Bone fixation system

A bone fixation system has a bone implant with an implant body. The implant body defines an upper surface, a bone-facing surface spaced from the upper surface along a transverse direction, and at least one aperture defined by an inner wall. A bone fixation element is configured for insertion at least partially through the aperture. The bone fixation element has a head and a shaft that extends relative to the head in a distal direction. The head defines a ridge and at least one thread that is spaced from the ridge in the distal direction. The ridge is configured to compress a bone implant against the at least one thread so as to fixedly retain the bone implant with respect to the head.

TECHNICAL FIELD

The present disclosure relates to a bone fixation system, and particularly to a bone implant and a bone fixation element, methods for coupling a bone implant to a bone fixation element, and methods for bone fixation.

BACKGROUND

Bone implants are designed to help heal bone fractures and/or replace damaged tissue. Principles that guide bone implant design include anatomic reduction of fracture fragments, stable fixation to improve tissue healing, minimal procedural invasiveness to preserve local blood supply, and early and pain-free mobilization so that the patient can return to normal function as soon as possible. These principles have guided the development of many examples of bone implants, such as bone plates, intramedullary nails, vertebral implants, etc., as well as screws and or anchors configured to hold the bone implant in the desired position at the intended tissue site.

SUMMARY

According to one embodiment of the present disclosure, a bone fixation system includes a bone implant and at least one bone fixation element. The bone implant includes an implant body that defines an upper surface and a bone-facing surface opposite the upper surface, and at least one bone fixation aperture that extends through the implant body from the upper surface to the bone-facing surface. The bone fixation aperture is at least partially defined by a threaded inner wall. The bone fixation element includes a head and a shaft that extends with respect to the head in a distal direction and is configured to be driven into a fixation site. The bone fixation element further defines a stop surface and the head defines a threaded region that is spaced from the stop surface along the distal direction. The threaded region is configured to threadedly engage the threaded inner wall as the bone fixation element rotates to advance the head in the distal direction in the aperture until at least a portion of the threaded inner wall is captured between the stop surface and the threaded region.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring toFIGS. 1A-1C, a bone fixation system20in accordance with one embodiment is configured to stabilize a bone that has been fractured at one or more fracture locations into a plurality of bone fragments. The bone fixation system20includes a bone implant24and a bone fixation element26configured for insertion at least partially through the bone implant24to secure the bone implant24to an underlying fixation site28. The fixation site28can be a bone fixation site defined by a bone27as illustrated, an implant, or a device configured to receive a bone fixation element. For instance, the bone27can define a pair of fixation sites, such as a first fixation site28aof a first bone fragment27aof the bone27, and a second fixation site28bof a second bone fragment27bof the bone27. The bone27can define a bone gap27c, which can be defined by a fracture location FL, that separates the first bone fragment27afrom the second bone fragment27b. The fixation sites28a-bcan be located at any anatomical location on a skeletal system. For instance, the fixation sites28a-bcan be located on the skull, the vertebral column, any long bone, such as the humerus, femur, tibia, fibula, or any other location on the skeleton system where fixation is desired. The fixation site28can also be an additional implant, device or prosthesis configured to receive the bone fixation element therethrough for securement to the bone.

The bone fixation element26is configured to be coupled to the bone implant24when the bone fixation element26is fully inserted in the bone implant24as illustratedFIG. 1A. For instance, the bone implant24includes an implant body30that is elongate substantially along a central implant axis32(seeFIGS. 2A-2B). The bone implant24can be elongate along the central implant axis32, which can be linear or nonlinear as desired. The implant body30includes lateral sides38and40that are spaced from each other along a lateral implant axis33or second direction that can be angularly offset, for instance perpendicular, with respect to the central implant axis32.

In accordance with one embodiment, the central implant axis32can extend along a longitudinal direction L, and the lateral sides38and40are spaced from each other along the lateral direction A that is substantially perpendicular to the longitudinal direction L. Thus, reference to the longitudinal direction L herein can equally refer to the central implant axis32, unless otherwise indicated. Further, reference to the lateral direction A herein can equally refer to the lateral implant axis33or the second direction, unless otherwise indicated. The implant body30can further define a bone facing surface52that is configured to face toward the fixation site28when the bone implant24is secured to the fixation site28, and an opposed or upper surface54that faces away from the fixation site28when the bone implant24is secured to the fixation site28. The bone facing surface52and the opposed upper surface54can be spaced from each other along a transverse direction T that is substantially perpendicular with respect to both the longitudinal direction L and the lateral direction A. The bone facing surface52is spaced from the upper surface54in a distal direction, and the upper surface54is spaced from the bone facing surface in a proximal direction.

The bone implant24defines a plurality of bone fixation apertures56that extend through the implant body30along the transverse direction T from the upper surface54to the bone facing surface52, and at least one inner wall53that extends between the upper surface54and bone-facing surface52and defines each bone fixation aperture56. At least a portion of each inner wall53can be curved as it extends along the transverse direction T. As will be described in more detail below, at least a portion of the inner walls53can be threaded so as to threadedly mate with complementary threads of the bone fixation element26when the bone fixation element26is driven into the respective bone fixation aperture56.

The bone implant24are described herein as extending horizontally along a longitudinal direction “L” and a lateral direction “A”, and vertically along a transverse direction “T”. Unless otherwise specified herein, the terms “longitudinal,” “transverse,” and “lateral” are used to describe the orthogonal directional components of various bone fixation system components and component axes. It should be appreciated that while the longitudinal and lateral directions are illustrated as extending along a horizontal plane, and that the transverse direction is illustrated as extending along a vertical plane, the planes that encompass the various directions may differ during use. Further, the description refers to bone fixation system components and/or portions of such components that include a “proximal end” and a “distal end.” Thus, a “proximal direction” or “proximally” refers to a direction that is oriented generally from the distal end toward the proximal end. A “distal direction” or “distally” refers to a direction that is oriented generally from the proximal end toward the distal end.

Referring now toFIGS. 2A-2C, the bone implant24includes at least one wire100that is shaped to define the implant body30including the plurality of apertures56that extend though implant body30from the upper surface54to the bone-facing surface52along a central aperture axis59that can be oriented in the transverse direction T. The bone implant24can be partially or completely made of wire, which can define any implant body and aperture size and shape as desired. The wire100can define a first wire segment102and a second wire segment104that are shaped to define the bone implant. The first and second wire segments102and104can be integral and monolithic to form the wire100. Alternatively, the first and second wire segments102and104can be separate from each other and defined by two different respective wires. The wire segments102and104can be defined be a respective single strand of wire or can be defined by multiple strands of wire that can be braided, twisted, or otherwise attached to each other so as to define the respective wire segments102and104. The wire100defines a wire outer surface101that defines the bone facing surface52, the opposed upper surface54, lateral sides38and40, and the at least one inner wall53.

The at least one inner wall53can include a first inner wall53aand a second inner wall53bthat faces the first inner wall53aalong the lateral direction A. For instance, the first wire segment102is shaped to define the first inner wall53a, and the second wire segment104is shaped to define the second inner wall53b, such that the first and second inner walls53aand53bdefine the plurality of bone fixation apertures56as detailed below. It should be appreciated that the wire segments102and104can be defined by a single monolithic wire100, or can alternatively be defined by two different wires that are disposed adjacent to each other so as to define the wire segments102and104. The wire segments102and104can define a circular cross-sectional shape such that the inner walls53aand53bcan be curved, for instance convex, as they extend along the transverse direction T. The inner walls53aand53bcan further be curved as they extend along the longitudinal direction L. Further, first portions42aof the first and second inner walls53aand53bare concave as they extend along the longitudinal direction L so as to define the bone fixation apertures56, and second portions42bof the first and second inner walls53aand53badjacent the first portions42aare convex as they extend along the longitudinal direction L so as to define necks108that are disposed between adjacent ones of the bone fixation apertures56.

The bone facing surface52and the upper surface54can lie in respective planes that are spaced from each other along the transverse direction T and are each defined by the longitudinal direction L and the lateral direction A. While the bone implant24can be defined by the first and second wire segments102and104as illustrated inFIGS. 1A-4C, the bone implant24alternatively be defined by a bone plate illustrated inFIG. 5, such that the at least one inner wall53can be defined by a single inner wall as described in more detailed below. Unless otherwise indicated, reference herein to the “inner wall53” can be used to identify at least one inner wall, including reference to the first and second inner walls53aand53b, and reference to a single inner wall.

As described above, the bone implant24defines the plurality of bone fixation apertures56that extend though the implant body30. For instance, the first and second inner walls53aand53bcan define each of the plurality of apertures56that include a first aperture56aand a second aperture56bthat is spaced from the first aperture56aalong the longitudinal direction L. The bone implant24can include any number of apertures as desired. The first and second apertures56aand56bare configured to receive respective ones of the bone fixation element26therein. In particular, the bone fixation system20can include a plurality of bone fixation elements26, including a first bone fixation element26athat is configured to be inserted into the first bone fixation aperture56aand a second bone fixation element26bthat is configured to be inserted into the second bone fixation aperture56b. For instance, the bone implant24can be positioned such that the first bone fixation aperture56ais aligned with the first bone fragment27a, and the second bone fixation aperture56bis aligned with the second bone fragment27b. Thus, the bone gap27cis positioned between the first and second bone fixation apertures56aand56b. The first bone fixation element26acan be inserted into the first bone fixation aperture56aand into the first bone fragment27aso as to secure the bone implant24to the first bone fragment27a, and the second bone fixation element26bcan be inserted into the second bone fixation aperture56band into the second bone fragment27bso as to secure the bone implant24to the second bone fragment27b. Thus, the bone implant24can be secured to the fixation site28and so as to promote fusion of the first bone fragment27ato the second bone fragment27b.

As described above, the first and second wire segments102and104define a plurality of necks108that can define one or both boundaries of the bone fixation apertures56along the longitudinal direction L. The necks108can be defined by respective locations where the first and second inner walls53aand53bare closest together at the respective second portions42b. For instance, the locations of the necks108can bifurcate the second portions42balong the longitudinal direction L. In accordance with one embodiment, the locations of the necks108define respective intersection points where the first inner wall53aand the second inner wall53babut each other. The first and second inner walls53aand53bcan further be secured, for instance soldered, welded, or otherwise attached, to each other at the locations of the necks108. The first wire segment102extends along the longitudinal direction L between adjacent necks108to define the first inner wall53a, and the second wire segment104extends along the longitudinal direction L between the adjacent necks108to define the second inner wall53b. The first and second wire segments102and104extend along the longitudinal direction L to define spaced apart longitudinal ends of the bone fixation apertures56defined by a pair of adjacent necks108. Thus, each bone fixation aperture56extends between a first one of the longitudinal ends and second one of the longitudinal ends that is spaced from the first one of the longitudinal ends along the central implant axis32between adjacent locations of the necks108. The locations of the necks108can be disposed on the central axis32.

With continuing reference toFIGS. 2A-2C, the inner wall53of the implant body30is threaded along the respective bone fixation apertures56. Thus, it can be said that at least a portion of the inner wall53, including at least a portion of the first inner wall53aand at least a portion of the second inner wall53b, is threaded. For instance, the first and second inner walls53aand53bdefines respective threads58that can be helically arranged and configured to threadedly mate with respective threads of the bone fixation element26when the bone fixation element26is inserted into the respective bone fixation aperture56. The threads of the first inner wall53a, when continued to the threads of the second inner wall53bopposite the threads of the first inner wall53along the lateral direction A, can define a helical path. Thus, the threads58can be referred to as internal threads. The threads58can be disposed at a respective first threaded region60defined by the first wire segment102and a respective second threaded region62defined by the second wire segment104. Thus, the first inner wall53adefines the first threaded region60and the second inner wall53bdefines the second threaded region62. The first threaded region60extends along the first wire segment102from a respective proximal end to a respective distal end that is spaced from the proximal end in the distal direction. Similarly, the second threaded region62extends along the second wire segment104from a respective proximal end to a respective distal end that is spaced from the proximal end in the distal direction. Further, the first and second threaded regions60and62extend along a portion of the inner walls53aand53b, respectively, along the longitudinal direction. For instance, the threads58extend along at least part of the first portions42aof the respective first and second inner walls53aand53b. For instance, the threads58can extend along both the first and second portions42aand42bof the respective first and second inner walls53aand53bfrom a first one of the necks108to an adjacent one of the necks108if desired.

Referring now toFIG. 2Cin particular, the inner wall53can combine so as to define a single thread58that extends about at least a portion of the perimeter of each bone fixation aperture56, or can alternatively define multiple intertwined threads that define what is known as a multiple start screw. Thus, it can be said that the inner wall53defines at least one thread58. In accordance with one embodiment, the at least one thread58of the first and second inner walls53aand53bcan be continuous with each other along a helical path.

Each at least one thread58includes a first surface72aand an opposed second surface72b. At least one or both of the first and second surfaces72aand72bconverges toward the other of the first and second surfaces72aand72bas the first and second surfaces72aand72bextend toward the central aperture axis59. In particular, each of the first and second surfaces72aand72bconverge from a root72cof the thread58to a crest72dof the thread58. The implant body30, and thus the bone implant24, defines a major diameter D1that is defined by the root72cand extends along a direction perpendicular to the central aperture axis59and intersects the central aperture axis59. The implant body30, and thus the bone implant24, defines a minor diameter d1that is defined by the crest72dand extends along a direction perpendicular to the central aperture axis59and intersects the central aperture axis59.

The first surface72ais spaced from the second surface72bin the proximal direction. Thus, the second surface72bis spaced from the first surface in the distal direction. The first surface72acan be referred to as a leading surface with respect to insertion of the bone fixation element26into the respective bone fixation aperture56, and the second surface72bcan be referred to as a trailing surface with respect to insertion of the bone fixation element26into the respective bone fixation aperture56. It should be appreciated, of course, that if the bone fixation element26is removed from the bone fixation aperture56, the second surface72bbecomes the leading surface and the first surface72abecomes the trailing surface. In accordance with the illustrated embodiment, each of the first and second surfaces72aand72b, in cross-section through a plane that is partially defined by the central aperture axis59, defines a first angle less than 90 degrees with respect to a reference plane that is oriented normal with respect to the central aperture axis59. For instance, the first and second surfaces72aand72b, in said cross section, can define equal and opposite first angles with respect to the reference plane.

In accordance with the illustrated embodiment, the inner walls53aand53bcan define as many intertwined screw threads58as desired, for instance one, two, three, or more. Thus, the inner walls53aand53bdefine a lead L1, which is defined by the axial advance of the bone fixation element26along the central aperture axis59when threadedly mated with the at least one thread58and rotated one complete 360 degree revolution. The inner wall53further defines a pitch P1, that is the axial distance along the central aperture axis59between adjacent ones of the crests72d, which can be defined by the same thread58, for instance if the inner surfaces53defines a single thread, or can be defined by different threads58, for instance if the inner wall53defines multiple intertwined threads58. Thus, the lead L1is a multiple of the pitch P1by the number of intertwined threads58defined by the inner wall53. When the inner wall53defines a single thread58, the multiple is one, and the lead L1is equal to the pitch P1.

Referring now also toFIGS. 3A-3B, the bone fixation element26is elongate along a central axis31that can extend along the transverse direction T, and defines a proximal end29aand a distal end29bthat is spaced from the proximal end29ain a distal direction along the central axis31. Thus, the proximal end29ais spaced from the distal end29bin a proximal direction. The central axis31is coaxial with the central aperture axis59when the bone fixation element26is disposed in the bone fixation aperture56. The bone fixation element26can be an anchor, rivet, bone pin or screw configured for securement to the fixation site28.

The bone fixation element26can include a head80and a shaft82that extends in the distal direction with respect to the head80. The shaft82can define a length in the transverse direction T that is greater than the length of the head80in the transverse direction T. For instance, the shaft82can extend directly from the head80, or the bone fixation element26can include a necked region83that extends between the head80and the shaft82. Thus, the proximal end29aof the bone fixation element26can be defined by the head80, and the distal end29bof the bone fixation element26can be defined by the shaft82. At least a portion of the shaft82can be threaded along the transverse direction T, and can define at least one external thread, such as a thread84. The thread84can be helical and can extend from a root85ato a crest85balong a direction away from the central axis31. The shaft82thus defines major diameter D2that is defined by the crest85band extends along a direction perpendicular to the central axis31and intersects the central axis31. The shaft82can further define a minor diameter d2that is defined by the root85aand extends along a direction perpendicular to the central axis31and intersects the central axis31. The thread84can be helical, and can define a pitch P2and a lead L2. The at least one thread84can be a single thread, such that the lead L2is equal to the pitch P2. Alternatively the shaft82can define multiple intertwined threads such that the lead L2is a multiple of the pitch P2as described above with respect to the thread58of the bone implant24.

The minor diameter d1of the at least one thread58of the bone implant24can be greater than the major diameter D2of the at least one thread84of the shaft82, such that the shaft82can be advanced through the bone fixation aperture56along the distal direction without rotating the bone fixation element26with respect to the bone implant24, and without causing at least one thread84to interfere with the at least one thread58. Accordingly, during operation, the shaft82can be advanced through one of the bone fixation apertures56, until the shaft82contacts the fixation site28. The bone fixation element26, including the shaft82, can be rotatably driven into the underlying fixation site28, such that the thread84purchases with the fixation site28, for instance the bone27, thereby securing the shaft82to the fixation site28. The thread84of the shaft82at the distal end29bcan define one or more cutting flutes such that the bone fixation element26is configured as a self-tapping screw. Alternatively, the at least one thread84can be devoid of cutting flutes, such that the bone fixation element26defines a standard screw whereby the threads84intermesh with the bone27through a pilot hole that has been pre-drilled into the bone27, thereby securing the shaft82to the fixation site28.

With continuing reference toFIGS. 3A-B, the head80can also be threaded along the transverse direction T, and can define at least one thread88, which can be configured as an external thread. The at least one thread88can include a single thread or a plurality of intertwined threads as described above with respect to the inner wall53of the bone implant24. Each of the threads88includes a first surface89aand an opposed second surface89b. At least one or both of the first and second surfaces89aand89bconverges toward the other of the first and second surfaces89aand89bas the first and second surfaces89aand89bextend away from the central axis31. In particular, each of the first and second surfaces89aand89bconverge from a root89cof the thread88to a crest89dof the thread88. The head80defines a major diameter D3that is defined by the crest89dand extends along a direction perpendicular to the central axis31and intersects the central axis31. The head80can further defines a minor diameter d3that is defined by the root89cand extends along a direction perpendicular to the central axis31and intersects the central axis31.

The necked region83defines an outer diameter D4that is less than the major diameter D3of the head80. Both the outer diameter D4of the necked region83and the major diameter D2of the shaft82are less than the minor diameter d1of the bone implant24such that both the shaft82and the necked region83can advance through the at least one bone fixation aperture56without interfering with the respective at least one thread58. The outer diameter D4of the necked region83can be less than one or both of the major diameter D2and the minor diameter d2of the shaft82, greater than one or both of the major diameter D2and the minor diameter d2of the shaft82, or equal to one or both of the major diameter D2and the minor diameter d2of the shaft82as desired.

The major diameter D3of the head80is greater than the major diameter D2of the shaft82and the outer diameter D4of the necked region83. For instance, the major diameter D3of the head80is less than the major diameter D1of the bone implant24and greater than the minor diameter d1of the bone implant24. Further, the minor diameter d3of the head80is less than the minor diameter d1of the bone implant24. Thus, when the central axis31of the bone anchor24is aligned with the central aperture axis59, and the distal end of the at least one thread88contacts the at least one thread58of the inner wall53, rotation of the bone anchor24in a first direction of rotation causes the at least one thread88to threadedly mate with the at least one thread58of the bone implant24, which advances the bone fixation element26along the distal direction with respect to the bone implant24, thereby advancing the head80in the respective bone fixation aperture56in the distal direction. It is further appreciated that rotation of the bone fixation element26in the first direction can further drive the shaft82into the underlying bone27. It is recognized that rotation of the bone fixation element26in a second direction of rotation that is opposite the first direction of rotation can cause the head80to retract from the respective bone fixation aperture56along the proximal direction until the head80is removed from the bone fixation aperture56. Furthermore, rotation of the bone fixation element26in the second direction of rotation can cause the shaft82to retract from the underlying bone27along the proximal direction until the shaft82is removed from the underlying bone27.

The bone fixation element26can further define an instrument engagement member that is configured to mate with a driving instrument so as to receive a drive force that causes the bone fixation element26to rotate in one of the first and second directions of rotation. The tool engagement member can, for instance, be configured as a socket93that extends into the head80in the distal direction along the central axis31. The socket93can have any suitable shape configured to receive the driving instrument. For instance, the socket93can be a square, hex, cross, slot, flat, star, hexalobular, or any other suitable shape to receive a tool. Further, the bone fixation element26can be cannualated from the socket93through the head80and through the shaft82along the central axis31, and further can include one or more bores that extend through the shaft82to the cannulation. The cannulation and the bores can be configured to receive a temporary guidewire, such as a Kirschner wire that can be temporarily driven into the fixation site28, such that the guidewire guides the bone fixation element26to the fixation site28during fixation of the bone fixation element26into the fixation site28. The guidewire can then be removed from the fixation site28and the cannulation. Further, the bores can be configured to receive for receiving additional fixation elements therethrough, such as a temporary guidewire or Kirschner wire, or an additional screw that can be inserted through the socket93and the transverse bore to secure to the bone27or the implant. The bores can also allow for bone ingrowth as wel.

The first surface89ais spaced from the second surface89bin the proximal direction. Thus, the second surface89bis spaced from the first surface89ain the distal direction. The second surface89bcan be referred to as a leading surface with respect to insertion of the bone fixation element26into the respective bone fixation aperture56, and the first surface89acan be referred to as a trailing surface with respect to insertion of the bone fixation element26into the respective bone fixation aperture56. Thus, the leading surface of the at least one thread88of the head80faces the leading surface of the at least one thread58of the bone implant24as the head80threadedly engages the bone implant24in the bone fixation aperture56. It should be appreciated, of course, that if the bone fixation element26is removed from the bone fixation aperture56, the first surface89abecomes the leading surface and the second surface89bbecomes the trailing surface. In accordance with the illustrated embodiment, each of the first and second surfaces89aand89b, in cross-section through a plane that is partially defined by the central axis31, defines a second angle less than 90 degrees with respect to a reference plane that is oriented normal with respect to the central axis31. For instance, the first and second surfaces89aand89b, in said cross section, can define equal and opposite second angles with respect to the reference plane. The second angle defined by the at least one thread88is substantially equal to the first angle defined by the at least one thread58of the bone implant24.

In accordance with the illustrated embodiment, the outer surface of the head80can define as many intertwined screw threads88as desired, for instance one, two, three, or more. Thus, the head80defines a lead L3, which is defined by the axial advance of the bone fixation element26along the central aperture axis59when threadedly mated with the at least one thread58and rotated one complete 360 degree revolution. The head80further defines a pitch P3, that is the axial distance along the central axis31between adjacent ones of the crests89d, which can be defined by the same thread88, for instance if the head80defines a single thread, or can be defined by different threads88, for instance if the head80defines multiple intertwined threads88. Thus, the lead L3is a multiple of the pitch P3by the number of intertwined threads88defined by the head80. When the head80define a single thread88, the multiple is one, and the lead L3is equal to the pitch P3. The lead L3is substantially equal to the lead L1of the bone implant24, and the pitch P3is substantially equal to the Pitch P1of the bone implant24. Further, the leads L1and L2of the head80and the bone implant24, respectively, can be substantially equal to the lead L3of the shaft82. Accordingly, the shaft82advances into the bone27in the distal direction at the same rate (e.g., distance per revolution of the bone fixation element26relative to the bone27) as the rate that the head80advances in the bone fixation aperture56in the distal direction (e.g., distance per revolution of the bone fixation element26relative to the bone implant24). The pitches P1and P2of the head80and bone implant24, respectively, can further be substantially equal to the pitch L3of the shaft82when, for instance, the at least one thread58of the respective bone fixation aperture56, the at least one thread88of the head80, and the at least one thread84of the shaft82define the same number of threads.

The major diameter D1of the at least one thread58of the bone implant24can be greater than the major diameter D2of the at least one thread84of the shaft82, such that the shaft82can be advanced through the bone fixation aperture56along the distal direction without rotating the bone fixation element26with respect to the bone implant24, and without causing at least one thread84to interfere with the at least one thread58. Accordingly, during operation, the shaft82can be advanced through one of the bone fixation apertures56, until the shaft82contacts the fixation site28. The bone fixation element26, including the shaft82, can be rotatably driven into the underlying fixation site28, such that the thread84purchases with the fixation site28, for instance the bone27, thereby securing the shaft82to the fixation site28. The thread84of the shaft82at the distal end29bcan define one or more cutting flutes such that the bone fixation element26is configured as a self-tapping screw. Alternatively, the at least one thread84can be devoid of cutting flutes, such that the bone fixation element26defines a standard screw whereby the threads84intermesh with the bone27through a pilot hole that has been pre-drilled into the bone27, thereby securing the shaft82to the fixation site28.

With continuing reference toFIGS. 3A-B, the head80defines a ridge92that is positioned adjacent the at least one thread88of the head80so as to be spaced from the at least one thread88along the proximal direction. Thus, the at least one thread88can be spaced from the ridge92along the distal direction. For instance, an entirety of the at least one thread88can be spaced from the ridge92along the distal direction. Alternatively, the at least one thread88can be partially defined by the ridge92, such that a portion of the at least one thread88extends distal with respect to the ridge92. The ridge92defines an outer cross-sectional dimension D5along a plane defined by the longitudinal direction L and the lateral direction A. The outer cross-sectional dimension D5is greater than the major diameter D3of the head80and further greater than at least the minor diameter d1of the bone implant24. Further, the outer cross-sectional dimension D5can be greater than the major diameter D1of the bone implant24. The ridge92can be circular in shape in a cross-section with respect to a plane that extends along the longitudinal and lateral directions, such that the outer cross-sectional dimension D5is a diameter. Alternatively, the ridge92can define any suitable alternative shape in said cross-section as desired. The ridge92defines a stop surface that is aligned with a portion of the bone implant24along the transverse direction T. Accordingly, as will be described in more detail below, the ridge92is configured to abut the bone implant24when the head80threadedly engages the bone anchor24in the respective fixation aperture56. The ridge92can be continuous about the perimeter of the head80or segmented about the perimeter of the head80.

Referring now toFIGS. 4A-4C, during operation the bone implant24is positioned at a location as desired with respect to the underlying bone27such that the bone facing surface52faces the underlying fixation site28or bone27, and the upper surface54faces away from the underlying fixation site28or bone27(see alsoFIG. 1A). For instance, the location can be such that the bone implant24is positioned against the underlying bone27or such that the bone implant24is spaced from the underlying bone as desired. The bone implant is positioned such that the bone gap is disposed between first and second ones of the bone fixation apertures56in the manner described above. A first bone fixation element26is driven through the first one of the bone fixation apertures56and into the first fixation site28a, and a second bone fixation element26is driven through the second one of the bone fixation apertures56and into the second fixation site28b. In particular, as each bone fixation element26is driven through the respective bone fixation aperture56an into the underlying fixation site28and rotated with respect to both the fixation site28and the bone implant24, the threaded shaft82can be threadedly driven into the underlying bone27in the manner described above. The bone fixation element26is driven into the underlying bone27until the at least one thread88of the head80begins to threadedly mate with the at least one thread58of the bone implant24. Continued rotation of the bone fixation element26with respect to both the fixation site28and the bone implant24causes the at least one thread88to further threadedly mate with the at least one thread58of the bone implant24as the head90advances in the distal direction in the bone fixation aperture56.

As illustrated inFIGS. 4B-4Cbecause the major diameter D3of the head80is less than the major diameter D1of the bone implant24, a gap90can be defined between the at least one thread88of the head80and the at least one thread58of the bone implant24along a line that extends in the transverse direction T, and thus parallel to the central axis31and the central aperture axis59. For instance, the gap90can be defined between the first surface89aof the head80and the at least one thread58, between the second surface89band the at least one thread58, or a first portion of the gap90can be defined between the first surface89aand the at least one thread58, and a second portion of the gap90can be defined between the second surface89band the at least one thread58. For instance, the gap90or the first portion of the gap90that is defined between the first surface89aand the at least one thread58can in particular be defined between the first surface89aand the second surface72b. The gap90or the second portion of the gap90that is defined between the second surface89band the at least one thread can in particular be defined between the second surface89band the first surface72a. It can further be said that the gap90can be defined between the first surface89aof the head80and the inner wall53, between the second surface89band the inner wall53, or a first portion of the gap90can be defined between the first surface89aand the inner wall53, and a second portion of the gap90can be defined between the second surface89band the inner wall53.

With further reference toFIGS. 1B-1CandFIGS. 4A-4C, the shaft82of the fixation element26is driven through the respective bone fixation aperture56along the distal direction, and can be rotated in the first direction of rotation, thereby causing the at least one thread84to threadedly purchase with the first fixation site28a, as the shaft82is driven into the first fixation site28a, which can be defined by the underlying bone27. As the shaft82is advanced in the first fixation site28a, the at least one thread88of the head80threadedly mates with the at least one thread58in the respective bone fixation aperture56of the bone implant24as illustrated inFIG. 4A. Continued rotation of the bone fixation element26in the first direction causes the ridge92to move distally with respect to the bone implant24until the ridge92, and in particular the stop surface of the ridge92, contacts the bone implant24at a contact location95, as illustrated inFIGS. 4B-4C. The contact location95can be defined by the inner wall53. It should be appreciated that at least a portion of the bone implant24, for instance at least a portion of the inner wall53, is disposed between the ridge92and a threaded region of the head80, which can be defined by the at least one thread88.

As described above, at least a portion of the gap90can be disposed between the first surface89aand the at least one thread58of the bone implant24, for instance the second surface72bof the at least one thread58. Thus, referring toFIGS. 4D-4E, the bone implant24can be prevented from jiggling with respect to the bone fixation element26along the transverse direction T, both in the proximal direction and in the distal direction, due to clearance provided by the gap90, also known as backlash. For instance, further rotation of the bone fixation element26in the first direction of rotation causes the ridge92, and in particular the stop surface of the ridge92, to bear against the implant body30at the contact location95, thereby driving the bone implant24in the distal direction with respect to the at least one thread88until the at least one thread58contacts the first surface89a. Thus, implant body30, and in particular the inner wall53, and thus the bone implant24, is compressed between the stop surface, for instance the ridge92, and the at least one thread88, for instance the leading surface of the at least one thread. In particular, the proximal end of the implant body30bears against the stop surface, which can be defined by the ridge92, and the at least one thread58bears against the at least one thread88. The implant body30is compressed between the ridge92and the at least one thread88while the at least one thread88is threadedly mated with the at least one thread58of the bone implant24. Accordingly, an entirety of the gap90is disposed between the second surface89band the at least one thread58, for instance the first surface72aof the at least one thread58. Accordingly, contact between the ridge92and the bone implant24prevents the bone implant24from moving in the proximal direction with respect to the bone fixation element26. Furthermore, contact between the first surface89aof the at least one thread88of the head80and the second surface72bof the at least one thread58of the bone implant24prevents the bone implant24from moving in the distal direction with respect to the bone fixation element26. Thus, relative movement is prevented between the bone fixation element26and the bone implant24along the transverse direction.

The ridge92can define a height along the transverse direction T from the contact location95to the proximal-most surface of the ridge92that is no greater than the height of the bone implant from the contact location95to the proximal-most end of the upper surface54. For instance, the proximal-most end of the upper surface54can lie within a first plane that is defined by the lateral direction A and the longitudinal direction L. The contact location95can lie in a reference plane that is defined by the lateral direction and the longitudinal direction L. The reference plane is spaced from the first plane along the transverse direction T a first height. The proximal-most end of the ridge92can lie within a second plane that is defined by the lateral direction A and the longitudinal direction L. The third plane is spaced from the reference plane along the transverse direction T a second height that is no greater than the first height. For instance, the second height of the ridge92can be less than the first height. Accordingly, when the ridge92is in contact with the bone implant24at the contact location95, the ridge92does not project out with respect to the proximal-most end of the upper surface54along the proximal direction.

Further, the ridge92can defines a height along the transverse direction T from the contact location95to the distal-most surface of the head80that is no greater than the height of the bone implant24from the contact location95to the distal-most end of the bone facing surface52. For instance, the distal-most end of the upper surface54can lie within a third plane that is defined by the lateral direction A and the longitudinal direction L. The third plane is spaced from the reference plane in the transverse direction T a third height. The distal-most end of the ridge92can lie within a fourth plane that is defined by the lateral direction A and the longitudinal direction L. The fourth plane is spaced from the reference plane so as to define a fourth height that is no greater than the third height. For instance, the fourth height of the ridge92can be less than the third height. Accordingly, when the ridge92is in contact with the bone implant24at the contact location95, the ridge92does not project out with respect to the distal-most end of the bone facing surface52along the distal direction. Because the head80does not project out with respect to the bone implant24along the transverse direction T in accordance with one embodiment, the head80does not irritate soft tissue that is in close proximity to the bone implant24.

In accordance with one embodiment, because the lead L1of the bone implant24and the lead L3of the head80are substantially equal to the lead L2of the shaft82, rotation of the bone anchor24in the first direction of rotation does not cause the bone implant24to move substantially toward or away from the underlying bone27as the shaft82threadedly purchases with the underlying bone at the respective fixation site28while the head80threadedly mates with the bone implant24in the respective fixation aperture56. Alternatively, it is appreciated that the lead L2of the shaft82can be different than each of the lead L1of the bone implant24and the lead L3of the head80. Accordingly, the bone implant24can move with respect to underlying bone27along the transverse direction T as the shaft82threadedly purchases with the underlying bone at the respective fixation site28while the head80threadedly mates with the bone implant24in the respective fixation aperture56. For instance, the lead L2of the shaft82can be greater than each of the lead L1of the bone implant24and the lead L3of the head80. Accordingly, the shaft82can advance in the fixation site in the distal direction during rotation of the bone fixation element at a first rate that is greater than a second rate at which the head80advances in the distal direction in the bone fixation aperture56. Thus, the bone implant24can move toward the underlying bone27in the distal direction as the shaft82threadedly purchases with the underlying bone at the respective fixation site28while the head80threadedly mates with the bone implant24in the respective fixation aperture56. Thus, the bone implant24can be placed adjacent the underlying bone27, such that the bone implant24is compressed against the underlying bone27as the shaft82threadedly purchases with the underlying bone27at the respective fixation site28while the head80threadedly mates with the bone implant24in the respective fixation aperture56. Alternatively still, the lead L2of the shaft82can be less than each of the lead L1of the bone implant24and the lead L3of the head80. Accordingly, the bone implant24can move away from the underlying bone27along the transverse direction T as the shaft82threadedly purchases with the underlying bone at the respective fixation site28while the head80threadedly mates with the bone implant24in the respective fixation aperture56.

Referring again toFIG. 1C, at least one first bone fixation element26ais secured to both the first fixation site28aand the bone implant24in a respective at least one first bone fixation aperture56aas described above, and at least one second bone fixation element26bcan be secured to both the second fixation site28band the bone implant24in a respective at least one second bone fixation aperture56b. The bone fixation system can include as many first bone fixation elements26aas desired, and as many second bone fixation elements26bas desired.

It should thus be appreciated that coupling the bone fixation elements26to the bone implant24and the underlying bone27provides 1) angularly stability between the bone fixation element26and the bone implant24, and 2) prevents relative movement between the bone fixation element26and the bone implant24along the transverse direction T. For instance, when a plurality of bone fixation elements26are coupled to bone implant24and secured to a corresponding fixation site28, angularly stable fixation is achieved because the bone implant24forms a stable bridging structure with the bone fixation elements26that spans the fracture location FL. Further, the bone fixation element26can be coupled to the bone implant24such that at least a portion of the bone implant24, for instance a portion of the inner wall53, is captured between 1) a stop surface of the bone fixation element26, for instance the head80, and 2) a threaded region of the head80. For instance, the stop surface can be defined by the ridge92, and the threaded region can be disposed distal from the ridge92, and can be defined by the at least one thread88of the head80.

Referring now toFIG. 5, it should be appreciated that, unless otherwise indicated, the bone implant24can be constructed in accordance with any suitable alternative embodiment. For instance, while the bone implant24can be defined by the first and second wire segments102and104as described above, the bone implant24can alternatively be defined by a bone plate97that defines the implant body30. The implant body30, and thus the bone plate97, defines the bone facing surface52and the upper surface54as described above, and further defines a plurality of inner surfaces53that define respective bone fixation apertures56that extend through the implant body30from the upper surface54to the bone facing surface52. At least a portion of the inner wall53defines the at least one thread58in the manner described above, such that the at least one thread88of the head80of the bone fixation element26can be threadedly secured to the at least one thread58of the bone implant24in the manner described above.

The bone fixation system20as constructed herein can be formed using any suitable biocompatible materials or combination of the materials. For instance, the bone implant24can be formed of metallic materials such as cobalt chromium molybdenum (CoCrMo), stainless steel, titanium, titanium alloys, magnesium, glass metals, ceramic materials, and polymeric materials include plastics, fiber reinforced plastics, polymeric materials that include polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and bioresorbable materials or shape memory materials. In one embodiment, the bone implant24can be formed of a combination of polymeric and metallic materials. For instance, the bone implant24can be formed of polymeric wire segments, metallic wire segments, or a combination of polymeric and metallic wire segments. The bone implant24may be coated an antibacterial coating, drug-eluting coating, or surface modifier such as a carbon diamond coating. In another example, the bone implant24may be chemically processed using, for example, anodization, electropolishing, chemical vapor deposition, plasma treatments, or any process to modify or enhance bone implant surface characteristics. The bone fixation elements26can also be formed of formed of metallic materials such as cobalt chromium molybdenum (CoCrMo), stainless steel, titanium, titanium alloys, nitinol and Gummetal®, magnesium, glass metals, ceramic materials, and polymeric materials include plastics, fiber reinforced plastics, polymeric materials that include polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and bioresorbable materials or shape memory materials. The bone fixation elements26can also be metallic or formed of metallic alloys, such as titanium. The bone fixation element26can also be formed of a combination of polymeric and metallic materials. For instance, the bone fixation elements26can have a polymeric head and metallic shaft. The bone fixation elements26may be coated an antibacterial coating, drug-eluting coating, or surface modifier such as a carbon diamond coating. In another example, the bone fixation elements26may be chemically processed using, for example, anodization, electropolishing, chemical vapor deposition, plasma treatments, or any process to modify or enhance bone fixation element surface characteristics.

Referring now toFIGS. 6A-6B, it should be appreciated that one or more up to all of the bone fixation elements26can be constructed in accordance with an alternative embodiment. For instance, as described above, the bone fixation element26includes the head80and the shaft82that extends in the distal direction with respect to the head80along the central axis31. The shaft82can define a length in the transverse direction T that is greater than the length of the head80in the transverse direction T. For instance, the shaft82can extend directly from the head80, or the bone fixation element26can include a necked region83that extends between the head80and the shaft82. Thus, the proximal end29aof the bone fixation element26can be defined by the head80, and the distal end29bof the bone fixation element26can be defined by the shaft82. The head80can include the ridge92which can be defined as a first ridge, and the head80can further include a second ridge94that is spaced distally from the first ridge92in the distal direction along the central axis31. The head further defines a groove96that extends between the first ridge92and the second ridge94. The groove96is configured to receive a portion of the inner wall53of the bone implant24to secure the bone fixation element26to the bone implant24. The groove96is recessed into the head80toward the central axis31between the first and second ridges92and94. Thus, the outer cross-sectional dimension of the head80at the groove96along a direction that intersects and is perpendicular to the central axis31is less than the outer cross-sectional dimension of the head80at the first ridge92, and can further be less than the outer cross-sectional dimension of the head80at the second ridge94. In the illustrated embodiment, the groove96is unthreaded, though it should be appreciated that the groove96can alternatively be threaded as desired. The cross-sectional dimension of the groove96can vary along its length along the transverse direction T. For example, the cross-sectional dimension of the groove96can be 3.0 mm, or any suitable alternative dimension between 1.0 mm and 15.0 mm.

The first ridge92is configured to engage a portion of the bone implant24. The first ridge92can be generally convex with respect to the central axis31so that the first ridge92extends outwardly from the central axis31. Further, the first ridge92can be circumferentially disposed about the head80and can be round or circular. The ridge92can be continuous about the head80or segmented as desired. The outer cross-sectional dimension of the first ridge92, along a direction that is perpendicular to the central axis31and intersects the central axis31, is greater than that of the outer diameter of the bone fixation aperture56, such that at least a portion of the first ridge92is aligned with the bone implant24along the transverse direction T parallel to the central axis31. The outer cross-sectional dimension of the first ridge92can range between about 1 mm and about 15 mm, such as about 3.5 mm. When the bone fixation element26is fully inserted through the bone fixation aperture56, the proximal-most surface of the head80a proximal-most portion of the upper surface54can lie on similar a plane that extends in the longitudinal direction L and the lateral direction A. In alternative embodiments, at least a portion of the first ridge92can be linear. Other ridge configurations are possible as desired.

The second ridge94is threaded, and thus configured to threadably engage the at least one thread58of the bone implant24as the bone fixation element24is inserted into the bone fixation aperture56. The second ridge94can also be generally convex with respect to the central axis31so that the second ridge94extends outwardly from the central axis31. The second ridge94can be circumferentially disposed around the head80, and can be continuous or segmented. The second ridge94can define an outer diameter that is substantially equal to the outer diameter of the first ridge92, though it should be appreciated that the outer diameter of the second ridge94can alternatively be less than the outer cross-sectional dimension of the first ridge92. The outer cross-sectional dimension of the second ridge94can range between about 1 and about 15 mm, such as about 3.5 mm.

At least a portion of the second ridge94can be threaded so as to threadedly engage with the at least one thread58as the bone fixation element26is advanced through the bone fixation aperture56. For instance, the second ridge94can define at least one thread97that is configured as described above with respect to the at least one thread88of the head80described above. When the bone fixation element26is fully inserted in the bone fixation aperture56as illustrated inFIG. 6B, the at least one thread97threadably disengages from the at least one thread58, and is spaced from the at least one thread58along the distal direction. When the at least one thread97disengages the at least one thread58, at least a portion of the inner wall53of the bone implant24is captured or seated between the first ridge56and the second ridge94. Thus, the bone fixation element26can be coupled to the bone implant24such that at least a portion of the bone implant24, for instance a portion of the inner wall53, is captured between 1) a stop surface, which can be defined by the bone fixation element26, for instance the head80, and 2) a threaded region of the head80. For instance, the stop surface can be defined by the ridge92, and the threaded region can be disposed distal from the ridge92, and can be defined by the at least one thread97of the second ridge94.

With continuing reference toFIGS. 6A-6B, the groove96is configured to receive a portion of the bone implant24. For instance, at least a portion of the inner wall53can be received by the groove96between the first and second ridges92and94. As discussed above, the groove96can generally conform in shape to the curved inner wall53such that the groove96is disposed adjacent and can abut the at least one thread58when the bone fixation element26is inserted in the bone fixation aperture56. In the illustrated embodiment, the groove96is concave and can conform to the convex inner wall53as well as portions of the upper surface54and bone-facing surface52. For instance, the concavity of the groove96can be defined by a radius of curvature that matches the radius of curvature of the inner wall53. The second ridge94defines a major diameter D6defined by the crest of the at least one thread97that is greater than the minor diameter d1of the at least one thread58. Accordingly, when the second ridge94is disposed adjacent the at least one thread58along the distal direction, the at least one thread97of the second ridge94is aligned with the at least one thread58, thereby preventing the head from being removed from the bone implant24by translating the bone fixation element26along the transverse direction T.

During operation, the shaft82of the bone fixation element26is driven into the fixation site28. For instance, the bone fixation element26can be rotated in the first direction of rotation so as to advance the shaft82into the fixation site28in the distal direction, such that the at least one thread84threadedly purchases with the fixation site28. As the bone fixation element26advances in the distal direction during rotation in the first direction of rotation, the at least one thread97of the second ridge94threadedly engages the at least one thread88of the head80. As the bone fixation element26rotates in the first direction of rotation after the at least one thread97has engaged the at least one thread54while the central axis31is aligned with the central aperture axis59, the second ridge94threadedly advances distally with respect to the at least one thread54until the at least one thread54, and thus a portion of the inner wall53, is captured in the groove96. When the portion of the inner wall53is captured in the groove96, the first and second ridges92and94movably couple the bone implant24to the bone fixation element26. For instance, the bone fixation element26can be further rotated so as to reposition the bone implant24along the transverse direction T relative to the fixation site28. Accordingly, the alignment between the bone implant24and the fixation site28along the transverse direction T can be adjusted when the bone fixation element26is coupled to the bone implant24.

It should be appreciated that in accordance with one aspect of the present disclosure, a surgical kit can include a plurality of bone implants24constructed in accordance with any one or more, up to all, embodiments described herein, and a plurality of bone fixation elements26constructed in accordance with any one or more, up to all, embodiments described herein. The kit may also include a drill and a drill guide, and a guidewire. The drill guide (may have a threaded end configured for insertion into the apertures of the bone implant24, so that a drill can be used to pre-drill a hole into which the bone fixation elements26can be inserted.