US20100114101A1 - Method of resecting a femoral head for implantation of a femoral neck fixation prosthesis - Google Patents

Abstract

A femoral neck fixation prosthesis and method of using same which reduces bone loss and the avoids the other shortcomings of the prior art by allowing the fixation of a stable femoral head replacement while reducing the amount of the femur which must be reamed for the insertion of the prosthesis. The preferred embodiment provides that the femoral head is attached to a fixation prosthesis, which extends coaxially through the canal of the femoral neck, into the femur, and is then attached to the opposite lateral wall of the femur. In this manner, the prosthesis serves to imitate the original structure of the femoral neck. No other support members, either crosspins or arms extending into the length of the femur, are required.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 10/779,353, filed Feb. 14, 2004, which is a continuation of U.S. patent application Ser. No. 10/228,907, filed Aug. 27, 2002, now U.S. Pat. No. 6,695,883, which claims priority to U.S. Provisional Application No. 60/371,837, filed Apr. 11, 2002. Priority is claimed to all of the above-mentioned applications and patents, and each application and patent is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention The present application relates generally to hip prostheses and more specifically to an improved method of implanting a femoral neck fixation prosthesis in the femoral neck.
• 2. Description of Related Art
• A widely used design for replacement of the proximal portion of a femur employs an elongate, often curved, shaft that extends into the medullary canal of the femur. This design has the tendency to place unnatural stresses on the femur, which lead to pain and the consequent curtailment of activity for the patient. Further, present techniques can lead to proximal bone loss and call for the resection of the majority of the femoral neck. Current designs also call for fixing the prosthesis in the proximal third of the femur. The useful life of an intramedullary implant is often less than the expected life span of a young patient.
• Previously known prostheses for replacing a femoral head that do not extend into the medullary canal have been mechanically complex or have proven troublesome in actual use. Huggler, U.S. Pat. No. 4,129,903 and Grimes, U.S. Pat. No. 4,795,473 are examples of prosthetic implants having a side plate attached to the exterior lateral side of the femur opposite the femoral head. Screws are used to secure the plate to the femur and one or more holes are drilled into the femur for securing the plate to the bone. The additional holes and the stresses at the site of fixation are believed to cause trauma to the bone.
• Masini, U.S. Pat. No. 5,571,203 discloses a device having a shaft that extends through a resected portion of the proximal femur, positioned co-axially relative to the longitudinal axis of the femur. The device is secured by a screw or similar locking device that extends into the femur from the lateral side, just below the greater trochanter. It is believed that the natural forces applied to the prosthesis during normal hip motion result in the application of shear forces to the greater trochanter. The shear forces can be harmful to the greater trochanter and can permit micro-movement of the prosthesis on the unsecured side.
• A conventional method for implanting the above types of femoral head implants is described in Campbell's Operative Orthopaedics, (Mosby, 7th ed., 1987) and typically includes making a large incision in the patient's lateral side at the hip joint and through the skin and muscle, dislocating the hip and then sawing off the femoral head. This method is considered invasive because of the need to dislocate the hip and cut through muscle surrounding the hip joint. Invasive procedures increase the trauma to the patient, the potential for complications, recovery time and the cost.
• Replacement of the proximal portion of the femur is sometimes necessary due to degenerative bone disorders or trauma to otherwise healthy bone caused by accidental injury. In the latter instance it is desirable to replace the traumatized portion of the bone without causing further trauma to healthy bone. There is a need, therefore, for an implant that replaces a traumatized portion of the femur, but also significantly minimizes stress to the remaining healthy bone and that can be implanted by a method that is less invasive.
• There are several other significant problems and issues relating to hip arthroplasty. One problem is encountered with the young, active patient. Younger patients are more likely to have failure of their primary arthroplasty both due to increased demand on the mechanical construct, and from a pure life expectancy standpoint. It follows that they are more likely to require a revision and a second revision, which may lead to a catastrophic bone loss situation.
• Another problem relates to instability of the hip following implantation of the prosthesis. This problem still occurs at the same rate that it did 50 years ago. Larger femoral heads may decrease the incidence, but no other significant technical changes have occurred to effect the incidence of this serious complication.
• Still another problem is related to bone loss in patients receiving hip prostheses. The overwhelming majority of present successful femoral prostheses achieve fixation at least as far distal as the proximal femoral metaphysis. When these prostheses fail, the next step usually involves diaphyseal fixation, often with a large diameter, stiff stem.
• Leg length inequality is another problem associated with hip arthroplasty. An average lengthening of the leg of 1 centimeter is common. Lengthening is sometimes accepted for the sake of improved stability; however, leg length inequality has been reported as the primary reason why surgeons are sued after hip arthroplasty.
• Finally, another problem associated with hip arthroplasty is surgical morbidity. The surgery usually involves significant blood loss, body fluid alterations, and pain. Shortly, the surgery is a big operation that hurts. It should be the goal of every compassionate surgeon to minimize these issues. If the operation can be made smaller, with less blood loss and less pain without diminishing long term results, every effort should be made to do so.
• It would therefore be desirable to provide a femoral neck prosthesis and method for implanting the prosthesis that overcomes these significant disadvantages.
BRIEF SUMMARY OF THE INVENTION
• It is therefore one object of the present invention to provide an improved apparatus and method for hip replacements.
• It is another object of the present invention to provide an improved and less-invasive prosthesis and implantation method that replaces the femoral head while retaining a substantially intact femoral neck.
• The foregoing objects are achieved as is now described. A femoral neck fixation prosthesis and method of implanting the prosthesis according to the principles of the present invention, reduce bone loss and avoid the other shortcomings of the prior art by allowing the fixation of a stable femoral head replacement while reducing the amount of the femur that must be removed and reamed for the insertion of the prosthesis. The preferred embodiment provides that the femoral head is attached to a fixation prosthesis, which extends coaxially through the central canal of the femoral neck, into the femur, and is then attached to the opposite lateral wall of the femur. In this manner, the prosthesis serves to imitate the original structure of the femoral neck. No other support members, either crosspins or arms extending into the length of the femur, are required.
• The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 illustrates a schematic of an anterior view of a prosthesis in accordance with the principles of the present invention;
• FIGS. 2A-2H depict a schematic of the cross-section at various levels of the body of a prosthesis in accordance with the present invention;
• FIG. 3 illustrates joining members used with a prosthesis in accordance with the present invention;
• FIG. 4 depicts a centering guide for placement of a starting pin in accordance with the present invention;
• FIG. 5 illustrates how the center of rotation of the femoral head can be reproduced in accordance with the present invention;
• FIG. 6 depicts a prosthesis in accordance with the principles of the present invention;
• FIG. 7 illustrates a prosthesis in accordance with the principles of the present invention;
• FIG. 8 depicts a posterior view of a human femur having a femoral head and a femoral neck;
• FIG. 9 illustrates multiple cross-sectional views of the femoral head and femoral neck ofFIG. 8 taken at A-A, B-B, and C-C;
• FIG. 10 depicts a perspective view of a femoral neck clamp according to the principles of the present invention positioned at an isthmus of the femoral neck ofFIG. 8;
• FIG. 11 illustrates a perspective view of the femoral neck clamp ofFIG. 10;
• FIG. 12 depicts a posterior view of a human femur with the femoral neck clamp ofFIG. 10 shown installed at an isthmus of the femoral neck, the handle members of the femoral neck clamp being omitted for clarity;
• FIG. 13 illustrates a cross-sectional distal view of the femur and femoral neck clamp ofFIG. 12 taken at XIII-XIII;
• FIG. 13A-13C depict alternative shapes of an inferior clamping member of the femoral neck clamp ofFIG. 13;
• FIG. 14 illustrates a posterior view of the femur and femoral neck clamp having superior and inferior clamping members, the inferior clamping member having a proximal clasp attached to a distal clasp by a connecting member according to principles of the present invention;
• FIG. 15 depicts a posterior view of a femur and femoral neck clamp similar to those ofFIG. 14, the femoral neck clamp having an alternative connecting member according to the principles of the present invention;
• FIG. 16 illustrates a posterior view of a femur and femoral neck clamp similar to those ofFIG. 14, the femoral neck clamp having an alternative connecting member according to the principles of the present invention;
• FIG. 17 depicts a side view of a femoral neck clamp according to the principles of the present invention;
• FIG. 18 illustrates a side view of a femoral neck clamp according to the principles of the present invention;
• FIG. 19 depicts a posterior view of a human femur having a femoral neck clamp attached to a femoral neck of the femur, a locator shaft connected to the femoral neck clamp, and a pin locator guide slidingly received on the locator shaft;
• FIG. 20 illustrates a perspective view of a human femur having a cutting guide positioned on pins placed in the femoral head using the pin locator guide ofFIG. 19;
• FIG. 20A depicts a method of resecting a femoral head according to the principles of the present invention;
• FIG. 21 illustrates a perspective view of a starter guide according to the principles of the present invention and a human femur having the femoral head of the femur resected;
• FIG. 22 depicts a posterior view of a human leg, including a human femur, and a drilling guide according to the principles of the present invention for preparing the femur for implantation of a femoral neck prosthesis;
• FIG. 23 illustrates a side view of the drilling guide ofFIG. 22;
• FIG. 23A depicts a method of preparing a femur for implantation of a prosthesis according to the principles of the present invention;
• FIG. 24 illustrates a posterior view of a femoral neck liner and a reamer path protector according to the principles of the present invention, the femoral neck liner being positioned within a femoral neck, and the reamer path protector being threadingly received by the femoral neck liner;
• FIG. 25 depicts a side view of the reamer path protector and femoral neck liner ofFIG. 23;
• FIG. 25A illustrates a method of preparing an acetabulum according to the principles of the present invention; and
• FIG. 26 depicts a method of implanting a prosthesis in a femur according to the principles of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof and in which is shown by way of illustration specific preferred embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is understood that other embodiments may be utilized and that logical mechanical, structural, and chemical changes may be made without departing from the spirit or scope of the invention. To avoid detail not necessary to enable those skilled in the art to practice the invention, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.
• The present invention provides a femoral neck fixation prosthesis and a method of implanting the prosthesis which reduces bone loss and avoids the other shortcomings of the prior art by allowing the fixation of a stable femoral head replacement while reducing the amount of the femur, that must be removed and reamed for the insertion of the prosthesis. The preferred embodiment provides that the femoral head is attached to a fixation prosthesis, which extends coaxially through the central canal of the femoral neck, into the femur, and is then attached to the opposite lateral wall of the femur. In this manner, the prosthesis serves to imitate the original structure of the femoral head while substantially retaining the natural femoral neck. No other support members, either crosspins or arms extending into the length of the femur, are required.
• A femoral neck fixation prosthesis in accordance with the principles of the present invention is designed to achieve fixation in the femoral neck with or without cement. Therefore, revision of the disclosed femoral neck fixation prosthesis would essentially become the complexity of a present day primary hip arthroplasty for the femoral component. The improved femoral neck fixation prosthesis would require an operation equivalent to a primary arthroplasty on the femoral side. Therefore it would be ideal for the younger patient, but would also be recommended for the older patients with accommodating anatomy.
• The innovative method for implanting the femoral neck fixation prosthesis would allow less muscular dissection, and the capsule can be repaired anteriorly at the end of the procedure. The disclosed femoral neck fixation prosthesis is designed to be used with larger diameter femoral heads. The combination of these factors would significantly improve stability of the hip. The goal is to minimize the need for hip position precautions postoperatively.
• One advantage of the preferred embodiment is that less bone would be resected initially using the femoral neck fixation prosthesis, and the stress would be transferred to the bone in the femoral neck. The metaphysis and the diaphysis of the proximal femur would be minimally disturbed. Only the femoral head itself will be resected.
• Another advantage of the preferred embodiment, is that the femoral neck length and offset would be accurately measured and reproduced when using the femoral neck fixation prosthesis. Leg length inequality due to hip arthroplasty could be minimized, and muscle mechanics could be accurately restored.
• Further, an operation using the femoral neck fixation prosthesis would be less invasive with less blood loss, less post operative pain, and less perioperative morbidity than an operation that employs the vast majority of commonly used prostheses.
• The economic implications of a shorter hospital stay, fewer blood transfusions, and fewer medical complications are significant.
• A femoral neck fixation prosthesis according to the principles of the present invention is shown inFIG. 1, whereinfemur100 is shown withfemoral neck105, joiningmember115, andprosthetic head110.
• An uncemented porous coatedfemoral prosthesis body125 with amodular head110 and joiningmember115 is provided. The metal used is preferably either titanium or chrome-cobalt based, and can be any metal commonly used in hip prosthesis construction. The modulus of elasticity of such a short segment will be of less significance than in a standard femoral stem. The coating is preferably either sintered beads or plasma sprayed, depending on the type of metal used for the body of the prosthesis.
• Thebody125 of the prosthesis will preferably be available in various diameters, approximately every 1-1.5 mm. The length of the prosthesis will preferably be chosen from one or two lengths, approximately 30 mm. Most of the fixation and ingrowth of the bone to the prosthesis will occur in the first 10-20 mm.
• As described in more detail below, fixation to the femur will be achieved by reaming thefemoral neck105 to accommodate a cylindrical porouscoated sleeve body125, which is supported by a proximal collar and given distal stability with acompression screw120 through the lateral wall of the femur just distal to the greater tuberosity (location140). Reaming will be progressive until the cortex of the femoral neck is encountered. A femoral component ½ mm greater than the last diameter reamed will then be selected.
• After insertion, the long axis of the body of thecomponent body125 will coincide with a longitudinal axis in thepreoperative femur100 corresponding to an imaginary line connecting the center of thefemoral neck105 with the center of thefemoral head110. Resection of the femoral head will be measured such that the center of rotation of thefemoral head110 can be measured and reproduced. Thefemoral neck105 will be reamed with a planar reamer that fits in the reamed canal of thefemoral neck105 to establish a flat surface. Theproximal body125 of the prosthesis will have the female end of a morse taper to allow the attachment of the joiningmember115.
• Acompression screw120 passes through the center of the body of the prosthesis. This screw attaches to abarrel nut130 in the lateral wall of the femur atpoint140 and preferably has a hexagonal head. Thescrew120 is preferably smooth in the segment within the body of the prosthesis and has threads on the distal end. The tunnel through the body of the prosthesis forms a snug fit around the smooth portion of thescrew120. Thebarrel nut130 is preferably angled to be flush with the lateral side of the femur atpoint140. The head of thescrew120 is preferably located in the base of the morse taper in thebody125 of the femoral component. Thisscrew120 adds stability to the construct by giving antero-posterior and varus-valgus stability to thebody125 of the prosthesis and by compressing the prosthesis on theneck105 of thefemur100. These screws will be available in various lengths.
• It is important to note that this innovative design allows the prosthesis to be installed and used without requiring any other fastener on the femur. In particular, the preferred embodiment does not require any additional screws or other fasteners to be placed in the femur, and does not require any sort of support plate on the lateral wall of the femur.
• Male-male morsetaper joining member115 acts as a joining portion in connecting thebody125 of the prosthesis to thefemoral head110. Adjustments in joining member length will occur in this segment with several lengths of joining member segments available for each femoral body and femoral head. The joining member segment needed to exactly reproduce the center of rotation of the femoral head will be known based on the amount of bone resected. In this embodiment, the joiningmember115 has male morse tapers135 on each side, and will have a variable-length section in between the morse tapers to fit the specific patient.
• Thefemoral head110 will have a female morse taper to connect to the joiningmember115. Femoral heads110 will be of various diameters depending on the acetabulum, and several exemplary sizes are shown inFIG. 1. Ideally, larger femoral head diameters (e.g., 36 mm to 50 mm) are used to both improve stability and prevent impingement of the neck on the acetabular rim. Thefemoral head110 is preferably polished chrome-cobalt, as the industry standard, but other materials can be used.
• In another embodiment of the present invention, a de-rotation component is added to reduce the likelihood of the rotation of the prosthesis within the femoral neck. This can be accomplished with a pin or stem with grooves or slots that passes through the lateral cortex into the body of the prosthesis. This would then be compressed with a screw, which would be put through the head end of the body of the prosthesis into the stem.
• It should be clear that the femoral neck fixation prostheses described herein can be used with or without cement.
• FIGS. 2A-2C show several cross-sectional views of the cylindrical porouscoated body225 of the prosthesis of the preferred embodiment.FIG. 2A shows a longitudinal cross-section of thebody225. In this view, acollar248 at the proximal end of thebody225 is illustrated, as is the femalemorse taper cavity246, which is fit to receive the joining member. Thecollar248 is configured to abut the proximal end of the resected femoral neck. Communicating withcavity246 istubular channel247 which will receive the compression screw. Below thecollar248, the exterior of thebody225 has a porouscoated layer249.
• While the preferred embodiment has a substantially circular cross-section, as shown inFIGS. 2A-2C, thebody member225 can also be configured with a triangular (FIG. 2E), scalloped (FIG. 2F), oval (FIG. 2H), or fluted (FIG. 2G) cross-section.
• FIG. 2B shows a lateral cross-section ofbody225 as cut across line B ofFIG. 2A. InFIG. 2B, thecavity246 is shown, and theproximal collar248 is also illustrated.
• FIG. 2C shows a lateral cross-section ofbody225 as cut across line C ofFIG. 2A. InFIG. 2C,channel247 for the compression screw is shown passing through the center ofbody225. On the exterior ofbody225 is shown the porouscoated layer249. A cross-section across line D ofFIG. 2A is the same as described for line C of that FIG.
• FIG. 3shows joining members316/317/318 of various sizes, which can be used for patients with differing requirements. Each joiningmember316/317/318 has a morse taper on each end, and a variable-length straight section connecting the morse tapers.
• FIG. 4 depicts the centering guide for placement of the starting pin in accordance with the principles of the present invention. In this FIG., femoralneck gripping clamp405 is to grip and hold the femoral neck after the femoralhead centering device410 has been placed over the patient's femoral head.
• The femoralneck gripping clamp405 is expanded or contracted usingadjustment piece420, which operates gears415.Cannulated rod425, which is connected to femoralhead centering device410, allows pin insertion into the cannula at435.
• Free nut430 is used to tighten the femoralhead centering device410. The centering guide shown inFIG. 4 is preferably made of a stiff metal, and can also be used as a retractor to expose the femoral head.
• FIG. 5 depicts how the center of rotation of the femoral head can be reproduced in accordance with a preferred embodiment of the present invention. First, distance A from the head to the lateral cortex is measured. After the femoral head is removed, distance B, from the cut surface to the lateral cortex, is measured. The diameter D of the femoral head is also measured. When these measurements are known, distance C is calculated using the formula
• 
  C=(A−D/2)−B
• Distance C then represents the distance from the cut surface of the femoral neck that the prosthetic femoral head center-of-rotation should be placed in order to reproduce the pre-operative femoral head center-of-rotation.
• In another embodiment shown inFIG. 6,compression screw620, preferably withwasher645, is inserted through the lateral wall of the femur atlocation640 and screwed into thebody625 of the femoral component. This simplifies the barrel nut portion of the design shown inFIG. 1. It would require that thescrew620 be of various lengths that would engage thebody625 of the prosthesis without reaching the depth of the hole in the femoral prosthesis. The body of the prosthesis would preferably be longer, usingoptional extension650 to provide enough length so that the compression screw will be stable within the body of the prosthesis.
• The remainder ofFIG. 6 is similar toFIG. 1. In this FIG.,femur600 is shown withfemoral neck605, joiningmember615, andprosthetic head610.
• This embodiment provides an uncemented porous coatedfemoral prosthesis body625 with amodular head610 and joiningmember615. Thebody625 of the prosthesis includethreads655 for receivingscrew620.
• As described in more detail below, fixation to the femur will be achieved by reaming thefemoral neck605 to accommodate a cylindrical porouscoated sleeve body625, which is supported by a proximal collar and given distal stability with acompression screw620 through the lateral wall of the femur just distal to the greater tuberosity (location640).
• After insertion, the long axis of the body of thecomponent body625 will coincide with a longitudinal axis in thepreoperative femur600 corresponding to an imaginary line connecting the center of thefemoral neck605 with the center of thefemoral head610. Resection of the femoral head will be measured such that the center of rotation of thefemoral head610 can be measured and reproduced as discussed with reference toFIG. 5. Thefemoral neck605 will be reamed with a flat reamer that fits in the reamed canal of thefemoral neck605 to establish a flat surface. Theproximal body625 of the prosthesis will have the female end of a morse taper to allow the attachment of thefemoral neck615.
• Compression screw620 passes through the center of the body of the prosthesis. Thescrew620 is preferably smooth in the segment within the body of the prosthesis and has threads on the proximal end, for engagingthreads655. The tunnel through the body of the prosthesis forms a snug fit around the smooth portion of thescrew620.Screw620 adds stability to the construct by giving antero-posterior and varus-valgus stability to thebody625 of the prosthesis and by compressing the prosthesis on theneck605 of thefemur600. These screws will be available in various lengths.
• Male-male morsetaper joining member615 connects thebody625 of the prosthesis to thefemoral head610. Adjustments in joining member neck length will occur in this segment with several lengths of joining member segments available for each femoral body and femoral head. The joining member segment needed to exactly reproduce the center of rotation of the femoral head will be known based on the amount of bone resected.
• Thefemoral head610 will have a female morse taper to connect to the joiningmember615. Femoral heads610 will be of various diameters depending on the acetabulum. Ideally larger femoral head diameters (e.g., 36 mm to 60 mm) are used to both improve stability and prevent impingement of the neck on the acetabular rim. Thefemoral head610 is preferably polished chrome-cobalt, as the industry standard, but other materials can be used.
• FIG. 7 shows a preferred embodiment of the femoral neck fixation prosthesis of the present invention. If thecompression screw720, withwasher745, is inserted through the lateral wall of the femur at740, the length of thebody725 of the prosthesis may not be long enough to provide adequate stability for thecompression screw720. In order to provide this stability for the compression screw, a fixedlength joining member760 on the body of the prosthesis would be necessary to act as a joining member, abandoning the modular joining member (115 inFIG. 1). The varied lengths required on the joining member would be incorporated into the femoral head either with separate individual lengths for each head diameter (2 to 3 for each diameter femoral head) or by using an interposing piece of metal to provide additional neck length. The latter is done with several femoral components available on the market today.
• The femoral neck fixation prosthesis is implanted by first preparing the femur for reception of the prosthesis. Referring toFIG. 8, several orientations and anatomical features relative to afemur811 should first be defined to more easily understand the process of preparing the femur and implanting the prosthesis. As used herein, the term “medial” shall mean “pertaining to the middle,” while the term “lateral” shall mean “pertaining to the side.” Thefemur811 includes amedial side813 and alateral side815. The term “proximal” shall mean “nearest the point of attachment, center of the body, or point of reference,” while the term “distal” shall mean “the opposite of proximal, or farthest from the center, from a medial line, or from the trunk.” The terms proximal and distal are generally used to convey positional or directional information relative to a particular feature, so it would not be entirely proper to refer to a proximal “side” of the femur or a distal “side” of the femur. However, these terms can be demonstrated by comparing some of the basic anatomy of the femur.Femur811 includes afemoral head821, afemoral neck823, ashaft825, agreater trochanter827, and alesser trochanter829. Since thefemoral head811 serves as a point of attachment when it is received by the acetabulum (not shown), thefemoral head821 is located proximal to thefemoral neck823 and theshaft825. Theshaft825 is located distal to both thefemoral neck823 and thefemoral head821. As used herein the term “superior” shall mean “higher than or situated above something else,” while the term “inferior” shall mean “beneath or lower.” The term “anterior” shall mean “before or in front of” and shall generally refer to the ventral or abdominal side of the body. The trem “posterior” shall mean “toward the rear” and shall generally refer to the back or dorsal side of the body. Aposterior side831 of thefemur811 is shown inFIG. 8, while the anterior side is hidden from view inFIG. 8.
• Alongitudinal axis845 of the femoral neck is difficult to precisely define because the geometry of thefemoral neck823 is usually not perfectly cylindrical. Theoretically speaking, if thefemoral neck823 were sectioned along its length at a finite number of cross-sectional planes (e.g. B-B and C-C inFIG. 8), and the center of each cross-section were determined, the line passing through the center of rotation of the femoral head (described previously with reference toFIG. 5) and passing through an average of the centers of the cross-sections would likely represent thelongitudinal axis845 of thefemoral neck823. In reality, it is difficult to locate the center of each cross-section of thefemoral neck823. It is also difficult to locate the plane at which each cross-section would be taken. Theoretically, each cross-section is located at a plane perpendicular to thelongitudinal axis845, but this presents a somewhat circular method for determining the orientation of the cross-sectional planes and thelongitudinal axis845.
• One method for determining the proper orientation of the cross-sectional planes would be to envision anisthmus849 of thefemoral neck823. Theisthmus849 is the narrowest point on thefemoral neck823 when viewed from the anterior or posterior side of thefemur811. Visualization of theposterior side831 of thefemur811 allows a lateral line to be constructed across thefemoral neck823 at theisthmus849. InFIG. 8, the line at section C-C represents anisthmus plane851, which is a cross-sectional plane extending through the femur in an antero-posterior direction. The visualization of this plane at theisthmus849 of thefemoral neck823 allows a close approximation of a plane that would be perpendicular to thelongitudinal axis845 of thefemur811. Other cross-sectional planes visualized through thefemoral neck823 would be parallel to the isthmus plane at theisthmus849.
• In practice, thefemoral neck823 is not actually cut at each of the cross-sectional planes discussed above. Rather, the visualization of these planes is helpful in determining, theoretically, where thelongitudinal axis845 of thefemoral neck823 would lie. It would be sufficient to define thelongitudinal axis845 as the line passing through the center of rotation of thefemoral head821 and the center of thefemoral neck823 at theisthmus849. However, as previously mentioned, it would also be appropriate and perhaps more accurate to define thelongitudinal axis845 as the line passing through the center of rotation of thefemoral head821 and the average of the centers of thefemoral neck823 taken at several cross-sections, all of which are parallel to theisthmus plane851. It should also be noted that for some patients, the center of rotation of the femoral head may not necessarily coincide with thelongitudinal axis845.
• Referring toFIG. 9, the visualization of the “center” of the femoral neck is not necessarily simple due to the varying geometry of thefemoral neck823. For example, a cross-section taken at A-A in a region of transition between thefemoral head821 and thefemoral neck823 is approximately round. However, the cross-sectional shapes of thefemoral neck823 taken at B-B and C-C are not perfectly round, and instead have various protrusions and other anatomical features that make it difficult to locate the center point of the cross-section. A cross-section from a more proximal portion of thefemoral neck823 is illustrated at B-B and demonstrates that this portion of the neck is somewhat circular in shape. Cross-section C-C at theisthmus849 of thefemoral neck823 illustrates several prominent features that cause thefemoral neck823 to deviate from a perfectly round shape. The features of the femoral neck at C-C include an antero-superior ridge850 and a postero-inferior ridge855. The antero-superior ridge850 is a pronounced feature of thefemoral neck823 at this part of thefemoral neck823 and joins thegreater trochanter827 in a region distal to theisthmus849. The postero-inferior ridge855 is less pronounced and joins thelesser trochanter829 in a region distal to theisthmus849. Thefemoral neck823 includes a relatively flatsuperior surface857, while aninferior surface859 is more rounded. These anatomical features of any particular femur will vary slightly and could vary greatly from person to person.
• Referring still toFIGS. 8 and 9, the center of any given cross-section will be at the mean geometric center for any particular cross-section. When several cross-sections are visualized along thefemoral neck823, the mean geometric centers of all the cross-sections may not be aligned such that the centers can be connected by a line. In this particular instance, a line representinglongitudinal axis845 could be drawn through the center of rotation of the femoral head and through the plurality of cross-sectional centers so as to minimize deviation with respect to the plurality of cross-sectional centers. If the femoral head is misshapen, thelongitudinal axis845 may be considered only with respect to the cross-sectional centers and not the center of rotation of the femoral head.
• Alternatively, the center of each cross-section could be located based on the shape of the cancellous bone at that cross-section. Since the prosthesis according to the principles of the present invention is to be implanted within the cancellous bone, it may be more appropriate to define the center of thefemoral neck823 based on the shape and location of the cancellous bone. The center of each cross-section would be the point at which a circle circumscribed around the point would most fully contact the surrounding cortex.
• The “location” and/or “visualization” of thelongitudinal axis845 of thefemoral neck823 is theoretical and is discussed to more easily explain how the femoral neck fixation prosthesis is oriented and implanted within thefemur811. It is not necessarily required that thelongitudinal axis845 be found prior to implanting the prosthesis; however, it is important to note that in most cases, the femoral neck fixation prosthesis will be installed in the femur such that a longitudinal axis of the prosthesis is substantially coaxial to thelongitudinal axis845 of thefemoral neck823 as described above. This implantation could be accomplished by using non-invasive techniques such as X-rays or magnetic resonance imaging (MRI) to visualize and locate thelongitudinal axis845 of thefemoral head823, but in most instances, the prosthesis will be implanted using specialized tools that properly orient the prosthesis based on anatomical landmarks on the femoral neck. We believe that the use of these tools and anatomical landmarks will closely align the prosthesis with the longitudinal axis of the femoral neck, thereby obviating the need for calculating or identifying the longitudinal axis during the procedure.
• It will be appreciated by those of ordinary skill in the art that certain femoral anatomical variations among patients may result in the prosthesis being implanted such that the longitudinal axis of the prosthesis is not coaxial to thelongitudinal axis845 of thefemoral neck823. In fact, the implantation of the prosthesis in some patients could result in the longitudinal axis of the prosthesis being located as much as 5 to 10 degrees from thelongitudinal axis845 of thefemoral neck823.
• Implantation of the femoral neck fixation prosthesis is accomplished by resecting thefemoral head821, reaming at least one passage through the femoral neck, reaming the acetabulum, and implanting the femoral neck fixation prosthesis into the reamed passage. Access to the femoral head and femoral neck is accomplished by making a small incision in the gluteus maximus to expose the hip joint. Thefemoral head821 is dislocated from the acetabulum in a manner similar to that employed in current hip arthroplasty procedures. The leg of the patient is then internally rotated (i.e. rotated such that the toe of the patient's foot are rotated toward a medial plane of the body) to expose the femoral head and neck through the incision. Following exposure, the femoral head may be resected as explained below from the internally rotated position. The remaining procedures (i.e. reaming the passages, reaming the acetabulum, and implanting the femoral neck fixation prosthesis) are performed as described below with the patient's leg in either the internally-rotated position or in a neutral position (i.e. non-rotated position). The procedures for preparing the femur and implanting the prosthesis could alternatively be accomplished by rotating the patient's leg externally if the location of the initial incision were moved.
• Referring toFIGS. 10-13, afemoral neck clamp1011 according to principles of the present invention assists in locating the cutting plane at which thefemoral head821 is to be resected. Thefemoral neck clamp1011 does this by locating theisthmus849 of thefemoral neck823 by grasping anatomical landmarks on the femoral neck, such as the antero-superior ridge850 and the inferior region of thefemoral neck823. Again, theisthmus849 defines a line that is substantially perpendicular to thelongitudinal axis845 of thefemoral neck823.
• Thefemoral neck clamp1011 includes aninferior clamping member1013 and asuperior clamping member1015. A locatorshaft guide member1021 includes acylindrical passage1023 and is attached to either theinferior clamping member1013 or thesuperior clamping member1015. Thesuperior clamping member1015 preferably includes anarcuate region1025 for securely gripping the antero-superior ridge850 (seeFIG. 9) of thefemoral neck823; however, thesuperior clamping member1015 could be substantially flat with no arcuate region. Theinferior clamping member1013 preferably includes aproximal clasp1031 and adistal clasp1033 that are connected by a connectingmember1035. Theinferior clamping member1013 cradles the inferior region of thefemoral neck823 with preferably at least two points of contact occurring between thefemoral neck823 and each of the proximal anddistal clasps1031,1033. It is important to note that while it is preferred that the shape of the proximal anddistal clasps1031,1033 is V-shaped, the shape could be hemi-circular (seeFIG. 13A), square (seeFIG. 13B), polygonal (seeFIG. 13C), or any other shape that provides adequate contact with thefemoral neck823. While the preferred embodiment includes the presence of a proximal and distal clasp, theinferior clamping member1013 may include only one clasp that is preferably aligned with thesuperior clamping member1015 to locate theisthmus849 of thefemoral neck823.
• Referring still toFIGS. 10 and 11, thefemoral neck clamp1011 preferably includes ahandle portion1041 having a pair ofhandle members1043 biased apart by aspring member1045. Thespring member1045 is preferably made from sheets of spring steel and shaped to hold thehandle members1043 apart in an open position. However, thespring member1045 could be any device used to apply such a force, including without limitation a helical spring, a leaf spring, or a resilient bushing. A pair ofrods1047 is rigidly attached to one of the handle members, and eachrod1047 passes through anaperture1049 in theother handle member1043. Since thehandle members1043 are not pivotally attached, therods1047 assist in guiding the movement of thehandle members1043 relative to one another. By applying a force to eachhandle member1043 directed toward the other handle members1043 (i.e. by squeezing the handle members1043), a surgeon can decrease the distance between the inferior andsuperior clamping members1013,1015 in order to position the clamping members securely around the femoral neck. When the squeezing force applied to thehandle members1043 is released or relaxed, thespring member1045 pushes thehandle members1043 apart, thereby returning thefemoral neck clamp1011 to the open position. The configuration of thehandle members1043,rods1047, andspring member1045 allow the inferior andsuperior clamping members1013,1015 to move in translational, parallel fashion relative to one another when thehandle members1043 are squeezed. Since rotation of thehandle members1043 relative to one another is avoided, the inferior andsuperior clamping members1013,1015 are allowed to more effectively grip the appropriate anatomical features of thefemoral neck823. A lockingmember1051 may be attached to thehandle portion1041 to lock the inferior andsuperior clamping members1013,1015 once positioned around thefemoral neck823. The lockingmember1051 shown inFIG. 11 is pivotally attached to one of thehandle members1043 and is rotatably positionable to engage a plurality ofteeth1053 on at least one of therods1047. InFIG. 11, two lockingmembers1051 are shown.
• Thefemoral neck clamp1011 is used to locate theisthmus plane851, which is represented by a line inFIG. 12 at theisthmus849 of thefemoral neck823. To find theisthmus plane851, the inferior andsuperior clamping members1013,1015 are first positioned on inferior and superior sides of thefemoral neck823, respectively, with thesuperior clamping member1015 and theproximal clasp1031 visually aligned with an area of thefemoral neck823 that appears to be theisthmus849. As thehandle members1043 are squeezed, thesuperior clamping member1015 and theproximal clasp1031 grip thefemoral neck823 in the area of theisthmus849. Further squeezing of thehandle members1043 and gentle side-to-side manipulation of thefemoral neck clamp1011 in a direction approximately parallel to thelongitudinal axis845 of thefemoral neck823 allows thesuperior clamping member1015 and theproximal clasp1031 to settle at theisthmus849 of thefemoral neck823. Further alignment of thefemoral neck clamp1011 is ensured by thedistal clasp1033, which prevents thefemoral neck clamp1011 from rotating about the line representingisthmus plane851 inFIG. 12. Thedistal clasp1033 accomplishes this by providing a second point of contact for theinferior clamping member1013 in the inferior region of thefemoral neck823. Preventing rotation of thefemoral neck clamp1011 about the line representingisthmus plane851 inFIG. 12 could also be accomplished by having aninferior clamping member1013 that included a single clasp with a wider area of contact on the inferior region of thefemoral neck823. However, widening either theinferior clamping member1013 or thesuperior clamping member1015 too much will decrease the ability of thefemoral neck clamp1011 to find theisthmus849 since the inferior andsuperior clamping members1013,1015 will be unable to properly settle into the concave portions of thefemoral neck823 as illustrated inFIG. 12.
• Both the inferior andsuperior clamping members1013,1015 take advantage of anatomical landmarks present on thefemoral neck823 to locate theisthmus849 and theisthmus plane851, which is typically substantially perpendicular to thelongitudinal axis845 of thefemoral neck823. As previously mentioned, thesuperior clamping member1015 primarily contacts and, depending on whether it includes anarcuate region1025, cradles the antero-superior ridge850 (seeFIG. 13). Theinferior clamping member1013, including the proximal anddistal clasps1031,1033, preferably is formed in one of the shapes previously described (seeFIGS. 13-13C) to cradle the postero-inferior ridge855 and other portions of the inferior region of thefemoral neck823. Thedistal clasp1033 of theinferior clamping member1013 provides stability to thefemoral neck clamp1011 to prevent rotation of thefemoral neck clamp1011 about the line representingisthmus plane851 inFIG. 12. Thedistal clasp1033 is preferably not directly connected to either handlemember1043, but rather is connected toproximal clasp1031 by the connectingmember1035, which allows rotation of thedistal clasp1033 relative to theproximal clasp1031. By connecting thedistal clasp1033 to the proximal clasp1031 (as opposed to the handle members1043), the application of force through thehandle members1043 is directed primarily to thesuperior clamping member1015 and theproximal clasp1031. This allows thesuperior clamping member1015 and theproximal clasp1031 to more easily locate theisthmus849 of thefemoral neck823, while thedistal clasp1033 maintains rotational stability of thefemoral neck clamp1011 without causing thesuperior clamping member1015 and theproximal clasp1031 to shift positions along thefemoral neck823.
• Referring toFIGS. 14-16 in the drawings, several different variations of the connectingmember1035 are shown, each of which would be suitable to allow rotation of thedistal clasp1033. InFIG. 14, a connectingmember1411 is rigidly connected to thedistal clasp1033 and pivotally connected to theproximal clasp1031. A torsion spring (not shown) is operably connected to theproximal clasp1031 and the connectingmember1411 to bias thedistal clasp1033 toward thefemoral neck823 in a counter-clockwise direction (with respect to the view shown inFIG. 14). InFIG. 15, a connectingmember1511 is rigidly connected to both the proximal anddistal clasps1031,1033. The connectingmember1511 is preferably made from a resilient material such as spring steel that allows rotation of thedistal clasp1033 relative to theproximal clasp1031, but provides sufficient force to thedistal clasp1033 to firmly contact thefemoral neck823. InFIG. 16, a connectingmember1611 is rigidly attached to thedistal clasp1031 and is pivotally attached to theproximal clasp1031. The connecting member includes aslot1615; and afastener1617, preferably a screw, a bolt, or a locking pin, is received through theslot1615 and is attached to theproximal clasp1031. Thefastener1617 allows rotation of thedistal clasp1033 to be selectively chosen. After rotating thedistal clasp1033 enough to firmly contact thefemoral neck823, the fastener can be tightened or locked in place to prevent further rotation of thedistal clasp1033 relative to theproximal clasp1031.
• Referring again toFIGS. 10-12, the locatorshaft guide member1021 of thefemoral neck clamp1011 is connected to thesuperior clamping member1015 or thehandle member1043 adjacent thesuperior clamping member1015. The locatorshaft guide member1021 is oriented such that thecylindrical passage1023 of the locatorshaft guide member1021 is substantially parallel to thelongitudinal axis845 of thefemoral neck823 when thefemoral neck clamp1011 is finally positioned at theisthmus849. Typically, the locatorshaft guide member1021 will be rigidly connected to thesuperior clamping member1015 because the anatomy of most femurs is such that the positioning offemoral neck clamp1011 at theisthmus849 will provide automatic, parallel alignment of the locatorshaft guide member1021 relative to thelongitudinal axis845 of thefemoral neck823. However, it is conceivable that certain anatomical features of some femurs may prevent proper alignment of the locatorshaft guide member1021, so the locatorshaft guide member1021 may be adjustably mounted to thesuperior clamping member1015 to allow for rotational adjustment and visual alignment of the locatorshaft guide member1021 relative to thelongitudinal axis845.
• Referring toFIG. 17, afemoral neck clamp1711 according to the principles of the present invention includes aninferior clamping member1713 and asuperior clamping member1715 similar to those offemoral neck clamp1011.Femoral neck clamp1711 includes a parallelogram, four-bar-linkage mechanism1721 to provide translational movement (as opposed to rotational movement) of theinferior clamping member1713 relative to thesuperior clamping member1715.Linkage mechanism1721 includes aninferior handle member1743 pivotally connected to asuperior handle member1745.Superior handle member1745 is pivotally connected at one end to acoupler link1747 that is rigidly connected to thesuperior clamping member1715. Aside link1751 is pivotally connected at one end to thecoupler link1747 and at another end to theinferior handle member1743. Theside link1751 and the portion of thesuperior handle member1745 extending between theinferior handle member1743 and thecoupler link1747 are preferably parallel and equal in length. Thecoupler link1747 and the portion of theinferior handle member1743 extending between thesuperior handle member1745 and theside link1751 are preferably parallel and equal in length. Atorsion spring1753, or other spring mechanism, may be operably connected to theinferior handle member1743 andsuperior handle member1745 to bias thehandle members1743,1745, and thus the inferior andsuperior clamping members1713,1715, apart. A lockingmember1755 may be pivotally attached to an end of either the inferior orsuperior handle members1743,1745. Preferably, the lockingmember1755 includes a plurality ofteeth1759 adapted to engage theother handle member1743,1745 and thus lock theinferior clamping member1713 relative to thesuperior clamping member1715. A locatorshaft guide member1765 is connected to either theinferior clamping member1713 or thesuperior clamping member1715 similar to locatorshaft guide member1021 ofFIG. 12. Alternatively, the locatorshaft guide member1765 could be connected tocoupler link1747,inferior handle member1743, orsuperior handle member1745 near the inferior andsuperior clamping members1713,1715.
• Referring toFIG. 18, afemoral neck clamp1811 according to the principles of the present invention includes aninferior clamping member1813 and asuperior clamping member1815 similar to those offemoral neck clamp1011.Femoral neck clamp1811 further includes aninferior handle member1843 pivotally connected to asuperior handle member1845. Atorsion spring1853, or other spring mechanism, may be operably connected to theinferior handle member1843 andsuperior handle member1845 to bias thehandle members1843,1845, and thus the inferior andsuperior clamping members1813,1815, apart. A lockingmember1855 may be pivotally attached to an end of either the inferior orsuperior handle members1843,1845. Preferably, the lockingmember1855 includes a plurality ofteeth1859 adapted to engage theother handle member1843,1845 and thus lock theinferior clamping member1813 relative to thesuperior clamping member1815. A locatorshaft guide member1865 is connected to either theinferior clamping member1813 or thesuperior clamping member1815 similar to locatorshaft guide member1013 ofFIG. 12.
• Referring toFIG. 19, the femoral neck clamp1011 (could also befemoral neck clamp1711 or1811) has been positioned around thefemoral neck823 at theisthmus849 such that thesuperior clamping member1015 and theproximal clasp1031 of theinferior clamping member1013 are aligned with theisthmus plane851. Thedistal clasp1033 also engages thefemoral neck823 to prevent rotation of thefemoral neck clamp1011 about the line representingisthmus plane851. Following positioning of thefemoral neck clamp1011 at theisthmus849, the locatorshaft guide member1021 is automatically aligned such that a longitudinal axis of thecylindrical passage1023 of the locatorshaft guide member1021 is oriented at an angle of approximately ninety (90) degrees to theisthmus plane851.
• Alocator shaft1911 is positioned within thecylindrical passage1023 of the locatorshaft guide member1021 after thefemoral neck clamp1011 has been positioned at theisthmus849 of thefemoral neck823. Abase plate1915 is rigidly connected to an end of thelocator shaft1911 such that following insertion of thelocator shaft1911 in thecylindrical passage1023, thelocator shaft1911 can be advanced in a distal/lateral direction until thebase plate1915 abuts thefemoral head821.Indicia1921 in the form of ruled demarcations is printed along thelocator shaft1911 for accurately positioning apin locator guide1925, which is slidingly received on thelocator shaft1911.Pin locator guide1925 preferably includes at least two spaced apart holes1931 that may be located on one side of thelocator shaft1911, or as illustrated inFIG. 19, may be located on opposite sides of thelocator shaft1911.Holes1931 are positioned on thepin locator guide1925 such that a line connecting the center of theholes1931 is preferably parallel to theisthmus plane851.
• Referring toFIGS. 19 and 20, by slidably positioning thepin locator guide1925 along the locator shaft1911 a selectable distance from the proximal end of thefemoral head821,pins2011 can be inserted through theholes1931 on thepin locator guide1925. The placement of thepins2011 in thefemoral head821 fixes the previously determined orientation of theisthmus plane851, which allows thefemoral neck clamp1011 to be removed from the femur. InFIG. 20, a cuttingguide2021 includes a pair ofholes2027 that are spaced apart the same distance as the holes on thepin locator guide1925. The cuttingguide2021 is placed over thepins2011 such that thepins2011 are received by theholes2027. Acutting slot2025 is positioned on thecutting guide2021 such that it is oriented substantially parallel to a line connecting the centers of the twoholes2027. When installed on thepins2011 as shown inFIG. 20, the cuttingguide2021 places the cutting slot2025 a known distance from thepins2011 to allow resection of thefemoral head821 along a cutting plane (not shown) that is substantially parallel to theisthmus plane851. Thefemoral head821 is resected from thefemur811 by inserting a cutting blade or other cutting tool through thecutting slot2025 and cutting through that portion of thefemur811.
• As mentioned previously, thelocator shaft1911 includesindicia1921 in the form of ruled demarcations that are spaced apart precise distances. These demarcations can be used to precisely locate the cutting plane relative to the proximal end of thefemoral head821. The amount of resection that will be performed depends on several factors. A prosthetic femoral head will be chosen to match the measured diameter of the patient's native femoral head. This is done to insure that the center of rotation is closely matched by the prosthesis and that the length of the patient's leg is not significantly lengthened or shortened. Based on the diameter chosen for the prosthetic femoral head, a height of the prosthetic femoral head (measured along longitudinal axis845) will be known. This height equates to the amount of bone resected from the proximal end of the nativefemoral head823. Since the distance between theholes2027 on thecutting guide2021 and thecutting slot2025 is known, thepin locator guide1925 can be accurately positioned along thelocator shaft1911 using theindicia1921 to place thepin locator guide1925 according to the amount of bone that needs to be resected. The placement of thepins2011 using thepin locator guide1925 then allows thecutting slot2025 to be accurately positioned at the correct location to remove the correct length of bone.
• It will be apparent to one of ordinary skill in the art that the cuttingguide2021 of the present invention could be combined with thefemoral neck clamp1011 to eliminate the need for alocator shaft1911 and apin locator guide1925. The combination clamp and cutting guide would allow the clamp to be positioned at theisthmus849 of thefemoral neck823 as previously described, but would provide a slot or other guide to allow resection of the femoral head along a cutting plane substantially parallel to theisthmus plane851. The slot or guide would be adjustable relative to theisthmus plane851 to allow a measured amount of bone to be resected from thefemur811. A cutting guide that aligns the cutting plane a measured distance from theisthmus plane851 would be particularly useful in the event that the femoral head is missing, deformed, substantially misshapen, or broken. Measurements could be performed preoperatively using radiographic measurement techniques (e.g. X-ray).
• Referring toFIG. 20A, a method of resecting a femoral head from a femur having afemoral neck2051 is illustrated. The first step at2055 includes positioning a locator shaft adjacent an exterior surface of the femoral head and substantially parallel to a longitudinal axis of the femoral neck. At step2059 a pin locator guide having a least two holes is positioned along the locator shaft. At step2063 a pin is inserted through each of the two holes in the pin locator guide and into the femoral head. The femoral head is resected by aligning a cutting guide relative to the pins atstep2065.
• Following resection of thefemoral head821, aproximal neck surface2111 is exposed that is substantially parallel to theisthmus plane851. Progressive reaming and drilling of thefemoral neck823 is needed to prepare passages between theproximal neck surface2111 and thelateral side815 of thefemur821. With the patient's leg still in an internally rotated position (or alternatively in an externally rotated position), astarter guide2121 having apositioning portion2125 and aguide portion2127 is placed against theproximal neck surface2111 such that the surface of thepositioning portion2125 opposite theguide portion2127 mates with theproximal neck surface2111. Thestarter guide2121 further includes aguide passage2131 that passes through both theguide portion2127 and thepositioning portion2125 such that a longitudinal axis of theguide passage2131 is substantially perpendicular to theproximal neck surface2111 when thestarter guide2121 is placed against theproximal neck surface2111. A starter passage, or main passage, or primary passage2141 (represented inFIG. 21 by dashed lines) is formed in thefemoral neck823 from theproximal neck surface2111 by first drilling asmall hole2145 using a drill bit or other boring tool placed in theguide passage2131. The starter passage is preferably drilled only partially into the femoral neck, and not through thelateral side815 of the femur. When placing thestarter guide2121 and drilling thehole2145, it is preferred to visualize the approximate center of the femoral neck on theproximal neck surface2111 so that thehole2145 is approximately centered within thefemoral neck823.
• After drilling thehole2145, thestarter guide2121 is removed from theproximal neck surface2111, and thefemoral neck823 is progressively reamed until thehole2145 extends to the cortical bone of thefemoral neck823, thereby forming thestarter passage2141. In practice, depending on the anatomical shape of the patient'sfemoral neck823, it may only be possible to form thestarter passage2141 to contact the cortical bone at two points of contact. It is of course preferable to maximize the number of contacts of the cortical bone, and in most instances, it will be possible to contact the cortical bone in at least three locations without significantly decreasing the wall thickness of the cortex in any location, Thestarter passage2141 is reamed to a depth that is preferably equal to the longitudinal length of thebody125,625,725 (seeFIGS. 1,6 and7) of the femoral neck prosthesis. The final diameter of thestarter passage2141, which is determined by how much reaming is needed to contact the cortical bone, will be slightly less than the chosen diameter of thebody125,625,725 of the prosthesis.
• The method for forming thestarter passage2141 described above is largely based on visualization of the center of the femoral neck and formation of ahole2145. In an alternative embodiment, a guide may be placed flush against theproximal neck surface2111 to orient a reamer at a ninety (90) degree angle to theproximal neck surface2111 and center the reamer relative to the longitudinal axis of the femoral neck. The neck is sequentially reamed until thestarter passage2141 extends to the cortex. In another embodiment, a guide pin may be inserted into the femoral neck substantially parallel to the longitudinal axis of the femoral neck. The pin may be placed based on visualization or guided into place with a guide that is fixed relative to the femoral neck. The guide pin would be used to direct sequential reaming of thestarter passage2141.
• Referring toFIGS. 22 and 23, adrilling guide2211 having ananchor member2215 rigidly connected by a connectingmember2217 to analignment sleeve2219 is used to drill a distal passage, or fastener passage, or secondary passage2221 (represented inFIG. 22 by dashed lines) from thelateral side815 of thefemur811. Thealignment sleeve2219 includes analignment passage2225 for receiving a drill bit or other boring tool. The connectingmember2217 may be C-shaped and connects theanchor member2215 to thealignment sleeve2219 such that a longitudinal axis of thealignment passage2225 is coaxial to the longitudinal axis of theanchor member2215, both of which are coaxial to alongitudinal axis2227 of thedrilling guide2211. Theanchor member2215 is cylindrical and sized to fit within thestarter passage2141. Theanchor member2215 could be interchangeable to allow different diameters to be used to properly fit within thestarter passage2141 of a particular patient. Alternatively, theanchor member2215 could be tapered to allow a snug fit withinstarter passages2141 of several different diameters. Theanchor member2215 may also include acollar2231 for further stabilizing thedrilling guide2211 against theproximal neck surface2111 when inserted into thestarter passage2141.
• After positioning theanchor member2215 within thestarter passage2141, thealignment sleeve2219 is located on thelateral side815 of thefemur811. The patient's skin and othersoft tissue2233 are located between thealignment sleeve2219 and thefemur821. The leg of the patient is then rotated to a neutral position, and anincision2235 is made through the soft tissue of the patient in the vicinity of thealignment sleeve2219. Adrilling bit2241 or other boring tool is inserted through thealignment passage2225 of thealignment sleeve2219 for drilling thedistal passage2221 to join thestarter passage2141. Because thealignment sleeve2219 is coaxial to theanchor member2215 and because theanchor member2215 is securely positioned within thestarter passage2141, thedistal passage2221 is easily formed coaxial to thestarter passage2221.
• As shown inFIG. 22, thedistal passage2221 is typically smaller in diameter than thestarter passage2141, since thedistal passage2221 will receive thefastener120,620,720 (seeFIGS. 1,6, and7) for securing to thebody126,625,725 of the femoral neck fixation prosthesis.
• The primary reason for using adrilling guide2211 to complete drilling through the femur is that it is less desirable to drill a hole completely through the femur from theproximal neck surface2111 toward thelateral side815 of thefemur811. When drilling from theproximal neck surface2111, the patient's leg would be in the internally rotated position. It is not as safe to drill through thelateral side815 of thefemur811 when the leg is internally rotated because the drill bit may contact and sever vital anatomy, such as the femoral artery or other vessels and nerves, upon exiting thefemur811. Since use of thedrilling guide2211 allows the leg to be rotated back to the neutral position, drilling can proceed from thelateral side815 of thefemur811 without fear of contacting vital anatomy.
• Referring toFIG. 23A, a method of preparing a femur for implantation of a femoralneck fixation prosthesis2321 includes two steps. The first step at2325 includes first forming a main passage in the femoral neck from a medial side of the femur substantially coaxial to a longitudinal axis of a femoral neck. The second step at2329 includes second forming a secondary passage from a lateral side of the femur that is coaxial to and joins the main passage.
• Although the preparation of the femur for implantation of the prosthesis includes forming two separate passages from different sides of the femur, the starter and distal passages could be formed from the same side of the femur. Following the formation of thestarter passage2141, a guide may be placed within thestarter passage2141 to guide drilling of thedistal passage2221 from the proximal side of thefemoral neck823. Since the leg of the patient would likely be in an internally rotated position during this drilling procedure, care would be taken to only slightly penetrate the cortex on the lateral side of thefemur821. This would help avoid major arteries and nerves in the patient's leg. After forming both the starter anddistal passages2141,2221 from the medial side of the femur, thedrilling guide2211 could be used to place thefastener120,620,720 in the femur during the implantation of the femoral neck prosthesis, which is described in more detail below.
• After forming both thestarter passage2141 and thedistal passage2221, thefemur811 is capable of receiving the femoral neck fixation prosthesis. However, prior to implantation of the prosthesis, it may be desirable to prepare the acetabulum for receipt of an acetabular component (not shown) that will mate with the head of the femoral neck fixation prosthesis. The starter anddistal passages2141,2221 may be used to guide the preparation of the acetabulum, which initially involves reaming.
• Referring toFIGS. 24 and 25, areamer path protector2411 includes aninsertion end2415 and ahandle end2419. The insertion end preferably includes a plurality ofthreads2421, while thehandle end2419 includes ahand guard2425. Apassage2427 passes through thereamer path protector2411. Afemoral neck liner2431 is also provided and includes amain body2435 having apassage2437 and acollar2439. Thepassage2437 includesinternal threads2441 at an end of the main body2335 opposite collar2339.
• In operation, thereamer path protector2411 is inserted from thelateral side815 of thefemur811 and into thedistal passage2221. Thefemoral neck liner2431 is inserted from theproximal neck surface2111 into thestarter passage2141 until thecollar2439 mates with theproximal neck surface2111. Thefemoral neck liner2431 is sized in diameter the same as or slightly less than the diameter of thestarter passage2141. As is the case with the anchor member2215 (seeFIG. 22) discussed previously, thefemoral neck liner2431 could be provided in different sizes to fit variouslysized starter passages2141, or thefemoral neck liner2431 could be tapered. After inserting thefemoral neck liner2431, thereamer path protector2411 is advanced further into thedistal passage2221 until it contacts thefemoral neck liner2431. Thereamer path protector2411 is then rotated to engage thethreads2421 withinternal threads2441. The attachment mechanism between thereamer path protector2411 and thefemoral neck liner2431 is not required to be accomplished by a threaded connection. The connection could be formed by any mechanism that would allow the components to be easily disassembled following reaming of the acetabulum.
• When thereamer path protector2411 is securely fastened to thefemoral neck liner2431, a sufficient portion of thereamer path protector2411 remains extending outside of thefemur811 to allow gripping by the surgeon or other person who will ream the acetabulum. Thereamer path protector2411 is therefore gripped in this area, and areamer shaft2451 is inserted through thepassage2427 and thepassage2437 to connect to areamer head2453 near theproximal neck surface2111. The acetabulum is then reamed by rotating the patient's leg into a neutral position and applying power to rotate thereamer shaft2451 andreamer head2453 from thelateral side815 of thefemur811. Some internal rotation of thefemur811 may also be necessary depending on the position of thefemur811 relative to flexion/extension and abduction/adduction. The acetabulum is progressively reamed until enough material has been removed to accommodate the acetabular component of the prosthesis. By reaming the acetabulum through the distal andstarter passages2221,2141 formed in thefemur811, a highly effective reaming process is accomplished. Since the patient's leg is positioned in the neutral position during the reaming process, and since the reamer head2353 is connected to thereamer shaft2451 along the same axis as that about which the head and body of the prosthesis will be oriented, the acetabulum can be efficiently reamed to closely match the shape of the head of the prosthesis.
• Following the reaming process, thereamer head2453 is removed from thereamer shaft2451, and thereamer shaft2451 is removed from thefemoral neck liner2431 and thereamer path protector2411. An impactor shaft (not shown) may be inserted into thereamer path protector2411 and thefemoral neck liner2431 similar to the original insertion of thereamer shaft2451. The impactor shaft is releasably connected to an impactor head (not shown) near theproximal neck surface2111. The impactor shaft and impactor head are used to apply force to and seat the acetabular component of the prosthesis in the reamed acetabulum. After the acetabular component is firmly seated, the impactor shaft, impactor head,femoral neck liner2431, and thereamer path protector2411 are disassembled and removed from thefemur811
• Referring toFIG. 25A, a method for preparing an acetabulum for receiving a head of afemoral prosthesis2521 is illustrated. Afirst step2525 includes forming a primary passage within the femur substantially coaxial to a longitudinal axis of the femoral neck. Atstep2529, a secondary passage is formed from a lateral side of the femur that joins and is coaxial to the primary passage.Step2531 includes inserting a reamer path protector having a reamer passage within the secondary passage. A reamer shaft is inserted through the reamer passage atstep2535. A reamer head is attached to the reamer shaft atstep2539, and the acetabulum is reamed atstep2541.
• The femoral neck fixation prosthesis is implanted into thefemur811 by inserting thebody125,625,725 of the prosthesis into thestarter passage2141. Preferably, the diameter of thebody125,625,725 is sized slightly larger than the diameter of thestarter passage2141 such that a secure fit within thestarter passage2141 is obtained when thebody125,625,725 is driven into thestarter passage2141. Thestarter passage2141 is deep enough to accommodate thebody125,625,725 of the prosthesis and allow the collar of thebody125,625,725 to mate with theproximal neck surface2111.
• Thefastener120,620,720 is then inserted into thedistal passage2221 from thelateral side815 of thefemur811. To properly feed thefastener120,620,720 through the soft tissue2233 (seeFIG. 22) of the patient's leg and into thedistal passage2221, a small diameter pin can be used to locate and mark the passage when the leg is in the neutral position. Thefastener120,620,720, which may be canullated (i.e. having a passage down the center of the shaft), can then be placed onto the pin and fed into thedistal passage2221. Thefastener120,620,720 is advanced into thedistal passage2221 until it contacts thebody125,625,725 of the prosthesis, at which time thefastener120,620,720 is threadingly connected to thebody125,625,725 to secure the body within thefemur811. Thehead110,610,710 of the prosthesis is then installed on themorse taper115,615,760 of the prosthesis be impacting the head of the prosthesis.
• Referring toFIG. 26, a method of implanting a prosthesis in afemur2611 according the principles of the present invention is illustrated. At step2615 a main passage is formed in the femoral neck from a medial side of the femur substantially coaxial to a longitudinal axis of the femoral neck. At step2619 a fastener passage is formed from a lateral side of the femur that is coaxial to and joins the main passage.Step2623 includes providing a femoral neck prosthesis having a body member connected to a head member. At step2627 a portion of the body member is inserted in the main passage. A fastener is inserted into the fastener passage atstep2633. Atstep2637 the fastener is connected to the body member to secure the femoral neck prosthesis within the femur.
• As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a tremendous range of applications, and accordingly the scope of patented subject matter is not limited by any of the specific exemplary teachings given.
• While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims (18)

1. A method of resecting a femoral head from a femur having a femoral neck, the method comprising the steps of:

positioning a locator shaft adjacent an exterior surface of the femoral head and substantially parallel to a longitudinal axis of the femoral neck;

positioning a pin locator guide having at least two holes along the locator shaft;

inserting a pin through each of the at least two of the holes in the pin locator guide and into the femoral head; and

resecting the femoral head by aligning a cutting guide relative to the pins in the femoral head.

2. A method according toclaim 1, wherein a locator plane formed by the pins is parallel to a cutting plane at which the femoral head is resected.

3. A method according toclaim 1, wherein:

a locator plane formed by the pins is parallel to a cutting plane at which the femoral head is resected; and

the cutting plane is perpendicular to the longitudinal axis of the femoral neck.

4. A method according toclaim 1, wherein the step of positioning a locator shaft further comprises the steps of:

providing a femoral neck clamp having a superior clamping member, an inferior clamping member, and a locator shaft guide member connected to at least one of the superior clamping member and the inferior clamping member; and

clamping the femoral neck clamp around the femoral neck at an isthmus of the femoral neck such that the superior clamping member is adjacent a superior region of the femoral neck, the inferior clamping member is adjacent an inferior region of the femoral neck, and a longitudinal axis of the locator shaft guide member is substantially parallel to the longitudinal axis of the femoral neck.

5. A method of resecting a femoral head from a femur having a femoral neck, the method comprising the steps of:

locating an isthmus plane at an isthmus of the femoral neck;

fixing the orientation of a cutting plane based on the isthmus plane; and

resecting the femoral head at the cutting plane.

6. A method according toclaim 5, wherein the step of fixing the orientation of the cutting plane further comprises the steps of:

inserting at least two pins into the femoral head.

7. A method according toclaim 6, wherein the pins are positioned along a line parallel to the isthmus plane.

8. A femoral neck clamp for locating a cutting plane on a femur for resecting a femoral head of the femur, the femoral neck clamp comprising:

a superior clamping member;

an inferior clamping member adjustably connected to the superior clamping member;

a locator shaft guide hole connected to at least one of the superior clamping member and the inferior clamping member; and

wherein the locator shaft guide hole is oriented substantially parallel to a longitudinal axis of the femoral neck when the femoral neck clamp is positioned at an isthmus of the femoral neck such that the superior clamping member is adjacent a superior region of the femoral neck and the inferior clamping member is adjacent an inferior region of the femoral neck.

9. A femoral neck clamp according toclaim 8, wherein the superior clamping member includes an arcuate region to contact an antero-superior ridge on the femoral neck.

10. A femoral neck clamp according toclaim 8, wherein the inferior clamping member is V-shaped to cradle the inferior region of the femoral neck.

11. A femoral neck clamp according toclaim 8, wherein:

the superior clamping member includes an arcuate region to contact an antero-superior femoral neck; and

the inferior clamping member is V-shaped to cradle the inferior region of the femoral neck.

12. A femoral neck clamp according toclaim 8, wherein the inferior clamping member further comprises:

a proximal clasp aligned with the superior clamping member; and

a distal clasp rotatably connected to the proximal clasp.

13. A femoral neck clamp according toclaim 12, wherein the distal clasp provides anti-rotational stability for the femoral neck clamp when secured around the femoral neck.

14. A femoral neck clamp according toclaim 12, wherein a connecting member is used to rotatably connect the proximal clasp to the distal clasp.

15. A femoral neck clamp according toclaim 12, further comprising:

a connecting member pivotally connected to the proximal clasp and rigidly connected to the distal clasp; and

a torsion spring operably connected to the connecting member and the proximal clasp to bias the distal clasp toward the femoral neck.

16. A femoral neck clamp according toclaim 12, further comprising:

a connecting member rigidly connected to the proximal clasp and rigidly connected to the distal clasp; and

wherein the connecting member is made from a flexible material to bias the distal clasp toward the femoral neck.

17. A femoral neck clamp according toclaim 16, wherein the connecting member is made from spring steel.

18. A femoral neck clamp according toclaim 12, further comprising:

a connecting member pivotally connected to the proximal clasp and rigidly connected to the distal clasp; and

a fastener connected between the connecting member and the proximal clasp to lock a rotational position of the distal clasp relative to the proximal clasp.

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