Abstract:
Devices and methods for treating degenerative conditions of the spine or for alleviating pain or discomfort associated with the spinal column are disclosed. In particular, laminoplasty fixation devices and methods are disclosed. Also disclosed, is a vertebral implant comprising a first bone engaging portion configured for securing to a first cut portion of a vertebra and a second bone engaging portion configured for securing to a second cut portion of the vertebra. A body portion is provided for associating the first and second bone engaging portions at a preselected spacing from each other, wherein the implant is adjustable to select said spacing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/554,210, filed on Nov. 26, 2014, which is a divisional of U.S. patent application Ser. No. 11/936,334, filed on Nov. 7, 2007, now U.S. Pat. No. 8,926,664, which claims priority to U.S. Provisional Application Ser. No. 60/864,731 filed on Nov. 7, 2006, all of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to devices and methods for treating degenerative conditions of the spine or for alleviating pain or discomfort associated with the spinal column. More specifically, the present invention is directed to laminoplasty fixation devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    In certain circumstances, the spinal canal extending through a patient&#39;s vertebrae is or becomes too narrow and constricts the spinal cord extending therethrough. Narrowing can be attributable to causes such as age, injury or removal of a spinal disk. 
         [0004]    For instance, cervical spondylosis is a common degenerative condition of the cervical spine that most likely is caused by age-related changes in the intervertebral disks. As disk degeneration occurs, mechanical stresses result in osteophytic spurs, which may form along the interior aspect of the spinal canal and can compress the spinal cord. The constriction of the spinal cord in the cervical spine, for example, often produces pain, weakness, or loss of feeling in extremities. Other causes for narrowing of the spinal canal include disc shrinkage, which causes the disc space to narrow and the annulus to bulge and mushroom out, resulting in pressure on the spinal cord. Degenerative arthritis of facet joints can cause joints to enlarge, or the vertebra to slip with respect to each other, also compressing the spinal cord. Instability between vertebrae, such as caused by stretched and thickened ligaments can also produce pressure on the spinal cord and nerve roots. 
         [0005]    Myelopathy, or affliction or injury of the spinal cord, occurs due to its compression. The rubbing of the spine against the cord can also contribute to this condition, and the spinal cord compression can ultimately compromise the blood vessels feeding the spinal core, further aggravating the myelopathy. 
         [0006]    Traditional procedures for decompressing the spinal cord include a laminectomy, in which the lamina and spinal processes are removed to expose the dura covering the spinal cord. Another known procedure is a laminoplasty, in which the lamina is lifted off the dura, but not completely removed. According to one laminoplasty procedure sometimes referred to as an “open door” procedure, an osteotomy is performed in which a complete cut is made through one side of the vertebra, approximately between the lamina and lateral mass, while a partial-depth cut is made on the opposite lateral side. The lamina is then hinged open about the partial cut to increase the cross-sectional size of the spinal canal to decompress the spinal cord therein. In certain procedures, a laminoplasty plate is then fixed between the facet and the hinged open lamina. According to some known methods, the plate of an appropriate size is selected and bent to the desired shape and generally has a plurality of screw holes. In other known techniques, a strut of bone may be placed in the open portion within the lamina and the facet to help hold the open position of the lamina. In general, prior to the operation, the surgeon needs to measure the vertebra to determine the size of the plate necessary for implantation. At that point, a plate can be selected with the appropriate dimensions, and implanted at the site. 
         [0007]    Improved laminoplasty fixation devices are needed. For example, a laminoplasty fixation device that may be varied in size prior to implantation is desirable so that a plate does not have to be custom selected and intensively shaped and formed prior to each surgery. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention generally relates to laminoplasty fixation devices and methods of use. One embodiment of a vertebral implant constructed according to the invention comprises a first bone engaging portion configured for securing to a first cut portion of a vertebra and a second bone engaging portion configured for securing to a second cut portion of the vertebra. A body portion is provided for associating the first and second bone engaging portions at a preselected spacing from each other, wherein the implant is adjustable to select said spacing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will be more readily understood with reference to the embodiments thereof illustrated in the attached figures, in which: 
           [0010]      FIG. 1  is a top view of one embodiment of a laminoplasty fixation device according to the invention; 
           [0011]      FIG. 2  is a side view of the embodiment of  FIG. 1  shown in an implanted position on a portion of a vertebral body; 
           [0012]      FIG. 3  is a side view of another embodiment of a laminoplasty fixation device shown in an implanted position on a portion of a vertebral body; 
           [0013]      FIG. 4  is a side view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0014]      FIG. 5  is a side view of another embodiment of a laminoplasty fixation device shown in an implanted position on a portion of a vertebral body; 
           [0015]      FIG. 5A  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0016]      FIG. 6  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0017]      FIG. 7  is a side view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0018]      FIG. 8  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0019]      FIG. 9  is a side view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0020]      FIG. 9A  is a partial top view of the embodiment of  FIG. 9 ; 
           [0021]      FIG. 9B  is a side view of another embodiment of a laminoplasty fixation device shown in an implanted position on a portion of a vertebral body; 
           [0022]      FIG. 10  is a side view of another embodiment of a laminoplasty fixation device shown in an implanted position on a portion of a vertebral body; 
           [0023]      FIG. 11  is a side view of another embodiment of a laminoplasty fixation device; 
           [0024]      FIG. 12  is a side view of another embodiment of a laminoplasty fixation device shown in an implanted position on a portion of a vertebral body; 
           [0025]      FIG. 13  is a side view of another embodiment of a laminoplasty fixation device shown in an implanted position on a portion of a vertebral body; 
           [0026]      FIG. 13A  is an exploded side view of the embodiment depicted in  FIG. 13 ; 
           [0027]      FIG. 14  is an exploded side and top view of an alternative to the embodiment depicted in  FIG. 13 ; 
           [0028]      FIG. 15  is an exploded side and top view of another embodiment of a laminoplasty fixation device; 
           [0029]      FIG. 16  is a perspective view of the embodiment depicted in  FIG. 15 ; 
           [0030]      FIG. 17  is a side view of another embodiment of a laminoplasty fixation device shown in an implanted position on a portion of a vertebral body; 
           [0031]      FIG. 18  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0032]      FIG. 18A  is a cross-sectional view of the embodiment of  FIG. 18 ; 
           [0033]      FIG. 18B  is a top and side view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0034]      FIG. 19  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0035]      FIG. 20  is a cross-sectional view of the embodiment of  FIG. 19 ; 
           [0036]      FIG. 21  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0037]      FIG. 22  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0038]      FIG. 23  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; 
           [0039]      FIG. 24  is a side view of another embodiment of a laminoplasty fixation device shown in an implanted position on a portion of a vertebral body; 
           [0040]      FIGS. 25-29  are a side views installation steps for implanting the laminoplasty fixation device of  FIG. 24 ; 
           [0041]      FIG. 30  is a perspective view of another embodiment of a laminoplasty fixation device according to the invention; and 
           [0042]      FIG. 31  is a side view of the embodiment of  FIG. 30  shown in an implanted position on a portion of a vertebral body. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    Embodiments of the invention will now be described. The following detailed description of the invention is not intended to be illustrative of all embodiments. In describing embodiments of the present invention, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. It is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
         [0044]    Referring to  FIGS. 1-29 , embodiments of devices or implants for use in a unilateral or “open door” laminoplasty procedure are shown. Generally, in an “open door” laminoplasty procedure, an osteotomy is performed in which a complete cut is made through one side of the vertebra, approximately between the lamina and lateral mass, while a partial-depth cut is made on the opposite lateral side. The lamina is then hinged open about the partial cut to enlarge the spinal canal. 
         [0045]    Referring to  FIGS. 1 and 2  one exemplary embodiment of a laminoplasty fixation device  10  according to the invention is shown. In general, fixation device  10  comprises a unitary plate body  12  with a first portion  14  and a second portion  16  separated by a bendable section  18 . Bendable section  18  generally comprises a thinner less rigid portion of plate body  12  configured allow second portion  16  to bend or rotate relative to first portion  14 . Plate body  12  generally comprises a plurality of openings or holes  20  for receiving a bone fastener, such as a bone screw. The holes  20  may be disposed for accessing and inserting the fasteners from the outside of the bone to facilitate implantation. According to one embodiment, fixation device  10  is configured for use in an “open door” laminoplasty procedure with the first portion  14  generally configured for securing to a portion of a lamina  22  that has been cut and hinged away from the lateral mass  24 . Second portion  16  of plate body  12  generally comprises a serrated or spiked free end  26 . The spikes or serrations  28  at end  26  are configured to engage the lateral mass to prop the lamina open when the second portion  16  is rotated with respect to first portion  14 . In one embodiment, plate  12  is made from a titanium material; however, in alternate embodiments any suitable implant material known to those skilled in the art may be used. In one embodiment a bone strut  29  may be attached to the inner surface of plate  12  to facilitate bone fusion or regeneration between the lateral mass and lamina. In alternate embodiments, plate  12  may comprise separate plate portions interconnected by a hinge member. 
         [0046]    Referring to  FIG. 3 , another embodiment of a laminoplasty implant  30  is shown. Implant  30  generally comprises a swing plate body  32  with a first portion  34  rotatably connected to a second portion  36 . Implant  30  is generally similar to plate  10  described above, except the integrated spikes  28  are replaced with a separate lateral mass anchor portion  38 . In operation, first portion  34  and anchor portion  38  can be attached or fixed to the lamina prior to cutting through the lamina thereby facilitating an easier implantation procedure than attaching the first and anchor portions  34 ,  38  after cutting through the lamina. In one variation, plate body  32  comprises a slotted hole  39  to provide adjustability. Once the lamina is cut, the second portion of the plate may be swung into place and may be attached or fixed to anchor portion  38  with a fixation device, such as a screw. In alternate embodiments, a latch mechanism may be used to fixably connect second portion  36  to anchor portion  38 . 
         [0047]    Referring to  FIG. 4 , another embodiment of a laminoplasty fixation device or implant  40  is shown. Implant  40  generally comprises an elongate body  42  with a first end portion  44  having one or more openings or holes  46  configured to receive fasteners and an opposite second end  47  comprising a bifurcated, yoked, or claw-like portion  48 . Bifurcated portion  48  comprises bone engaging or locking features such as serrations, knurls, or teeth  49  positioned along the inner portion thereof. Claw  48  is configured to be deformable to compress teeth  49  against bone to fix plate body  42  to bone. According to one application of plate  42  for a laminoplasty, first end  44  may be attached to the lateral mass and second end  47  may be crimped to the lamina once it is cut and rotated or opened during the laminoplasty procedure. According to one embodiment, implant  40  may be made from titanium; however, in alternate embodiments any suitable biocompatible material may be used. 
         [0048]    Referring to  FIG. 5  another embodiment of a laminoplasty device or implant  50  constructed according to the invention is shown. Implant  50  generally comprises a flexible mesh body  52  that may be screwed or otherwise secured adjacent the lateral mass at one end and adjacent the lamina or spinous process at the opposite end. A rigid strut  54  may be attached to mesh body  52  for positioning between the lamina  56  and lateral mass  58 . In one embodiment, mesh body  52  may be attached to bone at any location along its length by, for example, fasteners or screws  59 . According to one embodiment, implant  50  may be made from a Dacron® or Gore-Tex® material. Referring to  FIG. 5A , another embodiment of an implant  60  constructed according to the invention is shown. Implant  60 , is similar to implant  50  except strut  64  is fixably slidably positionable along flexible strap  66 . In one variation, strut  64  may comprise strap receiving members or slots  68  adjacent an upper sidewall  69  to slidingly accommodate strap  66  therethrough. In the embodiment of  FIG. 5A , rigid strut  64  may be made from a PEEK material and may have a through-hole to permit bone growth and/or packing with bone or DBM material. The lateral ends of strut  64  may be indented or comprise a birdmouth-like profile to capture cut portions of the lateral mass and lamina and generally prevent movement of strut  64  in the posterior-anterior direction, i.e. into the spinal canal. Also, strap  66  generally prevents strut  64  from migrating. One advantageous feature of such a flexible mesh or strap body is that the implant may readily conform to the anatomy and it generally provides variability in placement of fasteners to secure the implant in place. 
         [0049]    Referring to  FIG. 6  another embodiment of a laminoplasty device or implant  70  constructed according to the invention is shown. Implant  70  generally comprises a unitary plate body  72  with a first portion  73  and a second portion  74  separated by an intermediate portion  75 . Body  72  has a general “S” shape when viewed from the side, as shown in  FIG. 6 . When implant  70  is used in an “open door” laminoplasty procedure, the first portion  73  is generally configured for securing to a portion of a cut lamina and the second portion  74  is generally configured for securing to a portion of the lateral mass. In one embodiment, first portion  73  comprises a bifurcated or yoked end with spaced tines  71  configured and dimensioned to receive a portion of the lamina therebetween. According to one embodiment, intermediate portion  75  may have a hollow central region  76 . The hollow region  76  may be packed with osteogenic material to facilitate fusion of the implant  70  with the patients cut bone portions. In addition, hollow region  76  allows access to cut bone portions after implantation and facilitates packing of osteogenic material therein. Also, a base wall may  79  be provided along the anterior side of hollow region  76  to prevent osteogenic material and bone growth from migrating into the spinal canal. In one variation, base wall  79  may be between about 1 mm and 2 mm thick. Plate body  72  generally comprises a plurality of openings or holes  77  for receiving a bone fastener, such as a bone screw. The holes  77  may be disposed for accessing and inserting the fasteners from the outside of the bone to facilitate implantation. In one embodiment, a countersink or scalloped region  78  may be provided adjacent openings or holes  77  to accommodate, among other things, a variable-angle screw to allow angulation of implant  70  with a fastener inserted therethrough. 
         [0050]    Instead of a unitary or single plate body, laminoplasty fixation devices may comprise multiple components. For example, as shown in  FIGS. 7-29 , fixation devices generally comprise more than one component. 
         [0051]    Referring to  FIG. 7  another embodiment of a laminoplasty implant  80  according to the invention is shown. Implant  80  is similar to implant  70  shown in  FIG. 6  and described above, except the implant body  82  comprises two separate components slidably connected together. According to one embodiment, first body portion  84  is slidably received within a receiving portion  85  of second body portion  86  with a dovetail fit. Such a sliding dovetail configuration facilitates distractability between the bone engaging end portions. As one skilled in the art may appreciate, such a feature is desirable for accommodating a variety of spacing between a lateral mass and lamina. According to one embodiment, the first and second body portions may be fixed relative to one another by a set screw or other know fixation device. 
         [0052]    Referring to  FIG. 8 , another embodiment of a laminoplasty implant  90  according to the invention is shown. Implant  90  is similar to implant  80  described above with respect to  FIG. 7  except the first and second body portions  92 ,  94  are adjustably connected by a ratchet mechanism. In one embodiment, first body portion has an upper surface comprising a plurality of ratchet features or teeth  96  that matingly interface with corresponding ratchet teeth (not shown) on the under surface of second body portion  94 . In one embodiment, teeth  96  are unidirectional and first body portion  92  may be fixed with respect to second body portion  96  with a unidirectional or distraction movement. Such a ratchet interconnection promotes adjustability, since it is easy for a practitioner to increase the distraction or spacing of the device. For example, the first and second body portions may be immediately locked in position or fixed with respect to one another, thus eliminating the need for a set screw or other additional fixation device. In this regard, such an arrangement permits one step distraction and generally eliminates the need to use a trial insert to find a proper fit. As a result, a set of implants for use in surgery may have fewer parts. In addition, the distraction or relative movement between the first and second body portions is unidirectional which prevents recoil, retraction, bounce back, or backward movement during insertion. 
         [0053]    Referring to  FIG. 9 , another embodiment of a laminoplasty implant  100  according to the invention is shown. Implant  100  is similar to implants  80  and  90 , described above, except that the first and second body portions  102 ,  104  are fixably adjustable with an elongate slot and screw connection. As best seen in  FIG. 9A , an elongate slot  105  is configured to receive a fastener such as a screw therethrough. In one variation, one or more indentations or scalloped portions  106  are positioned about the perimeter of slot  105  to locate or position the fastener along the length of slot  105 . According to one embodiment, first body portion  102  may be able to articulate with respect to bone engaging end portion  107 . In this regard, bone engaging portion  107  may be attached to a lamina portion prior to bending or hinging of the lamina during the laminoplasty procedure. In one embodiment, a pivot pin  108  extends through first body portion  102  and bone engaging portion  107  to facilitate articulation. In an alternate embodiment, illustrated in  FIG. 9B , first and second body portions  102 ,  104  may comprise unitary arched plate bodies with a slot  105  provided in one body portion for receiving a fastener  109  therethrough to facilitate fixable relative adjustment of the first and second body portions  102 ,  104 . 
         [0054]    Referring to  FIG. 10 , another embodiment of a laminoplasty implant  110  according to the invention is shown. Implant  110  is similar to implants  80 ,  90  and  100  described above, except the intermediate body portion comprises an elongate rod  112  fixably adjustable between first and second bone engaging portions  114 ,  116 . First and second bone engaging portions  114 ,  116  are configured to receive one or more fasteners to secure portions  114 ,  116  to bone. In one variation, shown in  FIG. 10 , first portion  114  comprises a yoke or forked end  118  with a top tine  120  and a bottom tine  122  and the tines  120 ,  122  are spacedly configured to engage opposite sides of a portion of bone, such as the lamina  124 . According to one embodiment, rod  112  may be able to slide or move with respect to bone engaging portions  114 ,  116 . Such a sliding configuration facilitates distractability between the bone engaging end portions. As one skilled in the art may appreciate, such a feature is desirable for accommodating a variety of spacing between a lateral mass and lamina. In addition, such a slidable rod configuration advantageously provides minimal canal encroachment while still allowing adjustable distraction. In another embodiment, one or both bone engaging portions  114 ,  116  may comprise a multi-axial screw and may allow screw angulation, such as adjacent the lateral mass  126 . 
         [0055]    Referring to  FIG. 11 , another embodiment of a laminoplasty implant  130  according to the invention is shown. Implant  130  is similar to implant  110  described above with respect to  FIG. 10 , except that the intermediate body portion or rod  132  is spherically connected to first bone engaging portion  134  and slidably connected to second bone engaging portion  136 . In this regard, such a spherical connection facilitates distractability between the bone engaging end portions while also allowing the first bone engaging portion  134  to articulate or move with distraction. 
         [0056]    Referring to  FIG. 12 , another embodiment of a laminoplasty implant  140  according to the invention is shown. Implant  140  is similar to implant  130  described above, except that the first body portion  142  comprises an elongate body with an integrated first bone engaging portion  144 . First bone engaging portion  144  comprises a yoke or forked end  146  with a top tine  147  and a bottom tine  148  and the tines  147 ,  148  are spacedly configured to engage opposite sides of a portion of bone, such as the lamina  149 . According to one embodiment, first body portion  142  may be able to slide or move with respect to second bone engaging portion  145 . Such a sliding configuration facilitates distractability between the bone engaging end portions. As one skilled in the art may appreciate, such a feature is desirable for accommodating a variety of spacing between a lateral mass and lamina. 
         [0057]    Referring to  FIGS. 13-14 , another embodiment of a laminoplasty implant  150  according to the invention is shown. Implant  150  is similar to implant  110 , described above with respect to  FIG. 10  except that a first body portion comprises an elongate body  152  with an integrated first bone engaging portion  154  at distal end  156 . First bone engaging portion  154  comprises a bottom hook portion  158  configured to engage opposite sides of a portion of bone, such as the lateral mass  159 , as illustrated in  FIG. 13 . According to one embodiment, elongate body  152  may be able to slide or move with respect to second bone engaging portion  160 . In one variation, elongate body  152  has a cylindrical cross-section and generally resembles a rod. In alternate embodiments, elongate member  152  may have a rectangular cross-section and generally resemble a bar. Second bone engaging portion  160  comprises a bottom hook portion  162  integrated with an upper receiving portion  164 . Hook portion  162  is generally configured to engage opposite sides of a portion of bone, such as the lamina  165 , as illustrated in  FIG. 13 . Receiving portion  164  is configured and dimensioned to fixably slidably receive a portion of elongate body  152 . According to one embodiment, elongate body  152  may be fixed with respect to receiving portion  164  with a set screw  166 . Such a fixable sliding configuration facilitates distractability between the bone engaging end portions. As one skilled in the art may appreciate, such a feature is desirable for accommodating a variety of spacing between a lateral mass and lamina. 
         [0058]    Referring to  FIGS. 15-16 , another embodiment of a laminoplasty implant  170  according to the invention is shown. Implant  170  is similar to implant  150 , described above with respect to  FIGS. 13-14  except that a first body portion  172  comprises an elongate bar  174  with an upper ratchet portion comprising a plurality of ratchet features or teeth  176 . According to one embodiment, bar  174  is integrated with a first bone engaging portion  178  at distal end  176  thereof. Bar  174  may be able to slide or move with respect to second bone engaging portion  180 . Similar to the embodiment of  FIGS. 13-14 , first and second bone engaging portions  174 ,  180  generally comprise bottom hook portions  178 ,  182  configured to engage opposite sides of a portion of bone, such as the lateral mass and lamina, when implant  170  is installed. Second bone engaging portion  180  comprises an upper portion with a bar receiving portion  184  configured to slidably receive a portion of bar  172 . According to this embodiment, receiving portion  184  generally comprises unidirectional teeth complimentary to ratchet teeth  176  of bar  172  and bar  172  may be fixed with respect to receiving portion  184  with a unidirectional ratchet mechanism. Such a ratchet interconnection facilitates easy adjustability. For example, the first and second bone engaging portions may be immediately locked in position or fixed with respect to one another, thus eliminating the need for a set screw or other additional fixation device. In this regard, such an arrangement permits one step distraction between the bone engaging portions  174 ,  180 . In addition, the distraction or relative movement between the first and second bone engaging portions  174 ,  180  is unidirectional which prevents recoil, bounce back, or backward movement during insertion. 
         [0059]    Referring to  FIG. 17  another embodiment of a laminoplasty implant  190  according to the invention is shown. Implant  190  is similar to implant  100  shown in  FIG. 9B  described above, except the first and second body portions  192 ,  194  are linkable together by a ball-and-socket connection. According to one embodiment, first body portion  192  comprises a ball shaped end  196  configured and dimensioned to be received within a correspondingly shaped female or socket end  198  of second body portion  194 . Such a ball-and-socket configuration facilitates angulation or hinging between the bone engaging end portions  193 ,  195 . As one skilled in the art may appreciate, such a feature is desirable for accommodating a variety of spacing between a lateral mass and lamina. In alternative embodiments, different types of linkages may be utilized. For example, in one variation a puzzle piece type connection may be used. In another embodiment a dovetail type linkage connection may be utilized. According to these various embodiments, one skilled in the art may appreciate that such removably linkable connections may facilitate insertion of first and second body portions individually. 
         [0060]    Referring to  FIGS. 18 and 18A , another embodiment of a laminoplasty implant  200  according to the invention is shown. Implant  200  is similar to implant  80  shown in  FIG. 7  described above; except the implant body  202  comprises a strut  204  fixably slidable with respect to body portion  202 . According to one embodiment, strut  204  may be slidably received within body portion  202  with a slotted fit, as best seen in  FIG. 18A . Such a sliding configuration facilitates distraction along the length of body portion  202 . According to one embodiment, the strut  204  may be fixed relative to body portion  202  by a set screw or other know fixation device. Referring to  FIG. 18B  an alternate embodiment of an implant with an adjustable strut member is shown. 
         [0061]    Referring to  FIGS. 19-20  another embodiment of a laminoplasty implant according to the invention is shown. Implant  210  comprises two separate components slidably connected together. According to one embodiment, first body portion  212  is slidably received within second body portion  214  with an offset finger fit. First body portion  212  generally comprises first and second finger portions  216 ,  218  extending longitudinally from opposite corner sections of a first bone engaging end  220 . Second body portion  214  generally comprises third and fourth finger portions  222 ,  224  extend longitudinally from opposite corner sections of a second bone engaging end  226 . As seen in  FIG. 19 , first and second finger portions  216 ,  218  of first body portion  212  are configured and dimensioned to meshingly longitudinally engage and fixably slide with respect to third and fourth finger portions  222 , 224  of second body portion  214 . As shown in  FIG. 20 , first and second finger portions  216 ,  218  are configured may be angularly offset with respect to third and fourth finger portions  222 ,  224  to facilitate uni-axial sliding of first body portion  212  with respect to second body portion  214  and prevent torsion or twisting. Such a sliding configuration facilitates distractability between the bone engaging end portions. As one skilled in the art may appreciate, such a feature is desirable for accommodating a variety of spacing between a lateral mass and lamina. According to one embodiment, the first and second body portions may be fixed relative to one another by a set screw or other know fixation device. Referring to  FIG. 19 , in one embodiment first and second body portions  212 ,  214  may have a hollow central region  228 . The hollow region  228  may be packed with osteogenic material to facilitate fusion of the implant  210  with cut bone segments. 
         [0062]    Referring to  FIG. 21 , another embodiment of a laminoplasty implant  230  according to the invention is shown. Implant  230  comprises two bone engaging strut members  232 ,  234  disposed along a track plate  236 . Struts  232 ,  234  generally comprise bone engaging portions configured to engage opposite sides of a portion of bone, such as the lamina and lateral mass in a laminoplasty procedure. According to one embodiment, track  236  is slidably received within hollow central portion  238  of strut members  232 ,  234  and strut members may generally be positioned anywhere along the length of track  236  as desired by a practitioner. In this regard, one ore more holes  237  or slots  239  may be provided along the length of track  236  for receiving a fastener therethrough to fix struts  232 , 234  in place along the length of track  236 . Such a fixable sliding configuration facilitates distractability between the struts  232 ,  234 . As one skilled in the art may appreciate, such a feature is desirable for accommodating a variety of spacing between a lateral mass and lamina. Referring to  FIG. 22 , in an alternate embodiment, strut members  232 ,  234  may be fixably slidably disposed along a lateral side of a track plate  236 . In another embodiment, shown in  FIG. 23 , strut members  232 , 234  may be positioned adjacent a scissor bar expansion mechanism  235  to facilitate fixable variable spacing of strut members  232 ,  234 . 
         [0063]    Referring to  FIGS. 24-29 , another embodiment of a laminoplasty implant  250  and installation method is shown. In this embodiment end plates  252  are inserted between cut bone segments with a distractor tool  254  to facilitate distraction, as best seen in  FIG. 24 . Plates  252  generally comprise an “L” shaped body  256  with a bone cover arm portion  258  extending distally from an elongate upper surface  260 . According to one embodiment, plates  252  are configured and dimensioned to be attached to a distractor tool  254 , as illustrated in  FIGS. 24-25 , to facilitate insertion between bone segments. Once the plate tips  252  are inserted between bone segments and sufficient distraction is achieved, plates  252  may be detached from distractor  254  and left in place against opposing portions  262 ,  264  of the spaced bone segments. Referring to  FIG. 27 , in one embodiment, a spacer insert  266  may then be inserted between end plates  252  to maintain the spacing between the bone segments and facilitate bony fusion. In one variation, spacer  266  may slide into place between arm portions  258  by a mating fit, such as a dovetail fit, to prevent movement of spacer  266  in a lateral or torsional direction. Spacer  266  may be various sizes and shapes as desired by a practitioner depending on the indication. As shown in  FIG. 29 , once installed between end plates  252 , spacer  266  may fixed in place with respect to the bone segments and endplates with a fastener  268 , such as a screw. According to one variation, endplates  252  and spacer  266  may be made from titanium. 
         [0064]    Referring to  FIGS. 30-31 , an embodiment of an implant for use in a bilateral or “french door” laminoplasty procedure is shown. In a “french door” laminoplasty procedure, the spinous process of a targeted vertebra is bisected along the saggital plane and the segments are separated to enlarge the spinal canal. 
         [0065]      FIGS. 30 and 31  are perspective and side views of another embodiment of an implant  300  according to the invention. Implant  300  comprises a general trapezoidal peripheral shape when viewed from the side with bone engaging end walls  302 ,  304  extending angularly inward from posterior wall  306  toward anterior wall  308 . In one variation anterior wall  308  is shorter in length than posterior wall  306 , thus forming a general wedge-like profile. A bird-mouth, shelf, or lip  310  may be provided along end walls  302 ,  304 . In one embodiment, lip  310  is positioned closer to anterior wall  308  than posterior wall  306 , such that end walls  302 ,  304  widen laterally outward from the lip toward anterior wall  308 . In this regard, such a bird-mouth or lip  310  facilitates secure engagement with an anterior portion of the bisected spinous process and generally prevents movement of implant  300  in the posterior direction when the implant is installed. In one variation, end walls  302 ,  304  of implant  300  may comprises serrations or ridges  312  to facilitate engagement or purchase with bone. In one embodiment, implant  300  may comprise a hollow central portion  314  to accommodate packing of osteogenic material therein, promote bone growth therethrough, and facilitate bone fusion. One or more through holes  316  may be provided to facilitate attachment via suture and/or bone fastener. In one embodiment, implant  300  may be made from a made of a polyether-ether-ketone (PEEK) plastic material; however any known biocompatible material may be used. Several known advantages of PEEK plastic material include that it is radiolucent and may be more easily sterilized than other plastics in addition to providing proven bio-compatibility with a modulus of elasticity approximating that of bone. 
         [0066]    While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations can be made thereto by those skilled in the art without departing from the scope of the invention.