Abstract:
A bone fixation system. The bone fixation system includes a fixation plate including at least one fixation hole, and at least one fastener, the fastener including a coupler and a shank for engaging a bone. The coupler is threadably engaged with the fixation hole. The shank is angulatably retained by the coupler and orientable relative to the fixation plate at a selectable angle.

Description:
INTRODUCTION  
       [0001]     In certain orthopedic surgical procedures, it is necessary to secure multiple bones or bone portions relative to each other. For example, in certain spinal surgeries, the fusion of two or more vertebral bodies is required to secure a portion of the spinal column in a desired position. This need may be the result of physical trauma from fractures or dislocations, degenerative diseases, or tumors.  
         [0002]     One such spinal fixation procedure involves the attachment of a prosthesis or plate to the anterior side of the cervical portion of the spine. The procedure requires anteriorly accessing the spine and securing a prosthetic plate to two or more cervical vertebrae. This allows fusion of the two or more cervical vertebrae in a particular orientation so to facilitate healing or to alleviate a condition of the patient.  
         [0003]     Various fusion plates and plating systems are known for anteriorly fusing the cervical spine. Such plates and plating systems must meet several requirements that often are in conflict. For example, the requirements associated with spinal stability and system reliability over an extended period of use often conflict with the requirements of an easy to use implant. Strength requirements for a fusion plate tend to make the plate bulky and adversely effect intra-operative and postoperative viewing of the associate area of the spine. Additionally, it is desirable that the affected region of the cervical spine be easily viewed using MRI or x-ray procedures to verify that the desired fusion of the cervical spine is complete and/or that the alignment of the cervical vertebrae is proper.  
         [0004]     It is further desirable to ensure that the bone screws placed into the vertebrae through the plating system do not loosen or back out from the plate. Furthermore, locking mechanisms should adequately permit the removal of an associated bone screw when required, and allow sufficient angular freedom for bone screws relative to a plate.  
         [0005]     It remains desirable in the pertinent art to provide an improved anterior cervical plating system that addresses all the requirements discussed above.  
       SUMMARY  
       [0006]     The present teachings provide a bone fixation system. In one aspect, the bone fixation system includes a fixation plate including at least one fixation hole, and at least one fastener. The fastener includes a coupler and a shank for engaging a bone. The coupler is threadably engaged with the fixation hole and the shank is angulatably retained by the coupler and orientable relative to the fixation plate at a selectable angle.  
         [0007]     In another aspect, the bone fixation system includes a fixation plate including at least one hole therethrough defining a center axis substantially perpendicular to the fixation plate, and an angulatable fastener insertable in the hole. The angulatable fastener includes a shank having a bone engagement portion, and a coupler for coupling the shank to the hole of the fixation plate. The shank is retained by the coupler and prevented from rotating about the center axis relative to the coupler. The shank can angulate relative to the coupler about at least one axis orthogonal to the center axis.  
         [0008]     In another aspect, the bone fixation system can include a fixation plate having a viewing window and a plurality of fastener-receiving threaded holes, at least one non-angulatable fastener threadably couplable to the fixation plate, and at least one angulatable fastener threadably couplable to the fixation plate. The angulatable fastener comprises a coupler and a shank retained by the coupler. The coupler is threadable to the fixation plate, and the shank is angulatable relative to the coupler.  
         [0009]     The present teachings also provide a method of surgically repairing bone with a fixation plate having at least one fixation hole. The method includes providing at least one fastener having a shank and a coupler, the shank angulatably retained by the coupler, threadably engaging the coupler with the fixation hole for preventing back out of the fastener from the fixation hole, and angulating the shank relative to the coupler for orienting the fastener at a selectable angle relative to the fixation plate.  
         [0010]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]      FIG. 1  is an isometric environmental view of a bone fixation system according to the present teachings, the bone fixation system shown operatively associated with first and second vertebral bodies of a human spine;  
         [0013]      FIG. 2  is an isometric view of the bone fixation system of  FIG. 1 ;  
         [0014]      FIG. 3  is an isometric view of a fixation plate for the bone fixation system of  FIG. 1 ;  
         [0015]      FIG. 4  is an isometric view of a non-angulatable fastener of the bone fixation system of  FIG. 1 ;  
         [0016]      FIG. 5  is an isometric view of an angulatable fastener of the bone fixation system of  FIG. 1 ;  
         [0017]      FIG. 6  is a sectional view of the angulatable fastener of  FIG. 5  shown in a non-angulating position;  
         [0018]      FIG. 7  is a sectional view of the angulatable fastener of  FIG. 5  shown in an angulating position;  
         [0019]      FIG. 8  is an isometric view of a coupler of the angulatable fastener of  FIG. 5 ;  
         [0020]      FIG. 9  is an isometric view of a shank of the angulatable fastener of  FIG. 5 ; and  
         [0021]      FIG. 10  is a sectional view of the angulatable fastener of  FIG. 5 , shown in a non-angulating position.  
     
    
     DETAILED DESCRIPTION  
       [0022]     The following description is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For example, although the present teachings are illustrated for internal fixation of the cervical spine, the present teachings can also be used for other orthopedic procedures in which it is necessary to secure two bone portions relative to one another.  
         [0023]     Referring to  FIG. 1 , an exemplary bone fixation system  100  according to the present teachings is illustrated as implanted in the anterior cervical spine for securing two cervical vertebrae  90 ,  90 ′ relative to one another, without interfering with any bone graft  80 , which may also be implanted therebetween.  
         [0024]     Referring to  FIGS. 2-5 , the bone fixation system  100  can include a fixation plate  102 , and a plurality of fixation fasteners, including angulatable (semi-constrained) fixation fasteners  104  and non-angulatable (constrained) fixation fasteners  106 . As used herein, the term “constrained” is intended to mean fixed in angular orientation. The term “semi-constrained” is intended to mean having a variable angle of angulation for orientation within a cone of angulation.  
         [0025]     The fixation plate  102  can include a large viewing window  112 , which allows graft visualization during surgery, and also in postoperative X-ray and MRI diagnostic procedures. The fixation plate  102  can also include a plurality of fixation holes  108  having threads  110  for interchangeably receiving the semi-constrained and/or constrained fixation fasteners  104 ,  106 . The fixation fasteners  104 ,  106  can include self-tapping and/or self-drilling bone engaging portions. Although the fixation plate  102  is illustrated with four fixation holes  108  pairwise arranged in two fixation levels for fixation of two bone portions, it will be appreciated that the fixation plate  102  can include additional fixation holes and corresponding fixation levels for fixation of three or more bone portions. Each fixation hole  108  defines a center axis A which is substantially perpendicular to the fixation plate  102 .  
         [0026]     Referring to  FIG. 4 , the constrained fixation fastener  106  can include a bone engaging portion  116  which can be threaded, and a head  113 . The head  113  can include an interior hex recess or other driver-receiving formation  118  to facilitate inserting the constrained fixation fastener  106  into the bone through one of the fixation holes  108  of the fixation plate  102 . The hex recess  118  can also be engaged by a driver to remove the fixation fastener  106  from the fixation plate  102 . The head  113  can also include external threads  114  for engaging the threads  110  of the fixation hole  108  to prevent backing out of the constrained fixation fastener  106  after implantation. The constrained fixation fastener  106 , once threaded into the fixation plate  102 , remains in a fixed orientation. In the embodiment illustrated in  FIG. 4 , the longitudinal axis of the constrained fixation fastener  106  coincides with the center axis A of the fixation hole  108  and is substantially perpendicularly to the fixation plate  102 .  
         [0027]     Referring to  FIGS. 5-10 , the semi-constrained fixation fastener  104  includes a shank  120  and a coupler  124 . The shank  120  defines a longitudinal axis B and has a bone-engaging portion  122  with threads  123 , and a coupler-engaging portion, such as a ball hex  128 . The ball hex  128  includes six spherical or curved portions  140  interconnected at ridges  142 . The ball hex  128  can also include a driver-receiving recess, such as a hex recess  130 . The coupler  124  can include external threads  132  engaging the threads  110  of the fixation hole  108  of the fixation plate  102  for preventing backing out of the semi-constrained fixation fastener  104  after implantation. When the coupler  124  is engaged with the fixation hole  108 , the coupler&#39;s center axis coincides with the center axis A of the hole. The coupler  124  also includes a prismatic hex opening  126  which receives and retains the ball hex  128 , and allows the shank  120  to angulate relative to the coupler  124 , as illustrated in  FIG. 7 . The shank  120  can be non-removably retained in the coupler  124  by crimping a retaining portion  127  of the coupler  124  around the shank  120 , as shown in  FIG. 5 . It will be appreciated that other known retaining devices can be used to the same effect.  
         [0028]     Referring to  FIGS. 5 and 6 , the coupler  124  and the shank  120  can rotate as an integral unit about the center axis A, without relative rotation between the shank  120  and the ball hex  128  about the center axis A, by using a driver that engages the recess  130  of the ball hex  128 . The shank  120  can angulate about the ball hex  128  by rotating relative to the ball hex  128  about axes that are orthogonal to the center axis A, as illustrated in  FIG. 7 . In the angulated position, the center axis A and the longitudinal axis B of the shank define an angle α. In this manner, the shank  120  can rotate relative to the fixation plate  102  within a cone of angulation that is defined by the maximum angle a that can be accommodated by the geometry of the semi-constrained fixation fastener  104 . For example, the angle a can take values ranging from 0° to 30°, although other angle ranges are possible.  
         [0029]     The fixation plate  102  and the fixation fasteners  104 ,  106  can be made of biocompatible materials, including, but not limited to, titanium, titanium alloys, such a Ti-6Al-4V, for example, or other materials.  
         [0030]     Referring to  FIGS. 1, 2  and  3 , in a cervical fixation procedure, the fixation plate  102  can be provisionally secured to the vertebrae  80  using bone pins through small holes  107  of the fixation plate  102 . One or more constrained fixation fasteners  106  can be threaded into corresponding fixation holes  108  of the fixation plate  102  and implanted into a first bone portion or vertebra  90 . One or more semi-constrained fixation fasteners  104  can be threaded into corresponding fixation holes  108  of the fixation plate  102  and implanted into a second bone portion or vertebra  90 ′. The semi-constrained fixation fasteners  104  can be angulated within a cone of angulation relative to the fixation plate  102 . It will be appreciated that the fixation plate  102  can be used with any combination of constrained and semi-constrained fixation fasteners  106 ,  104 , including all constrained fixation fasteners  106  or all semi-constrained fixation fasteners  104 .  
         [0031]     The foregoing discussion discloses and describes merely exemplary arrangements of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.