabular rim.

Additional points can be combined with either of the groups of points listed above. For example, in one embodiment, point “D” is used. Point D is the midpoint of the inferior border of the acetabular notch. As discussed in connection withFIG. 36 below, point D corresponds to thebottom landmark380B used to form theline382. Point D is used in that approach to provide patient specific refinements to the positioning.

A further key benefit of certain embodiment discussed herein is that the foregoing plane transformation capabilities increase the accuracy of the transformation between the proxy Acetabular Plane registered and the Anterior Pelvic Plane above the general population average data by the user inputting certain patient-specific information, such as gender.

Additionally, certain embodiments of systems including one or more of theorientation device172,sensor204, or a separate computer may have modules that are operable, e.g., by processing software, to allow the user to input an angular or plane relationship between an proxy Acetabular Plane and Anterior Pelvic Plane that the surgeon measured based on pre-operative imaging, allowing for a partial or whole plane transformation based on patient-specific data rather than population data. By way of example, the surgeon may choose to pre-operatively measure an angle created by (a) landmarks that are both visible on an A/P pelvis x-ray and that can be referenced during posterior hip replacement, and (b) landmarks that are both visible on the pelvis x-ray and that are directly associated with inclination measurement in the Anterior Pelvic Plane. If this angular relationship is inputted into a module of a system including one or more of theorientation device172, thesensor204, or a separate computer, which module is capable of making calculations processing software and the surgeon registers the landmarks described in (a), inclination navigation will be based specifically on that patient rather than a population average. Landmarks (D) and (H) listed above are examples of landmarks that are both visible on an A/P pelvis x-ray and that can be referenced to create a proxy Acetabular Plane in posterior hip replacement.

These aspects of the systems adapted for posterior approach hip joint replacement can greatly enhance both workflow and accuracy in such procedures.

4. Posterior Approach: Further Systems with an Orientation Sensing Device and Camera

FIG. 18 shows ahip navigation system600 adapted to navigate a hip joint procedure with reference to anatomical landmarks. Thesystem600 is shown mounted on a pelvis in a posterior approach inFIG. 18.FIG. 18 shows an early phase of a procedure prior to the joint being dislocated but after thesystem600 is mounted to the pelvis. Thesystem600 can be adapted for various techniques. As discussed further below, such variations involve registering the femur prior to and after the joint is replaced to confirm an aspect of the relative position and/or orientation of the femur, e.g., leg length, joint offset, and rotational orientation of the femoral neck. Thesystem600 can include any component described herein. Thesystem600 can be used in any technique or method step described herein.

Thesystem600 can include afixation base602, afirst assembly604 and asecond assembly606. Thefirst assembly604 is rigidly connected to the hip in the illustrated configuration so that motion of the hip cause corresponding motion of sensor(s) in thefirst assembly604 as discussed below. Sensing this motion enables thesystem600 to eliminate movement of the patient as a source of error in the navigation. Thesecond assembly606 provides a full range of controlled motion and sensor(s) that are able to track the motion, in concert with sensor(s) in thefirst assembly604. Additional details of systems, devices, sensors, and methods are set forth in U.S. Pat. No. 8,118,815; US US2010/0076505; and U.S. Pat. No. 8,057,479 which are all incorporated by reference herein in their entireties for all purposes. The sensors in

assemblies

604,606 preferably transfer data among themselves and in some cases with external devices and monitors wirelessly, using Bluetooth, Wifi® or other standard wireless telemetry protocol.

Thesystem600 can include one or more fixation pins. In the illustrated embodiment, afirst fixation pin610 and asecond fixation pin612 are shown. Other configurations are contemplated (e.g., one fixation pin, three fixation pins, four fixation pins, etc.). The fixation pins610,612 can be elongate structures.FIG. 19 shows thefixation pin610. In some embodiments, the fixation pins610,612 are identical or substantially similar. In some embodiments, the fixation pins610,612 are different and can be adapted to be inserted into different anatomic locations.

Thefixation pin610 can be substantially cylindrical, as shown inFIG. 19. Thefixation pin610 can have adistal end614 that can be advanced to a pelvic bone at an anatomical location or landmark or other selected location. In the illustrated embodiment, thedistal end614 is threaded. Thedistal end614 can include a sharpened tip designed to penetrate bone. Thefixation pin610 can have aproximal end616. Theproximal end616 can include attachments features to couple thefixation pin610 with a driver. In the illustrated embodiment, theproximal end616 includes a tri-flat shape designed to couple with a tri-flat socket. Thefixation pin610 can include one or more markings along the length of thefixation pin610. The markings can indicate the orientation of thefixation base602 relative to thefixation pin610.

Referring back toFIG. 18, each

fixation pin

610,612 can be driven into the ilium on the pelvis. As discussed further below, each

fixation pin

610,612 can be coupled with other bones in other techniques. For example, one of the fixation pins610,612 can be coupled with the ischium or the pubis. In some techniques, one of the fixation pins610,612 is mounted to a pelvic bone but not at a landmark. One of the fixation pins610,612 can be coupled at a point superior to the superior-most point on the acetabular rim. In some techniques, one of the fixation pins610,612 is about 10 mm above the superior-most point on the acetabular rim. In some techniques, three or more anatomical landmarks disposed about the acetabulum can be acquired, as discussed below. When one of the fixation pins610,612 is coupled with a landmark, only two additional landmarks are acquired in some embodiments as discussed below. One reason for mounting the fixation pins610,612 away from the landmarks is that the landmarks may not be visible or accessible before dislocating the hip joint. If the clinician wishes to use thesystem600 to reference the femur as discussed below, it may be required to mount the fixation pins610,612 away from the landmarks.

Thesystem600 can include thefixation base602 shown inFIGS. 20A-20H. Thefixation base602 can function as a clamp with the one or more fixation pins610,612.FIG. 20A shows an exploded view of thefixation base602.FIGS. 20B-20D show other views of thefixation base602. Thefixation base602 can include aplatform620 and asupport622. Theplatform620 can interact with thesupport622 to function as a clamp. In the illustrated embodiment, thefixation base602 can include one ormore fixation devices624. In the illustrated embodiment, two fixation devices are shown but other configurations are contemplated (e.g., one, three, four, etc.). Thefixation devices624 can include one or more threaded sections. In the illustrate embodiment, thefixation devices624 are screws with a head and a threaded shank. Theplatform620 can include one or more holes. Thesupport622 can include one or more holes. Thefixation devices624 can pass through or engage one or more holes in thesupport622. In some embodiments, each hole in thesupport622 is threaded. Thefixation devices624 can pass through or engage one or more holes in theplatform620. In some embodiments, each hole in theplatform620 is threaded. Rotation of thefixation devices624 can cause thesupport622 to move toward theplatform620 and/or theplatform620 to move toward thesupport622.

Theplatform620 and thesupport622 form one or more channels therebetween, as shown inFIG. 20C. The number of channels can correspond to the number of fixation pins. In the illustrated embodiment, afirst channel626 and asecond channel628 are shown. The channels extend from a top surface of theplatform620 and/or thesupport622 to a bottom surface of theplatform620 and/or thesupport622. The

channels

626,628 extend in a direction transverse to the direction of thefixation devices624 when thefixation devices624 are engaged with theplatform620 and thesupport622. Thefirst channel626 is sized to accept thefirst fixation pin610 and thesecond channel628 is sized to accept thesecond fixation pin612. Rotation of thefixation devices624 can cause thesupport622 to move toward theplatform620. The

channels

626,628 can decrease in diameter with the rotation of thefixation devices624. Upon rotation of thefixation devices624, each

fixation pin

610,612 is retained between theplatform620 and thesupport622. Thefixation base602 can includedivot630. Thedivot630 can be associated with a parked configuration or home position, as described herein. Thedivot630 is an example of a registration feature disposed on thesystem600.

Thefixation base602 can include afirst coupler632. Thefirst coupler632 can couple to one or more components of thesystem600. In some embodiments, thefirst coupler632 is a universal coupler. Thefirst coupler632 can include anelongate post635. In some embodiments, thefirst coupler632 can have a regular shape (e.g., cylindrical). In some embodiments, thefirst coupler632 can have an irregular shape (e.g., triangular, teardrop, elliptical, rectangular). The irregular shape may facilitate alignment of other components of thesystem600 with theplatform620 of thefixation base602. In the illustrated embodiment, the other components of thesystem600 can mate with thefirst coupler632 in a single orientation.

Thefirst coupler632 can include aslot634. Theslot634 can be transverse to the longitudinal axis of thefirst coupler632. Theslot634 can form an angle with an axis transverse to the longitudinal axis. This angle can be approximately 10°, between 5° and 15°, between 0° and 20°, etc. Theslot634 can be designed to interact with detents of other components of thesystem600, as described herein. Thefirst coupler632 can include atapered surface636. Thetapered surface636 can facilitate entry of thefirst coupler632 within other components of thesystem600. Thetapered surface636 can move the detent of other components of thesystem600 when thefirst coupler632 is inserter within the other component. As shown inFIG. 20A, thefirst coupler632 can include theelongate post635 coupled to a hole on the top surface of theplatform620. As shown inFIG. 20E, in an alternative embodiment, thefirst coupler632A is integrally formed with theplatform620. Apost632B can be inserted from a bottom surface of theplatform620 to support thefirst coupler632A.

Thesystem600 can include thefirst assembly604 shown inFIGS. 21A-21G. Thefirst assembly604 can include apelvic bracket638. In the illustrated embodiment, thepelvic bracket638 can be substantially vertical in use, as shown inFIG. 18. Thefirst assembly604 can be designed to couple with thefirst coupler632 of thefixation base602. Thefirst assembly604 can include alock lever640. Thelock lever640 can be coupled to thepelvic bracket638 with pivot pins. Thelock lever640 can be pivoted relative to thepelvic bracket638. In some embodiments, thetapered surface636 of thefirst coupler632 causes the pivoting of thelock lever640. In some embodiment, the surgeon causes the pivoting of thelock lever640. Thelock lever640 can include adetent642. Thedetent642 is sized and shaped to be received within theslot634. The engagement of thedetent642 and theslot634 can rigidly couple thefirst assembly604 with thefixation base602.

Thesurgical orientation device172 detects orientation and rotation of thedevice172 relative to a reference frame. Thesurgical orientation device172 preferably comprises at least one sourceless sensor, such as an accelerometer, a gyroscope, or a combination of these sensors and other sensors. In some embodiments, thesurgical orientation device172 includes a three axis accelerometer to detect orientation relative to gravity and a plurality of gyroscopes to detect rotation. Other sensors could be used in various modifications. Examples of specific sensor combinations include Analog Devices ADIS 16445 and Invensense MPU-6050 or MPU-9150 among others. In some approaches, thesurgical orientation device172 can be disposable and so the sensors preferably are less expensive sensors. In some embodiments, thesurgical orientation device172 is disposable.

Theextension644 can include asecond coupler648. In some embodiments, thesecond coupler648 is a universal coupler. Thesecond coupler648 can be substantially similar to thefirst coupler632 described herein. Thesecond coupler648 can be designed to couple with thesecond assembly606. The

couplers

632,648 are designed to secure to other components of thesystem600 in a secure but releasable manner. The engagement between thecoupler632 and thefirst assembly604 minimizes or prevents relative movement therebetween to avoid any mechanical relative movement during navigation procedures so that movement of thesurgical orientation device172 corresponds to movement of the hip. Thesecond coupler648 provides a stable manner to position thesecond assembly606 relative to thefirst assembly604.

Thesystem600 can include thesecond assembly606 shown inFIG. 22A-22F. Thesecond assembly606 can include aprobe bracket652. In the illustrated embodiment, theprobe bracket652 can be substantially angled with respect to thepelvic bracket638 when in use, as shown inFIG. 18. Thesecond assembly606 can be designed to couple with thesecond coupler648 of thefirst assembly604. Thesecond assembly606 can include alock lever654. Thelock lever654 can be coupled to theprobe bracket652 with pivot pins. Thelock lever654 can be pivoted relative to theprobe bracket652. In some embodiments, the tapered surface of thesecond coupler648 causes the pivoting of thelock lever654. In some embodiment, the surgeon causes the pivoting of thelock lever654. Thelock lever654 can include adetent656. Thedetent656 is sized and shaped to be received within the slot of thesecond coupler648. The engagement of thedetent656 and the slot can rigidly couple thesecond assembly606 with thefirst assembly604.

In the illustrated embodiment, thesecond assembly606 includes amount658. Themount658 can be coupled to theprobe bracket652 to allow relative movement therebetween. Themount658 can be received within an opening in theprobe bracket652. Themount658 can permit rotation about a longitudinal axis of themount658 relative to theprobe bracket652.

Thesecond assembly606 can include adock662. Thedock662 can be coupled to themount658 to allow relative movement therebetween. Thedock662 can be coupled to themount658 with one or more pivot pins660. Thedock662 can have two degrees of freedom relative to the probe bracket652 (e.g., rotational motion and pivoting motion). Thedock662 can include a sliding support with a throughlumen664. The throughlumen664 is sized to accept aprobe678. Theprobe678 has adistal end680 designed to touch locations, as described herein. Thedistal end680 can be straight as shown inFIG. 22A. In other embodiments, thedistal end680 is slanted or curved, e.g., as shown inFIGS. 4 and 17.

The throughlumen664 of thedock662 permits slideable extension of theprobe678. Thedock662 is movable relative to the probe bracket652 (e.g., via rotation of themount658 and pivoting of the pivot pin660). Thedock662 can be rotated about a longitudinal axis of themount658 to different rotational positions relative to the attachment location of the fixation pins610,612. This may require movement of themount658 in a rotational manner relative to theprobe bracket652. Thedock662 can be pivoted about the longitudinal axis of the pivot pins660 to different positions relative to the attachment location of the fixation pins610,612. This may require movement of thedock662 in a pivoting manner relative to themount658.

Theprobe678 can be coupled to thedock662 such that theprobe678 is movable relative to the probe bracket652 (e.g., via rotation of themount658 and pivoting of the pivot pin660). This maneuverability enables thedistal end680 of theprobe678 to pivot or rotate to contact anatomical landmarks, as discussed herein. Theprobe678 can be slid relative to thedock662 to different translational positions relative to the attachment location of the fixation pins610,612. The slideability of theprobe678 within thedock662 enables thedistal end680 to move to reach anatomical landmarks in the same plane of theprobe678 but closer to or farther from thedistal end680.

Thesecond assembly606 permits a range of motion of adistal end680 of theprobe678 to facilitate acquiring a plurality of landmarks that are different distances from the attachment location of the fixation pins610,612, as discussed further below. In other words, thedistal end680 of theprobe678 can be extended away from the axis of the sliding support of thedock662 or can be retracted to a position closer to the axis of the sliding support of thedock662.

Thedock662 can include athird coupler668. In some embodiments, thethird coupler668 is a universal coupler. In some embodiments, thethird coupler668 is identical or substantially similar to thesecond coupler648. This permits theorientation sensing device204 to couple to either thesecond coupler648 or thethird coupler668, as described herein. In some embodiments, thethird coupler668 can be substantially similar to thefirst coupler632 described herein. Thethird coupler668 can be designed to couple with theorientation sensing device204.FIG. 23A-23C illustrate an embodiment of theorientation sensing device204. Thesecond assembly606 can include anextension670. Theextension670 can couple to thethird coupler668 of thedock662. The engagement between thethird coupler668 and theextension670 minimizes or prevents relative movement therebetween to avoid any mechanical relative movement during navigation procedures. Theextension670 can include amount672 designed to couple with theorientation sensing device204. In the illustrated embodiment, themount672 includes a lock and release lever that can pivot relative to theextension670. Theorientation sensing device204 can include features to mate with the lock and release lever. Other configurations are contemplated. Theorientation sensing device204 is rigidly coupled to theextension670 when engaged with themount672.

Theorientation sensing device204 can be angled when coupled to thesecond assembly606, as shown inFIG. 18. Theorientation sensing device204 can be angled approximately 35° from the horizontal axis. Other angles from the horizontal axis are contemplated, (e.g., 5°, 10°, 15°, 20°, 25°, 30°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, or 85°, between 30°-40°, between 25°-45°). In some embodiments, the angle of theorientation sensing device204 improves visibility.

Theorientation sensing device204 detects orientation and rotation of theprobe678, as described herein. Theorientation sensing device204 preferably comprises at least one sourceless sensor, such as an accelerometer, a gyroscope, or a combination of these sensors and other sensors. In some embodiments, theorientation sensing device204 includes a three axis accelerometer to detect orientation relative to gravity and a plurality of gyroscopes to detect rotation. Other sensors could be used in various modifications. In some embodiments, theorientation sensing device204 is reusable.

Referring back toFIGS. 22A and 22C, theprobe678 can include a marking682. The marking682 can indicate length or extension of theprobe678 relative to thedock662. The marking682 can include a scale. In some embodiments, the marking682 can be over a range of from about 8 inches, 10 inches, 12 inches, approximately 8-12 inches, etc. The marking682 can be printed on theprobe678. In some embodiments, the marking682 can be on a separate component such as aprobe inlay676. Theprobe inlay676 can be received within a portion of theprobe678. In some embodiments, theprobe inlay676 is separated a distance from thedistal end680 of theprobe678.

Referring toFIG. 23C, thesystem600 can include acamera684. Thecamera684 can capture images of the marking682. In some embodiments, thecamera684 and/or theorientation sensing device204 can include a light to illuminate the marking682. In some embodiments, the light is a LED. In some embodiments, thedock662 includes a window to permit thecamera684 to capture images. In other embodiments, thecamera684 captures images of the marking682 extending beyond thedock662. Thecamera684 can read the marking682 to provide accurate determination of the translational position of theprobe678 relative to thedock662. This can enable one of the sensors in theorientation sensing device204 to be eliminated or inactivated. In another embodiment, camera data derived from the marking682 can be used to confirm the data from sensors in theorientation sensing device204.

In some embodiments, thecamera684 is integrally formed with theorientation sensing device204. In some embodiments, thecamera684 is a separate component from theorientation sensing device204. Thecamera684 can be held in a fixed position relative to thedock662. The marking682 can be positioned on theprobe678 beneath thecamera684 when theprobe678 is positioned within the throughlumen664. Thecamera684 can be directly above the marking682. Thecamera684 can be fixed relative to the throughlumen664 of thedock662. Thedock662, thecamera684 and theorientation sensing device204 can move as a unit to allow positioning of theprobe678. One advantage of orienting theorientation sensing device204 as illustrated insystem600 is improved visibility. The lower-profile construct is less likely to obstruct the user's view. One advantage of orienting theorientation sensing device204 as illustrated insystem600 is ease of manufacturing. Thecamera684 can be mounted flush on the circuit board. The corresponding transparent window (not shown), which can allow thecamera684 to capture images, in the housing of theorientation sensing device204 is oriented in the direction of the mold pull. The shorter distance to the marking682 also better accommodates the available camera, which has a short focal length. In some embodiments, thecamera684 captures an image though a lumen (not shown) in thedock662. One advantage of having thecamera684 read the marking682 through the lumen is this shields thecamera684 from outside light sources. Light, such as OR light, may interfere with the camera function such as the function of capturing an image of the marking682. In other embodiments, thecamera684 may incorporate a shroud feature to block ambient light. In some embodiments, thecamera684 is pointed downward from a back side of theorientation sensing device204. In some embodiments, theorientation sensing device204

shields camera

684 from light.

FIG. 18 illustrates a parked configuration or home position of theprobe678. In some embodiments, a portion of thedistal end680 is moved into engagement with theplatform620. In some techniques, thedistal end680 of theprobe678 engages thedivot630 of theplatform620. The parked configuration enables thenavigation system600 to manage errors that can compound in some inertial sensors. For example, the parked configuration advantageously includes the ability to position and hold the

devices

172,204 stable for substantially no relative movement. Also the relative position of the sensors in the

devices

172,204 when coupled with the first and

second assemblies

604,606 can be known from the geometry of thefirst assembly604 and thesecond assembly606. For example, in one embodiment, gyroscopic sensors in thesurgical orientation device172 and in theorientation sensing device204 can be synchronized when a stable and known orientation is detected and one or more of the gyroscopes, e.g., the gyroscope in theorientation sensing device204, can be zeroed after that condition is met. Further techniques employing the parked configuration will be discussed further below.

At the surgeon's discretion thesystem600 can be used to navigate a condition of the femur prior to hip replacement. Theorientation sensing device204 can be initialized or zeroed such as by placing it back in the parked configuration on theplatform620 as inFIG. 18. Thereafter, thedistal end680 of theprobe678 can be brought into contact with thepoints690. Theorientation sensing device204 can be stationary relative to thedock662. Thesurgical orientation device172 can be stationary relative to the pelvis. Thesurgical orientation device172 can be signaled to record the orientation of theorientation sensing device204. Thecamera684 can record the extension of theprobe678 relative to thedock662. The distance from thecamera684 to thedistal end680 of theprobe678 or the distance from thesystem600 to the anatomy being registered can then be recorded in thesurgical orientation device172. The position can be based on reading by thecamera684 of the marking682. The distance can be captured automatically by thecamera684. In other embodiments, the user reads a measurement from the marking682 and inputs the distance into thesurgical orientation device172.

Thesystem600 can include features that provide notable advantages for the surgeon. Thesystem600 can include modular instruments. In some embodiments, thefixation base602 can include alow profile platform620 and alow profile support622. The lowprofile fixation base602 can prevent the obstruction of the surgical field. Thefixation base602 can be easily removed when not in use. The clamping action between theplatform620 and thesupport622 allow thefixation base602 to be easily removed from the fixation pins610,612. In the illustrated embodiment, rotation of thefixation devices624 can cause thesupport622 to move away from theplatform620. The

channels

626,628 can increase in diameter. Theplatform620 and thesupport622 can be decoupled from the fixation pins610,612.

The one or more fixation pins610,612 can be spaced apart from one another. This can permit the fixation pins610,612 to be driven into different locations on the anatomy of the patient. In the illustrated embodiment, two

fixation pins

610,612 are provided. The utilization of two or more fixation pins may provide more stability for thefixation base602. The fixation pins610,612 allow the surgeon much more flexibility when anchoring thesystem600. The surgeon has flexibility in the location and/or depth of placement. The surgeon can optimize the penetration angle. In some techniques, the surgeon can enter the bone more perpendicularly. The fixation pins610,612 can be placed in locations to avoid sensitive anatomical structures.

Thesystem600 can include one or more couplers. Thesystem600 can include thefirst coupler632 coupled to theplatform620 of thefixation base602. Thefirst coupler632 can couple thefixation base602 to thefirst assembly604 as shown inFIG. 18. Thefirst coupler632 can couple thefixation base602 to any other component of thesystem600. Thesystem600 can include thesecond coupler648 coupled to thefirst assembly604. Thesecond coupler648 can couple thefirst assembly604 to thesecond assembly606 as shown inFIG. 18. Thesecond coupler648 can couple thefirst assembly604 to theextension670 as described herein. Thesecond coupler648 can couple thefirst assembly604 to any other component of thesystem600. Thesystem600 can include thethird coupler668 coupled to thedock662 of thesecond assembly606. Thethird coupler668 can couple thedock662 to theextension670 as shown inFIG. 18. Thethird coupler668 can couple thesecond assembly606 to any other component of thesystem600.

Other tools or assemblies, such as the tools and assemblies described herein can include one or more couplers. The couplers allow components to rigidly couple. In some embodiments wherein the couplers have an irregular shape, the couplers can couple components in a single orientation. The slot of the couplers, such asslot634 of thefirst coupler632, can be angled relative to the horizontal axis. This can prevent inadvertent detachment of the components from the couplers.

Thesystem600 can include thecamera684. Thecamera684 can be a component of theorientation sensing device204. Theorientation sensing device204 can be coupled to thedock662 with thethird coupler668. Thecamera684 can be in a fixed location relative to theprobe678. Thecamera684 can remain fixed in position as theprobe678 is moved. Thecamera684 can be oriented such that thecamera684 faces the marking682. In addition, theorientation sensing device204 can be in a fixed location relative to theprobe678. Theorientation sensing device204 can remain fixed in position as theprobe678 is moved. Theorientation sensing device204 can be oriented such that a flat back side of theorientation sensing device204 faces the marking682.

Thecamera684 can capture an image of the marking682. The image can correspond with a distance of theprobe678. The distance changes as theprobe678 slides through the throughlumen664 of thedock662. In some embodiments, thecamera684 can read a binary code of the marking682. In some embodiments, thecamera684 can read a scale or other markings. Thecamera684 can be positioned directly over the marking682.

FIGS. 25A-25C show ahip navigation system600A adapted to navigate a hip joint procedure with reference to anatomical landmarks. Thesystem600A is shown mounted on a pelvis in a posterior approach inFIGS. 25A-25C. Thesystem600A can include any of the features described above with reference tosystem600 and any component described herein. Thesystem600A can be used in any technique or method step described herein. As one example, thesystem600A can include thesurgical orientation device172 described herein. As another example, hesystem600A can include theorientation sensing device204 described herein. As an example, thesystem600A includes acamera684 described herein.

Thesystem600A can include afixation base602A, afirst assembly604A and asecond assembly606A. Thefirst assembly604A is rigidly connected to the hip in the illustrated configuration so that motion of the hip cause corresponding motion of sensor(s) in thefirst assembly604A as discussed below. Sensing this motion enables thesystem600A to eliminate movement of the patient as a source of error in the navigation. Thesecond assembly606A provides a full range of controlled motion and sensor(s) that are able to track the motion, in concert with sensor(s) in thefirst assembly604A.

Thesystem600A can include thefixation base602A as shown inFIGS. 26A-26C. The fixation base can include aplatform620A. Theplatform620A can include one ormore holes611A. Theholes611A can be sized to accept afastener613A to secure thefixation base602A to the bone, shown inFIG. 25B. Theplatform620A can include one ormore spikes615A. Thespikes615A can secure thefixation base602A to the bone. Thefixation base602A can includedivot630A. Thedivot630A can be associated with a parked configuration or home position, as shown inFIG. 25B. Thedivot630A can be a registration feature of thesystem600.

Referring toFIG. 25B, eachfastener613A can be driven into the ilium on the pelvis. As discussed further below, eachfastener613A can be coupled with other bones in other techniques. For example, one of thefasteners613A can be coupled with the ischium or the pubis. In some techniques, one of thefasteners613A is mounted to a pelvic bone but not at a landmark. One of thefasteners613A can be coupled at a point superior to the superior-most point on the acetabular rim. In some techniques, one of thefasteners613A is about 10 mm above the superior-most point on the acetabular rim. In some techniques, three or more anatomical landmarks disposed about the acetabulum can be acquired, as discussed below. When one of thefasteners613A is coupled with a landmark, only two additional landmarks are acquired in some embodiments as discussed below. One reason for mounting thefastener613A away from the landmarks is that the landmarks may not be visible or accessible before dislocating the hip joint. If the clinician wishes to use thesystem600A to reference the femur as discussed below, it may be required to mount thefasteners613A away from the landmarks.

Thefixation base602A can include thefirst coupler632. Thefirst coupler632 can couple to one or more components of thesystem600A. Thesystem600A can include thefirst assembly604A shown inFIGS. 25A-25B. Thefirst assembly604A can include apelvic bracket638A. In the illustrated embodiment, thepelvic bracket638A can be substantially vertical in use, as shown inFIG. 25A. Thefirst assembly604A can be designed to couple with thefirst coupler632 of thefixation base602A. Thepelvic bracket638A ofsystem600A can be longer than thepelvic bracket638 ofsystem600.

Thesystem600A can include thesecond assembly606A shown inFIG. 25A. Thedistal end680A of theprobe678A can pivot or rotate to contact anatomical landmarks, similar to probe678A described herein. Thedistal end680 can be angled, slanted or curved. The curvature of thedistal end680A of theprobe678A can facilitate the acquisition of landmarks or other points as described herein. Theprobe678A can be slid to different translational positions relative to the attachment location of thefixation base602A. Thesecond assembly606A permits a range of motion of adistal end680A of theprobe678A to facilitate acquiring a plurality of landmarks that are different locations from the attachment location of thefixation base602A.

Thesystem600A can include afemur tracker686A as shown inFIG. 25C. Thefemur tracker686A can be coupled to afemur base687A as shown inFIG. 25C. Thefemur tracker686A can be used to track the position of the femur during the procedure. Thefemur base687A can include one or more fixation structures. In the illustrated embodiment, the fixation structures areholes688A shown inFIG. 28C. Theholes688A are sized to permit a fastener therethrough (e.g., a screw, pin, k-wire, etc.). Thefemur base687A can includespikes685A as shown inFIGS. 28A-28B. Thespikes685A can anchor thefemur base687A to the femur.

Thefemur tracker686A and/or thefemur base687A can include one ormore points690. Thepoints690 can include Points A, B, C as described herein. Thefemur tracker686A and/or thefemur base687A can include threepoints690. In the illustrated embodiment, thefemur base687A includes onepoint690 and thefemur tracker686A includes twopoints690. Other configurations are contemplated (e.g., one point on thefemur base687A, two points on thefemur base687A, three points on thefemur base687A, four points on thefemur base687A, five points on thefemur base687A; one point on thefemur tracker686A, two points on thefemur tracker686A, three points on thefemur tracker686A, four points on thefemur tracker686A, five points on thefemur tracker686A, etc.). Thepoints690 can include divots. Thepoints690 can include markings. Thefemur tracker686A and thefemur base687A can be separate components. In other embodiments, thefemur tracker686A and thefemur base687A can be a unitary structure.

Thefemur tracker686A can include abracket689A as shown inFIG. 27A-27C. In the illustrated embodiment, thebracket689A can be substantially vertical in use, as shown inFIG. 25C. Thefemur tracker686A can include alock lever691A. Thelock lever691A can be coupled to thebracket689A with pivot pins. Thelock lever691A can be pivoted relative to thebracket689A. Thefemur tracker686A can include anextension693A. Theextension693A can include thepoints690.

Thefemur base687A can include afifth coupler695A as shown inFIG. 28A-28C. Thefemur tracker686A can be designed to couple with thefifth coupler695A of thefemur base687A. In some embodiments, the tapered surface of thefifth coupler695A causes the pivoting of thelock lever691A. In some embodiment, the surgeon causes the pivoting of thelock lever691A. Thelock lever691A can include a detent which is sized and shaped to be received within theslot697A. The engagement of the detent and theslot697A can rigidly couple thefemur tracker686A with thefemur base687A.

FIG. 25B illustrates a parked configuration or home position of theprobe678A. In some embodiments, a portion of thedistal end680A is moved into engagement with theplatform620A. In some techniques, thedistal end680A of theprobe678A engages thedivot630A of theplatform620A. At the surgeon's discretion thesystem600A can be used to navigate a condition of the femur prior to hip replacement.

Thesystem600A can include features that provide notable advantages for the surgeon. Thesystem600A can include modular instruments. In some embodiments, thefixation base602A can include alow profile platform620A. The lowprofile fixation base602A can prevent the obstruction of the surgical field. Thefirst assembly604A can be easily removed when not in use. Thedistal end680A of theprobe678A can be angled, bent or curved to facilitate acquiring one or more landmarks or points. Thedistal end680A of theprobe678A can be bent or curved to reach the home position. Thefemur tracker686A can be releasably coupled to thefemur base687A. Thefemur tracker686A can be easily removed when not in use. Thefemur tracker686A and/or thefemur base687A can provide points on multiple planes.

5. Posterior Approach: Methods an Orientation Sensing Device and a Camera

FIGS. 18 and 25A illustrate a step of a navigated hip joint implant procedure discussed in detail below. Some of the preceding steps involve removing the to-be-replaced joint, navigating the hip joint, preparing the implant location for the artificial joint, and placing the joint, as elaborated below. As discussed further below,FIGS. 18 and 25B illustrate a technique for confirming that these steps were properly performed.

Referring back toFIG. 2, Points A-H are locations on the anatomy that may be relevant to various methods and systems herein. In some embodiments, the

navigation system

600,600A is configured to locate a relevant anatomical feature to aid in proper placement of a prosthetic hip joint. In some methods, pre-operative imaging techniques are used. In some methods of use, the surgeon can use a standing or supine anteroposterior (AP) pelvic x-ray.FIG. 29 shows standing AP radiograph taken with patient standing with feet in neutral rotation and shoulder width apart in stance. The x-ray tube-to-film distance should be 120 cm, with the crosshairs centered on the midpoint between the superior border of the pubic symphysis and a line drawn connecting the anterior superior iliac spines (ASIS). The coccyx should be centered in line with the pubic symphysis, and the iliac wings, obturator foramina and radiographic teardrops should be symmetrical in appearance. For appropriate pelvic inclination, a 1-3 cm gap should be seen between the tip of the coccyx and the superior border of the pubic symphysis. This positioning can be important for measuring the patient specific Rim Teardrop (RT) angle.

To obtain the patient specific Rim Teardrop (RT) angle from the AP pelvic x-ray the surgeon can complete one or more of the following steps. The surgeon can draw a line on the x-ray connecting the bottom of the teardrops. The surgeon can draw a line from the most lateral point on the rim of the acetabulum (R) on the operative side through the bottom of the teardrop (T) to the horizontal inter-teardrop line. If osteophytes are present on the rim (R), the surgeon can draw a line through the most lateral osteophyte. The surgeon can measure the angle between the inter-teardrop line and the RT line just drawn. This patient specific RT inclination angle can be an input for the

system

600,600A.

FIG. 30 shows the patient positioning for the posterior hip approach. In the posterior hip approach, the patient should be placed in the lateral decubitus position. When positioning the patient prior to surgery, the surgeon should take care to align the anterior pelvic landmarks (both ASIS and pubic tubercle) in a vertical plane parallel to the long edge of the operating table. The surgeon should ensure that the pelvis is securely held by an appropriate positioning device such as a peg board or vise-type patient positioner.

Thesurgical orientation device172 and theorientation sensing device204 should be turned on. If different programs are present, the surgeon should select the hip procedure program. If different programs are present, the surgeon should select the posterior hip approach. The surgeon can verify that patient is positioned in the standard lateral decubitus position. Thesurgical orientation device172 can include a display screen. The display screen can confirm the communication between thesurgical orientation device172 and theorientation sensing device204.

The

system

600,600A can be partially assembled for calibration as shown inFIG. 31. Thepelvic bracket638 can be coupled to theextension644, if separate components. Thesurgical orientation device172 can be coupled to themount646. In some techniques, theextension670 can be coupled to thesecond coupler648. Theorientation sensing device204 can be coupled to themount672. Thesurgical orientation device172 and theorientation sensing device204 form a general V-shaped configuration. Theorientation sensing device204 can be fixed in position relative to thesurgical orientation device172.

Thesurgical orientation device172 and theorientation sensing device204 can be calibrated. The

assemblies

604,606 or604A,606A can be angled forward so that the backside of thesurgical orientation device172 rests on a level surface. The surgeon can hold the

assemblies

604,606 or604A,606A steady until thesurgical orientation device172 indicates completion. The

assemblies

604,606 or604A,606A can be angled backward so that the backside of theorientation sensing device204 rests on a level surface. The surgeon can hold the

assemblies

604,606 or604A,606A can be placed on the left side so that the left side of thesurgical orientation device172 rests on a level surface. The surgeon can hold the

assemblies

604,606 or604A,606A can be angled forward again so that the backside of thesurgical orientation device172 rests on a level surface to verify calibration. The surgeon can hold the

assemblies

604,606 or604A,606A steady until thesurgical orientation device172 indicates completion. In some embodiments, the displayed angles should be less than 2°, less than 1°, approximately 0° etc. to verify calibration.

Theextension670 can be decoupled to thesecond coupler648. The

second assembly

606,606A can be assembled as shown inFIGS. 22B and 25A. Themount658 can be coupled to theprobe bracket652. Themount658 can rotate relative to theprobe bracket652. Themount658 can be coupled to thedock662. Thedock662 can pivot relative to themount658 about one or more pivot pins660. Theextension670 can be coupled to thethird coupler668 of thedock662. Theorientation sensing device204 can be coupled to themount672. Theprobe bracket652 can be coupled to thesecond coupler648. The

first assembly

604,604A can be coupled to the

second assembly

606,606A as shown inFIGS. 18 and 25A.

Theprobe678 can be inserted within the throughlumen664 of thedock662. The marking682 can be beneath thecamera684. The surgeon can verify thecamera684 is capturing the measurements of the marking682 by sliding theprobe678 to different positions. Thesurgical orientation device172 can display different positions of theprobe678 as theprobe678 is moved. Theprobe678A can be similarly positioned within thesecond assembly606A as shown inFIG. 25A.

The

system

600,600A can be attached to the pelvis. The fixation pins610,612 can be inserted into the bone. In some techniques, one or more of the fixation pins610,612 are positioned approximately 10 mm above the most superior point on the acetabular rim. The fixation pins610,612 can be perpendicular to the long axis of the patient. The fixation pins610,612 can be inserted by use of a driver. In other embodiments, the fixation pins610,612 are driven into bone with a mallet until the distal ends are fully seated within the bone.

The fixation pins610,612 can be inserted into the

channels

626,628 prior to or after the fixation pins610,612 are driven into the bone. Thesupport622 can be brought toward theplatform620, thereby decreasing the diameter of the

channels

626,628. The fixation pins610,612 can be secured to thefixation base602. Thefirst assembly604 can be coupled to thefirst coupler632. Thesurgical orientation device172 can be coupled to thefirst assembly604. Thesecond assembly606 can be coupled to thesecond coupler648. Theorientation sensing device204 can be coupled to thesecond assembly606. Thesystem600 can be positioned as shown inFIG. 18. The fixation base202A can be affixed withfasteners613A, as shown inFIG. 25B. Thesystem600A can be positioned as shown inFIG. 25B.

The

femur tracker

686,686A can be coupled to the femur. Thefemur tracker686 can be positioned on the greater trochanter. The curved end of thefemur tracker686 can be pointing toward the head of the patient. One or more fixation devices can be placed through the eachhole688 of thefemur tracker686 to secure thefemur tracker686 to the femur. Thefemur tracker686 can be positioned as shown inFIG. 18. Thefemur base687A can be positioned on the greater trochanter. Thefemur tracker686A can be assembled as shown inFIG. 25C. Thefemur tracker686A can be coupled to thefemur base687A as described herein.

If different programs are present, the surgeon should select which hip is being operated on (e.g., right or left hip). The surgeon can verify that patient is positioned in the standard lateral decubitus position. If different programs are present, the surgeon should select the gender of the patient being operated on (e.g., male or female). If different programs are present, the surgeon should select the target cup inclination angle. This angle can be selected based upon the radiographic inclination angle. If different programs are present, the surgeon should select the target cup anteversion angle. This angle can be selected based upon the radiographic anteversion angle. If different programs are present, the surgeon should select the RT inclination angle. This angle can be selected based upon the radiographic RT inclination angle, such as from the A/P pelvic x-ray.

The surgeon can register a parked configuration or home position. In some techniques, the

distal end

680,680A of the

probe

678,678A can be engaged with a point on the

platform

620,620A. The

platform

620,620A can include the

divot

630,630A. The

divot

630,630A can be sized to accept the

distal end

680,680A of the

probe

678,678A. This position is shown inFIGS. 18 and 25B. The

probe

678,678A can be angled relative to vertical in the home position. Thedock662 can be angled relative to vertical in the home position. Theorientation sensing device204 coupled to thedock662 can be angled relative to vertical in the home position. Thesurgical orientation device172 can be also angled relative to vertical in the home position.

Theorientation sensing device204 can register the operating table, in other words perform table registration. The patient can be positioned so that the sagittal plane of the pelvis is level. The surgeon can align the

probe

678,678A with the horizontal. The

probe

678,678A can be parallel with the coronal plane. The

system

600,600A can calculate cup angles based on the assumption that the pelvis of the patient is correctly positioned during table registration.

The femur can be positioned in a neutral reference position with respect to flexion, abduction and rotation. This neutral position can be representative of a standing position of the patient. The femur should be maintained in this position during the initial registration ofpoints690, such as Points A, B, and C, shown inFIGS. 24A and 25C. The surgeon can confirm that theorientation sensing device204 is coupled to thedock662. The surgeon can position the

distal end

680,680A of the probe at Point A ofpoints690. In some methods, the

distal end

680,680A is place within a divot at Point A on thefemur tracker686,femur base687A. The surgeon can enter an input to register Point A (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate that Point A was recorded. The surgeon can position the

distal end

680,680A of the probe at Point B ofpoints690. In some methods, the

distal end

680,680A is place within a divot at Point B on the

femur tracker

686,686A. The surgeon can enter an input to register Point B (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate that Point B was recorded. The surgeon can position the

distal end

680,680A of the probe at Point C ofpoints690. In some methods, the

distal end

680,680A is place within a divot at Point C on the

femur tracker

686,686A. The surgeon can enter an input to register Point C (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate that Point C was recorded.

The surgeon can position the

distal end

680,680A of the

probe

678,678A at various anatomical landmarks.FIG. 32 illustrates four landmarks which can be utilized in some techniques. In one technique,Point1 is the most superior point of rim. The surgeon should not remove any osteophytes from this landmark prior to registration ofPoint1.Point1 registered landmark should match the anatomy identified on the pre-operative x-ray. In some methods, the

distal end

680,680A of the

probe

678,678A is placed atPoint1. The surgeon can enter an input to register Point1 (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate thatPoint1 was recorded.

Point

2 can be the most inferior point of the acetabular notch. The surgeon should not remove any osteophytes from this landmark prior to registration ofPoint2.Point2 registered landmark should match the anatomy identified on the pre-operative x-ray. The transverse acetabular ligament (TAL) straddles the inferior limit of the bony acetabulum. It is a strong load-bearing structure and, in the normal hip, in association with the labrum, provides part of the load-bearing surface for the femoral head. In some methods, the

distal end

680,680A of the

probe

678,678A is placed atPoint2. The surgeon can enter an input to register Point2 (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate thatPoint2 was recorded.

Point3 can be the posterior insertion of the transverse acetabular ligament (TAL). The surgeon should remove any osteophytes from this landmark prior to registration of Point3. This will uncover or replicate native anatomy of the landmark. In some methods, the

distal end

680,680A of the

probe

678,678A is placed at Point3. The surgeon can enter an input to register Point3 (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate that Point3 was recorded.

Point4 is the anterior insertion of the transverse acetabular ligament (TAL) in one embodiment. The surgeon should remove any osteophytes from this landmark prior to registration of Point4. This will uncover or replicate native anatomy of the landmark. In some methods, the

distal end

680,680A of the

probe

678,678A is placed at Point4. The surgeon can enter an input to register Point4 (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate that Point4 was recorded.

When registering the anatomical points or points690 on thefemur tracker686, thecamera684 captures an image of the marking682. Thecamera684 can read the marking682 to provide accurate determination of the translational position of theprobe678 relative to thedock662. Thecamera684 can be directly above the marking682. In some methods, thecamera684 can read a binary code of the marking682.

In some methods, theorientation sensing device204 converts the image of thecamera684 into an extension measurement of theprobe678. In some embodiments, thesurgical orientation device172 converts the image of thecamera684 into an extension measurement of theprobe678. The distance related to the extension of theprobe678 can be used in conjunction with the orientation and positional data from theorientation sensing device204. Thesurgical orientation device172 can use the length measurement from thecamera684 and the data from theorientation sensing device204 to determine the location of thedistal end680 of theprobe678. In some embodiments, the surgeon will enter an input (e.g., depress a button) to collect data from theorientation sensing device204. In some methods, the surgeon will enter an input (e.g., depress a button) to collect data from thecamera684. In some embodiments, the surgeon will enter an input (e.g., depress a button) to collect data from theorientation sensing device204 and thecamera684 simultaneously. In some methods, theorientation sensing device204 and/or thecamera684 will only send data to thesurgical orientation device172 if theorientation sensing device204 is stable or non-moving. Thepoints690 can include divots to stabilize the

distal end

680,680A of the

probe

678,678A when thepoints690 are registered.

The surgeon can set the angle of the cup. Later in the procedure, the surgeon can check cup angle after the angle has been set. The surgeon can remove the

second assembly

606,606A from the

first assembly

604,604A. The surgeon can remove theextension670 from thethird coupler668. The surgeon can couple theextension670 to animpactor300B, shown inFIGS. 56A-56F. Theimpactor300B can have afourth coupler338B. In some embodiments, thefourth coupler338B is a universal coupler. In some embodiments, thefourth coupler338B is identical or substantially similar to thesecond coupler648 and thethird coupler668. This permits theorientation sensing device204 to couple to either thesecond coupler648, thethird coupler668 or thefourth coupler338B, as described herein Thefourth coupler338B can be similar to thefirst coupler632 described herein. Thefourth coupler338B can extend from a side surface of theimpactor300B. Thefourth coupler338B can extend perpendicularly to the longitudinal axis of theimpactor300B. Theextension670 can couple to thefourth coupler338B. Themount672 can be coupled to theorientation sensing device204. The acetabular shell can be threaded onto the shell adaptor, similar toFIG. 11C. The shell adaptor can be snapped onto the end of theimpactor300B, similar toFIG. 11B.

The acetabular shell can be inserted into the acetabulum and positioned at the desired angle. Thesurgical orientation device172 can guide the surgeon in setting the appropriate cup angle. Thesurgical orientation device172 can graphically display when theorientation sensing device204 is located at the inclination and anterversion angles entered previously. Thesurgical orientation device172 can graphically display the inclination and anterversion angles as theorientation sensing device204 is moved. The surgeon can enter an input to set the desired angle (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can output all inclination and anteversion angles according to radiographic definitions. Anteversion (Radiographic Anteversion) is the angle between the acetabular axis and the coronal plane. Inclination (Radiographic Inclination) is the coronal plane projection of the angle between the acetabular axis and the longitudinal axis of the body. Once theorientation sensing device204 is coupled to theimpactor300B, thesurgical orientation device172 can display the radiographic inclination and anteversion angles of theimpactor300B relative to the frontal pelvic plane.

The inclination and anteversion cup angles can be displayed statically. The inclination and anteversion cup angles can be displayed statically. The anatomic angles are those calculated by thesystem600 based on the pelvic landmark registration. The table angles are those calculated by thesystem600 based on the initial positioning of the pelvis during table registration. In some embodiments, theorientation sensing device204 can register the operating table by aligning the

probe

678,678A with the horizontal. In some embodiments, only the direction of the projection of the

probe

678,678A onto a horizontal plane is used. The

probe

678,678A can be in an infinite number of angles from horizontal, which would result in the same software result. This is convenient due to the mechanical constraints imposed by the pivot configuration of thesystem600. The angles displayed can be an average between the anatomic reference and table reference. The inclination angle is calculated based as an average between the anatomic reference and table reference. The anteversion angle is calculated based on the table reference. The surgeon can check cup angle after the angles are set.

The surgeon can register the hip center. The surgeon can couple the

second assembly

606,606A to the

first assembly

604,604A as shown inFIGS. 18 and 25A. Themount672 can be coupled to theorientation sensing device204. Themount646 can be coupled to thesurgical orientation device172. The surgeon can confirm that the components of

system

600,600A are rigidly coupled. The surgeon can select the first set of points on the rim of theshell360 to be registered, as shown inFIG. 33. In the illustrated method, the first set of points is selected on the rim of the shell. The surgeon can place the

distal end

680,680A of the

probe

678,678A on each of the first set of points shown inFIG. 33. In some methods, the surgeon can select the second set of points on the rim of the shell to be registered. In the illustrated method, the second set of points is selected on the rim of the shell. The surgeon can place the

distal end

680,680A of the

probe

678,678A on each of the second set of points. In some methods, the surgeon should select the third set of points on the rim of the shell to be registered. In the illustrated method, the third set of points is selected on the rim of the shell. The surgeon should place the

distal end

680,680A of the

probe

678,678A on each of the third set of points. In some methods, the minimum separation distance allowed between points is 25 mm. In some methods, the maximum separation distance allowed between points is 65 mm.

The inclination and anteversion angles of the shell are displayed on thesurgical orientation device172. These angles are based on the plane determined by the three points registered on the rim. The surgeon can enter the offset of the liner to be used. The offset is the distance from the center of the shell face to the center of the femoral head. If the shell is hemispherical and the head and shell are concentric, the surgeon can enter zero. In some methods, the offset is between 0 mm and 10 mm. The surgeon can repeat this step if the linear offset is changed later in the procedure. Thesurgical orientation device172 can calculate the center of rotation (COR) of the hip using the set of points on the rim of the shell.

The surgeon can register the leg length and offset after implantation of the acetabular shell. The surgeon can couple the

second assembly

606,606A to the

first assembly

system

600,600A are rigidly coupled. The femur can be repositioned within +/−20° flexion from the pre-operative position. The femur can be repositioned within +/−15° abduction from the pre-operative position. The femur can be repositioned within +/−20° rotation from the pre-operative position.

In some methods, the

distal end

680,680A of the

probe

678,678A is place within a divot at Point A ofpoints690. The surgeon can enter an input to register Point A (e.g., depress a button on surgical orientation device172). The surgeon can position the

distal end

680,680A of the probe at Point B ofpoints690. The surgeon can enter an input to register Point B (e.g., depress a button on surgical orientation device172). The surgeon can position the

distal end

680,680A of the probe at Point C ofpoints690. The surgeon can enter an input to register Point C (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate that Points A, B, and C were recorded. Using Points A, B, and C, thesurgical orientation device172 can calculate the change in angle between the pelvis and the femur since the initial registration prior to dislocation. Thesurgical orientation device172 can mathematically rotate the femoral points, Points A, B, and C, around the center of rotation (COR) of the hip to align the femur with its initial position. The new position of the centroid of the femoral points, Points A, B, and C, is compared to the initial position. The femoral points, Points A, B, and C, can be located on the

femur tracker

686,686A or femur base687.

The leg length and offset are displayed on thesurgical orientation device172. The change in leg length is in the proximal distal direction. The joint offset is in the medial lateral direction. If the angle between the femur and the pelvis has changed by more than a hard coded limit in any axis, then thesurgical orientation device172 can display an error message. The hard coded limit can be 15°, between 10-20°, between 5-25°, etc. Thesurgical orientation device172 can display guidance on repositioning the femur (e.g., abduct femur, flex femur, etc.). The surgeon can exchange or reposition the shell to adjust leg length and offset. The surgeon can exchange or reposition the shell based upon goals from pre-operative templates or images. If desired and possible, the leg length and offset may be adjusted according to the surgeon's standard surgical procedure.

The surgeon can register the home position. The surgeon can couple the

second assembly

606,606A to the

first assembly

system

600,600A are rigidly coupled. The surgeon can verify the parked configuration or home position. The

distal end

680,680A of the

probe

678,678A can be engaged with a point on the

platform

620,620A. The

platform

620,620A can include the

divot

630,630A. The

divot

630,630A can be sized to accept the

distal end

680,680A of the

probe

678,678A. This position is shown inFIGS. 18 and 25B. The change in the home position is displayed on thesurgical orientation device172. The number may not be zero due to mechanical play and/or sensor noise. If the displayed number is greater than 3 mm, the surgeon may wish to verify the rigid connection between the components of the

system

600,600A.

B. Navigation Using Inertial Sensors and Jigs for Referencing Anatomical Landmarks with Anterior Approach

1. Anterior Approach: Systems with an Orientation Sensing Device Coupled to a Probe

FIGS. 34-38 illustrate ahip navigation system500 adapted to navigate a hip joint procedure from an anterior approach. Anterior approach to hip replacement advantageously can be less invasive than posterior approach. In particular, the anterior approach can enable smaller incisions, less soft tissue dissection, and shorten recovery time for patients. Thesystem500 includes ananchor system504, analignment assembly508 and alandmark acquisition assembly512.

FIG. 34 shows theanchor system504 in more detail. Thesystem504 is configured to securely couple thenavigation system500 to the hip, such that movement between the system and the hip are minimized or eliminated. Theanchor system504 includes acannula516 having adistal end520 and aproximal end524 with alumen532 extending between the distal and proximal ends. Theproximal end524 of thecannula516 is coupled with aplatform536, for example adjacent to one lateral end of the platform. Theplatform536 is similar to those hereinbefore described having a plurality of

docking device

538,538A disposed away from the location where theproximal end524 and theplatform536 are connected.

Thedocking devices538 are configured to couple with detachable mounting devices that securely but temporarily couple sensor to theanchor system504. The twodocking device538 on the top surface of theplatform536 enable theanchor system504 to be used for either left or right hip procedures. As shown inFIG. 34, thedocking device538 on the side of theplatform536 closest to the medial plane of the patient is preferably used for docking. The top side docking feature not in use inFIG. 34 would in fact be used in performing a procedure from the other side of the patient. Thedocking device538A on the side surface of theplatform536 is provided for a temporary intra-procedure mounting of a sensor to theplatform536. As discussed further below, this temporary mounting provides a known orientation and/or location of two sensors relative to each other during a procedure, which enables thesystem500 to control sources of error with certain types of sensors.

Theplatform536 also can have achannel540 disposed away from thecannula516. Thechannel540 can have a lumen disposed along an axis substantially parallel to thelumen532 of thecannula516. In one embodiment, theanchor system504 is configured to securely couple theplatform536 to the hip by placement of two spaced apart pins544A,544B.FIG. 34 shows that thepin544A can be advanced through thecannula516 such that a distal end of thepin544A contacts and penetrates a bony prominence of the pelvis. In one technique thepin544A is positioned at or as close as possible to the anterior superior iliac spine (ASIS) of the pelvis. Thepin544B is advanced through thechannel540 and into the pelvis at a location offset form the ASIS. The distance between the

pins

544A,544B and the precise positioning of thepin544B are not critical, but are determined by the locations of the connection of thecannula520 to theplatform536 and of thechannel540.

The

pins

544A,544B can take any suitable form but preferably have the same cross-sectional profile as the lumens in thecannula520 and in thechannel540, e.g., they can be circular in cross-section. The

pins

544A,544B can be modified Stienmann pins, e.g., configured to extend at least about 5 cm above theplatform536 and having a diameter of about 4 mm.

Theanchor system504 also has a locking device556 for securing theplatform536 to the

pins

544A,544B. In one embodiment, the portion of the platform disposed around the pins comprises medial andlateral portions560M,560L that can move away from each other to release the

pins

544A,544B or toward each other to frictionally engage the pins. For example, a pair of hex-driven screws can engage the medial andlateral portion560M,560L to translate them toward and away from each other respectively. The locking device556 preferably is quickly and easily removed from the pins such that other instrument, such as X-Ray or other diagnostic devices can be brought into the vicinity of the surgical field during the procedure. Preferably the

pins

544A,544B have markings along their length such that if theplatform536 is removed for imaging or other reasons it can be quickly re-positioned at the same elevation.

Thecannula520 also has afoot568 adjacent to or at thedistal end528 to minimize or eliminate error that could arise due to uneven penetration depth of theanchor system504 when compared to the position of a distal probe of thelandmark acquisition system512 when landmarks are being acquired. Thefoot568 can include an annular projection disposed outward of thecannula520. Preferably thefoot568 extends laterally from the outer surface of thecannula520 by a distance equal to or greater than the wall thickness of thecannula520. In some embodiment, the surface area beneath the foot is equal to or grater than the surface area of the cannula when viewed in cross-section at a location where thefoot568 is not located, e.g., at an elevation about thefoot568.

Thealignment assembly508 is similar to those hereinbefore described. It can have a rigid extension570 configured to detachably secure aorientation device172 to thedocking device538.

Thelandmark acquisition assembly512 is similar to those hereinbefore described, but is configured to be unobstructed in use by soft tissue anterior to the pelvis of the patient. In one embodiment, anextension578 is provided to elevate a pivoting and slidingmechanism582. The pivoting and sliding mechanism enables aprobe arm584 to slide away from theextension578 toward the location of landmarks to be acquired. The pivoting and slidingmechanism582 can be similar to any of those discussed above. The distal (lower) end of theextension578 can be coupled to theplatform536 in any suitable way. For example, the distal end can include a pin-like projection that is received in, e.g., friction fit in, anaperture578A having the same shape. Detents or other locking features can be provided to securely connect the extension to theplatform536 in theaperture578A.FIG. 35 shows that theaperture578A can be formed in a portion of theplatform536 that is elevated compared to the portions of the platform through which thepin544A extends. This portion is elevated to provide sufficient bearing engagement to minimize play. It also has a slot generally parallel to the top surface of theplatform536 which serve the function of engaging a ball detent on the lower end of theextension578.

Theprobe arm584 can be configured as an elongate member with a plurality of markings, discussed below. A distal end of theprobe arm584 can include anangled tip586 that assists in probing anatomy in some techniques, e.g., portions of the femur for leg length and femoral head positioning confirmation. In the posterior approach, theangled tip586 is used to directly contact anatomy.

In the anterior approach, theangled tip586 is coupled with aprobe extension590 configured to contact selected anatomy. Theprobe extension590 has anupright member592 that is configured to extend, in the anterior approach, between the elevation of theprobe584 down toward the elevation of the tissue to be probed. Afoot594 on the distal (lower) end of theupright member592 is configured to engage the tissue in a way that minimizes error due to uneven tissue compression between the point of mounting of thepin544A and thefoot594. For example, thefoot594 can have a cross configuration that spreads out the force or pressure applied by thelandmark acquisition system512 in use. The proximal end of theextension590 includes acoupler596 that connects a distal end of theprobe arm584 with theupright member592. Preferably thecoupler596 is easily manipulable by the user to modify connect to theprobe arm584. The coupler can include an L-shaped member with an aperture configured to receive thetip586 of theprobe arm584. A set screw can be advanced through the L-shaped portion to lock thearm584 in place. The L-shaped portion is configured to couple to thearm584 such that the tip of theangled tip586 rests on a projection of the longitudinal axis of theupright member592.

2. Anterior Approach: Methods with an Orientation Sensing Device Coupled to a Probe

Thesystem500 can be used to navigate from an anterior approach in the following ways. Theorientation device172 and thesensor204 can be paired such that they are in wireless communication with each other. This permits one or other of thedevice172 andsensor204 to control the other, store data from the other, and/or display information based on signals from the other. In one method, theorientation device172 has a display that confirms to the surgeons certain angles based on the data sensed by thesensor204. The pairing the device and

sensor

172,204 can involve coupling them together and comparing sensor output between the two devices at a plurality of orientations, e.g., horizontal, vertical, and angled at 30 degrees. Some of these positions may be repeated with a plurality of attitudes, e.g., vertical with left side up, vertical with right side up, and vertical with top side up.

As noted above, the components discussed herein can be provided as a kit that enables the surgeon to select among different surgical approaches, e.g., posterior and anterior approaches. Theorientation device172 andsensor204 may operate differently in these different approaches. Thus, in one method the user will enter into one or both of the orientation device and

sensor

172,204 which approach is being used. This will implement a software module in the orientation device172 (or in thesensor204 is the processor running the software is located there) corresponding to the selected approach.

In various embodiments suitable for the anterior approach, theorientation device172 and thesensor204 can both have a plurality of sourceless sensors. These components can have both accelerometers and gyroscopes in some embodiments. Some gyroscopes are subject to accumulated error that can be significant in the time frames relevant to these methods. Accordingly, various methods are provided to prevent such errors from affecting the accuracy and reliability of the angles displayed to the surgeon by thesystem500. Some approaches can be performed with accelerometers only. For example, variations of the anterior approach can be performed with accelerometers with somewhat less but still acceptable accuracy using accelerometers only. The reduction in accuracy of the accelerometers is balanced against the benefit of eliminating the accumulated error that arises with some gyroscopes. The resolution of accelerometers is sufficient because the points navigated are relatively far apart.

The calculations performed by thesystem500 are unique to the hip being treated in some embodiment, so the system receives input of the hip being treated.

Thefoot568 is placed on a selected anatomical location, e.g., on the ASIS as discussed above. With thecannula520 in an approximately vertical orientation theplatform536 is secured to the hip. Securing theplatform536 to the hip can be done in any suitable way, such as with two spaced apart Stienmann pins. Thereafter, theorientation device172 and thesensor204 are attached to theplatform536 in the manner shown inFIG. 36A. Depending on the nature of the sensing devices deployed in thesensor204 it may be advantageous to initialize the sensor at this point of the procedure. As discussed above, certain inertial sensors (e.g., some gyroscopes) are subject to accumulated error. One technique for managing this error source is to periodically initialize or zero out this error. Some techniques involve initialing at this point.

In some embodiment, a frame of reference based on the plane of the table can be input into thesystem500. The table reference frame can be a secondary reference frame. In one technique, thesensor204 is moved from the platform dock position ofFIG. 36A to the navigating position on theprobe arm584 as shown inFIG. 34. Theprobe arm584 is then pivoted by themechanism582 such that the arm points in a direction that is parallel to the patient's medial-lateral mid-plane and theangled tip586 superiorly (generally toward the patient's head). Theprobe arm584 is also held substantially parallel to the plane of the table. With this heading and orientation the user interacts with a user interface on theorientation device172 to signal to theorientation system508 to capture the orientation of thesensor204. This orientation provides an estimation of the orientation of the anterior pelvic plane. This estimation may be tracked in thesystem500 and may alone provide an improvement over the state of the art in un-navigated hip replacement, which involves discrete maneuvers guided by the unaided eye.

At the surgeon's discretion thesystem500 can be used to navigate a condition of the femur prior to hip replacement. A mark Fm may be made on the proximal femur. Thereafter thesensor204 can be initialized or zeroed such as by placing it back in the dock position on the platform (as inFIG. 36A). Thereafter, theprobe tip586 can be brought into contact with the femur mark Fm and locked in place in such contact. SeeFIG. 37. Thesensor204 can be transferred to the proximal end of theprobe584 and theorientation device172 can be signaled to record the orientation of thesensor204. A distance from the point of attachment of thecannula520 to the ASIS to the marked position on the femur can then be recorded in theorientation device172. The position can be based on reading graduated marks on theprobe584 or can be captured automatically by a camera system or a sensor built into thesystem500. In one embodiment, graduated marks are read at anupright edge598 within a bight of a sliding portion of the pivoting and slidingmechanism582.

FIG. 36A illustrates a further step of navigating the anterior pelvic plane. As shown, thesensor204 is docked on theplatform536, in which position any accumulated error associated with some sensors can be eliminated. In a preceding step, theextension590 is coupled with the distal portion of theprobe584. Thefoot594 is brought into contact with the contralateral ASIS. Thereafter, thesensor204 can be attached to the proximal end of the probe284 as shown inFIG. 34. Thelandmark acquisition system512 can be immobilized and the orientation of thesensor204 can be recorded in memory in theorientation device172. Additionally, the distance that theprobe584 is extended to contact the contralateral ASIS can be recorded in theorientation device172. As noted above, that distance can be read from the scale on theprobe584 at theupright edge598.

The process to record the contralateral ASIS can be repeated for one or more additional points. Thesensor204 can be docked to the platform as inFIG. 36A to eliminate sources of accumulated error. Theprobe584 can then be moved to cause thefoot594 to be in contact with a pubic tubercle. Theprobe584 can be immobilized and the sensor coupled with the proximal end as shown inFIG. 36B. Thereafter data indicative of the orientation of thesensor204 and the distance to the pubic tubercle are recorded in theorientation device172 in any of the manners discussed above.

Once the foregoing points of the pelvis have been navigated and the data recorded into theorientation device172 the anterior pelvic plane can be calculated from data indicating the navigated points. The orientation of the anterior pelvic plane is a baseline for placement of the cup portion of a hip prosthesis.

Thesensor204 and theorientation device172 can at this point be used to guide placement of thecup360 in the prescribed orientation. Prior to placement the

impactor

300,300A is provided. For example, theimpactor300A can be provided by selecting theappropriate tip component348 onto the distal end of theshaft316A. Thetip component348 is coupled with thecup360, e.g., by threads. The rotational orientation of thecup360 to theshaft316A that is most convenient given hole patterns and position of thesensor204 is selected by matching up the

flats

350A,350B as appropriate. During the process of providing theimpactor300 thesensor204 can be docked to theplatform536 and source of accumulated error can be eliminated just prior to navigating thecup360 into place in the acetabulum.

In one technique, thecup360 is inserted into the acetabulum and placed to approximately the correct orientation. Thereafter thesensor204 is connected to adocking device338 on the impactor as shown inFIG. 11A. Theorientation device172 is the activated to display angles indicative of the orientation of the cup, e.g., degrees of inclination and anteversion with respect to the anterior pelvic plane. The angle displayed can directly reflect the table reference frame discussed above. The angle displayed can directly reflect the frame of reference from the acquisition of landmarks. In some cases, angles can be displayed that directly reflect both table reference frame and landmark reference frame. In other embodiments, the table reference frame is not displayed but rather causes a user instruction to be displayed on theorientation device172, such as a direction to re-acquire landmarks due to disagreement between the angles generated by the two reference frames.

Any of the foregoing combinations of table and landmark reference frames provides redundancy that ensures that the angle information provided to the user is accurate and reliable such that the procedures performed will be better contained within the “safe zone”.

When the correct angles are achieved, a tool is used to strike the proximal end of theimpactor300 to lodge thecup360 in place at the desired angle. In some techniques, thesensor204 is removed prior to striking the proximal end of theimpactor300. Thesystem500 includes a module that monitors signals from thesensor204 and if a large deviation in the readings occurs, the module prevents the angles on the display of the orientation device from changing. This “freezing” of the display is both a safety and an accuracy precaution because a large force due to impact can affect the accuracy of thesensor204.

If femoral landmarks are acquired in the procedure prior to separating the natural joint, the same landmarks can be acquired after the prosthetic joint is placed to confirm that the replacement of the joint has not changed either the length of the leg, the off-set of the leg from the trunk of the patient or both. For example, thesensor204 can be docked to thedocking device538A as shown inFIG. 36A. Sources of accumulated error can be eliminated by initializing thesensor204. Thereafter, theprobe arm538 can be brought into contact with the same landmark (e.g., Fm) acquired early in the procedure. SeeFIG. 38. Theprobe arm538 can be locked into place and thereafter thesensor204 can be coupled with the proximal end of theprobe arm538. The orientation of the sensor and the distance to theprobe arm538 can be input into theorientation device172. These data enable theorientation device172 to output amounts of change in leg length and leg offset.

In one variation a plurality of points, e.g., three points, on the femur are acquired before and after the joint is replaced. This approach enables a further confirmation that the rotation orientation of the neck of the femur relative to an axis extending through the center of thecup360 perpendicular to the plane of the acetabulum is unchanged after the procedure.

Of course, the femur registration procedures enable correction of diagnosed deformities including excessive leg length offset and joint offset, as well as mal-orientation of the femoral neck in the natural joint. In other words, the surgeon can begin the procedure with the intent of adding some offset or changing rotational orientation to improve the patient's bone positions and/or orientations post-operatively.

3. Anterior Approach: Systems with an Orientation Sensing Device and Camera

FIG. 39 shows thesystem600 adapted to navigate a hip joint procedure with reference to anatomical landmarks from an anterior approach. Thesystem600 can include theorientation sensing device204, not shown inFIG. 39, as described above Thesystem600 can be adapted for either a posterior approach as described above, or an anterior approach.

FIG. 40-42 shows ahip navigation system600B adapted to navigate a hip joint procedure with reference to anatomical landmarks from an anterior approach. As noted above, in the anterior approach, the patient is in the supine position. Thesystem600B can include any of the features described above, including with reference tosystem600. Thesystem600B can be used in any technique or method step described herein. Thesystem600B can include thesurgical orientation device172 described herein. Thesystem600B can include theorientation sensing device204 described herein. Thesystem600B can include acamera684 described herein.

Thesurgical orientation device172 and theorientation sensing device204 can be turned on before the procedure begins. If the system can be used in a posterior or anterior approach, one method can involve a surgeon selecting a module corresponding to the approach. For example, the surgeon can select an anterior hip approach module or a posterior hip approach module in thesurgical orientation device172. In some embodiments, the method can involve the step of inputting the surgical technique into thesurgical orientation device172. The surgeon can verify that patient is positioned in an appropriate position, e.g., in a supine position. Thesurgical orientation device172 can include a display screen. The display screen can confirm the communication between thesurgical orientation device172 and theorientation sensing device204.

The

system

600,600B can be partially assembled for calibration. In some embodiments, thefirst assembly604 can be assembled. Thepelvic bracket638 can be coupled to theextension644, if separate components. Thesurgical orientation device172 can be coupled to themount646. In some techniques, theextension670 can be coupled to thesecond coupler648. Theorientation sensing device204 can be coupled to themount672. Thesurgical orientation device172 and theorientation sensing device204 form a general V-shaped configuration, similar to the orientation shown inFIG. 31. Theorientation sensing device204 can be fixed in position relative to thesurgical orientation device172.

Thesurgical orientation device172 and theorientation sensing device204 can be calibrated. Thesurgical orientation device172 can be rested on a level horizontal surface with the display pointed upward. The surgeon can hold the

assemblies

604,606 or604B,606B steady until thesurgical orientation device172 indicates completion. Thesurgical orientation device172 can be rested on a level vertical surface with the display pointed sideways. The surgeon can hold the

assemblies

604,606 or604B,606B steady until thesurgical orientation device172 indicates completion. The

assemblies

604,606 or604B,606B can be placed on the left side so that the left side of thesurgical orientation device172 rests on a level surface. The surgeon can hold the

assemblies

604,606 or604B,606B can be angled forward to verify calibration. The surgeon can hold the

assemblies

604,606 or604B,606B steady until thesurgical orientation device172 indicates completion.

Theextension670 can be decoupled from thesecond coupler648, as described herein. Thesecond assembly606 can be assembled as shown inFIGS. 39 and 40. The

first assembly

604,604B can be coupled to the

second assembly

606,606B as shown inFIGS. 39 and 40. The

probe

678,678B can be inserted within the through lumen of the

dock

662,662B. The marking682 can be beneath thecamera684. The surgeon can verify thecamera684 is capturing the measurements of the marking682 by sliding the

probe

678,678B to different positions. An error message can be displayed if thecamera684 is not reading themarkings682.

The

system

600,600B can be attached to the pelvis. The fixation pins610,612 can be inserted into the bone. In some techniques, one or more of the fixation pins610,612 are positioned over the ASIS on the operative side. In some techniques, one or more of the fixation pins610,612 are positioned on the iliac crest. The fixation pins610,612 can be approximately vertical. The fixation pins610,612 can be inserted by use of a driver. The

fixation base

602,602B can be rotated as needed to place the fixation pins610,612 within the

channels

626,628 as shown inFIG. 20C. Thesupport622 can be brought toward theplatform620, thereby decreasing the diameter of the

channels

626,628. The fixation pins610,612 can be secured to thefixation base602,612B.

The

first assembly

604,604B can be coupled to thefirst coupler632 as described herein. Thesurgical orientation device172 can be coupled to the

first assembly

604,604B. The

second assembly

606,606B can be coupled to thesecond coupler648 as described herein. Theorientation sensing device204 can be coupled to thesecond assembly606. Thesystem600 can be positioned as shown inFIGS. 39 and 41.

The surgeon can register a parked configuration or home position as shown inFIG. 41. In some techniques, thedistal end680,680B of the

probe

678,678B can be engaged with a point on theplatform620 orcannula621B. Theplatform620 orcannula621B can include thedivot630 as described herein. Thedivot630 can be sized to accept thedistal end680,680B of the

probe

678,678B. Thedistal end680,680B of the

probe

678,678B can be curved or bent to facilitate locating anatomical landmarks or points, as shown inFIGS. 39 and 40. The

probe

678,678B can be vertical in the home position. Theorientation sensing device204 can be vertical in the home position.

Theorientation sensing device204 can register the operating table or perform table registration for the anterior approach. The patient can be positioned so that the coronal plane of the pelvis is level. In some embodiments, the surgeon can align the

probe

678,678B with the horizontal. In some embodiments, only the direction of the probe's678,678A projection onto a horizontal plane is used. The

probe

678,678A can be in an infinite number of angles from horizontal, which would result in the same software result. This is convenient due to the mechanical constraints imposed by the pivot configuration of thesystem600. The

probe

678,678B can be parallel with the sagittal plane. The

system

600,600B can calculate cup angles based on the assumption that the pelvis of the patient is correctly positioned during table registration.

At the surgeon's discretion the

system

600,600B can be used to navigate a condition of the femur prior to hip replacement. A mark Fm may be made on the proximal femur. Thereafter theorientation sensing device204 can be initialized or zeroed such as by placing it back in the home position, as described herein. Thereafter, thedistal end680,680B of the

probe

678,678B can be brought into contact with the femur mark Fm. Thesurgical orientation device172 can be signaled to record the orientation of theorientation sensing device204. A distance from the point of attachment of the fixation pins610,612 to the marked position on the femur can then be recorded in thesurgical orientation device172. The position can be based on capturing themarkings682 the

probe

678,678B orprobe inlay676 by thecamera684, in combination with inertial data from theorientation sensing device204.

The femur can be positioned in a neutral reference position with respect to flexion, abduction and rotation. This neutral position can be representative of a standing position of the patient.

The surgeon can position thedistal end680,680B of the

probe

678,678B at various anatomical landmarks. The surgeon can hold the hip stable. In some methods,Point1 of the system is the mounting point of one or more fixation pins610,612. Referring back toFIG. 39, each

fixation pin

610,612 can be driven into the pelvis. In some techniques, one of the fixation pins610,612 is mounted to a pelvic bone at a landmark. When one of the fixation pins610,612 is coupled with a landmark, only two additional landmarks are acquired in some embodiments as discussed below. In some methods, thedistal end680,680B of the

probe

678,678B is placed at the contralateral ASIS landmark. The surgeon can enter an input to register Point2 (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate thatPoint2 was recorded. The

probe

678,678B can be immobilized and the orientation of theorientation sensing device204 can be recorded by thesurgical orientation device172. Additionally, the distance that the

probe

678,678B is extended, as captured by thecamera684, to contact the contralateral ASIS can be recorded by theorientation device172.

The process to record the contralateral ASIS can be repeated for one or more additional points. In some methods, thedistal end680,680B of the

probe

678,678B is placed at the pubic tubercle. The surgeon can enter an input to register Point3 (e.g., depress a button on surgical orientation device172). Thesurgical orientation device172 can indicate that Point3 was recorded. In some methods, either pubic tubercle may be used as a reference. The

probe

678,678B is extended, as captured by thecamera684, to contact the pubic tubercle can be recorded by theorientation device172.

When registering the anatomical points, thecamera684 captures an image of the marking682. Thecamera684 can read the marking682 to provide accurate determination of the translational position of the

probe

678,678B relative to thedock662. Thecamera684 can be directly above the marking682. In some methods, thecamera684 can read a binary code of the marking682.

In some methods, theorientation sensing device204 converts the image of thecamera684 into an extension measurement of the

probe

678,678B. In some embodiments, thesurgical orientation device172 converts the image of thecamera684 into an extension measurement of the

probe

678,678B. The distance related to the extension of the

probe

678,678B can be used in conjunction with the orientation and positional data from theorientation sensing device204. Thesurgical orientation device172 can use the length measurement from thecamera684 and the data from theorientation sensing device204 to determine the location of thedistal end680,680B of the

probe

678,678B. In some embodiments, the surgeon will enter an input (e.g., depress a button) to collect data from theorientation sensing device204. In some methods, the surgeon will enter an input (e.g., depress a button) to collect data from thecamera684. In some embodiments, the surgeon will enter an input (e.g., depress a button) to collect data from theorientation sensing device204 and thecamera684 simultaneously. In some methods, theorientation sensing device204 and/or thecamera684 will only send data if theorientation sensing device204 is stable or non-moving.

Once the foregoing points of the pelvis have been navigated and the data recorded into thesurgical orientation device172, the anterior pelvic plane can be calculated from data indicating the navigated points. The orientation of the anterior pelvic plane is a baseline for placement of the cup portion of a hip prosthesis.

Theorientation sensing device204 and thesurgical orientation device172 can at this point be used to guide placement of the cup in the prescribed orientation. The surgeon can set the angle of the cup. Later in the procedure, the surgeon can check cup angle after the angle has been set. The surgeon can remove thesecond assembly606 from thefirst assembly604. The surgeon can remove theextension670 from thethird coupler668. The surgeon can couple theextension670 to animpactor300B, shown inFIGS. 56A-56F. Theimpactor300B can have thefourth coupler338B. This permits theorientation sensing device204 to couple to thefourth coupler338B. The acetabular shell can be threaded onto the shell adaptor, similar toFIG. 11C. The shell adaptor can be snapped onto the end of theimpactor300B, similar toFIG. 11B.

The acetabular shell can be inserted into the acetabulum and positioned at the desired angle. Thesurgical orientation device172 can guide the surgeon in setting the appropriate cup angle. Thesurgical orientation device172 can graphically display when theorientation sensing device204 is located at the inclination and anterversion angles entered by the surgeon. Thesurgical orientation device172 can graphically display the inclination and anterversion angles as theorientation sensing device204 is moved. The surgeon can enter an input to set the desired angle (e.g., depress a button on surgical orientation device172).

The inclination and anteversion cup angles can be displayed statically. The anatomic angles are those calculated by thesystem600 based on the pelvic landmark registration. The table angles are those calculated by thesystem600 based on the initial positioning of the pelvis during table registration. The surgeon can check cup angle after the angles are set.

If femoral landmark Fm is acquired in the procedure prior to separating the natural joint, the same landmark can be acquired after the prosthetic joint is placed to confirm that the replacement of the joint has not changed either the length of the leg, the off-set of the leg from the trunk of the patient or both. Thereafter, thedistal end680,680B of the

probe

678,678B can be brought into contact with the same landmark (e.g., Fm) acquired early in the procedure. The orientation of theorientation sensing device204 and the extension of the

probe

678,678B can be input into thesurgical orientation device172. These data enable thesurgical orientation device172 to output amounts of change in leg length and leg offset.

In one variation described above in connection with the

system

600,600B andFIG. 24A, a plurality of points, e.g., three points, on the femur are acquired before and after the joint is replaced, for instance with the use of thefemur tracker686. This approach enables a further confirmation that the rotation orientation of the neck of the femur relative to an axis extending through the center of the cup perpendicular to the plane of the acetabulum is unchanged after the procedure.

The surgeon can register the home position. The surgeon can couple the

second assembly

606,606B to the

first assembly

604,604B as shown inFIGS. 39 and 40. Themount672 can be coupled to theorientation sensing device204 as described herein. Themount646 can be coupled to thesurgical orientation device172 as described herein. The surgeon can confirm that the components of

system

600,600B are rigidly coupled. The surgeon can verify the parked configuration or home position. Thedistal end680,680B of the

probe

678,678B. The change in the home position is displayed on thesurgical orientation device172.

C. Navigation Using Pre-Operative Imaging and Patient Specific Jigs

Although the foregoing approaches can improve the standard of care currently in place, further increases in accuracy and even better outcomes and streamlining of the procedure can be provided if the system is configured to account for patient specific anatomical variability.

1. Patient Specific Jigs: Navigation Using Fixation Pins Mounted Therethrough

FIG. 43 shows the placement of a hipmovement tracking sensor204 on apin732 adjacent to the acetabulum. This position is not limiting, in that the hipmovement tracking sensor204 can be mounted anywhere on the pelvis, but adjacent to the acetabulum is convenient. Thepin732 has been placed with the aid of a pre-operative characterization of the hip of the specific patient. In these methods thepin732 is placed without the need for intra-operative landmark acquisition.

In one approach, a pre-operative three-dimensional characterization of the acetabulum is performed using any suitable technology, such as CT scan or MRI. This pre-operative procedure can be performed to fully characterize the pelvis and, in some cases, the proximal femur. Thereafter, the shape, location and orientation of the acetabulum are known. Also, the bony features around the acetabulum are known. From this data, acustom jig700 can be fabricated specific to the patient. Thecustom jig700 not only has features that are specific to the individual patient's anatomy but also aregistration feature702 that will be at a known orientation to the plane of the acetabulum and to the anterior pelvic plane.

FIG. 44 shows an example of thecustom jig700. Thejig700 has ananterior side704 and aposterior side708. Theposterior side708 is formed with an acetabular portion712 configured to mate with at least one feature of the acetabulum in a secure manner. For example, the acetabular portion712 can fit snugly over the acetabular rim with a central portion of theposterior side708 positioned in the acetabulum. Thejig700 preferably has only one pre-defined orientation. A surface on a posterior portion of the jig can define a plane that corresponds to a preferred orientation angle of the cup post-implantation. One ormore channels716 can be formed on theposterior side708 that receive the local bony prominences of the acetabular rim only when thejig700 is in the proper position and orientation. In another approach, theregistration feature702 of thejig700 has a face or a hole that is oriented in the desired orientation for the shell or cup of the implant. Thus, once thejig700 is placed, thesensing device204 can be positioned against the face or surface or, if coupled with apin732, the pin can be inserted into the hole. From the orientation of the device when so placed, the orientation of the acetabular rim or a proxy thereof can be recorded in one or both of the

devices

172,204. Thehole702 preferably extends from theanterior side704 to theposterior side708 of thejig700. The distance between the anterior and

posterior surfaces

704,708 provides the depth of thehole702 being sufficient to guide a pin to specific anatomy along a specific direction.

FIG. 45 shows initial placement of thejig700 in the acetabulum in an orientation dictated by the fit of thejig700 over the anatomy. The profile of theposterior side708 including the channel(s)716 receives the specific patient's acetabular rim including local prominences and recesses of the bone at and around the acetabulum. Thehole702 is located on aperipheral projection720 of thejig700. The configuration of theprojection720 is such that thehole702 is disposed over a specific bone or bone region of the hip. In this example, theprojection720 is configured to be disposed over the bone superior to the acetabulum. Other regions of bone around the acetabulum can be used if sufficiently thick or strong and in a convenient position to not block actions of the surgeon during the procedure. The precise location of theprojection720 chosen can be determined by the pre-operative imaging and factored into the forming thecustom jig700.

FIG. 46 shows that after the jig is placed thepin732 can be placed through thehole702. Thepin732 has a length that extends above theanterior surface704 of thejig700 such that thesensor204 can be mounted thereto. Once thesensor204 is mounted to the pin, the sensor can track any movement of the pelvis during the procedure. There is no need for registration of landmarks in this technique because the position and orientation of the pin relative to the acetabulum and/or to the anterior pelvic plane are known from the pre-operative imaging.

FIG. 47 shows that theplug700 advantageously can include an alignment guide736 to control rotational orientation of thesensor204 on thepin732. The alignment guide736 can be a line extending along a specific direction relative to theregistration feature702. As noted above, the sensing devices inside thesensor204 can be sensitive to the direction of gravity. Tilting of the sensor about thepin732 can change the readings of these sensing devices. To eliminate sources of error associated with this sensitivity, the navigation system incorporating thesensor204 can be programmed to assume that the sensor will be at a specific rotation position about the longitudinal axis of thepin732. Thesensor204 may be mechanically or visually aligned with the guidingmark738 to assure that this assumption is met in use. In one variation, thesensor204 has a laser that projects onto thejig700 and can be aligned with the mark736 to facilitate alignment. Alternatively, thepin732 may be configured to only enter the hole in a unique orientation (for example, with an asymmetric non-circular cross-section), and to allow the sensor to mount to the pin in a unique orientation (by including asymmetric coupling features).

Once thesensor204 is mounted to thepin732, thejig700 can be removed from the surgical area. For example, thejig700 can be made of material can be cut along aline742 in a lateral edge of the jig. A saw or rongeur can be used to cut through thejig700. Thereafter, the majority of the body of thejig700 can be removed from the surgical area.FIG. 49 shows that in some methods, theprojection720 is left in place so that the position and orientation of thesensor204 is not disrupted.

Asecond sensor204 is attached to a cup impactor, which may be the same as inFIGS. 11A-11C. The impactor guides the placement of the cup with reference to the signals from thesensor204 mounted on thepin732 on the pelvis. Signals from the sensor on the impactor can be corrected if movement of the hip is detected by the sensor on thepin732.

FIGS. 50-52 illustrate one way of implementing cannulated guide delivery methods. Cannulated methods are advantageous in that once a guide member is mounted, the tracking of orientation is simplified and may no longer be necessary in some cases, which can eliminate accumulated errors, sensor drift, or erroneous readings of other sorts as a concern.

Acustom jig750 is formed by the process discussed above in connection with thejig700. Thejig750 has many of the same components as those of thejig700, including aregistration feature752 extending between the anterior and

posterior surfaces

754,758. A guidingmark738 can be provided on theanterior surface754 to align thesensor204 rotationally about thepin732. Thejig750 also has aguide channel762 located generally centrally in thejig750. Theguide channel762 has an anterior opening on theanterior surface754, a posterior opening on theposterior surface758, and a wall extending between these openings. The wall is disposed about a central axis A. The position and orientation of the axis A can be determined based on the pre-operative characterization of the acetabulum. In one embodiment, an MRI or CT scan reveals an optimal axis for delivering a prosthetic cup along. The wall forming theguide channel762 is formed about the axis A which coincides with this optimal axis when thejig750 is placed on the specific patient's acetabulum.

FIG. 51 shows that theimpactor300A can then be advanced along the axis A into theguide channel762. Adistally facing shoulder766 on theimpactor300A can mate in a pre-defined way with theanterior surface754 and the entrance to thechannel762 and when so mated the orientation of thesensor204 on theimpactor300A can be recorded. In this technique, thejig750 is a cannula with thechannel762 configured to receive theimpactor300A. If patient movement is possible, thesensor204 on thepin732 can be retained in place to track such movement. If not, thesensor204 on thepin732 can be removed. Thesensor204 on theimpactor300A will have stored the orientation of the axis A in memory and will be able to inform the user of any variance of the impactor from this axis. It is preferred to retain thesensor204 on thepin732, as the orientation can only be accurate stored by thesensor204 on theimpactor300A for a short time due to accumulated error (e.g., drift) of some sensors, e.g., some lower cost gyroscopes.

In one variation, theimpactor300A has a central channel that coincides with the axis A when the impactor is placed into theguide channel762 and theshoulder766 abutted with thesurface754. A guide pin can be advanced through this channel and into the acetabulum. The guide pin can be lodged in the base of the acetabulum. Thesensor204 coupled with the pelvis by thepin732 can be removed because the guide pin placed through the channel of theimpactor300A provides a mechanical way of tracking movement of the hip. Thereafter theimpactor300A with the cup mounted thereon can be slide over the guide pin and into place in the acetabulum.

In a further variation, thesensor204 coupled with theimpactor300A can also be removed. In this further variation, the guide pin is configured along with the cup to prevent tilting of the prosthetic cup relative to the axis A. In particular, an interface between the guide member and the cup of the hip prosthesis could be made to have sufficient length along the axis A that tilting is prevented by this interface. In some cases, thecup360 is coupled to the

impactor

300,300A. A variation of the

impactor

300,300A can be tubular or have another feature for interfacing with, e.g., tracking along the guide pin in the pelvis.

2. Patient Specific Jigs: Navigation Using Inertial Sensors Mounted on Impactor

FIGS. 53-60 shows another embodiment of a custom jig. The systems described herein can be used with a patientspecific jig1000, shown inFIG. 55. In some embodiments, the

system

600,600A,600B or components thereof, can be used with the patientspecific jig1000.

Referring toFIG. 53, thesystem600A can include afixation base602A. Thefixation base602A can include aplatform620A. Theplatform620A can include one ormore holes611A. Theholes611A can be sized to accept afastener613A to secure thefixation base602A to the pelvis. Thefixation base602A can includedivot630A. Thedivot630A can be a registration feature associated with a parked configuration or home position. Eachfastener613A can be driven into the ilium on the pelvis. As discussed further below, eachfastener613A can be coupled with other bones in other techniques. For example, one of thefasteners613A can be coupled with the ischium or the pubis. One of thefasteners613A can be coupled at a point superior to the superior-most point on the acetabular rim. In some techniques, one of thefasteners613A is about 10 mm above the superior-most point on the acetabular rim.

Thefixation base602A can include thefirst coupler632. Thefirst coupler632 can couple to one or more components of thesystem600A. Thesystem600A can include thefirst assembly604A shown inFIG. 54. Thefirst assembly604A is rigidly connected to the hip in the illustrated configuration so that motion of the hip cause corresponding motion of sensor(s) in thefirst assembly604A as discussed below. Thefirst assembly604A can include apelvic bracket638A. In the illustrated embodiment, thepelvic bracket638A can be substantially vertical in use, as shown inFIG. 54. Thefirst assembly604A can be designed to couple with thefirst coupler632 of thefixation base602A.

Thefirst assembly604A can include anextension644A. Theextension644 can be coupled to thepelvic bracket638A. Theextension644A can include a mount (not shown) designed to couple with thesurgical orientation device172. Thesurgical orientation device172 can include features to mate with the mount (not shown). Thesurgical orientation device172 is rigidly coupled to theextension644A when engaged with the mount.

Thesystem600A can include thesecond assembly606A or a portion thereof. Thesecond assembly606A can include anextension670. Theextension670 can couple to thesecond coupler648. The engagement between thesecond coupler648 and theextension670 minimizes or prevents relative movement therebetween to avoid any mechanical relative movement during navigation procedures. Theextension670 can include amount672 designed to couple with theorientation sensing device204. In the illustrated embodiment, themount672 includes a lock and release lever that can pivot relative to theextension670. Theorientation sensing device204 can include features to mate with the lock and release lever. Other configurations are contemplated. Theorientation sensing device204 is rigidly coupled to theextension670 when engaged with themount672. In some methods of use, thesystem600, or a portion thereof, is coupled to the pelvis instead of thesystem600A.

The surgeon can select the hip (e.g., right or left) using thesurgical orientating device172. The surgeon can input the target cup inclination angle into thesurgical orientation device172. The inclination angle can be radiographic inclination as described herein. The surgeon can input the target cup anteversion angle into thesurgical orientation device172. The anteversion angle can be radiographic anteversion as described herein.

Thesecond assembly606 includes theextension670 and themount672, as shown inFIG. 23A. Theorientation sensing device204 can be coupled to themount672. Theextension670 can be coupled to thesecond coupler648. Theorientation sensing device204 and thesurgical orientation device172 can be calibrated as described herein. Thesystem600 can be mounted similar tosystem600A shown inFIG. 54. The method step of coupling theorientation sensing device204 with thesecond coupler648 can relate the orientation data of theorientation sensing device204 to a reference frame of thesurgical orientation device172.

In some embodiments, a pre-operative three-dimensional characterization of the acetabulum is performed using any suitable technology, such as CT scan or MRI. This pre-operative procedure can be performed to fully characterize the pelvis and, in some cases, the proximal femur. Thereafter, the shape, location and orientation of the acetabulum are known. Also, the bony features around the acetabulum are known. From this data, the patientspecific jig1000 can be fabricated specific to the patient. The patientspecific jig1000 not only has features that are specific to the individual patient's anatomy but also aregistration feature1002 shown inFIG. 55 that will be at a known orientation to the plane of the acetabulum and to the anterior pelvic plane.

FIG. 55 shows an example of the patientspecific jig1000. The patientspecific jig1000 has ananterior side1004 and aposterior side1008. Theposterior side1008 is formed with a three dimensional shape configured to mate with at least one feature of the acetabulum in a secure manner. For example, anacetabular projection1012 can be provided that fits snugly over the acetabular rim with a central portion of theposterior side1008 positioned in the acetabulum. The patientspecific jig1000 preferably has only one pre-defined orientation. A surface on aposterior side1008 of the patientspecific jig1000 can define a plane that corresponds to a preferred orientation angle of the cup post-implantation. One ormore channels1016 can be formed on theposterior side1008 that receive the local bony prominences of the acetabular rim only when the patientspecific jig1000 is in the proper position and orientation.

In some embodiments, theregistration feature1002 of the patientspecific jig1000 can include a recess, a hole, or a projection. In one method of using the illustrated embodiment, theorientation sensing device204, not shown but described herein, is coupled to animpactor300B. Theimpactor300B can be inserted into theregistration feature1002. Thus, once the patientspecific jig1000 is placed, theorientation sensing device204 can be positioned in a known orientation relative to theregistration feature1002. From the orientation of theorientation sensing device204 when so placed, the orientation of the acetabular rim or a proxy thereof can be recorded in one or both of the

devices

172,204. Theregistration feature1002 preferably extends from theanterior side1004 toward theposterior side1008 of the patientspecific jig1000. The distance between the anterior and

posterior surfaces

1004,1008 provides the depth of theregistration feature1002 being sufficient to securely couple to theimpactor300B. In other embodiments, theregistration feature1002 extends anteriorly of theanterior side1004 of thejig1000, e.g., as a projection or post.

FIGS. 56A-56F show theimpactor300B. Theimpactor300B can be substantially similar to impactors described herein, and can include any features of impactors described herein. Theshaft316B can include plurality offlats350B on the distal end of theshaft316B as shown inFIG. 56F. Theflats350B permit proximal-distal sliding of theregistration feature1002 of the patientspecific jig1000 over the distal end of theshaft316B into or out of thefeature1002 shown inFIG. 57. In some embodiments, adetent device351B or other locking mechanism is provided between theshaft316B and theregistration feature1002. This mechanism may prevent inadvertent release of the patientspecific jig1000 from theimpactor300B. The flats prevent theshaft316B from rotating relative to the patientspecific jig1000. Theflats350B can enable many discrete alternate relative angular positions of the patientspecific jig1000 to theshaft316B. The number of orientations of theimpactor300B relative to the patientspecific jig1000 can depend on the number of flats.

FIG. 58A-58B shows initial placement of the patientspecific jig1000 in the acetabulum in an orientation dictated by the fit of the patientspecific jig1000 over the anatomy. The method can include the step of coupling the patientspecific jig1000 to a rim of the acetabulum. The profile of theposterior side1008 including the channel(s)1016, shown inFIG. 55, receives the specific patient's acetabular rim including local prominences and recesses of the bone at and around the acetabulum. Theacetabular projection1012 can be peripheral projection of the patientspecific jig1000. The configuration of theacetabular projection1012 is such that theacetabular projection1012 is disposed over a specific bone or bone region of the hip. In this example, theacetabular projection1012 is configured to be disposed over the bone superior to the acetabulum. Other regions of bone around the acetabulum can be used if sufficiently thick or strong and in a convenient position to not block actions of the surgeon during the procedure. The precise location of theacetabular projection1012 chosen can be determined by the pre-operative imaging and factored into the forming the patientspecific jig1000.

Theimpactor300B can be placed in theregistration feature1002 before or after the patientspecific jig1000 is placed in the acetabulum. Theimpactor300B has a length that extends above theanterior surface1004 of the patientspecific jig1000 such that thesensor204 can be mounted thereto. Referring back toFIG. 54, theorientation sensing device204 can be undocked from thesecond coupler648. Theorientation sensing device204 can thereafter docked to thefourth coupler638B of theimpactor300B. The fourth coupler is shown inFIG. 58B.

The patientspecific jig1000 can include analignment guide1038 to control rotational orientation of theorientation sensing device204 on theimpactor300B. Thealignment guide1038 can be a line extending along a specific direction relative to theregistration feature1002. As noted above, theorientation sensing device204 can be sensitive to the direction of gravity. The rotation of theorientation sensing device204 about theimpactor300B can change the readings of these sensing devices. To eliminate sources of error associated with this sensitivity, the navigation system incorporating theorientation sensing device204 can be programmed to assume that theorientation sensing device204 will be at a specific rotation position around the longitudinal axis of theimpactor300B. Thealignment guide1038 can correspond to the desired rotation positionorientation sensing device204.

In the illustrated embodiment, thefourth coupler338B may be mechanically or visually aligned with thealignment guide1038 to assure that this assumption is met in use. In the illustrated embodiment, thealignment guide1038 is an elongate arrow. The elongate arrow can align with the longitudinal axis of thefourth coupler338B. The surgeon can look down theimpactor300B from the proximal end to the distal end. The surgeon can verify the alignment of thealignment guide1038 and thefourth coupler338B. The alignment between thealignment guide1038 and thefourth coupler338B constrains theorientation sensing device204 in the third degree of freedom. Thesurgical orientation device172 can be programed with this known angle of theorientation sensing device204 when theimpactor300B is coupled to the patientspecific jig1000. In some embodiments, the surgeon will enter an input (e.g., depress a button) when the patientspecific jig1000 is seated with theimpactor300B and theorientation sensing device204 coupled thereto. Thesurgical orientation device172 can calculate the orientation of thesurgical orientation device172 relative to the pelvis when the input is pressed. This step may replace registering the pelvic landmarks with the probe, as discussed herein.

In some embodiments, theorientation sensing device204 has a laser that projects onto the patientspecific jig1000 and can be aligned with thealignment guide1038 to facilitate alignment. Alternatively, theimpactor300B may be configured to only enter theregistration feature1002 in a unique orientation (for example, with an asymmetric non-circular cross-section), and to allow theorientation sensing device204 to mount to the patientspecific jig1000 in a unique orientation (by including asymmetric coupling features).

Once theorientation sensing device204 is mounted to theimpactor300B, the surgeon can hold theorientation sensing device204 steady. In some embodiments, the surgeon will enter an input (e.g., depress a button) to collect data fromorientation sensing device204. The data can include the impactor angle. The impactor angle can be fixed during the method such that the angle can be known to the system or in the method in directing placement of the hip implant components. In some embodiments, the impactor angle can be 10° inclination, 20° inclination, 30° inclination, 40° inclination, 50° inclination, 60° inclination, 70° inclination, 80° inclination, 90° inclination, between 30°-70° inclination, between 40°-60° inclination, etc. In some embodiments, the impactor angle can be 10° anteversion, 20° anteversion, 30° anteversion, 40° anteversion 50° anteversion, 60° anteversion, 70° anteversion, 80° anteversion, 90° anteversion, between 0°-40° anteversion, between 10°-30° anteversion, etc. In the illustrated embodiment, the impactor angle is 50° inclination, 20° anteversion. The impactor angle can be based upon the orientation of theregistration feature1002 relative to the patientspecific jig1000. The impactor angle can be set during fabrication of the patientspecific jig1000. In some embodiments, the impactor angle must be known by the software of thesurgical orientation device172. In some embodiments, the impactor angle is constant for all jigs and hard-coded into thesurgical orientation device172. In some embodiments, the impactor angle can be input by the user at the time of surgery. The surgeon can input the impactor angle into thesurgical orientation device172 using the user interface as described herein.

Theorientation sensing device204 can transmit orientation and positional data to thesurgical orientation device172. Thesurgical orientation device172 can register the guide angle when theorientation sensing device204 is coupled to the patientspecific jig1000. In some methods, thesurgical orientation device172 can perform a bias elimination step. Thesurgical orientation device172 can track motion of the pelvis and to generate an output that eliminates error due to the movement of the pelvis. Thesurgical orientation device172 can include a display providing a user interface. The method can include the step of registering the orientation of a proxy for the plane of the acetabular rim using theorientation sensing device204 coupled with the patientspecific jig1000.

Theorientation sensing device204 can track any movement of the pelvis during the procedure. There is no need for registration of landmarks in this technique because the position and orientation of theimpactor300B and/ororientation sensing device204 relative to the acetabulum and/or to the anterior pelvic plane are known from the pre-operative imaging. From the known orientation of theorientation sensing device204 with respect to the pelvis, the system can calculate the orientation of thesurgical orientation device172 with respect to the pelvis.

The surgeon can remove the patientspecific guide1000 from the patient as shown inFIG. 59. The surgeon can remove theimpactor300B from the patientspecific guide1000. The surgeon can prepare the acetabulum. In some embodiments, the surgeon can ream the acetabulum. Theimpactor300B can be used to position a shell in the acetabulum. Theshaft316B can include plurality offlats350B on the distal end of theshaft316A as shown inFIG. 56F. Referring toFIGS. 11B-C and60, the impactors described herein can be coupled with thetip component348.FIG. 11C shows that thetip component348 can have arecess352 formed on the proximal side thereof. Therecess352 can comprises a plurality offlats350B corresponding to a plurality offlats350B on the distal end of theshaft316B. Theflats350B permit proximal-distal sliding of therecess352 over the distal end of theshaft316B. Preferably a detent device or other mechanism is provided between thetip component348 and theshaft316B so that thetip component348 does not disengage. Theflats350B prevent thetip components348 from rotating relative to theshaft316B Theengagement device356 comprises threads in one embodiment so that the cup of the prosthetic hip can be screwed onto the distal end of thetip component348. The flats enable many discrete alternate relative angular positions of the tip component348 (and hence the cup) to theshaft316B. A plurality of flutes or elongateaxial ridges364 on the outer surface of thetip component348 enable the user to securely grasp the tip component for mounting and dismounting the tip component on theshaft316B. The surgeon can position the cup in the acetabulum. The surgeon can hold theimpactor300B steady.

During orienting, inertial data from theorientation sensing device204 can be used to confirm a proper orientation of the acetabular cup. Thesurgical orientation device172 can register the guide angle when the cup is positioned within the acetabulum. In some embodiments, the surgeon will enter an input (e.g., depress a button) to collect data fromorientation sensing device204. Thesurgical orientation device172 can display the cup angle. The surgeon can move the cup to change the inclination angle. The surgeon can move the cup to change the anteversion angle. The surgeon can move the shell until the inclination angle and anterversion angle matches the preoperative angles. The method can include the step of changing the orientation of theimpactor300B in response to an output reflecting the inertial data generated by theorientation sensing device204. In the illustrated embodiment, the preoperative impactor angle can be 50° inclination, 20° anteversion. In some methods, thesurgical orientation device172 can perform a bias elimination step. In some methods, thesurgical orientation device172 can perform a gyro propagation step. Examples of bias elimination steps and gyro propagation steps are discussed in U.S. Ser. No. 13/011,815, filed Jan. 21, 2011, which is hereby incorporated by reference for this and all other purposes. Thesurgical orientation device172 and/or theorientation sensing device204 can include any of the software algorithms described therein.

The surgeon can seat the cup in the acetabulum using theimpactor300B. Thesurgical orientation device172 can remain coupled to thefirst assembly604. Theorientation sensing device204 can be coupled to thefourth coupler338B on theimpactor300B, as shown inFIG. 60.

In some embodiments, the surgeon will enter an input (e.g., depress a button) to collect data from orientation sensing device. The data can include the impactor angle. The impactor angle can be known. At this step, the impactor angle can be 50° inclination, 20° anteversion. The impactor angle can be based upon the orientation of theregistration feature1002 relative to the patientspecific jig1000. The impactor angle can be set during fabrication of the patientspecific jig1000. In some embodiments, theimpactor300B can be rotated to a set number of positions within theregistration feature1002. Theimpactor300B can be rotated by the surgeon to align a feature of theimpactor300B with thealignment guide1038. Thefourth coupler338B can be aligned with thealignment guide1038. Theimpactor300B can be positioned such that thefourth coupler338B can be pointed superiorly. In other embodiments, theimpactor300B has a single orientation within theregistration feature1002. The position of theorientation sensing device204 can be therefore known relative to the patientspecific jig1000, when theorientation sensing device204 is coupled to theimpactor300B. Thesurgical orientation device172 can calculate and record the orientation of thesurgical orientation device172 with respect to the pelvis.

Theimpactor300B may be struck to seat the implant. In some embodiments, theorientation sensing device204 remains on theimpactor300B as theimpactor300B is struck. Referring toFIG. 60, theimpactor300B has ashell312B that is moveable relative to theshaft316B. Theshell312B can include thefourth coupler338B that can couple to theorientation sensing device204. The moveability of theshell312B helps to isolate theorientation sensing device204 from the forces that are transmitted through theimpactor300B. These forces are applied by a mallet or other device for forcibly moving the cup into position. By providing at least some force isolation between theshell312 and theorientation sensing device204, impact on the sensors in theorientation sensing device204 can be reduced. Excessive force being applied to theorientation sensing device204 can put theorientation sensing device204 out of service, for example until synched with thesurgical orientation device172. The movement of ashell312B is cushioned by a plurality of

spring members

340B,344B which are configured to absorb at least some of the shock of the impact on theimpactor300B.

3. Custom Jigs: Navigation Using Fixation Pins Mounted Therethrough

FIGS. 61-63 show an example of thecustom jig1100. Thejig1100 has ananterior side1104 and aposterior side1108. Theposterior side1108 is formed with anacetabular portion1112 configured to mate with at least one feature of the acetabulum in a secure manner. Thejig1100 preferably has only one pre-defined orientation. In some embodiments, aregistration feature1102 of thejig1100 has a plurality of, e.g., two, holes. Theregistration feature1102 can be located on theacetabular portion1112 or any other portion of thecustom jig1100. The holes are sized to accept

fixation pins

610,612 of thesystem600. In a variation ofFIGS. 44-52, a patient specific guide can be provided with a registration feature including a single hole. The hole or holes can accept fixation pin(s)610 in a single orientation relative to the patient or relative to thecustom jig1100. The method can include the step of inserting at least afixation pin610 through the patientspecific jig700 orjig1100 along an axis disposed at a pre-defined angle corresponding to the reference frame of thesurgical orientation device172.

Thefirst hole1105 of theregistration feature1102 can accept afixation pin610 and asecond hole1107 can acceptfixation pin612. Thesystem600 can be placed in a single orientation relative to thecustom jig1100. Thus, once thejig1100 is placed, thesurgical orientation device172 and/or theorientation sensing device204 can be positioned in a known orientation. In some embodiments, from the orientation of thesystem600 when so placed, the orientation of the acetabular rim or a proxy thereof can be recorded in one or both of the

devices

172,204. In some embodiments, the reference frame can be based directly on more general pelvic landmarks such as the anterior pelvic plane. The acetabular rim or a proxy can be used as an intermediate step to get to the reference frame based directly on more general pelvic landmarks. Theregistration feature1102 preferably extends from theanterior side1104 to theposterior side1108 of thejig1100. The distance between the anterior and

posterior surfaces

1104,1108 provides the depth of the

holes

1105,1107 being sufficient to guide the fixation pins610,612 to specific anatomy along a specific direction. The method can include the step of inserting at least two

fixation pins

610,612 through the patientspecific jig1100 along axes disposed at a pre-defined angle corresponding to the reference frame of thesurgical orientation device172.

Once the

devices

172,204 are mounted to thesystem600, the sensors can track any movement of the pelvis during the procedure. There is no need for registration of landmarks in this technique because the position and orientation of the fixation pins610,612 relative to the acetabulum and/or to the anterior pelvic plane are known from the pre-operative imaging.

4. Navigation Using Inertial Sensors and Pre-Operative Imaging

In another technique using less comprehensive imaging, a correspondence between one or more linear dimensions and an angle can be exploited to enhance accuracy. For example, a clinician can use an X-ray or other standard radiographic imaging device to provide an anterior pelvic bone image. This image can be read to derive the location of the anterior pelvic plane and a dimension on the anatomy. For example, an angle between top and bottom landmarks around the acetabulum (as further describe below) and a trans-ischial line or other anatomic medial-lateral reference line can be a useful patient specific variable to minimize patient-to-patient variation in at least one relevant angle, e.g., the abduction angle.

Patient specific data can be provided for use by the surgeon based on best medical judgment. For example, any of the systems herein can be used in a mode that is based on broad population studies. Such studies can define a distribution of patients with sufficient clarity and detail to enable significant improvement over the current standard of care. In one mode, the dimensions taken from radiograph or CT can be used to inform the surgeon whether some patient specific adjustments should be considered. Alternatively, patient specific adjustments can be coded into the system described herein so that they are transparent to the doctor. Such adjustments can be downloaded to either or both of the

devices

172,204 or into a separate monitor or control device that communicates wirelessly with the

devices

172,204. Thus, the system described herein can either fully implement patient specific adjustment, e.g., for anteversion, abduction, leg length, joint offset, or other parameter or can enable the surgeon to make a judgment as to whether to do so.

FIG. 68 illustrates an example of a pre-operative image that can be used in one technique. The lines380 point to landmarks which are used intraoperatively and are also visible in an anterior pelvic radiograph. Thetop landmark380A is about lcm superior to most superior point of acetabulum. In another approach, thetop landmark380A can be the most superior point on the acetabular rim. Thebottom landmark380B is adjacent to or at the acetabular notch (tear drop). An angle betweenline382 and theline384 is a patient-specific abduction of line formed by landmarks, which can be entered into an interface of the system100 (or the other systems herein) at time of surgery to provide patient specific reference frame.Line384 may be any anatomic medial-lateral reference line. Examples include trans-ischial line and line across the inferior borders of the obturator foramina (shown inFIG. 68).

5. Navigation Using Drift Insensitive Inertial Sensors

In one variation, one or both of the

devices

172,204 can comprise only accelerometers and can be configured as tilt meters, or the devices could be put into a mode that relies mostly on the accelerometer data or otherwise be configured to be insensitive to accumulated errors that arise from integration of data. If the patient is set in a reproducible and stable position, patient movement and mis-orientation can be eliminated. This enables some methods to be performed without using rate sensor data. In one variation of this tilt-meter approach, one or both of the

sensors

172,204 can be configured to inform the surgeon if a condition is sensed that suggests a landmark acquisition approach would yield a superior alignment outcome. This method can advantageously be used for procedures that do not require complex movements, like freehand motions. Where freehand motion is involved, incorporating some indication of heading (gyroscopes, magnetometer, or other indication of heading) would be useful.

6. Navigation Using Inertial Sensors to Track Motion to Define a Patient-Specific Safe Zone

In another technique illustrated byFIG. 64, a patient-specific “safe zone” is defined by recording the patient's natural range of motion of one more of the patient's joints. For example, if a hip procedure is to be performed, the patient's range of motion can be recorded pre-operatively. If the hip to be replaced is not overly arthritic, the range of motion can be determined on the hip to be replaced. If the range of motion of the hip to be replaced is unnatural due to disease state, the contralateral hip can be characterized.

In one hip replacement technique a sensor S is coupled with the femur. The sensor can be coupled above the knee to prevent movements at the knee from affecting the measurements made. The sensor S can be connected below knee if the knee is immobilized. The sensor S can be initialized and otherwise prepared to record accurate readings. Thereafter one or more movements of the hip joint can be performed with the output of the sensor recorded and processed. The movements can include, for example, movement in anterior and posterior (A-P) directions to the full extent of the range of motion and movement in medial and lateral (M-L) directions to the full extent of the range of motion. These motions define the patient's natural range of motions in these planes.

Based on the extents of motion in the A-P and M-L directions, a cone of motion CM can be defined. The cone of motion CM can be defined as originating at a point defined as the center of rotation of the femoral head and extending out from the acetabulum to a circular base located a distance from the center of rotation equal to the distance to the mount point of the sensor. The circular base can be defined as having a radius equal to the average extent of motion in the A-P and M-L directions. InFIG. 64, the cone of motion is shown on the contralateral side for clarity. As noted above, the data collected to estimate the cone of motion can be based on the leg to be treated or the contralateral leg.

Placement of the cup of the hip prosthesis is dictated by some metric of centering within the cone of motion. For example, the cup can be centered such that an axis extending perpendicular to the plane of the entrance to the cup crosses the circular base of the cone of motion precise in the center of the cone. In some systems, the orientation of the cup is controlled such that the crossing point of the axis so projecting is closer to the center of the circular base than it is to the periphery of the circular base. In other systems, the orientation of the cup is controlled such that the crossing point of the axis so projecting is within a distance from the center point that is less than 25% of the radius of the circular base.

In a class of patients, the movement of the hip is not symmetrical in each of the A-P and M-L directions. As such, the cone of motion can have a more complex geometry. For example, the cone of motion can originate at the center of rotation of the femoral head and extend to a base having an oblong shape, for example shortened in the medial direction, but longer in the lateral, anterior, and/or posterior directions. Various metrics of “within the safe zone” can be defined based on these irregular shaped cones. For example the geometric center of a complex base shape can be calculated and the cup of the prosthetic joint can be centered such that an axis extending perpendicular to the plane of the entrance to the cup crosses the irregular shaped base of the cone of motion at or within some maximum distance of the centroid of the cone.

Any suitable set of motions can be used to obtain the center of rotation of the femoral head and/or the boundaries of the base of the cone of motion. Examples of methods for determining the center of rotation of a femoral head using inertial sensors are discussed in U.S. Pat. No. 8,118,815, which is hereby incorporated by reference for this and all other purposes. A more complete perimeter of the base of the cone of motion can be directly recorded using sensors that are capable of tracking both position and orientation. For example, several other points between the A-P and M-L direction can be taken so that six, eight, ten, twelve or more extents are recorded. In other embodiments, arcuate motions of along all or portions of the perimeter of the base of the cone of motion can be traced and recorded. Because several degrees of freedom of the sensor S are constrained, the sensor can operate based on accelerometers only in some approaches, which simplifies sensor S and enables it to be disposable and/or less expensive to make. Such approaches may be most accurate if rotations about a vertical axis are minimized or eliminated.

In one embodiment, the procedure illustrated inFIG. 64 generates an origin and a direction that can be input to a cup placement system. The origin can be the center of rotation of the femoral head and the corresponding center of rotation of a prosthetic socket. The direction can be a line connecting the origin and the point of intersection with the base of the cone of motion. This data is transferred to a cup placement system, such as any of those discussed above. For example, theimpactor300A can include thesensor204 to which this data has been saved. Thereafter movements of theimpactor300A can be tracked with reference to this origin and direction to assure proper placement of the cup. Such placement can be with the aid of a patient movement tracking sensor pinned to the pelvis for example.

In other embodiments, cannulated systems can be used to minimize the number of steps during which inertial sensors are used. For example, once the origin and direction of the axis connecting the center of rotation and the intersection with the base of the cone of motion are determined, a guide member can be placed via a cannulated impactor (or other cannula). The guide member can dock with an impactor-mounted cup. The cup can be slid over the guide member into place in the acetabulum. The direction and origin information collected in the steps illustrated byFIG. 64 are preserved by the guide member and by the tilt preventing features on the guide member and/or prosthetic cup.

If the patient's joint is subject to extensive disease, a cone of motion can be established by a combination of data collected in motions similar to those discussed above in connection withFIG. 64 and pre-operative imaging. For example, X-rays can be taken when the femoral neck is moved close to the acetabular rim to supplement some of the data points defining the cone of motion. Thus, the cone of motion can be in part established by inertial sensing and in part by imaging to characterize the native anatomy.

D. Adaptable Systems for Anterior or Posterior Approach

The systems described herein can be adapted for use in the anterior approach, the posterior approach or both the anterior and posterior approach. As one example,system600 is shown herein mounted for a posterior approach inFIG. 18, the anterior approach inFIG. 39, and in combination with a patient specific jig inFIG. 63.

FIGS. 69-72 illustrate a system900 for navigating a hip procedure. The system900 can be adapted for use in both the anterior approach and the posterior approach. The system900 can be similar to some of those discussed above. But, while some of the foregoing systems are specialized for a particular approach, the system900 includes afirst sub-system900A adapted for a posterior approach and asecond sub-system900B adapted for an anterior approach. As discussed more below, both

systems

900A,900B are configured to enable navigation to be conducted without requiring gyroscopic or other sensors that are subject to accumulated error (drift). This refinement makes the system simpler to implement and to use in a wider variety of settings and with more patients.

Thesystem900A includes ajig904A that is adapted for hip joint navigation from a posterior approach. Thejig904A is similar in some respects to thejig454, and any consistent description thereof is incorporated herein. Thejig904A includes aplatform908, acannula coupling device912, and a registrationjig mounting feature914. Theplatform908 can have any shape, but in some implementations can be elongate, e.g., having afirst end916 and asecond end920. The elongate shape enables at least a portion of thejig904A to be low profile in one direction and to provide a plurality of positions along a length for coupling devices to the jig. Thefirst end916 is configured to be oriented inferiorly and thesecond end920 to be oriented superiorly when the navigation jig is applied to the patient. The medial-lateral dimensions or extent can be minimized to not obstruct the surgical field or the surgeon.

Thecannula coupling device912 is disposed adjacent to thefirst end916 and is configured to enable acannula924 to be held adjacent to a bottom surface of theplatform908. Thecannula924 can have a top surface connected to a bottom surface of theplatform908. A connection between these components can be secured by a device disposed above within or below theplatform908. In one form, a proximal structure of thecannula924 can be received within a bottom recess of theplatform908 and can be held within the recess by a compression device, such as a set screw S. Details of several variants ofcannula coupling devices912 are discussed below in connection withFIGS. 73-75B. A connection to a bone adjacent to a hip joint is made through thecannula924. For example, apin928 can be placed through theplatform908 and thecannula924 into the bone.

Ananterior approach cannula926 is shown inFIGS. 71 and 72 and is similar to thecannula516, the description of which is incorporated herein. The description of thecannula coupling device912 applies equally to thecannula924 for posterior approach and to thecannula926 for anterior approach.

The registrationjig mounting feature914 is disposed on a top surface932 of theplatform908 adjacent to thefirst end916. In one form, the mountingfeature914 includes an elevated portion of the platform. The mounting feature can include one or more, e.g., two recesses into which pins can be received. In one embodiment, the elevated portion includes a window, e.g., a through hole, for viewing such a pin to confirm correct placement. As illustrated inFIG. 73, in one variant, a circular recess can be provided for a first pin and an U-shaped slot can be provided for another pin or member.

Thehip navigation jig904A also includes registration jig940. The registration jig940 can have some features similar to those discussed above. The registration jig940 includes anupright member942, arotatable member948, and a probe952. Theupright member942 is configured to be detachably coupled to theplatform908 at the registrationjig mounting feature914. For example, a plurality of (e.g., two) pins can project from a lower surface of theupright member942, the pins being configured to be received in corresponding recesses in the registrationjig mounting feature914. One of such pins is visible through the window in the registrationjig mounting feature914 seen inFIG. 70. Theupright member942 includes afirst portion944 and asecond portion946 disposed above thefirst portion944. Thefirst portion944 is substantially vertical and increases the elevation of thesecond portion946 when the registration jig940 is mounted to the registrationjig mounting feature914. Thesecond portion946 is inclined away from a vertical longitudinal axis of thefirst portion944. The incline of thesecond portion946 provides several advantages. It enables theupright member942 to be out of the way of the range of motion of the probe952, as discussed below. This is important because the probe952 has to be able to easily and quickly reach a plurality of anatomical features.

The incline of thesecond portion946 also provides a simple way to incline an angle of rotation of therotatable member948 relative to a vertical axis. Therotatable member948 is coupled with theupright member942 for rotation about an axis A that is not vertical when the jig is mounted to the bone adjacent to a hip joint and the upright member is disposed generally vertically. This arrangement is one way to enable a navigation system employing inertial sensors to eliminate the need to manage sensor drift. As discussed above, certain sensors, such as gyroscopes, are more subject to accumulated errors (drift). The orientation of the axis A enables the jig904 to be used in a system that includes accelerometers and other sensors that are sufficiently sensitive if activated and moved about axes that are not vertical.

As in the registration devices discussed above, other degrees of freedom of rotation and position can be provided in the registration jig940 and such description is incorporated here.

The probe952 had atip956 for engaging anatomy. Theanatomy engaging tip956 is disposed at a distal end of an elongate body960 coupled with the rotatable member for rotation about the axis. The orientation and position of the elongate body960 of the probe can be adjusted to bring the anatomy engaging tip into contact with a plurality of anatomical landmarks during a landmark acquisition maneuver. Such adjustments can be by sliding through a sliding support, similar to those hereinbefore described.

Theupright member942 can include acradle954 that allows the elongate body960 of the probe952 to be held in place when not in use during a procedure. Thecradle954 can be used to latch thesensor204, as discussed above. In various implementations, the system900 does not require any steps of zeroing, however, since the sensors are configured to be generally drift insensitive. Eliminating sensitivity to drift can be achieved by configuring thesensor204 as a tilt meter, and/or by using any sort of inertial sensor that will not introduce excessive error due to drift during the procedure time. As such, even sensors that have some drift can be used, so long as their accumulation of error does not reach a significant level until during the procedure. Thecradle954 could be used to zero error if a procedure was unexpectedly long and the sensor were subject to some drift. In one advantageous embodiment, thesensor204 can operate solely with signals from accelerometers, which are insensitive to drift.

FIGS. 69-72 show that the

systems

900A,900B can include one or more sensors for detecting orientation of the probe952. The sensors can take any form, e.g., can include thesurgical orientation device172 and thesensor204 discussed above. Accordingly, the jig904 can include a sensor mounting feature962 disposed on theplatform908. Where the platform is elongate, the sensor mounting feature962 can be disposed at thesecond end920. Another advantage of the

jig

904A,904B is that it is symmetrical and can be used on both hips. The

jig

904A,904B thus can have a single sensor mounting feature disposed on a plane of symmetry. If theplatform908 is elongate, the sensor mounting feature962 can be located on a vertical mid-plane of the platform. Vertical here refers to the orientation of the

jig

904A,904B when applied to the hip in a posterior or anterior approach.

The registration jig940 can include a sensor mounting feature964 disposed thereon for movement with the probe952. For example, the sensor mounting feature964 can be located at a proximal end of the elongate body960. This location is one of convenience, placing thesensor204 at the proximal end. However, the sensor mounting feature964 and thesensor204 could be located on a side surface of the elongate body960.

As discussed herein, the orientation of the axis of rotation A of therotatable member948 enables the change of orientation of thesensor204 to be other than in the horizontal plane. This is accomplished by orienting the axis A other than in the vertical direction. With this arrangement, it is possible to configure at least thesensor204 as a tilt meter, e.g., using primarily or only accelerometers to output a signal indicative of orientation of a component, such as of the prove952. Example of angles or ranges of angles of the axis A that can be provided include about 20 degrees from horizontal, about 30 degrees from horizontal, about 45 degrees from horizontal, at less than about 60 degrees from horizontal.

FIG. 70 shows a further feature of thesystem900A, which includes thejig904A and thecannula924. Thecannula924 is adapted for posterior approach is similar to or the same as thehollow fixation member466. An upper or first end of thecannula924 is configured to couple with thecannula coupling device912, such as by a set screw as discussed above. A second end of thecannula924 is configured to couple with a bone adjacent to the hip joint. The bone can be any of those discussed above for coupling thefixation member466 or other analogous structures discussed in any embodiments above. A home point feature968 is disposed adjacent to the second (lower) end of thecannula924. The home point feature968 is in a predefined, known position and can receive theanatomy engaging tip956 of the probe952. When these structures contact, they are in a predefined position and orientation. The home point feature968 can be similar to theregistration feature473 discussed above.

Because the system900 can be adapted for posterior approach or for anterior approach (discussed below), thecannula924 should be made removable from theplatform908 in the operating room or at a back table in preparation for surgery. As such, the connection between thecannula924 and theplatform908 can be made orientation specific. This reduces a potential source of operator error, i.e., the home point feature968 always faces toward the surgical field from the hip bone attachment location, e.g., faces inferiorly if the jig904 is mounted to a superior location of the surgical field. For example, a projection on a proximal portion of thecannula924 and a corresponding projection in a recess on the lower side of theplatform908 can define only one rotational orientation of the cannula relative to the platform in which these components can be coupled.

As discussed above, thecannula926 is provided in the system900 to enable a surgeon to switch to an anterior approach. Anterior approach is discussed in great detail above, e.g., in connection withFIGS. 34-42, which description are incorporated here as well. Thesystem900B differs from thesystem500 in that the orientation of the axis A of rotation in thesystem900B is not vertical, as discussed above. As such, the sensors can be greatly simplified compared to thesystem500. Thecannula926 has ahome point feature968B. Thehome point feature968B is in a predefined, known position and can receive theanatomy engaging tip956 of the probe952. When these structures contact, they are in a predefined position and orientation. Thehome point feature968B can be similar to theregistration feature473 discussed above. Thecannula926 and theplatform908 can be configured for limited, e.g., only one, rotational position of attachment. This assures that when thejig904B is assembled in the operating room or back table that thejig904B will be properly set up.

In one method to maximize the accuracy of the landmark acquisition,jig904B is coupled with the patient in an anterior approach. Thetip956 is put into contact with thehome point feature968B. Thereafter, user input can be applied to thesurgical orientation device172A to indicate that thetip956 is in thehome point feature968B. Thereafter, the system registers movements and landmark acquisition in the manner discussed above. These data provide a basis to guide the placement of the acetabular cup, as discussed above.

The placement of the acetabular cup using a device such as theimpactor300A can be an operation that benefits from inertial sensors that may include one or more drift-sensitive sensors, e.g., gyroscopes. The system900 provides acalibration mount998 for coupling asensor204 in a known, fixed position and orientation relative to thesurgical orientation device172A. Thecalibration mount998 is a docking device that positions thesensor204 just prior to a step of eliminating any potential source of accumulated error, e.g., zeroing a drift-sensitive sensor.FIG. 69-70 show that theysystem900A can include twosensors204, one mounted to the registration jig940 and one to thecalibration mount998. These twosensors204 can be identical or can be dedicated for their specific function.FIGS. 71 and 72 shows only onesensor204. In this system, asingle sensor204 is used to gather landmark data and to work in combination with theimpactor300A to place an acetabular implant.

FIGS. 73-75B illustrate various features for clamping structures to theplatform908. In particular, these figures show fixationpin securement devices970 that are incorporated into theplatform908. The fixationpin securement devices970 can have low profile to be out of the way of other tools in the surgical field.FIG. 73-73A show one embodiment of apin securement device970 that includes acompression member972. Thecannula coupling device912 can include a similar mechanism to clamp a pin disposed through thecannula924. Theplatform908 includes a slot or plurality of slots formed on a surface thereof, e.g., on the top surface. Theslots974 are larger in at least one direction than thecompression member972 such that the compression member can fit in the slot and move to some extent therein. Thecompression member972 has a taperedchannel976. Movement of atapered member978 vertically in the taperedchannel976 shifts thecompression member972 to narrow a gap G between thecompression member972 and a rigid feature of the platform. The gap G can be between a curved lateral surface of thecompression member972 and a curved surface of theplatform908.

In one method, a pin or other fixation member is advanced through the gap G and into the bone. Theplatform908 is positioned on the fixation member at an appropriate height and thepin securement device970 is affixed to the fixation member. The fixation member can be a Steinmann pin or other similar device. In one technique, the taperedmember978 is a threaded elongate body that is advanced along internal threads formed in theplatform908 until the tapered surface thereof acts on thetapered surface976 to shift thecompression member972 laterally to narrow the gap G. Further advancement of the taperedmember978 further shifts thecompression member972 to enhanced securement of the fixation member. The method can be repeated for a second pin, where one pin extends through thecannula924 and one extends parallel to thecannula924, but off-set superiorly therefrom on the patient.

FIGS. 74-74B illustrate another approach to a fixationpin securement devices970A in which the fixation pin securement device comprises a compression member972A pivotally mounted to theplatform908.FIG. 74A shows two compression members972A, each of which is mounted to pivot about a pin orshaft980. Thesecurement device970A on the left inFIG. 74A corresponds to a configuration in which a fixation member can freely pass through a gap G in the mechanism. Thesecurement device970A on the right inFIG. 74A corresponds to a configuration in which the gap G is narrowed and a fixation member disposed in the gap G will be securely clamped and unable to move relative to theplatform908. A rigid surface of theplatform908 opposite the pivotingcompression member972 along with the compression member holds the fixation member in place.

In one method, pins or other fixation members are placed in the fixationpin securement device970A and thecannula coupling device912. In the illustrated embodiment, these devices can employ similar clamping mechanisms. Thereafter, screws982 are advanced to cause thecompression member972 to pivot about the pin orshaft980 from a first position in which the gap G provided between a clamping surface of the compression member972A and a rigid surface of theplatform908 is larger to a second position in which the gap G is smaller. The second position is a clamped position for the fixation member and will retain the platform in position until thescrew982 is withdrawn enlarging the gap G.

FIGS. 75-75B illustrate another approach to a fixationpin securement devices970B in which the fixation pin securement device comprises a compression member972B configured to clamp a plurality of segments of an outside surface of a fixation member. Theplatform908 includes a plurality ofprojections984 extending upward from an upper surface of the platform. The projections preferably are threaded. Each projection includes acollet986 or similar device disposed therein having an inner lumen sized to receive a fixation member. A plurality of slots extends downward from an upper surface of thecollet986 and an angled surface988 is disposed between top ends of each member defined between a pair of such slots. A corresponding angled surface990 is provided on an inside of acap992. Thecap992 has internal threads that act on the threads of theprojection984 to advance the angled surfaces990 onto the angled surfaces988. Further advancement collapses the slots of thecollet986 causing compression about the outer surface of the fixation member.FIG. 75 shows that this approach can be used for the fixationpin securement devices970B and/or for thecannula coupling device912.

While the systems discussed above are well suited for specific approaches, the system900 can be adapted for a posterior approach or for an anterior approach. This provides a great deal of flexibility to the surgeon and only adds minimal additional components to a universal kit. The orientation of the axis of rotation A (seeFIGS. 70 and 72) enhances the sensitivity of a system that incorporates accelerometers and other sensor drift insensitive components. The home point features968A,968B enable the surgeon to obtain maximal accuracy by allowing the acquisition of position and orientation data for a number of anatomical landmarks at close range to the home point position. This allows the system to initialize the sensors near the points to be acquired to enhance accuracy.

II. Navigation Using Optical Components

Many of the foregoing systems advantageously use inertial sensors to aid in navigation of procedures. Certain embodiments discussed herein can advantageously use optical techniques alone or in combination with inertial sensor systems discussed herein to provide additional features and advantages.

A. Optical Tracking of System Components

FIG. 65 illustrates one embodiment of asystem800 that includes close-range optical tracking capabilities. In this context “close range” is a broad term that means near the patient, such as any of in the surgical field, directly above the pelvis but below the surgeon's head, within the boundaries of the surgical table, etc. This term is intended to exclude systems where cameras are outside the surgical fields. Close range greatly reduces or eliminates “line of sight” problems that plague traditional optical navigation.

In the illustrated embodiment, ajig system804 is provided for connecting to patient bone. Thejig system804 can include any of the features of any of the jig systems discussed herein. For simplicity, the jig system is illustrated with that ofFIG. 1, e.g., including thecannula124 and theplatform136. Asurgical orientation device172A is mounted to theplatform136. Theorientation device172A can be similar to those hereinbefore described, but also includes one ormore cameras812. Preferably theorientation device172A includes two ormore cameras812 to enable capture of binocular data. The cameras preferably are small cameras, for example the Aptina MT9T111, which is discussed at http://www.aptina.com/products/soc/mt9t111d00stc/. The cones projecting from the lower side of thedevice172A schematically represent the direction of the field of view of thecameras812.

This data can at least be used to determine the heading of and in some cases six degrees of freedom of astylus816. The stylus has adistal end828 configured to touch landmarks as part of a landmark acquisition maneuver, as discussed above. A proximal (or other)portion832 of thestylus816 has an array oftrackers836 that can be tracked by thecameras812 to provide orientation, position, heading, attitude, or other combinations of spatial characteristics of portions of thestylus816 or anatomy with which it is coupled.

Thecameras812 can operate without any additional sensor, such as inertial sensors. In some embodiments, thecameras812 are used in concert with inertial sensors to confirm or to improve accuracy of the sensors. For example, drift in a rate sensor, e.g., accumulated errors, can be monitored by comparing the output of the rate sensor with the viewed position from the cameras. The system can intervene if the sensor output drifts too much, for example, telling the user to reset the rate sensors.

Another optical device such as a laser or anIR emitter814 can be provided in theorientation device172A. An IR emitter can be useful to illuminate the fiduciaries to make them more readily detectable by the cameras under the intense lighting in the surgical field.

B. Optical Component for Femur Tracking

FIGS. 76-78 illustrate an embodiment of asystem600 that includes anoptical component674. In this context, optical component is a broad term. Thesurgical orientation device172 can compriseoptical component674 that can be located on the top side, the bottom side, or sidewalls of thesurgical orientation device172. Theoptical component674 can comprise transparent window integrated into thesurgical orientation device172. The windows can permit visible light (e.g. laser light) to emit from theoptical component674 of thesurgical orientation device172. Theoptical component674 can provide a visual guide to replicate the original position of the femur relative to the pelvis.

With continued reference toFIG. 76, theoptical component674 can comprise one or more lasers, which can be configured to project laser light through the windows described above. For example, theoptical component674 can comprise a forward laser. The laser light can be used to project a point, a plane, and or a cross-hair onto a target or targets, including but not limited to an anatomical feature or landmark.

Theoptical component674 can provide alternative or additional orientation information to a surgeon regarding the orientation of thesurgical orientation device172. For example, laser light can be used to project a plane on a portion of bone to indicate a resection line and a cross-hair laser pattern can be used to ensure alignment along two perpendicular axes. In certain embodiments, theoptical component674 can be used to determine an alignment of an anatomical feature or landmark. For example, theoptical component674 can project laser light to a target such as an anatomical feature. The surgeon can mark one or more points along the line of the projection of theoptical component674. The surgeon can complete any steps described herein. The surgeon, thereafter, can verify the one or more points are along the line of the projection of theoptical component674.

In the illustrated embodiment, theoptical component674 is a component of thesurgical orientation device172. Other configurations are contemplated. Theoptical component674 can be a component of thefixation base602. Theoptical component674 can be a component of one or more fixation pins610,612. Theoptical component674 can be an integral feature of any component ofsystem600. Theoptical component674 can be a separate component from any component ofsystem600. Theoptical component674 can be a stand-alone device which attaches to the pelvis.

Thesystem600 can be modified to accommodate theoptical component674. Thefixation base602C can include aplatform620C as shown inFIGS. 79-80. Theplatform620C can include ahead609C. Thehead609C can be coupled to aplatform611C and asupport613C. Theplatform611C and thesupport613C can function as a clamp with thehead609C.FIG. 80 shows an exploded view of thefixation base602C.

In the illustrated embodiment, thefixation base602C can include one ormore fixation devices615C. In the illustrated embodiment, onefixation devices615C is shown but other configurations are contemplated (e.g., two, three, four, etc.). Thefixation device615C can include one or more threaded sections. In the illustrate embodiment, thefixation device615C is a screw with a head and a threaded shank. Theplatform611C can include one or more holes. Thesupport613C can include one or more holes. Thefixation device615C can pass through or engage one or more holes in thesupport613C. In some embodiments, each hole in thesupport613C is threaded. Thefixation devices615C can pass through or engage one or more holes in theplatform611C. In some embodiments, each hole in theplatform611C is threaded. Rotation of thefixation device615C can causes thesupport613C to move toward theplatform611C and/or theplatform611C to move toward thesupport613C. Theplatform611C and thesupport613C form achannel617C. Thechannel617C can be sized to accept thehead609C. When theplatform611C and thesupport613C are separated, the head608 can have pivotal or polyaxial movement. When theplatform611C and thesupport613C are brought together by thefixation device615C, the head608C can be fixed in position.

Theplatform611C can include thefirst coupler632 described herein. Thefirst coupler632 can couple to thefirst assembly604 as described herein. InFIG. 18, thefirst coupler632 can be parallel to the

pins

610,612. InFIG. 76, thefirst coupler632 can be angled relative to the

pins

610,612. In the anterior approach, the

pins

610,612 can be offset from vertical. The probe678 (not shown) can be bent or curved as described herein. The shape of theprobe678 can facilitate the touching of points or anatomical landmarks in the anterior approach.

The assembly shown inFIG. 76 can permit the surgical orientation device to be moved relative to the anatomy of the patient. The clamping of theplatform611C and thesupport613C can fix the position of thesurgical orientation device172 during surgery. The display of thesurgical orientation device172 can indicate whether theoptical component674 is on or off. The display of thesurgical orientation device172 can include an instructions related to the method of using theoptical component674.

In a preferred arrangement, thesurgical orientation device172 can be positioned and/or moved until theoptical component674 projects a beam on a portion of the anatomy. To achieve this centering, theoptical component674 can emit a laser beam or beams distally from thesurgical orientation device172. This laser beam or beams can illuminate a portion of the femur. This laser beam or beams can illuminate a portion of the knee joint. This laser beam or beams can illuminate a portion of the tibia. This laser beam or beams can illuminate a portion of the ankle. This laser beam or beams can illuminate a portion of the foot. This laser beam or beams can illuminate a portion of the foot constrained within a positioning boot. Thesurgical orientation device172 can be moved until the laser beam is aligned with at least one anatomical region. In some methods, the laser beam is aligned with at least one anatomical region with little soft tissue. The soft tissue may move relative to the underlying bone. The surgeon can select locations to mark where the skin is close to the underlying bone.

Theoptical component674 can be used in conjunction with the anterior and posterior approach described herein. When measuring changes in leg length and lateral joint offset, the apparent changes are sensitive to changes in the orientation of the femur relative to the pelvis. The changes are particularly sensitive to the abduction angle. The changes are moderately sensitive to the rotation about the mechanical axis of the femur. There may be two methods available to the surgeon. The first method is to reposition the femur prior to measuring the change such that the orientation of the femur relative to the pelvis is the same as that when the preoperative baseline measurement was made. Surgeons attempt to use the first method but this method is not very accurate. The method is not accurate primarily because the sugeon has poor visibility of the pelvis of the patient, which is hidden by soft tissue and surgical drapes.

The second method is to measure the orientation of the femur relative to pelvis during preoperative baseline and postoperatively and then correct for changes in orientation by doing a virtual rotation about the postoperative center of rotation of the femur. The second method is described herein with respect to the posterior approach and the anterior approach. The second method may require obtaining three points of the femur, such aspoints690 shown inFIGS. 24A and 25C. The second method may require calculating the center of rotation (COR) of the hip using the set of points on the rim of the shell, as shown inFIG. 33. The second method is usually used in navigation systems but adds extra steps. In the case of the posterior approach described above, for example, threepoints690 on the femur,

femur tracker

686,686A orfemur base687A must be registered to resolve for the femur orientation preoperatively and then postoperatively each time the leg length is to be measured. Also, the center of rotation must be determined which is done by registering three points on the acetabular cup after it has been inserted.

Theoptical component674 can reduce the number of registrations. Theoptical component674 can be mounted on the pelvis. The orientation of theoptical component674 can be fixed throughout the procedure. Theoptical component674 can project a beam distally onto the leg. The surgeon can mark one or more points. These marks can guide the surgeon in replicating the orientation of the femur relative to the pelvis each time a leg length measurement is needed.

In some embodiments, theoptical component674 can be a “fan” style laser projection. Theoptical component674 can project a line or pattern onto the leg. The method can, in variation, include any of the following steps. The following method is described in the context of an anterior approach in which the patient is supine as shown inFIG. 76. The method can include positioning the operative leg in a fully extended position to simulate a standing position. The method can include projecting the laser onto the anterior surface of the leg, running up the foot. The laser could be mounted on a lockable ball joint to facilitate adjustments to line up the laser and then lock it in place, as shown inFIG. 79. The method can include marking one or more marks Lm on the surface of the leg and foot coincident with the laser line. The method can include performing the baseline leg length measurement or registration on the exposed bone of the femur as close to the center of rotation as possible. This may minimize errors. This step can include placing a mark Fm on skin over the femur as described herein. For example, a mark placed at the distal femur may provide enhanced accuracy by eliminating error due to movement of the joints distal thereof. Such a location may also simplify an accurate procedure by eliminating the need to constrain the distal joints including the knee and ankle. The method can include performing the hip replacement. The method can include replicating the orientation of the femur by lining up the one or more marks Lm with the laser line again. The method can include performing the postoperative leg length measurement to determine changes in leg length and lateral offset. This step can include registering the mark Fm on the femur as described herein.

The method described herein can reduce the need to add a

femur tracker

686,686A orfemur base687A to the femur. The method described herein can reduce the need to drill holes in the femur to attach the

femur tracker

686,686A orfemur base687A. This can prevent fractures or further damage to the femur. In some methods, theoptical component674 is used in combination with a camera. The camera can be thecamera684 described herein. The camera can becamera812 described herein. The camera can capture a photographic image of the laser or laser beam. The camera can capture a photographic image of the one or more marks Lm. The camera can capture a photographical image of the leg and/or foot. Thesurgical orientation device172 and/or theorientation sensing device204 as described herein can convert the photographic image to orientation and/or positional information of the anatomy of the patient.

Although these inventions have been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that this application extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the inventions have been shown and described in detail, other modifications, which are within the scope of the inventions, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the application. For example, the application contemplates the connection hub alone or in combination with any of the other modules could comprise a separate aspect. Or, any one or a combination of the modules could be directly connected to an umbrella hub or overhead support to form another separate aspect. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed embodiments. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.