Patent Abstract:
A spinal implant extendable across a facet joint to aid in fixation of the facet joint includes an elongate connecting member, a bone allograft, and a locking member. The elongate connecting member is sized to extend across a facet joint and includes a distal bone anchor. The bone allograft is sized for placement in a bore formed through the facet joint and configured to be placed about the elongate connecting member. The locking member includes a longitudinal bore sized to receive the elongate connecting member, and the locking member has an unlocked condition permitting movement relative the elongate connecting member and a locked condition rigidly fixing the locking member in place on the elongate connecting member. The locking member is configured to cooperate with the distal bone anchor to compress the facet joint, and the locking member is configured to lock the spinal implant across the facet joint.

Full Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the field of fixation mechanisms for facet joint stabilization. 
       BACKGROUND 
       [0002]    The vertebrae in a patient&#39;s spinal column are linked to one another by the intervertebral disc and the facet joints. Each vertebra has four facet joint surfaces: a pair of articulating surfaces located on the left side, and a pair of articulating surfaces located on the right side. Each facet joint is a synovial joint consisting of two overlapping articulating surfaces, an superior articular process of one vertebra and an inferior articular process of the vertebra directly above it. The biomechanical function of each facet joint is to guide and limit the motion of the spinal motion segment. These functions can be disrupted by disc or bone degeneration, dislocation, fracture, injury, trauma-induced instability, osteoarthritis, and surgery. Such damage to the facet joint can result in pain, a misaligned spine, impinged nerves, and loss of mobility. In certain cases, partial or complete immobilization of one or more facet joints by intervertebral stabilization is desirable to alleviate the patient&#39;s symptoms. 
         [0003]    Intervertebral stabilization is designed to prevent or restrict relative motion between the vertebrae of the spine. One method of intervertebral stabilization is to directly fasten one or both of the facet joints in a spinal motion segment together, thereby limiting intervertebral motion. From a surgical perspective, the facet joint is more easily accessible than the vertebral body or the pedicles, thus reducing operative time, decreasing blood loss, decreasing incision size, reducing incidence of reoperation, and decreasing the risk of potential deleterious effects on nearby anatomic structures, including the spinal cord. 
         [0004]    In order to provide effective fixation of the facet joint, a fixation device should create compression between the two articular processes. The compression, which causes or enhances immobilization of the joint by encouraging stability through the joint, should be maintained over a significant length of time. In addition, the device must work to prevent loosening of the device. Because the facet joint is designed to be a mobile, weight-bearing joint, forces will continue to be transmitted through the joint after the implantation of a fixation device. Without a specific way to prevent loosening of the device, loosening will likely occur as a result of the micromotion caused by such forces. Once the device has loosened, the device may begin to protrude or regress from the bone, causing pain, joint damage, or danger to the surrounding tissues. 
         [0005]    Surgeons have used various fixation devices, including bone screw assemblies, to immobilize the facet joint. Examples of facet fixation devices currently used to stabilize the spine include trans-lamina facet screws and trans-facet pedicle screws. The previously proposed facet fixation devices, however, have presented significant shortcomings. Both trans-lamina facet screws and trans-facet pedicle screws can be difficult to surgically place, have long trajectories, and may deleteriously interfere with the local anatomy once implanted. In addition, though a standard fully threaded bone screw may be sufficient for adjoining two bone surfaces, a fully threaded screw may not be capable of creating a desirable amount of compression between two bone surfaces. Any compression generated between the bone surfaces would be limited to the compressive forces generated by the screw threads themselves. Further, a bone screw may loosen overtime. When a screw is over-tightened and threads are stripped within the bone, or when threads strip over time as a result of micromotion, the compressive force between the facet joint surfaces will diminish and loosening will likely occur. To prevent loosening, still other bone screws are designed such that a portion of the screw expands within the bone after the device is implanted. However, the expansion of the device within bone generates great stress on the bone, making this device ill-suited for use in the relatively small bones of the facet joint. In an attempt to simultaneously maintain compression and prevent loosening, nut-and-bolt type assemblies have been presented as a method of facet joint immobilization. In this type of assembly, a threaded bolt or screw is passed through the facet joint and a nut with mating threads is placed around the distal end of the bolt or screw. Though this approach is successful in maintaining compression and preventing loosening, this approach mandates a surgical procedure that is more invasive than desired because the nut must be introduced to the back side of the facet joint. 
         [0006]    Thus, though various systems in the prior art have attempted to achieve effective facet joint fixation, none of the prior art systems enable facet joint fixation through a minimally invasive, compressive, and stable facet fixation device. Accordingly, there is a need for instrumentation and techniques that facilitate the safe and effective stabilization of facet joints. Therefore, it would be advantageous to provide a system and method of facet joint fixation that can be implanted simply, accurately, and quickly, while providing suitable stabilization to the facet joint. 
         [0007]    The device and methods disclosed herein overcome one or more of the shortcomings discussed above and/or in the prior art. 
       SUMMARY 
       [0008]    The present invention relates to devices and methods for accomplishing bone fixation, and more particularly in some embodiments, to devices and methods for fixation of spinal facet joints. 
         [0009]    In one exemplary aspect, the present disclosure is directed to a spinal implant extendable across a facet joint to aid in fixation of the facet joint. The implant may comprise an elongate connecting member sized to extend across a facet joint, a bone allograft, and a locking member. The elongate connecting member may have a distal end comprising a distal bone anchor. The bone allograft may be sized for placement in a bore formed through the facet joint and configured to be placed about the elongate connecting member. The locking member may include a longitudinal bore sized to receive the elongate connecting member, and may have an unlocked condition permitting movement relative the elongate connecting member and a locked condition rigidly fixing the locking member in place on the elongate connecting member. The locking member may be configured to cooperate with the distal bone anchor to compress the facet joint, and the locking member may be configured to lock the spinal implant across the facet joint. 
         [0010]    In another exemplary aspect, the present disclosure is directed to a spinal implant for fixation of a facet joint. The implant may comprise an elongate connecting member sized to extend across a facet joint, a bone allograft, a locking member, and a stabilization member. The elongate connecting member may have a distal end comprising a distal bone anchor. The bone allograft may be sized for placement in a bore formed through the facet joint and configured to be placed about the elongate connecting member. The locking member may include a longitudinal bore sized to receive the elongate connecting member, and may have an unlocked condition permitting movement relative the elongate connector and a locked condition rigidly fixing the locking member in place on the elongate connecting member. The locking member may be configured to cooperate with the distal bone anchor to compress the facet joint, and the locking member may be configured to lock the spinal implant across the facet joint. The stabilization member may include a bone contacting surface and an opposing surface, and the stabilization member may be configured to seat the locking member on the opposing surface. The stabilization member may include a hole extending therethrough sized to receive the elongate connecting member, wherein the stabilization member slides over a portion of the elongate connecting member such that the portion extends through the hole. 
         [0011]    In another exemplary aspect, the present disclosure is directed to a method for fixation of a facet joint, the facet joint having a superior articular process and an inferior articular process. The method may comprise: forming a drill hole through the facet joint, inserting an elongate connecting member having a distal anchor into the facet joint and advancing the elongate connecting member and the distal anchor into the facet joint until the elongate connecting member spans the facet joint, drilling a well circumferentially around the elongate connector member, packing the well with a bone allograft, sliding a locking member over the elongate connector member such that locking member contacts the inferior articular process, and compressing the locking member around the elongate connector member to stabilize the facet joint. 
         [0012]    Further aspects, forms, embodiments, objects, features, benefits, and advantages of the present invention shall become apparent from the detailed drawings and descriptions provided herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
           [0014]      FIG. 1  is a lateral view of a portion of the lumbar spine with a portion of a facet joint in cross-section, showing a spinal implant disposed within the facet joint in accordance with a first embodiment of the present disclosure. 
           [0015]      FIG. 2  is a perspective view of the spinal implant shown in  FIG. 1 . 
           [0016]      FIG. 3  is a highly simplified drawing of a portion of a vertebral arch, showing a delivery cannula positioned through the skin and against the inferior articular process of a facet joint. 
           [0017]      FIG. 4  is a lateral, partial cross-sectional view of a spinal motion segment showing an elongate connecting member and a distal anchor of the spinal implant of  FIG. 1  inserted into a facet joint. 
           [0018]      FIG. 5  is a lateral, partial cross-sectional view of a spinal motion segment showing a cannulated drill positioned around the elongate connecting member and against the inferior articular process. 
           [0019]      FIG. 6  is a lateral, partial cross-sectional view of a spinal motion segment showing a drilled intrafacet cavity. 
           [0020]      FIG. 7  is a lateral, partial cross-sectional view of a spinal motion segment showing a bone allograft within the intrafacet cavity. 
           [0021]      FIG. 8  is a lateral, partial cross-sectional view of a spinal motion segment showing insertion of a locking member around the elongate connecting member. 
           [0022]      FIG. 9  is a lateral view of a spinal motion segment showing a spinal implant inserted into and fixed against the facet joint. 
           [0023]      FIG. 10  is a perspective view of a spinal implant in accordance with a second embodiment of the present disclosure. 
           [0024]      FIG. 11   a  is a highly simplified, partial cross-sectional view of the first embodiment of the spinal implant in its final, expanded state. 
           [0025]      FIG. 11   b  is a highly simplified, partial cross-sectional view of the second embodiment of the spinal implant in its final, expanded state. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments, or examples, illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0027]    This disclosure describes implants and methods for stabilizing a facet joint. The implants described herein are structurally designed to span the facet joint and, due to the placement of a bone allograft across the joint, create stable fixation through fusion. The implants fasten one or both of the facet joints in a spinal motion segment together, thereby limiting intervertebral motion and alleviating the patient&#39;s symptoms. 
         [0028]      FIG. 1  illustrates an implant  10  according to an exemplary embodiment of the present invention for fixing, stabilizing, and/or immobilizing a joint. The spinal implant  10  is shown implanted within a facet joint formed by a superior articular process  12  of one vertebra  14  and an inferior articular process  16  of the vertebra  18  immediately above. The implant  10  can also be utilized to stabilize other joints besides the facet joint. The implant  10  includes an elongate connecting member  20 , a distal anchor  22 , a bone allograft  24 , and a locking member  26 .  FIG. 1  shows the implant  10  inserted into the facet joint such that the distal anchor  22  protrudes outside and lateral to the superior articular process  12  while the elongate connecting member  20  and the bone allograft  24  remain within the bony tissue of the facet joint. Accordingly, the elongate connecting member  20  is disposed through both the superior articular process  12  and the inferior articular process  16  through a drill hole formed through both the processes  12 ,  16 . The bone allograft  24  promotes bone fusion between the superior articular process  12  and the inferior articular process  16 . The locking member  26 , which is sized to have a wider diameter than the drill hole, is positioned flush against the exterior surface of the inferior articular process  16 . The implant  10  provides stabilization and immobilization of the facet joint formed by the processes  12 ,  16  through compressive forces applied by the distal anchor  22  and the locking member  26 . In addition, the amount of compressive force applied by the implant  10  can vary with the position of the locked locking member  26  relative to the distal anchor  22 . The closer to the distal anchor  22  that the locking member  26  is locked, the greater the compressive forces exerted on the facet joint. 
         [0029]      FIG. 2  illustrates the exemplary implant  10  in an expanded state. As indicated above, the implant  10  includes the elongate connecting member  20 , the distal anchor  22 , the bone allograft  24 , and the locking member  26 . In the embodiment shown in  FIG. 2 , the elongate connecting member  20  is approximately cylindrical and configured to be received within the prepared drill hole through the superior articular process  12  and the inferior articular process  16  of the facet joint. The elongate connecting member  20  is made of a flexible and durable biocompatible material configured as a cable. For example, the elongate connecting member  20  can be constructed of surgical stainless steel, titanium, cobalt-chromium alloy, Nitinol, ultra-high molecular weight polyethylene, poly(tetraflouroethylene) or poly(tetraflouroethene) (PTFE), polyethylene terephthalate (PET), or any other biocompatible material as is known in the art of medical device manufacture. Alternatively, the elongate connecting member could be configured as a wire, a braid, or a rod. Optionally, the elongate connecting member  20  can be constructed of a radiolucent material, such as polyaryletheretherketone (PEEK) or the like, such that it can be medically imaged and visualized. Further, the elongate connecting member  20  can be treated with growth factors, stem cells, or any other device coating known in the art, to be selected based on the desired outcome of the procedure. In some embodiments, the elongate connecting member  20  is substantially taut and rigid, while in other embodiments, the elongate connecting member  20  can flex. In these embodiments, the elongate connecting member  20  is flexible enough to be positioned within a prepared drill hole formed through the facet joint, but is rigid enough to immobilize the superior articular process  12  and the inferior articular process  16  with respect to one another. In some examples, the elongate connecting member  20  is configured to flex or bend laterally, but is configured to substantially resist axial elongation. 
         [0030]    As shown in  FIG. 2 , the elongate connecting member  20  extends from a proximal portion  30  to a distal portion  28  which is attached to the distal anchor  22 . In some embodiments, the distal portion  28  may extend to integrally form the distal anchor  22 . The elongate connecting member  20  is of a length suitable to fit through the facet joint from the exterior surface of the inferior articular process  16  to the exterior surface of the superior articular process  12 . The elongate connecting member  20  can include a variety of lengths and dimensions as required for different spinal morphologies. 
         [0031]    The distal anchor  22  may be configured to have an unexpanded configuration or state and an expanded configuration or state. In the unexpanded configuration or state, the distal anchor  22  may be sized and configured to pass through a pilot hole formed through the facet joint. In the expanded configuration or state, the distal anchor  22  may be sized and configured as a hook-like structure to anchor the implant  10  and resist axial regression through the pilot hole. In the embodiment pictured in  FIG. 2 , the distal anchor  22  in an expanded state has an arrowhead-like configuration including an exterior surface  32 , at least two flanges  34 , and bone-engaging surfaces  36 . In the example shown in  FIG. 2 , the flanges  34  are moveable between two positions: an insertion position or unexpanded state wherein the flanges  34  are approximately parallel with a longitudinal axis  37  of the elongate connecting member  20 , and a bone-engaging position or expanded state wherein the flanges  34  are angled with respect to the longitudinal axis  37  of the elongate connecting member  20 . More specifically, in the insertion, unexpanded state, the flanges  34  are positioned generally flush against the distal portion  28  of the connecting member  20 . Upon emerging from the prepared drill hole through the facet joint, the flanges  34  flare away from the connecting member  20  and the distal anchor  22  assumes a bone-engaging, expanded state. At least a portion of the bone-engaging surfaces  36  of the distal anchor  22  then engages the exterior surface of the superior articular process  12 . The material composition of the distal anchor  22  resiliently biases the flanges  34  toward the bone-engaging, expanded state. In this example, the distal anchor  22  is made of a flexible, surgical-grade material that is configured to allow extensive short-term deformation without permanent deformation, cracks, tears, or other breakage. In particular, in this example, the distal anchor is made of a shape memory alloy having a memory shape in the expanded configuration. In other embodiments, the distal anchor  22  is formed of an elastic material allowing the flanges  34  to elastically deform to an unexpanded state to fit through the drilled hole, and spring back to an expanded state when the distal anchor  22  advances clear of the hole. In the embodiment pictured in  FIG. 2 , the exterior surface  32  is smooth. However, in other embodiments, the exterior surface  32  can include features that engage bony tissue. The features can resemble screw threads or any other configuration that would interface with and provide friction with bony tissue. The features can include structures of various sizes, dimensions, shapes, and configurations. 
         [0032]    As the embodiment pictured in  FIG. 2  shows, the implant  10  also includes a bone allograft  24 . The bone allograft  24  has a generally cylindrical shape having generally planar and circular ends and a generally cylindrical sidewall. The bone allograft  24  includes a centrally disposed and cylindrically shaped bore  38 . The diameter of bore  38  is slightly larger than the diameter of the elongate connecting member  20 , such that the elongate connecting member  20  is slidable within the bore  38 . In some embodiments, the bone allograft  24  is composed of a bone dowel. In other embodiments, the bone allograft  24  is composed of loose allograft material, such that the allograft material surrounds the elongate connecting member  20  when the implant  10  is in final position across the facet joint. 
         [0033]    As the embodiment pictured in  FIG. 2  shows, the implant  10  also includes a locking member  26 . The locking member  26  is approximately cylindrical, and has a proximal surface  40 , a bone-engaging surface  42 , and a centrally disposed and cylindrically shaped longitudinal bore  44 . The proximal surface  40  can be flat or rounded or have a variety of configurations compatible with the adjacent anatomical tissue. In the example shown, the proximal surface  40  is rounded to avoid edges that may introduce additional tissue trauma. The bone-engaging surface  42  can be flat or curved or have a variety of configurations compatible with the exterior surface of the inferior articular process  16 . In some embodiments, the locking member  26  can be approximately spherical. In some embodiments, the locking member  26  can be non-continuous in that a longitudinal slot comprising the length of the locking member  26  extends from the sidewall  45  to the bore  44 . 
         [0034]    The implant  10  pictured in  FIG. 2  has features  46  that extend perpendicularly from the bone-engaging surface  42 . Here, the features  46  are triangular protrusions capable of stabilizing the locking member  26  against the exterior surface of the inferior articular process  16 . Pressure can be exerted on the locking member  26  to embed the features  46  in the surface of the inferior articular process  16 . The locking member  26  may include any number of features  46 . The features  46  can include structures of various sizes, dimensions, shapes, and configurations. Further, a single locking member  26  can include features  46  of different sizes, dimensions, shapes, and configurations. In addition, the locking member  26  can include any orientation of features  46  on the bone-engaging surface  42 . For example, the features can be equally spaced around the circumference of the bone-engaging surface, thereby allowing the locking member  26  to engage the inferior articular process  16  and adding to the overall stability of the implant  10 . In other embodiments, the features  46  can extend at acute or obtuse angles from the bone-engaging surface  42 . 
         [0035]    The bore  44  extends longitudinally through the locking member  26  from the proximal surface  40  to the bone-engaging surface  42 . The diameter of bore  38  is slightly larger than the diameter of the elongate connecting member  20 , such that the elongate connecting member  20  is slidable within the bore  44 . The inner surface of the bore  44  can be textured such that the bore  44  of locking member  26  grips the connecting member  20 . 
         [0036]    The locking member  26  is formed of a deformable and durable surgical-grade material. For example, the locking member  26  can be constructed of surgical stainless steel, titanium, cobalt-chromium alloy, Nitinol, ultra-high molecular weight polyethylene, poly(tetraflouroethylene) or poly(tetraflouroethene) (PTFE), polyethylene terephthalate (PET), or any other deformable biocompatible material as is known in the art of medical device manufacture. Optionally, the locking member  26  can be constructed of a radiolucent material, such as polyaryletheretherketone (PEEK) or the like, such that it can be medically imaged and visualized. In one example, after the implant  10  is positioned across the facet joint, the locking member  26  is fixedly secured to the elongate connecting member  20  by crimping the locking member  26  to the connecting member  20  such that the desired amount of compression is achieved across the facet joint. 
         [0037]    The implant  10  is utilized to stabilize and/or immobilize the facet joint by limiting the motion between the superior articular process  12  and the inferior articular process  16 . The implant  10  is assembled and implanted in the following manner, described with reference to  FIGS. 3-9 . In  FIGS. 3-9 , the vertebrae are depicted in dashed lines to indicate that the drawings illustrate the two-dimensional positional relationship of the implant  10  relative to the three-dimensional vertebral structures. 
         [0038]    First, access to the facet joint is gained through any suitable surgical technique using any suitable device. Advantageously, referring to  FIG. 3 , the implant  10  can be implanted through a minimally invasive surgical procedure involving a single midline incision  50  through the skin S over the spinous process  52  of the vertebra  18  superior to the target facet joint. In FIG.  3 , a custom delivery cannula  54  (that is part of a delivery device) is shown resting against the inferior articular process  16  after being inserted through a midline incision  50 . The cannula  54  is operable to route the elongate connecting member  20 , the distal anchor  22 , the bone allograft  24 , and the locking member  26  into correct positions relative to the facet joint. The cannula  54  is made of a surgical-grade material, and in particular stainless steel, though other materials are suitable. The cannula  54  is cylindrical with an longitudinal passage extending along its entire length from a proximal end  56  to a distal end  58 . The diameter of the cannula  54  is larger than the diameter of the implant  10  in an expanded configuration such that the implant  10  in an expanded configuration is slidable within the passage of the cannula  54 . Further, the diameter of the cannula  54  is such that the bone allograft  24  and the locking member  26  are slidable within the passage of the cannula  54 . 
         [0039]    The distal end  58  of the delivery cannula  54  includes at least one docking feature  60  that extends in the same plane as the longitudinal passage of the cannula  54 . The docking feature  60  is capable of stabilizing the cannula  54  to an anatomical structure. For example, the docking feature  60  can serve as a docking point on which the cannula  54  may securely rest against or penetrate the inferior articular process  16 , thereby preventing the cannula  54  from slipping from the surface of the inferior articular process  16  during the implantation procedure. Pressure can be exerted on the delivery cannula  54  to temporarily embed the feature in the surface of the inferior articular process  16 . The delivery cannula  54  may include any number of such docking features  60 . The docking features  60  can include structures of various sizes, dimensions, shapes, and configurations. Further, a single cannula  54  can include docking features  60  of different sizes, dimensions, shapes, and configurations. In addition, the cannula  54  can include any orientation of such docking features  60  on the bone contacting surface. For example, the docking features  60  can be equally spaced around the circumference of the distal end of the cannula  54 . In some embodiments, the docking feature  60  may be angled away from the side of the cannula  54 . 
         [0040]    A hole is then formed through the facet joint by any of various mechanisms as are known in the art. An exemplary mechanism for forming a hole through the facet joint involves directing a drill through the cannula  54 , positioning the drill against the exterior surface of the inferior articular process  16 , and drilling a continuous hole through both the inferior articular process  16  and the superior articular process  12 . The hole is formed in a desired location to provide optimal stabilization/immobilization of the facet joint. The hole is dimensioned to allow passage of the elongate connecting member  20  and the distal anchor  22 . Other mechanisms for forming the hole are also contemplated. For example, an 11-gauge needle could be used to “punch” a hole through the facet joint. After the hole is prepared, the drill or other instrument used to form the hole is withdrawn from the cannula  54 . 
         [0041]    Referring to  FIG. 4 , the elongate connecting member  20  and the distal anchor  22  are passed through the cannula  54  to be inserted into the prepared drill hole in an insertion, unexpanded state. In this example, when in the insertion, unexpanded state, the flanges  34  of the distal anchor  22  are positioned generally flush against the distal portion  28  of the connecting member  20  such that the connecting member  20  and the folded distal anchor  22  possess a smaller diameter than the diameter of the prepared drill hole. The connecting member  20  is then pushed forward through the prepared drill hole until the distal anchor  22  emerges through the superior articular process  12 . Upon emerging from the prepared drill hole, the flanges  34  of the distal anchor  22  flare away from the connecting member  20  and the distal anchor  22  assumes a bone-engaging, expanded state. More specifically, once the distal anchor  22  has passed all the way through the inferior articular process  16 , across any gap between the inferior articular process and the superior articular process, and all the way through the superior articular process  12 , the flanges  34  of the distal anchor  22  flare out from their insertion, unexpanded position—in substantial alignment with the longitudinal axis  37  of the elongate connecting member  20 —into their bone-engaging, expanded position at an angle with the longitudinal axis  37  of the elongate connecting member  20 , as shown in  FIG. 2 . At least a portion of the bone-engaging surfaces  36  of the distal anchor  22  then engages the exterior surface of the superior articular process  12 . Once in position, the elongate connecting member  20  and the distal anchor  22  function to properly align and hold the superior articular process  12  against the inferior articular process  16 . It is worth noting that although the elongate connecting member  20  is shown with a limited length, in some embodiments, the elongate connecting member  20  has an overall length greater than the length of the cannula  54 . Accordingly, the elongate connecting member  20  may extend out the proximal end of the cannula  54  for easy access by the surgeon. 
         [0042]    Referring to  FIG. 5 , a cannulated drill  70  is advanced through the cannula  54  and around the proximal portion  30  of the elongate connecting member  20  until it rests against the surface of the inferior articular process  16 . Using the cannulated drill, an intrafacet cavity  76  is drilled around the elongate connecting member  20  all the way through the inferior articular process  16 , and partially into the superior articular process  12  such that the intrafacet cavity  76  extends to a depth in the range of, for example, one third to one half of the thickness of the superior articular process  12 , as shown in  FIG. 6 . In some embodiments, the cannulated drill  70  is configured to debride the cartilaginous tissue between the inferior articular process  16  and the superior articular process  12 , thereby “bloodying” the intrafacet cavity  76  and creating a favorable environment for the bone allograft  24 . In some embodiments, the cannulated drill  70  includes a suction channel, which is operatively arranged to remove excess bone and tissue debris created by the drilling process. After the intrafacet cavity  76  is prepared, the cannulated drill  70  is withdrawn from the cannula  54 . 
         [0043]    Referring to  FIG. 6 , the intrafacet cavity  76  is shown extending all the way through the inferior articular process  16  and extending partially into the superior articular process  12 . The intrafacet cavity  76  is shaped and sized to accommodate the bone allograft  24 . 
         [0044]    Referring to  FIG. 7 , the bone allograft  24  is passed through the cannula  54  and slid over the proximal portion  30  of the elongate connecting member  20 . In particular, the bore  38  of the bone allograft  24  is positioned to encircle the proximal portion  30  of the elongate connecting member  20 , and then the bone allograft  24  is slid down the elongate connecting member to rest in the intrafacet cavity  76 . The bone allograft  24  promotes bone fusion between the superior articular process  12  and the inferior articular process  16 . 
         [0045]    Referring to  FIG. 8 , after insertion of the bone allograft  24  into the intrafacet cavity  76 , the locking member  26  is passed through the cannula  54  and slid over the proximal portion  30  of the elongate connecting member  20 . In particular, the bore  44  of the locking member  26  is positioned to encircle the proximal portion  30  of the elongate connecting member  20 , and then the locking member  26  is slid down the elongate connecting member to rest against the exterior surface of the inferior articular process  16 . The features  46  on the bone-engaging surface  42  of the locking member  26  engage with the exterior surface of the inferior articular process  16  such that the locking member is stabilized against the exterior surface of the inferior articular process  16 . Pressure can be exerted on the locking member  26  to embed the features  46  in the surface of the inferior articular process  16 . Due to the diameter of the locking member  26 , which is greater than the diameter of the intrafacet cavity  76  into which the bone allograft  24  is inserted, the locking member  26  provides a mechanism by which the bone allograft is isolated within the facet joint and the implant  10  is fixed within the facet joint, thereby stabilizing the facet joint. Tension is provided by pulling the proximal portion  30  of the elongate connecting member  20  through the locking member  26 . As tension is provided, the locking member  26  is pushed against the inferior articular process  16  to achieve the desired alignment and compression of the facet joint. Specifically, the proximal portion  30  of the elongate connecting member  20  is pulled in the longitudinal axis  37  in a direction away from the distal anchor  22  while the locking member  26  is simultaneously pushed against the inferior articular process such that the desired alignment and compression of the superior articular process  12  against the inferior articular process  16  is achieved. After the desired alignment and amount of compression are realized, the locking member  26  is fixedly secured to the elongate connecting member  20  by crimping the locking member  26  to the connecting member  20  such that the desired alignment and amount of compression is maintained across the facet joint. 
         [0046]    The implant  10  provides stabilization and immobilization of the facet joint formed by the processes  12 ,  16  through compressive forces applied by the distal anchor  22  and the locking member  26 . In addition, the amount of compressive force applied by the implant  10  can vary with the position of the locked locking member  26  relative to the distal anchor  22 . The closer to the distal anchor  22  that the locking member  26  is locked, the greater the compressive forces exerted on the facet joint. 
         [0047]      FIG. 9  shows the spinal implant  10  inserted into and fixed against the facet joint. The proximal portion  30  of the elongate connecting member  20  is shown extending proximally through the locking member  26 . The surgeon clips the proximal portion  30  of the elongate connecting member  20  such that the elongate connecting member  20  no longer substantially extends past the proximal surface  40  of the locking member  26 , as shown in  FIG. 11   a .  FIG. 11   a  shows the spinal implant  10  spanning across the inferior articular process  16  and the superior articular process  12  in its final, expanded state. 
         [0048]      FIG. 10  illustrates a second embodiment of the spinal implant  10  in its expanded state. In the embodiment illustrated in  FIG. 10 , the implant  10  includes the elongate connecting member  20 , the distal anchor  22 , the bone allograft  24 , a locking member  78 , and a stabilization member  80 . The locking member  78  is substantially similar in shape and size to the locking member  26 , but the locking member  78  includes a distal surface configured to interface with a proximal surface of the stabilization member  80 . In this embodiment, the stabilization member  80  is configured as a gimbaled washer. As such, the stabilization member  80  includes a proximal surface  84  configured to seat the locking member  78 . The stabilization member  80  also includes a bone contacting surface  82  being configured to engage the exterior surface of the inferior articular process  16 . The stabilization member  80  includes a hole  86  extending from the bone contacting surface  82  to the proximal surface  84  sized to encircle the elongate connecting member  20 . The diameter of the hole  86  is less than the diameter of the locking member  78 , thereby allowing the stabilization member  80  to seat the substantially hemispherical bottom portion of the locking member  78  on the concave proximal surface  84 . As such, the hemispherical bottom portion of the locking member  78  being seated in the stabilization member  80  enables polyaxial motion of the locking member  78  relative to the stabilization member  80 . Providing such a polyaxial coupling allows greater versatility of the implant  10  because the stabilization member  80  and the locking member  78  can adjust to anatomical structures of various shapes, thereby allowing for a more personalized and precise fit of the implant  10 . 
         [0049]    The stabilization member  80  includes at least one feature  88  extending perpendicularly from the bone contacting surface  82  capable of stabilizing the stabilization member  80  against the inferior articular process  16 . The features  88  can include structures of various sizes, dimensions, shapes, and configurations. Further, a single stabilization member  80  can include features  88  of different sizes, dimensions, shapes, and configurations. For example, the features  88  can be configured as any one of spikes, teeth, serrations, grooves, or ridges. Referring to  FIG. 10 , the stabilization member  80  includes a plurality of features  88  configured as triangular protrusions adapted to pierce the outer portion of the inferior articular process  16 . The stabilization member  80  may include any number of such features. In addition, the stabilization member  80  can include any orientation of such features  88  on the bone contacting surface  82 . For example, the features  88  can be equally spaced around the circumference of the bone-contacting surface  82 , thereby allowing the stabilization member  80  to engage the inferior articular process  16  and adding to the overall stability of the implant  10 . In other embodiments, the features  88  can extend at acute or obtuse angles from the bone contacting surface  82 . 
         [0050]      FIG. 11   b  shows the second embodiment of the spinal implant  10 , as illustrated in  FIG. 10 , spanning across the inferior articular process  16  and the superior articular process  12  in its final, expanded state. 
         [0051]    The devices, systems, and methods described herein provide an improved and more accurate system of facet joint stabilization. Applicants note that the procedures disclosed herein are merely exemplary and that the systems and methods disclosed herein may be utilized for numerous other medical processes and procedures. Although several selected embodiments have been illustrated and described in detail, it will be understood that they are exemplary, and that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the following claims.

Technology Classification (CPC): 0