US20060195103A1 - Proximal anchors for bone fixation system - Google Patents

Abstract

Disclosed is a bone fixation device of the type useful for connecting soft tissue or tendon to bone or for connecting two or more bones or bone fragments together. The device comprises an elongate body having a distal anchor thereon. An axially moveable proximal anchor is carried by the proximal end of the fixation device, to accommodate different bone dimensions and permit appropriate tensioning of the fixation device.

Description

• The present application is a continuation of U.S. patent application Ser. No. 10/745,360, filed Dec. 23, 2003, which is a continuation of U.S. patent application Ser. No. 09/990,587, filed Nov. 19, 2001, now U.S. Pat. No. 6,685,706, the entire contents of these applications are hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to bone fixation devices, and, more particularly, to an improved proximal anchor for a bone fixation device.
• 2. Description of the Related Art
• Bones which have been fractured, either by accident or severed by surgical procedure, must be kept together for lengthy periods of time in order to permit the recalcification and bonding of the severed parts. Accordingly, adjoining parts of a severed or fractured bone are typically clamped together or attached to one another by means of a pin or a screw driven through the rejoined parts. Movement of the pertinent part of the body may then be kept at a minimum, such as by application of a cast, brace, splint, or other conventional technique, in order to promote healing and avoid mechanical stresses that may cause the bone parts to separate during bodily activity.
• The surgical procedure of attaching two or more parts of a bone with a pin-like device requires an incision into the tissue surrounding the bone and the drilling of a hole through the bone parts to be joined. Due to the significant variation in bone size, configuration, and load requirements, a wide variety of bone fixation devices have been developed in the prior art. In general, the current standard of care relies upon a variety of metal wires, screws, and clamps to stabilize the bone fragments during the healing process. Following a sufficient bone healing period of time, the percutaneous access site or other site may require re-opening to permit removal of the bone fixation device.
• Long bone fractures are among the most common encountered in the human skeleton. Many of these fractures and those of small bones and small bone fragments must be treated by internal and external fixation methods in order to achieve good anatomical position, early mobilization, and early and complete rehabilitation of the injured patient.
• The internal fixation techniques commonly followed today frequently rely upon the use of Kirschner wires (K-wires), intramedullary pins, wiring, plates, screws, and combinations of the foregoing. The particular device or combination of devices is selected to achieve the best anatomic and functional condition of the traumatized bone with the simplest operative procedure and with a minimal use of foreign-implanted stabilizing material. A variety of alternate bone fixation devices are also known in the art, such as, for example, those disclosed in U.S. Pat. No. 4,688,561 to Reese, U.S. Pat. No. 4,790,304 to Rosenberg, and U.S. Pat. No. 5,370,646 to Reese, et al.
• A variety of elongated implants (nail, screw, pin, etc.) have been developed, which are adapted to be positioned along the longitudinal axis of the femoral neck with a leading (distal) end portion in the femoral head so as to stabilize a fracture of the femoral neck. The elongated implant may be implanted by itself or connected to another implant such as a side plate or intramedullary rod. The leading end portion of the implant typically includes means to positively grip the femoral head bone (external threads, expanding arms, etc.), but the inclusion of such gripping means can introduce several significant problems. First, implants with sharp edges on the leading end portion, such as the externally threaded implants, exhibit a tendency to migrate proximally towards the hip joint bearing surface after implantation. This can occur when the proximal cortical bone has insufficient integrity to resist distal movement of the screw head. Such proximal migration under physiological loading, which is also referred to as femoral head cut-out, can lead to significant damage to the adjacent hip joint. Also, the externally threaded implants can generate large stress concentrations in the bone during implantation which can lead to stripping of the threads formed in the bone and thus a weakened grip. The movable arms of known expanding arm devices are usually free at one end and attached at the other end to the main body of the leading end portion of the implant. As a result, all fatigue loading is concentrated at the attached ends of the arms and undesirably large bending moments are realized at the points of attachment. In addition, conventional threaded implants generally exhibit insufficient holding power under tension, such that the threads can be stripped out of the femoral head either by overtightening during the implantation procedure or during post operative loading by the patient's weight.
• Notwithstanding the common use of the K-wire to achieve shear-force stabilization of bone fractures, K-wire fixation is attended by certain known risks. For example, a second surgical procedure is required to remove the device after healing is complete. Removal is recommended, because otherwise the bone adjacent to an implant becomes vulnerable to stress shielding as a result of the differences in the modulus of elasticity and density between metal and the bone.
• In addition, an implanted K-wire may provide a site for a variety of complications ranging from pin-tract infections to abscesses, resistant osteomyelitis, septic arthritis, and infected nonunion.
• Another potential complication involving the use of K-wires is in vivo migration. Axial migration of K-wires has been reported to range from 0 mm to 20 mm, which can both increase the difficulty of pin removal as well as inflict trauma to adjacent tissue.
• As conventionally utilized for bone injuries of the hand and foot, K-wires project through the skin. In addition to the undesirable appearance, percutaneously extending K-wires can be disrupted or cause damage to adjacent structures such as tendons if the K-wire comes into contact with external objects.
• Notwithstanding the variety of bone fasteners that have been developed in the prior art, there remains a need for a simple, adjustable bone fixation device which may be utilized to secure soft tissue or tendon to the bone.
SUMMARY OF THE INVENTION
• There is provided in accordance with one aspect of the present invention, a fixation device for securing a first bone fragment to a second bone fragment. Alternatively, the fixation device may be used to secure soft tissue to a bone. The fixation device comprises an elongate pin, having a proximal end and a distal end. At least one axially advanceable anchor is carried by the pin.
• Another aspect of the present invention is a bone fixation device, for securing a first bone fragment to a second bone fragment. The bone fixation device comprises an elongate pin, having a proximal end, a distal end and a first retention structure. The bone fixation device also includes at least one distal anchor carried by the elongate pin and a proximal anchor, axially moveable with respect to the elongate pin and comprising a second retention structure. At least a portion of the second retention structure is moveable between a first position and a second position. The second position is located closer to a longitudinal axis of the elongate pin as compared to the first position so as to engage at least a portion of the first retention portion and prevent proximal movement of the proximal anchor with respect to the elongate pin while the first position allows distal movement of the proximal anchor with respect to the elongate pin.
• Another aspect of the invention is a bone fixation device, for securing a first bone fragment to a second bone fragment. The device comprises an elongate pin, having a proximal end and a distal end, at least one distal anchor carried by the pin and an actuator, axially moveable with respect to the pin and comprising a tubular hosing and a flange. The device also includes means for permitting proximal movement of the elongate pin with respect to the actuator but resisting distal movement of the pin with respect to the actuator.
• Further features and advantages of the present invention will become apparent to those of skill in the art in view of the detailed description of preferred embodiments which follows, when considered together with the attached claims and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a cross-sectional schematic view of a bone fixation device positioned within a fractured bone.
• FIG. 2 is a side elevational view of a pin body of the bone fixation device ofFIG. 1.
• FIG. 3 is a distal end elevational view of the pin body ofFIG. 2.
• FIG. 4 is a longitudinal cross-sectional view through the pin body ofFIG. 2.
• FIG. 5 is an enlarged detail view of the distal end of the device shown inFIG. 2.
• FIG. 6 is a cross-sectional view of a proximal anchor of the bone fixation device ofFIG. 1.
• FIG. 7 is a proximal end view of the proximal anchor ofFIG. 6.
• FIG. 8 is a side view of a locking guide wire.
• FIG. 9 is a longitudinal cross-sectional view of the locking guide wire ofFIG. 8 and the pin body ofFIG. 8.
• FIG. 10 is a posterior elevational posterior cross section through the proximal portion of the femur, having another embodiment of a bone fixation device positioned therein.
• FIG. 11 is a side elevational cross section of a fixation device similar to that ofFIG. 10.
• FIG. 12 is a cross sectional view through an angularly adjustable proximal anchor plate.
• FIG. 13 is a front perspective view of the anchor plate ofFIG. 12.
• FIG. 14 is a side elevational view of a double helix distal anchor.
• FIG. 15 is an anterior view of the distal tibia and fibula, with fixation devices across lateral and medial malleolar fractures.
• FIG. 16 is a perspective view of another embodiment of a proximal anchor.
• FIG. 17 is a side elevational view of the proximal anchor ofFIG. 16.
• FIG. 18 is a longitudinal cross-sectional view of the proximal anchor ofFIG. 16.
• FIG. 19 is an enlarged detail view of a portion of the proximal anchor shown inFIG. 18.
• FIG. 20 is a perspective view of another yet embodiment of a proximal anchor.
• FIG. 21 is a side elevational view of the proximal anchor ofFIG. 20.
• FIG. 22 is a longitudinal cross-sectional view of the proximal anchor ofFIG. 20.
• FIG. 23A is an enlarged detail view of a portion of the proximal anchor ofFIG. 22 shown in a first position.
• FIG. 23B is an enlarged detail view of a portion of the proximal anchor ofFIG. 22 shown in a second position.
• FIG. 24 is a perspective view of another embodiment of a proximal anchor.
• FIG. 25 is a side elevational view of the proximal anchor ofFIG. 24.
• FIG. 26 is a longitudinal cross-sectional view of the proximal anchor ofFIG. 24.
• FIG. 27A is an enlarged detail view of a portion of the proximal anchor ofFIG. 26 shown in a first position.
• FIG. 27B is an enlarged detail view of a portion of the proximal anchor ofFIG. 26 shown in a second position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• Although the application of the present invention will be initially disclosed in connection with the simplified bone fracture ofFIG. 1, the methods and structures disclosed herein are intended for application in any of a wide variety of bones and fractures, as will be apparent to those of skill in the art in view of the disclosure herein. For example, the bone fixation device of the present invention is applicable in a wide variety of fractures and osteotomies in the hand, such as interphalangeal and metacarpophalangeal arthrodesis, transverse phalangeal and metacarpal fracture fixation, spiral phalangeal and metacarpal fracture fixation, oblique phalangeal and metacarpal fracture fixation, intercondylar phalangeal and metacarpal fracture fixation, phalangeal and metacarpal osteotomy fixation as well as others known in the art. A wide variety of phalangeal and metatarsal osteotomies and fractures of the foot may also be stabilized using the bone fixation device of the present invention. These include, among others, distal metaphyseal osteotomics such as those described by Austin and Reverdin-Laird, base wedge osteotomies, oblique diaphyseal, digital arthrodesis as well as a wide variety of others that will be known to those of skill in the art. Fractures and osteotomies and arthrodesis of the tarsal bones such as the calcaneus and talus may also be treated. Spiked washers can be used, attached to the collar or freely movable beneath the collar. The bone fixation device may be used with or without plate(s) or washer(s), all of which can be either permanent, absorbable or comprising both.
• Fractures of the fibular and tibial malleoli, pilon fractures and other fractures of the bones of the leg may be fixated and stabilized with the present invention with or without the use of plates, both absorbable or non-absorbing types, and with alternate embodiments of the current invention. One example is the fixation of the medial malleolar avulsion fragment fixation with the radially and axially expanding compression device. Each of the foregoing may be treated in accordance with the present invention, by advancing one of the fixation devices disclosed herein through a first bone component, across the fracture, and into the second bone component to fix the fracture.
• The fixation device of the present invention may also be used to attach tissue or structure to the bone, such as in ligament reattachment and other soft tissue attachment procedures. Plates and other implants may also be attached to bone, using either resorbable or nonreabsorbable fixation devices disclosed herein depending upon the implant and procedure. The fixation device may also be used to attach sutures to the bone, such as in any of a variety of tissue suspension procedures.
• For example, peripheral applications for the fixation devices include utilization of the device for fastening soft tissue such as capsule, tendon or ligament to bone. It may also be used to attach a synthetic material such as marlex mesh, to bone or allograft material such as tensor fascia lata, to bone. In the process of doing so, retention of the material to bone may be accomplished with the collar as shown, with an enlarged collar to increase contact surface area, with a collar having a plurality of spikes to enhance the grip on adjacent tissue, or the pin and or collar may be modified to accept a suture or other material for facilitation of this attachment.
• Specific examples include attachment of the posterior tibial tendon to the navicular bone in the Kidner operation. Navicular-cuneiform arthrodesis may be performed utilizing the device and concurrent attachment of the tendon may be accomplished. Attachment of the tendon may be accomplished in the absence of arthrodesis by altering the placement of the implant in the adjacent bone.
• Ligament or capsule reattachment after rupture, avulsion of detachment, such as in the ankle, shoulder or knee can also be accomplished using the devices disclosed herein.
• The fixation devices may be used in combination with semi tubular, one-third tubular and dynamic compression plates, both of metallic and absorbable composition, preferably by modifying the collar to match the opening on the plate.
• The cannulated design disclosed below can be fashioned to accept an antibiotic impregnated rod for the slow release of medication and/or bone growth or healing agents locally. This may be beneficial for prophylaxis, especially in open wounds, or when osteomyelitis is present and stabilization of fracture fragments is indicated. The central lumen can also be used to accept a titanium or other conductive wire or probe to deliver an electric current or electromagnetic energy to facilitate bone healing.
• A kit may be assembled for field use by military or sport medical or paramedical personnel. This kit contains an implanting tool, and a variety of implant device size and types, a skin stapler, bandages, gloves, and basic tools for emergent wound and fracture treatment. Antibiotic rods would be included for wound prophylaxis during transport.
• Referring toFIG. 1, there is illustrated generally abone10, shown in cross-section to reveal an outercortical bone component12 and an innercancellous bone component14. Afracture16 is schematically illustrated as running through thebone10 to at least partially divide the bone into what will for present purposes be considered aproximal component19 anddistal component21. Thefracture16 is simplified for the purpose of illustrating the application of the present invention. However, as will be understood by those of skill in the art, thefracture16 may extend through the bone at any of a wide variety of angles and depths. The bone fixation device of the present invention may be useful to stabilize two or more adjacent components of bone as long as each component may be at least partially traversed by the bone fixation device and anchored at opposing sides of the fracture to provide a sufficient degree of stabilization.
• Aproximal aperture18 is provided in theproximal component19 of thebone10, such as by drilling, as will be discussed. Adistal aperture20 is provided in an opposing portion of bone such as indistal bone component21 and is connected to theproximal aperture18 by way of a throughhole22, as is known in the art, in a through hole application. The fixation device may also be useful in certain applications where the distal end of the device resides within the bone (i.e., a blind hole application).
• Thebone fixation device24 is illustrated inFIG. 1 in its installed position within the throughhole22. Thebone fixation device24 generally comprises anelongate pin26 having aproximal end28, adistal end30, and anelongate pin body32 extending therebetween. The illustratedbone fixation24 device and modified embodiments of thebone fixation device24 are disclosed in U.S. patent application Ser. No. 09/832,289, filed Apr. 10, 2001, which is hereby incorporated by reference herein.
• Thedistal end30 ofpin26 is provided with adistal anchor34, as will be discussed below. Aproximal anchor36 is also provided.
• The radially interior surface of thetubular housing40, in the illustrated embodiment, is provided with a plurality ofretention structures42.Retention structures42 cooperate withcorresponding retention structures44 on the surface ofpin body32 to permit advancement of theproximal anchor36 in the direction of thedistal anchor34 for properly sizing and tensioning thebone fixation device24.Retention structures42 then cooperate withretention structures44 to provide a resistance to movement of theproximal anchor36 in the proximal direction relative to pinbody32.
• In the embodiment illustrated inFIGS. 6 and 7, theproximal anchor36 comprise acollar38 for contacting theproximal bone component19.Collar38 may comprises a radially-outwardly extending annular ramp or flange to optimize contact with theproximal bone component19. Alternatively,proximal collar38 may comprise one or more radially-outwardly extending stops, a frusto-conical plug, or other structures which stop the distal progress ofproximal anchor36 with respect to the throughhole22 or blind hole, depending upon the application. Thecollar38 is connected to atubular housing40 adapted to coaxially receive thepin body32 therethrough.
• In use, the proximal projection ofpin26 which extends beyond theproximal anchor36 after tensioning is preferably removed, such as by cutting, to minimize the projection of thebone fixation device24 from the surface of the bone.
• One embodiment of thepin26, adapted for fixing oblique fractures of the fibula or metatarsal bone(s) is illustrated inFIG. 2. Thebone fixation device24 of this embodiment uses a generallycylindrical pin body32. Although the present invention is disclosed as embodied in apin body32 having a generally circular cross section, cross sections such as oval, rectangular, square or tapered to cause radial along with axial bone compression or other configurations may also be used as desired for a particular application.
• Pin body32 generally has an axial length of within the range of from about 5 mm or about 10 mm to about 70 mm in the as-manufactured condition. In one embodiment intended for small bones in the foot, thepin body32 has an axial length of about 19 mm. The illustrated embodiment shows a cannulatedpin body32, which defines acentral lumen11 to allow introduction of the pin over a wire as is understood in the art. Hollow tubular structures may also be used. However, in other embodiments, a solid pin body may be provided. Such an embodiment is disclosed in co-pending U.S. patent application Ser. No. 09/832,289, filed Apr. 10, 2001, which was incorporated by reference above.
• In the illustrated embodiment, theretention structures44 of thepin26 comprise a plurality of threads, adapted to cooperate with thecomplimentary retention structures42 on theproximal anchor36, which may be a complimentary plurality of threads. In this embodiment, theproximal anchor36 may be distally advanced along thepin26 by rotation of theproximal anchor36 with respect to thepin26.Proximal anchor36 may advantageously be removed from thepin26 by reverse rotation, such as to permit removal of thepin26 from the patient. For this purpose, the collar38 (seeFIGS. 6 and 7) is preferably provided with a gripping configuration or structure to permit a removal tool to rotatecollar38 with respect to thepin26. Any of a variety of gripping surfaces may be provided, such as one or more slots, flats, bores, or the like. In the illustrated embodiment, thecollar38 is provided with a polygonal, and in particular, a hexagonal circumference, as seen inFIG. 7.
• Theproximal end28 of thepin26 is similarly provided with astructure29 for permitting rotational engagement with an installation or a removal tool. Rotational engagement may be accomplished using any of a variety of shapes or configurations, as will be apparent to those of skill in the art. One convenient structure is to provide theproximal end26 with one or more flat side walls, for rotationally engaging a complimentary structure on the corresponding tool. As illustrated inFIG. 4, theproximal end26 may be provided with astructure29 having a square cross-section. Alternatively, the exterior cross-section throughproximal end28 may be any of a variety of configurations to permit rotational coupling, such as triangular, hexagonal, or other polygons, or one or more axially extending flat sides or channels on an otherwise round body. In still other embodiments, theproximal end28 of thecentral lumen11 may be configured with an non-round cross-section for rotational. engagement with an installation or removal tool.
• Theretention structures44 can also comprise a plurality of annular ramp or ratchet-type structures which permit theproximal anchor36 to be advanced in a distal direction with respect to pinbody32, but which resist proximal motion ofproximal anchor36 with respect to pinbody32. Any of a variety of ratchet-type structures can be utilized in the present invention. Such a ramp or ratchet-type structure provide, among other advantages, the ability of the ratchet to function regardless of the rotational orientation of theproximal anchor36 with respect to thepin body32. In an embodiment having a noncircular cross section, or having a rotational link such as an axially-extending spline on thepin body32 for cooperating with a complementary keyway onproximal anchor36, theretention structures42 can be provided on less than the entire circumference of the pin body as will be appreciated by those of skill in the art. Thus, ratchet structures can be aligned in an axial strip such as at the bottom of an axially extending channel in the surface of the pin body.
• A single embodiment of the bone fixation device can be used for fixing fractures in bones having any of a variety of diameters. This is accomplished by providing theretention structures44 over a predetermined axial working length of thepin body32. For example, in the illustrated embodiment, theretention structures44 commence at aproximal limit46 and extend axially until adistal limit48. Axially extending the retention zone betweenlimits46 and48 will extend the effective range of bone thicknesses which thepin32 can accommodate. Although theretention structures44 may alternatively be provided throughout the entire length of thepin body32,retention structures44 may not be necessary in the most distal portions ofpin body32 in view of the minimum diameter of bones likely to be fixed.
• In one embodiment of the invention, thedistal limit48 ofretention structures44 is spaced apart from thedistal end30 ofpin body32 by a distance within the range of from about 4 mm to about 20 mm, and, in embodiments for small bones in the foot, from about 4 mm to about 8 mm. The axial length of the portion of thepin body32 havingretention structures44 thereon, fromproximal limit46 todistal limit48, is generally within the range of from about 4 mm to about 8 mm, and was approximately 6 mm in an embodiment having a pin body length of about 19 mm. Depending upon the anchor design, the zone betweenproximal limit46 anddistal limit48 may extend at least about 50%, and in some embodiments in excess of about 75% or even in excess of 90% of the length of the pin body.
• In general, the minimum diameter of thepin body32 is a function of the construction material of the pin and the desired tensile strength for a given application. The maximum diameter is established generally by the desire to minimize the diameter of the throughhole22 while still preserving a sufficient structural integrity of thefixation device24 for the intended application.
• The diameter ofpin body32 will generally be in the range of from about 1.5 mm or 1.8 mm for small bones of the foot and hand to as large as 7.0 mm or larger for bones such as the tibia. In one absorbable embodiment of the invention intended for use in the first metatarsal, thepin24 comprises poly (L, co-D,L-lactide) and has a diameter of about 1.8 mm. Any of a variety of other materials may also be used, as discussed infra.
• In a similar manner, the overall length of thetubular housing40 may be maximized with respect to the depth of the target borehole for a particular application. For example, in a device intended to fix bones having a diameter within the range of from about 15-20 mm, the axial length of thetubular body40 is preferably at least about 8 mm or 10 mm, and, more preferably, at least about 12 mm or 14 mm. In this manner, the axial length of the zone ofretention structures42 is maximized, thereby increasing the tensile strength of the implanted device. Theproximal anchor36 can be readily constructed using other dimensions and configurations while still accomplishing the desired function, as will be apparent to those of skill in the art in view of the disclosure herein.
• Theretention structures42 may comprise any of a variety of complementary surface structures for cooperating with the correspondingstructures44 on thepin32, as is discussed above. In the illustrated embodiment, the retention structures are in the form of a plurality of annular rings or helical threads, which extend axially throughout the length of thetubular housing40. Theretention structure42 may alternatively comprise a single thread, ridge or groove or a plurality of structures which extend only part way (e.g., at least about 10% or 25% or more) along the length of thetubular housing40. Retention force may be optimized by providing threads or other structures along a substantial portion, e.g., throughout at least 75% or 80% of the axial length of thetubular housing40.
• With reference toFIGS. 2-5, thedistal anchor34 in the illustrated embodiment comprises a plurality of ramped extensions orbarbs50 for engaging the distal cortical bone, the interior cancellous bone or other surfaces. As will be explained below, the extensions orbarbs50 are positioned or compressible radically inward for the purpose of advancing thepin32 into, and, in some applications, through thehole22.Barbs50 preferably exert a radially outwardly directed bias so that they tend to extend radially outwardly from thepin body32 once thedistal anchor34 has advanced out through thedistal aperture20 inbone10. Proximal traction on theproximal end28 ofpin body32 will thereafter tend to causebarbs50 to seat firmly against the outside surface ofdistal bone component21, as illustrated inFIG. 1.
• The illustrated embodiment includes four barbs50 (FIG. 3), oriented at 90° with respect to each other. However, anywhere from one to about twelve ormore barbs50 may be utilized as will be apparent to those of skill in the art in view of the disclosure herein. Thebarbs50 may be radially symmetrically distributed about the longitudinal axis of thepin26. Eachbarb50 is provided with atransverse engagement surface21, for contacting the distal surface of the cortical bone or other structure or surface against which thebarb50 is to anchor. Transverse engagement surfaces21 may lie on a plane which is transverse to the longitudinal axis of thepin26, or may be inclined with respect to the longitudinal axis of thepin26.
• Each of the transverse engagement surfaces21 in the illustrated embodiment lies on a common plane which is transverse to the longitudinal axis of thepin26. Two or more planes containing engagement surfaces21 may alternatively be provided. The transverse engagement surfaces21 may also lie on one or more planes which are non-normal to the longitudinal axis ofpin26. For example, the plane of a plurality of transverse engagement surfaces21 may be inclined at an angle within the range of from about 35° or 45° to about 90° with respect to the longitudinal axis of thepin26. The plane of the transverse engagement surface may thus be selected to take into account the angle of the distal surface of the bone through which the pin may be positioned, as may be desired in certain clinical applications.
• In order to facilitate the radially inward compression of thebarbs50 during the implantation process, followed by radially outward movement of thebarbs50 to engage the distal bone surface, eachbarb50 in the illustrated embodiment is carried by a flexible or hingedlever arm23. Leverarms23 may be formed by creating a plurality ofaxial slots15 in the sidewall of thepin26. Theaxial slots15 cooperate with acentral lumen11 to isolate eachbarb50 on aunique lever arm23. The axial length of theaxial slots15 may be varied, depending upon the desired length over which flexing is desirably distributed, the desired range of lateral motion, and may vary depending upon the desired construction material. For a relatively rigid material such as titanium, axial lengths of theaxial slot15 in excess of about 0.1 inches and preferably in excess of about 0.2 inches are utilized on apin26 having an outside diameter of about 0.1 inches and a length of about 1.25 inches.Axial slots15 will generally extend within a range of from about 5% to about 90%, and often within about 10% to about 30% of the overall length of thepin26.
• The circumferential width of theslots15 at thedistal end30 is selected to cooperate with the dimensions of thebarbs50 to permit radial inward deflection of each of thebarbs50 so that thepin26 may be press fit through a predrilled hole having an inside diameter approximately equal to the outside diameter of thepin26 just proximal to the transverse engagement surfaces21. For this purpose, each of theslots15 tapers in circumferential direction width from a relatively larger dimension at thedistal end30 to a relatively smaller dimension at the proximal limit of theaxial slot15. SeeFIG. 2. In the illustrated embodiment, eachslot15 has a width of about 0.20 inches at the proximal end and a width of about 0.035 inches at the distal end in the unstressed orientation. The width of theslot15 may taper continuously throughout its length, or, as in the illustrated embodiment, is substantially constant for a proximal section and tapered over a distal section of theslot15. The wall thickness of thelever arm23 may also be tapered to increase the diameter of thecentral lumen11 in the distal direction. This will allow a lower compressed crossing profile before the inside surfaces of the lever arms bottom out against each other.
• Although any of a variety of alternate designs fordistal anchor34 may be utilized in the context of the present invention, any suchdistal anchors34 preferably permit axial distal motion ofpin body32, and thereafter resist proximal withdrawal of thepin body32. As will be appreciated by those of skill in the art, this feature allows thebone fixation device24 to be set within a bone through a single proximal percutaneous puncture or incision, without the need to expose thedistal component20 or “backside” of the bone. This can be accomplished by biased anchors which are formed integrally with the pin, or which are attached during manufacturing. Distal anchors may also be hinged to the pin body, and may be deployed by a push or pull wire extending through the pin body if the desired construction material does not permit adequate spring bias.
• Additional description of the distal anchor and alternate distal anchor designs are described in co-pending U.S. patent application Ser. No. 08/832,289, which is hereby incorporated by reference herein.
• For a through hole having a diameter of about 2.3 mm,pin bodies32 having an outside diameter of about 1.8 mm in the areas other thanretention structures44, and a maximum outside diameter of about 2.24 mm in the area ofretention structures44 have been found to be useful. In this embodiment, the maximum outside diameter of thedistal anchor34 was approximately 2.92 mm in the relaxed state. The axial length from the distal tip ofdistal end30 to the proximal extent ofextensions50 was about 1.21 mm.
• In use, a bone is first identified having a fracture which is fixable by a pin-type fixation device. The clinician assesses the bone, selects a bone drill and drills a throughhole22 in accordance with conventional techniques.
• Abone fixation device24 having an axial length and outside diameter suitable for the throughhole22 is selected. Thedistal end30 of thebone fixation device24 is percutaneously or otherwise advanced towards the bone, and subsequently advanced through the throughhole22 untildistal anchor34 exits thedistal aperture20. Theproximal anchor36 may be positioned on thebone fixation device24 prior to positioning of thepin body32 in the throughhole22, or following placement of thepin body32 within throughhole22.
• The foregoing structures enable the use of an installation and/or deployment tool having a concentric core within a sleeve configuration in which a first component (e.g. a sleeve) engages theproximal anchor36 and a second component (e.g. a core) engages the proximalrotational engagement structure29 ofpin26. The first component may be rotated with respect to the second component, so that theproximal anchor36 may be rotated onto or off of theretention structures44 onpin26. In a modified arrangement, a first tool (e.g., a pair of pliers or a wrench) may be used to engage theproximal anchor36 and a second tool (e.g., a pair of pliers or a wrench) may be used to engage the proximalrotational engagement structure29 ofpin26. In such an arrangement, the first tool may be rotated with respect to the second tool (or vice versa), so that theproximal anchor36 may be rotated onto or off theretention structures44 on thepin26.
• Alternatively, theretention structures42 on theproximal anchor36 may be toleranced to permit distal axial advancement onto thepin26, such as by elastic deformation, but require rotation with respect to thepin26 in order to remove theproximal anchor36 from thepin26.
• Following appropriate positioning of theproximal anchor36, theproximal end28 of thepin body32 may be cut off and removed.Pin body32 may be cut using conventional pin cutters which are routinely available in the clinical setting. Alternatively, a pin may be selected such that it is sized to fit the treatment site such that following tension no proximal extension remains.
• Following trimming theproximal end28 ofpin26, the access site may be closed and dressed in accordance with conventional wound closure techniques.
• As mentioned above, in some embodiments, theretention structures44 on the surface of the pin body comprise a plurality of ratchet-type structures. In such embodiments, proximal traction is preferably applied to theproximal end28 ofpin body32, to seat thedistal anchor34. While proximal traction is applied to theproximal end28 ofpin body32, such as by conventional hemostats or a calibrated loading device, theproximal anchor36 is advanced distally until theanchor36 fits snugly against theproximal component19 of the bone. Appropriate tensioning of thebone fixation device24 is accomplished by tactile feedback or through the use of a calibration device for applying a predetermined load on implantation
• For any of the ratchet-type embodiments disclosed above, installation can be simplified through the use of an installation tool. The installation tool may comprise a pistol grip or plier-type grip so that the clinician can position the tool at the proximal extension ofpin32 and through one or more contractions with the hand, theproximal anchor36,52 anddistal anchor34 can be drawn together to appropriately tension against the bone fragments. The use of a precalibrated tool can permit the application of a predetermined tension in a uniform manner from pin to pin.
• Calibration of the installation device to set a predetermined load on the pin can be accomplished through any of a variety of means which will be understood to those of skill in the art. For example, thepin32 may be provided with one or more score lines or transverse bores or other modifications which limit the tensile strength of the part at one or more predetermined locations. In this manner, axial tension applied to theproximal end28 with respect to the collar54 will apply a predetermined load to the bone before thepin32 will separate at the score line. Alternatively, internal structures within the installation tool can be provided to apply tension up to a predetermined limit and then release tension from the distal end of the tool.
• Preferably, the clinician will have access to an array ofbone fixation devices24, having different diameters and axial lengths. These may be packaged one or more per package in sterile envelopes or peelable pouches, or in dispensing cartridges which may each hold a plurality ofdevices24. Upon encountering a bone for which the use of a fixation device is deemed appropriate, the clinician will assess the dimensions and load requirements of the bone, and select a bone fixation device from the array which meets the desired specifications.
• Any of a variety of alternative retention structures may be configured, to permit removal of theproximal anchor36 such as following implantation and a bone healing period of time. For example, theretention structures44 such as threads on thepin26 may be provided with a plurality of axially extending flats or interruptions, which correspond with a plurality of axial flats on theretention structures42 ofproximal anchor36. This configuration enables a partial rotation (e.g. 90°) of theproximal anchor36 with respect to thepin26, to disengage the corresponding retention structures and permit axial withdrawal of theproximal anchor36 from thepin26. One or both of theretention structures44 and42 may comprise a helical thread or one or more circumferentially extending ridges or grooves. In a threaded embodiment, the thread may have either a fine pitch or a course pitch. A fine pitch may be selected where a number of rotations ofproximal anchor36 is desired to produce a relatively small axial travel of theanchor36 with respect to thepin26. In this configuration, relatively high compressive force may be achieved between theproximal anchor36 and thedistal anchor34. This configuration will also enable a relatively high resistance to inadvertent reverse rotation of theproximal anchor36. Alternatively, a relatively course pitch thread such as might be found on a luer connector may be desired for a quick twist connection. In this configuration, a relatively low number of rotations or partial rotation of theproximal anchor36 will provide a significant axial travel with respect to thepin26. This configuration may enhance the tactile feedback with respect to the degree of compression placed upon the bone. The thread pitch or other characteristics of the corresponding retention structures can be optimized through routine experimentation by those of skill in art in view of the disclosure herein, taking into account the desired clinical performance.
• Referring toFIG. 2, at least afirst break point31 may be provided to facilitate breaking the proximal portion of thepin26 which projects proximally of thecollar38 following tensioning of the fixation system.Break point31 in the illustrated embodiment comprises an annular recess or groove, which provides a designed failure point if lateral force is applied to theproximal end28 while the remainder of the attachment system is relatively securely fixed. At least asecond break point33 may also be provided, depending upon the axial range of travel of theproximal anchor36 with respect to thepin26.
• In one embodiment having two ormore break points31,33, thedistal break point31 is provided with one or more perforations or a deeper recess than theproximal break point33. In this manner, thedistal break point31 will preferentially fail before theproximal break point33 in response to lateral pressure on theproximal end28. This will ensure the minimum projection of thepin26 beyond thecollar38 following deployment and severing of theproximal end28 as will be appreciated in view of the disclosure herein.
• Proximal projection of theproximal end28 from theproximal anchor36 following implantation and breaking at abreakpoint31 may additionally be minimized or eliminated by allowing thebreakpoint31 or33 to break off within theproximal anchor36. Referring toFIG. 6, theretention structure42 may terminate at apoint61 distal to aproximal surface63 on theanchor36. An inclined or taperedannular surface65 increases the inside diameter of the central aperture throughproximal anchor36, in the proximal direction. After theproximal anchor36 has been distally advanced over apin26, such that abreakpoint31 is positioned between theproximal limit61 and theproximal surface63, lateral pressure on theproximal end28 ofpin26 will allow thebreakpoint31 to break within the area of theinclined surface65. In this manner, the proximal end of thepin26 following breaking resides at or distally of theproximal surface63, thus minimizing the profile of the device and potential tissue irritation.
• FIG. 8 illustrates a lockingguide wire150 that may be used with the fixation device described above. The guide wire has adistal end152 and aproximal end154. The illustratedguide wire150 comprises a lockingportion156 that is located at thedistal end152 of theguide wire150 and anelongated portion158 that preferably extends from thedistal portion156 to theproximal end154 of theguide wire150. The diameter D1 of theelongated portion158 is generally smaller than the diameter D2 of thedistal portion154. Theguide wire150 can be made from stainless steel, titanium, or any other suitable material. Preferably, in all metal systems, theguidewire150 and lockingportion156 are made from the same material as the remainder of the fixation device to prevent cathodic reactions.
• The lockingportion156 onguidewire150 can take any of a variety of forms, and accomplish the intended function as will be apparent to those of skill in the art in view of the disclosure herein. For example, a generally cylindrical locking structure, as illustrated, may be used. Alternatively, any of a variety of other configurations in which the cross section is greater than the cross section of theproximal portion158 may be used. Conical, spherical, or other shapes may be utilized, depending upon the degree of compression desired and the manner in which the lockingportion156 is designed to interfit with thedistal end30 of the pin.
• Theguide wire150 is configured such that its proximal end can be threaded through thelumen11 of thepin26. With reference toFIG. 9, thelumen11 preferably comprises afirst portion160 and asecond portion162. Thefirst portion160 is generally located at thedistal end30 within the region of the lever arms of thepin26. Thesecond portion162 preferably extends from thefirst portion160 to theproximal end28 of thepin26. The inside diameter of thefirst portion160 is generally larger than the diameter of thesecond portion162. As such, the junction between thefirst portion160 and thesecond portion162 forms a transverseannular engagement surface164, which lies transverse to the longitudinal axis of thepin26.
• As mentioned above, theguide wire150 is configured such that its proximal end can be threaded through thelumen11 of thepin26. As such, the diameter D1 of theelongated portion158 is less than the diameter of thesecond portion162 of thelumen11. In contrast, the diameter D2 ofdistal portion156 preferably is slightly smaller than equal to or larger than the diameter of thefirst portion160 and larger than the diameter of thesecond portion162. This arrangement allows thedistal portion156 to be retracted proximally into thefirst portion160 but prevents thedistal portion156 from passing proximally through thepin26.
• In addition, any of a variety of friction enhancing surfaces or surface structures may be provided, to resist distal migration of the lockingguidewire150, post deployment. For example, any of a variety of radially inwardly or radially outwardly directed surface structures may be provided along the length of the lockingguidewire150, to cooperate with a corresponding surface structure on the inside surface of thelumen11, to removably retain the lockingguidewire150 therein. In one embodiment, a cylindrical groove is provided on the inside surface of thelumen11 to cooperate with a radially outwardly extending annular flange or ridge on the outside diameter of the lockingguidewire150. The complementary surface structures may be toleranced such that the locking guidewire or guide pin may be proximally retracted into thelumen11 to engage the locking structure, but the locking structure provides a sufficient resistance to distal migration of the lockingguidewire150 such that it is unlikely or impossible to become disengaged under normal use.
• In use, after the clinician assesses the bone, selects a bone drill and drills a throughhole22, thedistal end152 of theguide wire150 and thedistal end30 of thepin26 are advanced through the through hole until thedistal portion156 and thebarbs50 exit thedistal aperture20. Theproximal anchor36 may be positioned on thebone fixation device24 prior to positioning of thepin body32 in the throughhole22, or following placement of thepin body32 within throughhole22.
• Theguide wire150 is preferably thereafter retracted until thedistal portion156 enters, at least partially, thefirst portion160 of the pin26 (seeFIG. 14). Theproximal anchor36 can then be rotated or otherwise distally advanced with respect to thepin body26 so as to seat thedistal anchor34 snugly against thedistal component21 of the bone. As such, at least a part of thedistal portion156 of theguide wire150 becomes locked within thefirst portion150 of thepin26. This prevents thebarbs50 andlever arms24 from being compressed radially inward and ensures that thebarbs50 remain seated snugly against thedistal component21 of the bone.
• Following appropriate tensioning of theproximal anchor36, theproximal end28 of thepin body32 and theproximal end154 of theguide wire150 are preferably cut off or otherwise removed. These components may be cut using conventional pin cutters which are routinely available in the clinical setting, or snapped off using designed break points as has been discussed.
• Referring toFIG. 10, there is illustrated a posterior side elevational view of the proximal portion of afemur210, having another embodiment of afixation device212 positioned therein. Detailed descriptions of this and alternative fixation devices can be found in co-pending U.S. patent application Ser. No. 09/822,803 filed on Mar. 30, 2001 entitled METHOD AND APPARATUS FOR FIXATION OF PROXIMAL FEMORAL FRACTURE, U.S. patent application filed on Nov. 13, 2001 entitled DISTAL BONE ANCHORS FOR BONE FIXATION WITH SECONDARY COMPRESSION and U.S. patent application filed on Nov. 13, 2001 entitled METHOD AND APPARATUS FOR BONE FIXATION WITH SECONDARY COMPRESSION, which are hereby incorporated by reference herein. Although this embodiment of a fixation device is disclosed in the context of fractures of the proximal femur, as with the embodiments described above, the methods and structures disclosed herein are intended for application in any of a wide variety of bones and fractures, as will be apparent to those of skill in the art in view of the disclosure herein.
• The proximal end of thefemur210 comprises ahead214 connected by way of aneck216 to the long body orshaft217 of thefemur210. As illustrated inFIG. 10, theneck216 is smaller in diameter than thehead214. Theneck216 andhead214 also lie on an axis which, on average in humans, crosses the longitudinal axis of thebody217 of thefemur210 at an angle of about 126°. The risk of fracture at theneck216 is thus elevated, among other things, by the angular departure of theneck216 from the longitudinal axis of thebody217 offemur210 and also the reduced diameter of theneck216 with respect to thehead214.
• Thegreater trochanter218 extends outwardly above the junction of theneck216 and thebody217 of thefemur210. On the medial side of thegreater trochanter218 is thetrochanteric fossa220. This depression accommodates the insertion of the obturator extemus muscle. Thelesser trochanter221 is located posteromedially at the junction of theneck216 and thebody217 of thefemur210. Both thegreater trochanter218 and thelesser trochanter221 serve for the attachment of muscles. On the posterior surface of thefemur210 at about the same axial level as thelesser trochanter221 is thegluteal tuberosity222, for the insertion of the gluteus maximus muscle. Additional details of the femur are well understood in the art and not discussed in further detail herein.
• FIG. 10 illustrates afracture224 which crosses the femur approximately in the area of thegreater trochanter218. Fractures of the proximal portion of thefemur210 are generally classified as femoral neck fractures, intertrochanteric fractures and subtrochanteric fractures. All of these fractures will be deemed femoral neck fractures for the purpose of describing the present invention.
• Referring toFIGS. 10 and 11, thefixation device212 comprises apin body228 extending between aproximal end230 and adistal end232. The length, diameter and construction materials of thebody228 can be varied, depending upon the intended clinical application. In an embodiment optimized for femoral neck fractures in an adult human population, thebody228 will generally be within the range of from about 45 mm to about 120 mm in length after sizing, and within the range of from about 3 mm to about 8 mm in maximum diameter. The major diameter of the helical anchor, discussed below, may be within the range of from about 6 mm to about 12 mm. In general, the appropriate dimensions of thebody228 will vary, depending upon the specific fracture. In rough terms, for a malleolar fracture, shaft diameters in the range of from about 3 mm to about 4.5 mm may be used, and lengths within the range of from about 25 mm to about 70 mm. For condylar fractures, shaft diameters within the range of from about 4 mm to about 6.5 mm may be used with lengths within the range of from about 25 mm to about 70 mm. For colles fractures (distal radius and ulna), diameters within the range of from about 2.5 mm to about 3.5 mm may be used with any of a variety of lengths within the range of from about 6 mm to about 120 mm.
• In one embodiment, thebody228 comprises titanium. However, as will be described in more detail below, other metals or bioabsorbable or nonabsorbable polymeric materials may be utilized, depending upon the dimensions and desired structural integrity of the finishedfixation device212.
• Thedistal end232 of thebody228 is provided with a cancellous bone anchor ordistal anchor234. Additional details of the illustrated cancellous bone anchor and other embodiments are described below and in co-pending U.S. patent application filed on Nov. 13, 2001 entitled DISTAL BONE ANCHORS FOR BONE FIXATION WITH SECONDARY COMPRESSION, which was incorporated by reference above. In general, thecancellous bone anchor234 is adapted to be rotationally inserted into the cancellous bone within thehead214 of thefemur210, to retain thefixation device212 within the femoral head.
• Theproximal end230 of thebody228 is provided with aproximal anchor236. As with the embodiments described with reference toFIGS. 1-9, theproximal anchor236 is axially distally moveable along thebody228, to permit compression of thefracture24 as will be apparent fromFIG. 10. Complimentary locking structures such as threads or ratchet like structures between theproximal anchor236 and thebody228 resist proximal movement of theanchor236 with respect to thebody228 under normal use conditions. Theproximal anchor36 can be axially advanced along thebody228 either with or without rotation, depending upon the complementary locking structures as will be apparent from the disclosure herein.
• In the illustrated embodiment,proximal anchor236 comprises ahousing238 such as a tubular body, for coaxial movement along thebody228. Thehousing238 is provided with one ormore surface structures240 such as radially inwardly projecting teeth or flanges, for cooperating withcomplementary surface structures242 on thebody228. Thesurface structures240 andcomplementary surface structures242 permit distal axial travel of theproximal anchor236 with respect to thebody228, but resist proximal travel of theproximal anchor236 with respect to thebody228. Any of a variety of complementary surface structures which permit one way ratchet like movement may be utilized, such as a plurality of annular rings or helical threads, ramped ratchet structures and the like for cooperating with an opposing ramped structure or pawl.
• Retention structures242 are spaced axially apart along thebody228, between aproximal limit254 and adistal limit256. The axial distance betweenproximal limit254 anddistal limit256 is related to the desired axial range of travel of theproximal anchor236, and thus the range of functional sizes of thefixation device212. In one embodiment of thefixation device212, theretention structure242 comprise a plurality of threads, adapted to cooperate with theretention structures240 on theproximal anchor236, which may be a complementary plurality of threads. In this embodiment, theproximal anchor236 may be distally advanced along thebody228 by rotation of theproximal anchor236 with respect to thebody228.Proximal anchor236 may be advantageously removed from thebody28 by reverse rotation, such as to permit removal of thebody28 from the patient. In this embodiment, aflange244 is preferably provided with a gripping structure to permit a removal tool to rotate theflange244 with respect to thebody228. Any of a variety of gripping structures may be provided, such as one or more slots, flats, bores or the like. In one embodiment, theflange244 is provided with a polygonal, and, in particular, a pentagonal or hexagonal circumference.
• Theflange244 seats against the outer surface of the femur or tissue adjacent the femur. Theflange244 is preferably an annular flange, to optimize the footprint or contact surface area between theflange244 and the femur. Circular or polygonal shaped flanges for use in femoral head fixation will generally have a diameter of at least about 4 mm greater than theadjacent body228 and often within the range of from about 4 mm to about 20 mm or more greater than theadjacent body228. In a modified embodiment, theflange244 can be curved to match the curved shape of the femur and further optimize the footprint or contact surface area between theflange244 and the femur.
• Tensioning and release of theproximal anchor36 may be accomplished in a variety of ways, depending upon the intended installation and removal technique. For example, a simple threaded relationship between theproximal anchor236 andbody228 enables theproximal anchor236 to be rotationally tightened as well as removed. However, depending upon the axial length of the threaded portion on thepin228, an undesirably large amount of time may be required to rotate theproximal anchor236 into place. For this purpose, the locking structures on theproximal anchor236 may be adapted to elastically deform or otherwise permit theproximal anchor236 to be distally advanced along thebody228 without rotation, during the tensioning step. Theproximal anchor236 may be removed by rotation as has been discussed. In addition, any of a variety of quick release and quick engagement structures may be utilized. For example, the threads or other retention structures surrounding thebody228 may be interrupted by two or more opposing flats. Two or more corresponding flats are provided on the interior of thehousing238. By proper rotational alignment of thehousing238 with respect to thebody228, thehousing328 may be easily distally advanced along thebody228 and then locked to thebody228 such as by a 90° or other partial rotation of thehousing238 with respect to thebody228. Other rapid release and rapid engagement structures may also be devised, and still accomplish the advantages of the present invention.
• In the embodiments illustrated inFIGS. 11 and 12, thebone contacting surface246 of theflange244 resides in or approximately on a plane which is inclined with respect to the longitudinal axis of thebody228. Any of a variety of angular relationships between thebone contacting surface246 of theflange244 and the longitudinal axis of thebody228 andhousing238 may be utilized, depending upon the anticipated entrance angle of thebody228 and associated entrance point surface of thefemur210. In general, the longitudinal axis extending through thehead214 andneck216 of the human femur is inclined at an angle of approximately 126° from the longitudinal axis of thelong body217 of thefemur210. Angles between the longitudinal axis ofbody228 andtissue contacting surface246 within the range of from about 90° to about 140° will generally be utilized, often within the range of from about 100° to about 120°, for fixed angle fixation devices. Perpendicular flanges (i.e., 90°) are illustrated inFIG. 11.
• The clinician can be provided an array ofproximal anchors236 of varying angular relationships between thebone contacting surface46 and the longitudinal axis of thebody228 and housing238 (e.g., 90°, 100°, 110°, 120°, and 130°). Asingle body228 can be associated with the array such as in a single sterile package. The clinician upon identifying the entrance angle of thebody228 and the associated entrance point surface orientation of thefemur210 can choose theanchor236 from the array with the best fit angular relationship, for use with thebody228.
• In accordance with an optional feature, illustrated inFIGS. 12 and 13, theflange244 is angularly adjustable with respect to the longitudinal axis of thebody228. More specifically, in this embodiment, thetubular housing238 is a separate component from theflange244. Thehousing238 and theflange244 preferably include corresponding semi-spherical or radiusedsurfaces245a, and245b. Thesurface245bsurrounds anaperture249 in theflange244. This arrangement allows thehousing238 to extend through and pivot with respect to theflange244. As such, the angular relationship between thebone contacting surface246 of theflange244 and the longitudinal axis of thebody228 can vary in response to the entrance angle.
• As an independent feature inFIGS. 8 and 9, theflange244 is enlarged and includes one or two ormore openings247 for receiving one or two or more femoral shaft screws (not shown). Theflange244 may be elongated anatomically distally parallel to the axis of the femur.
• With reference back toFIGS. 10 and 11, theproximal end230 of thebody228 is preferably additionally provided withrotational coupling248, for allowing thebody228 to be rotationally coupled to a driving device. Any of a variety of driving devices may be utilized, such as electric drills or hand tools which allow the clinician to manually rotate thecancellous bone anchor234 into the head of the femur. Thus, therotational coupling248 may have any of a variety of cross sectional configurations, such as one or more flats or splines.
• In one embodiment, therotational coupling248 comprises a proximal projection of thebody228 having a polygonal cross section, such as a hexagonal cross section. Therotational coupling248 is illustrated as a male component, machined or milled or attached to theproximal end230 of thebody228. However, the rotational coupling may also be in the form of a female element, such as a hexagonal or other noncircular cross sectioned lumen extending throughout a proximal portion or the entire length of thebody228. Although illustrated as solid throughout, thebody228 may be cannulated to accommodate installation over a placement wire as is understood in the art. The cross section of the central cannulation can be made non circular, e.g., hexagonal, to accommodate a corresponding male tool for installation or removal of the device regardless of the location of the proximal break point, as will be discussed.
• Thebody228 may be provided with at least one and preferably two or three ormore break points250 spaced axially apart along the proximal portion of thebody28. Break points50 comprise a weakened transverse plane through thebody28, which facilitate severing of the proximal portion of thebody28 following proper tensioning of theproximal anchor36.Break point50 may be constructed in any of a variety of ways, such as by machining or milling an annular recess into the exterior wall of thebody28, or created one or more transverse perforations through thebody28 such as by mechanical, laser, or EDM drilling.
• In the embodiments illustrated herein, thedistal anchor234 comprises ahelical locking structure260 for engaging cancellous bone. The lockingstructure260, such as a flange, may either be wrapped around acentral core262 or an axial lumen, as discussed below. The flange extends through at least one and generally from about two to about 250 or more full revolutions depending upon the axial length of the distal anchor and intended application. For most femoral neck fixation devices, the flange will generally complete from about 2 to about 20 revolutions. Thehelical flange260 is preferably provided with a pitch and an axial spacing to optimize the retention force within cancellous bone, to optimize compression of the fracture.
• The helical flange60 of the embodiment illustrated inFIG. 10 is shaped generally like a flat blade or radially extended screw thread. However, it should be appreciated that thehelical flange260 can have any of a variety of cross sectional shapes, such as rectangular, triangular or other as deemed desirable for a particular application through routine experimentation in view of the disclosure herein. The outer edge of thehelical flange260 defines an outer boundary. The ratio of the diameter of the outer boundary to the diameter of thecentral core262 can be optimized with respect to the desired retention force within the cancellous bone and giving due consideration to the structural integrity and strength of thedistal anchor234. Another aspect of thedistal anchor234 that can be optimized is the shape of the outer boundary and thecentral core262, which in the illustrated embodiment are generally cylindrical with a tapereddistal end232.
• Thedistal end232 and/or the outer edges of thehelical flange260 may be atraumatic (e.g., blunt or soft). This inhibits the tendency of thefixation device212 to migrate anatomically proximally towards the hip joint bearing surface after implantation (i.e., femoral head cut-out). Distal migration is also inhibited by the dimensions and presence of theproximal anchor236, which has a larger footprint than conventional screws.
• Referring toFIG. 14, a variation of thedistal anchor34 is illustrated. In this embodiment, the distal anchor comprises a double helix structure. Each helix is spirally wrapped about an imaginary cylinder through at least one and preferably from about two to about 20 or more full revolutions. As with the previous embodiment, the elongated body60 is provided with a pitch and an axial spacing to optimize the retention force within cancellous bone, which optimizes compression of the fracture. The tip72 of the elongated body60 may be pointed.
• In any of the embodiments herein, an antirotation lock may be provided between the distal anchor and the proximal collar or plate, such as a spline or other interfit structure to prevent relative rotation of the proximal and distal ends of the device following implantation.
• In use, the clinician first identifies a patient having a fracture such as, for example, a femoral neck fracture, which is fixable by an internal fixation device. The clinician accesses the proximal femur, reduces the fracture if necessary and selects a bone drill and drills ahole280 in accordance with conventional techniques. Preferably, thehole280 has a diameter within the range from about 3 mm to about 8 mm. This diameter may be slightly larger than the diameter of thedistal anchor34. Thehole280 preferably extends up to or slightly beyond thefracture224.
• Afixation device212 having an axial length and outside diameter suitable for the throughhole280 is selected. Thedistal end232 of thefixation device212 is advanced distally into thehole280 until thedistal anchor234 reaches the distal end of thehole280. Theproximal anchor236 may be carried by thefixation device212 prior to advancing thebody228 into thehole280, or may be attached following placement of thebody228 within thehole280. Once thebody228 is in place, the clinician may use any of a variety of driving devices, such as electric drills or hand tools to rotate thecancellous bone anchor234 into the head of the femur.
• While proximal traction is applied to theproximal end230 ofbody228, such as by conventional hemostats, pliers or a calibrated loading device, theproximal anchor236 is advanced distally until theanchor236 fits snugly against the outer surface of the femur or tissue adjacent the femur. Appropriate tensioning of thefixation device212 is accomplished by tactile feedback or through the use of a calibration device for applying a predetermined load on the implantation device. One advantage of the structure of the present invention is the ability to adjust compression independently of the setting of thedistal anchor234.
• Following appropriate tensioning of theproximal anchor236, theproximal extension230 of thebody228 is preferably cut off or snapped off and removed.Body228 may be cut using conventional saws, cutters or bone forceps which are routinely available in the clinical setting. Alternatively, the fixation device can be selected such that it is sized to length upon tensioning, so no proximal projection remains.
• Following trimming theproximal end230 ofbody228, the access site may be closed and dressed in accordance with conventional wound closure techniques.
• Preferably, the clinician will have access to an array offixation devices212, having, for example, different diameters, axial lengths and angular relationships. These may be packaged one per package in sterile envelopes or peelable pouches, or in dispensing cartridges which may each hold a plurality ofdevices212. Upon encountering a fracture for which the use of a fixation device is deemed appropriate, the clinician will assess the dimensions and load requirements, and select a fixation device from the array which meets the desired specifications.
• Thefixation device212 of the described above may be used in any of a wide variety of anatomical settings beside the proximal femur, as has been discussed. For example, lateral and medial malleolar fractures can be readily fixed using the device of the present invention. Referring toFIG. 15, there is illustrated an anterior view of thedistal fibula320 andtibia322. Thefibula320 terminates distally in thelateral malleolus324, and thetibia322 terminates distally in themedial malleolus326. Afixation device212 is illustrated as extending through thelateral malleolus324 across the lateralmalleolar fracture328 and into thefibula320.Fixation device212 includes adistal anchor34 for fixation within thefibula320, anelongate body228 and aproximal anchor236 as has been discussed.
• FIG. 15 also illustrates afixation device212 extending through themedial malleolus326, across a medialmalleolar fracture330, and into thetibia322. AlthoughFIG. 15 illustrates fixation of both a lateralmalleolar fracture328 and medial malleolar fracture130, either fracture can occur without the other as is well understood in the art. Installation of the fixation devices across malleolar fractures is accomplished utilizing the same basic steps discussed above in connection with the fixation of femoral neck fractures
• FIGS. 16-19 illustrate a modified embodiment of aproximal anchor400, which can be used with the bone fixation devices described above.
• With initial reference toFIGS. 16 and 17, a proximal end of afixation device404 is illustrated. Although the distal anchor of thefixation device404 is not illustrated, any of the bone anchors previously described or incorporated by reference herein may be used with the illustrated embodiment. Moreover, although thebody405 of the illustratedfixation device404 is solid, the fixation device can be cannulated as mentioned above.
• As described above, the proximal end of thebody405 is provided with a plurality ofretention structures406. Theretention structures406 are spaced apart axially along the fixation device between a proximal limit and a distal limit (not shown). As discussed above, the axial distance between proximal limit and distal limit is related to the desired axial travel of the proximal anchor, and thus the range of functional sizes of the bone fixation. In the illustrated embodiment, theretention structures406 comprise a plurality of annular ridges or grooves, adapted to cooperate withcomplementary retention structures408 on theproximal anchor400, which will be described in detail below.
• Theproximal anchor400 comprises ahousing412 such as a tubular body, for coaxial movement along thebody405. Theproximal anchor400 also includes a flange414 that sets against the outer surface of the bone or tissue adjacent the bone as described above. As best seen inFIG. 17, the flange414 defines abone contacting surface415, which preferably forms an obtuse angle with respect to the exterior of thehousing412.
• Referring toFIG. 19, in the illustrated embodiment, thecomplementary retention structures408 comprise an inwardly projecting teeth or flanges, for cooperating with thecomplementary rentention structures406 of thefixation device404. The projecting teeth or flanges are located near or at the proximal end of thecollar400. As mentioned above, thecomplementary retention structures406 of the fixation device preferably comprise a plurality of annular ridges orgrooves406. As shown inFIG. 19, the plurality of annular ridges orgrooves406 preferably defines at least afirst surface407 and asecond surface409. Thefirst surface407 generally faces the proximal direction and is preferably inclined with respect to the longitudinal axis of thebody405. In contrast, thesecond surface409 generally faces the distal direction and lies generally perpendicular to the longitudinal axis of thebody405.
• As shown, inFIGS. 16 and 17, theproximal anchor400 preferably includes a plurality ofaxial slots416. Theaxial slots416 cooperate to form lever arms418 (seeFIG. 19) on which the teeth orprojections408 are positioned. Thus, as theanchor400 is pushed towards the distal end of the body305, theteeth408 can slide along thefirst surface407 and be lifted over theretention structures406 of thebody405 as thelever arms418 are flexed away from thebody405.
• After appropriate tensioning of theproximal anchor400, the bone pushes on the angled portionbone contacting surface415 of theproximal anchor400. This force is transmitted to theteeth408 through thelever arms418. As such, theteeth408 are prevented from flexing away from thebody405, which keeps theteeth408 engaged with theretention structures406 of thebody405. By increasing the tensioning force, theteeth408 are forced further into theretention structures406 of thebody406, thereby increasing the retention force of theproximal anchor400. In this manner, theteeth408 cannot be lifted over thesecond surface409 and proximal movement of theproximal anchor400 is prevented.
• The axial length and width of theslots416 may be varied, depending upon the desired flexing of thelever arms418 when theproximal anchor400 is moved distally over thebody405 and the desired retention force of the distal anchor when appropriately tensioned. For a relatively rigid material such as titanium, axial lengths and widths of theslots416 are approximately 0.5 mm for a proximal anchor having a length of approximately 4 mm, an inner diameter of approximately 3 mm. As such, in the illustrated embodiment, theslots416 extend through the flange414 and at least partially into thetubular housing412.
• Another embodiment of aproximal anchor420 is illustrated inFIGS. 20-23B. Theproximal anchor420 includes aflange424 and atubular housing426. In this embodiment, the complementary structure of theproximal anchor420 comprises anannular ring430, which is positioned within anannular recess432 that is preferably positioned at the distal end of the tubular housing. SeeFIGS. 23A and 23B. Theannular recess432 includes aproximal portion434 and adistal portion436.
• With specific reference toFIG. 23A, theproximal portion434 is sized and dimensioned such that as theproximal anchor420 is advanced distally over thebody405 theannular ring430 can slide along thefirst surface407 and over thecomplementary retention structures406 of thebody405. That is, theproximal portion434 provides a space for the annular ring to move radially away from thebody405 as the proximal anchor is advanced distally. Preferably, theannular ring430 is made from a material that provides sufficient strength and elasticity such as, for example, stainless steel or titanium. Theannular ring430 is preferably split such that it can be positioned over thebody405. Although thering430 is illustrated as having a circular cross section, it may alternatively have a non circular cross section such as rectangular or square.
• With reference toFIG. 23B, thedistal portion436 is sized and dimensioned such that after theproximal anchor420 is appropriately tensioned theannular ring430 becomes wedged between thesecond surface409 and an angled engagement surface of thedistal portion436. In this manner, proximal movement of theproximal anchor420 is prevented.
• Another embodiment of a distal anchor is shown inFIGS. 24-27B. In the illustrated embodiment,proximal anchor440 comprises ahousing442 such as a tubular body, for coaxial movement along thebody405. Thehousing442 is provided with one ormore surface structures444 such as a radially inwardly projecting flange446 (seeFIGS. 27A and 27B), for cooperating with thecomplementary surface structures406 on thebody405.
• In the illustrated embodiment, thecomplimentary surface structures406 comprise a series of annular ridges or grooves, which define afirst surface407 and asecond surface409 configured as described above. Thesurface structures444 andcomplementary surface structures406 permit distal axial travel of theproximal anchor440 with respect to thebody28, but resist proximal travel of theproximal anchor440 with respect to thebody405. For example, as best seen inFIG. 27A, the proximal end of theflange446 is biased towards the longitudinal axis of thebody405. As such, when theproximal anchor440 is moved proximally with respect to thebody405, theflange446 engages thesecond surface409 of the grooves orridges406. This prevents proximal movement of theproximal anchor440 with respect to thebody405. In contrast, as best seen inFIG. 27B, when theproximal anchor440 is moved distally with respect to thebody405, theflange446 can glide along thefirst surface407, bending outwardly away from thebody405 and over theridges406 so as to allow theproximal anchor440 to move distally. Of course, those of skill in the art will recognize that there are a variety of other complementary surface structures, which permit one way ratchet like movement. For example, a plurality of annular rings or helical threads, ramped ratchet structures and the like for cooperating with an opposing ramped structure or pawl can also be used.
• For the embodiments discussed herein, the pin, together with the distal anchor and other components of the present invention can be manufactured in accordance with any of a variety of techniques which are well known in the art, using any of a variety of medical-grade construction materials. For example, the pin body and other components of the present invention can be injection-molded from a variety of medical-grade polymers including high or other density polyethylene, nylon and polypropylene. The distal anchor can be separately formed from the pin body and secured thereto in a post-molding operation, using any of a variety of securing techniques such as solvent bonding, thermal bonding, adhesives, interference fits, pivotable pin and aperture relationships, and others known in the art. Preferably, however, the distal anchor is integrally molded with the pin body, if the desired material has appropriate physical properties.
• Retention structures can also be integrally molded with the pin body. Alternatively, retention structures can be machined or pressed into the pin body in a post-molding operation, or secured using other techniques depending upon the particular design.
• A variety of polymers which may be useful for the anchor components of the present invention are identified below. Many of these polymers have been reported to be biodegradable into water-soluble, non-toxic materials which can be eliminated by the body:
• Polycaprolactone
• Poly (L-lactide)
• Poly (DL-lactide)
• Polyglycolide
• Poly (L-Lactide-co-D, L-Lactide)
• 70:30 Poly (L-Lactide-co-D, L-Lactide)
• 95:5 Poly (DL-lactide-co-glycolide)
• 90:10 Poly (DL-lactide-co-glycolide)
• 85:15 Poly (DL-lactide-co-glycolide)
• 75:25 Poly (DL-lactide-co-glycolide)
• 50:50 Poly (DL-lactide-co-glycolide)
• 90:10 Poly (DL-lactide-co-caprolactone)
• 75:25 Poly (DL-lactide-co-caprolactone)
• 50:50 Poly (DL-lactide-co-caprolactone)
• Polydioxanone
• Polyesteramides
• Copolyoxalates
• Polycarbonates
• Poly (glutamic-co-leucine)
• The desirability of any one or a blend of these or other polymers can be determined through routine experimentation by one of skill in the art, taking into account the mechanical requirements, preferred manufacturing techniques, and desired reabsorption time. Optimization can be accomplished through routine experimentation in view of the disclosure herein.
• Alternatively, the anchor components can be molded, formed or machined from biocompatible metals such as Nitinol, stainless steel, titanium, and others known in the art. In one embodiment, the components of thebone fixation device24 are injection-molded from a bioabsorbable material, to eliminate the need for a post-healing removal step. One suitable bioabsorbable material which appears to exhibit sufficient structural integrity for the purpose of the present invention is poly-p-dioxanone, such as that available from the Ethicon Division of Johnson & Johnson. Poly (L-lactide, or co-DL-lactide) or blends of the two may alternatively be used. As used herein, terms such as bioabsorbable, bioresorbable and biodegradable interchangeably refer to materials which will dissipate in situ, following a sufficient bone healing period of time, leaving acceptable byproducts. All or portions of any of the devices herein, as may be appropriate for the particular design, may be made from allograft material, or synthetic bone material as discussed elsewhere herein.
• The bioabsorbable implants of this invention can be manufactured in accordance with any of a variety of techniques known in the art, depending upon the particular polymers used, as well as acceptable manufacturing cost and dimensional tolerances as will be appreciated by those of skill in the art in view of the disclosure herein. For example, any of a variety of bioabsorbable polymers, copolymers or polymer mixtures can be molded in a single compression molding cycle, or the surface structures can be machined on the surface of the pin or sleeve after the molding cycle. It is also possible to use the techniques of U.S. Pat. No. 4,743,257, the entire disclosure of which is incorporated herein by reference, to mold absorbable fibers and binding polymers together, to create a fiber-reinforced absorbable anchor.
• An oriented or self-reinforced structure for the anchor can also be created during extrusion or injection molding of absorbable polymeric melts through a suitable die or into a suitable mold at high speed and pressure. When cooling occurs, the flow orientation of the melt remains in the solid material as an oriented or self-reinforcing structure. The mold can have the form of the finished anchor component, but it is also possible to manufacture the anchor components of the invention by machining injection-molded or extruded semifinished products. It may be advantageous to make the anchors from melt-molded, solid state drawn or compressed, bioabsorbable polymeric materials, which are described, e.g., in U.S. Pat. Nos. 4,968,317 and 4,898,186, the entire disclosures of which are incorporated herein by way of this reference.
• Reinforcing fibers suitable for use in the anchor components of the present invention include ceramic fibers, like bioabsorbable hydroxyapatite or bioactive glass fibers. Such bioabsorbable, ceramic fiber reinforced materials are described, e.g., in published European Patent Application No. 0146398 and in WO/96/21628, the entire disclosures of which are incorporated herein by way of this reference.
• As a general feature of the orientation, fiber-reinforcement or self-reinforcement of the anchor components, many of the reinforcing elements are oriented in such a way that they can carry effectively the different external loads (such as tensile, bending and shear loads) that are directed to the anchor as used.
• The oriented and/or reinforced anchor materials for many applications have tensile strengths in the range of about 100-2000 MPa, bending strengths in the range of about 100-600 MPa and shear strengths in the range of about 80-400 MPa, optimized for any particular design and application. Additionally, they are relatively stiff and tough. These mechanical properties may be superior to those of non-reinforced or non-oriented absorbable polymers, which often show strengths between about 40 and 100 MPa and are additionally may be flexible or brittle. See, e.g., S. Vainionpaa, P. Rokkanen and P. Tormnld, “Surgical Applications of Biodegradable Polymers in Human Tissues”, Progr. Polym. Sci., Vol. 14, (1989) at 679-716, the full disclosure of which is incorporated herein by way of this reference.
• The anchor components of the invention (or a bioabsorbable polymeric coating layer on part or all of the anchor surface), may contain one or more bioactive substances, such as antibiotics, chemotherapeutic substances, angiogenic growth factors, substances for accelerating the healing of the wound, growth hormones, antithrombogenic agents, bone growth accelerators or agents, and the like. Such bioactive implants may be desirable because they contribute to the healing of the injury in addition to providing mechanical support.
• In addition, the anchor components may be provided with any of a variety of structural modifications to accomplish various objectives, such as osteoincorporation, or more rapid or uniform absorption into the body. For example, osteoincorporation may be enhanced by providing a micropitted or otherwise textured surface on the anchor components. Alternatively, capillary pathways may be provided throughout the pin and collar, such as by manufacturing the anchor components from an open cell foam material, which produces tortuous pathways through the device. This construction increases the surface area of the device which is exposed to body fluids, thereby generally increasing the absorption rate. Capillary pathways may alternatively be provided by laser drilling or other technique, which will be understood by those of skill in the art in view of the disclosure herein. In general, the extent to which the anchor can be permeated by capillary pathways or open cell foam passageways may be determined by balancing the desired structural integrity of the device with the desired reabsorption time, taking into account the particular strength and absorption characteristics of the desired polymer.
• One open cell bioabsorbable material is described in U.S. Pat. No. 6,005,161 as a poly(hydroxy) acid in the form of an interconnecting, open-cell meshwork which duplicates the architecture of human cancellous bone from the iliac crest and possesses physical property (strength) values in excess of those demonstrated by human (mammalian) iliac crest cancellous bone. The gross structure is said to maintain physical property values at least equal to those of human, iliac crest, cancellous bone for a minimum of 90 days following implantation. The disclosure of U.S. Pat. No. 6,005,161 is incorporated by reference in its entirety herein.
• The anchors of the present invention may be sterilized by any of the well known sterilization techniques, depending on the type of material. Suitable sterilization techniques include heat sterilization, radiation sterilization, such as cobalt60 irradiation or electron beams, ethylene oxide sterilization, and the like.
• The specific dimensions of any of the bone fixation devices of the present invention can be readily varied depending upon the intended application, as will be apparent to those of skill in the art in view of the disclosure herein. Moreover, although the present invention has been described in terms of certain preferred embodiments, other embodiments of the invention including variations in dimensions, configuration and materials will be apparent to those of skill in the art in view of the disclosure herein. In addition, all features discussed in connection with any one embodiment herein can be readily adapted for use in other embodiments herein. The use of different terms or reference numerals for similar features in different embodiments does not imply differences other than those which may be expressly set forth. Accordingly, the present invention is intended to be described solely by reference to the appended claims, and not limited to the preferred embodiments disclosed herein.

Claims (2)

1. A bone fixation device, comprising:

an elongate pin, having a proximal end, a distal end and a first retention structure;

at least one distal anchor carried by the elongate pin; and

a proximal anchor, axially moveable with respect to the elongate pin and comprising a second retention structure;

wherein at least a portion of the second retention structure is moveable between a first position and a second position, the second position being located closer to a longitudinal axis of the elongate pin as compared to the first position so as to engage at least a portion of the first retention portion and prevent proximal movement of the proximal anchor with respect to the elongate pin while the first position allows distal movement of the proximal anchor with respect to the elongate pin.

2-18. (canceled)

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