Abstract:
Fixation devices and methods for stabilization of the lamina after laminoplasty are described. The device comprises of a plate with several holes that receive bone fasteners. The plate is curved at the ends to contour to the vertebral structure and has appendages to engage the displaced lamina in a fixed position. Alternatively, the plate has a bone fusion spacer in the middle to engage and fuse the lamina in the displaced position. Several methods of dynamically stabilizing the lamina after either the open door, double door or expansive laminoplasty technique are provided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Cervical stenosis with spinal cord compression and consequent myelopathy is a very common problem encountered by the spine surgeon. The usual cause of multilevel cervical stenosis is spondylosis and/or ossification of the posterior longitudinal ligament. Surgical decompression either through an anterior or posterior approach can be undertaken.  
           [0002]    An anterior approach usually involves multilevel corpectomy with fusion and stabilization. The main drawback of this technique is the increased time and complexity of the procedure as well as the risk of pseudoarthrosis and accelerated degeneration at the levels above and below the fusion.  
           [0003]    A posterior approach has traditionally involved a simple laminectomy, laminectomy with facet fusion, or more recently laminoplasty. The drawback of a simple laminectomy is the risk of late clinical deterioration form either kyphosis or postlaminectomy scar formation. Laminectomy with facet fusion decreases the risk of kyphosis but it also decreases the range of motion in the spine and increases the risk of accelerated degeneration at the levels above and below the fusion.  
           [0004]    Laminoplasty either through open door or double door technique developed more recently provides greater stability and range of motion when compared with laminectomy alone. This technique entails laminoplasty for decompression with laminar fusion with allo- or autograft bone and/or fixation with a plate. The principle behind laminar fusion and fixation is that it maintains the decompression following laminoplasty as well as the displaced lamina in a fixed position thereby providing stabilization also.  
           [0005]    U.S. Pat. No. 6,080,157 to Cathro et al. describes an implant to stabilize the lamina after laminoplasty. A major limitation of this implant and technique is that a single implant extends to all the laminoplasty levels and is followed by posterior autograft fusion thereby disabling the inherent mobility between the cervical spine levels which laminoplasty attempts to preserve.  
           [0006]    The present invention is an apparatus for use in laminoplasty to fuse and stabilize the lamina individually in the cervical, thoracic or lumbar spine thereby preserving the range of motion as well as providing stability.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention relates a laminar fusion and fixation system following laminoplasty. This system with the bone fusion spacer or resorbable fusion graft and plate reduces surgical time and simplifies laminar fusion and fixation after laminoplasty.  
           [0008]    The bone fusion spacer consists of a bicortical bone graft with variable length but uniform width and thickness specific for the cervical, thoracic or lumbar spine. The edges are contoured with a notch to allow securement to the lamina on one side and the lateral mass or facet on the other side.  
           [0009]    In another embodiment of the bone fusion spacer, the edges have a superior cuff or shoulder that allows securement against the lamina and facet on either sides as well prevent migration of the bone graft into the spinal canal.  
           [0010]    The resorbable fusion graft has a design similar to the allograft bone graft but is made of hydroxyapatite or similar absorbable material which is eventually resorbed and/or replaced with autologous bone during the fusion process.  
           [0011]    The invention also comprises a plate made of titanium or similar alloy with magnetic resonance imaging compatibility of variable thickness which is contoured at the edges to allow fixation of the laminoplasty and securement of the bone graft. The contoured design of the plate allows screw placement in the lamina or spinous process on one side and the facet on the other side.  
           [0012]    In another embodiment the allograft bone or resorbable graft and plate are constructed as a unit with the bone graft attached to the plate in the middle through either screws or an adhesive material.  
           [0013]    In another embodiment, the bone graft and plate are designed for laminar fusion and fixation following double door laminoplasty. The bone graft in the middle allows for laminar fusion in the decompressed position with the plate design bent on either end securing the graft to the lamina and facet.  
           [0014]    In another embodiment, the plate has appendages that engage the lamina and facet in a fixed position without the use of a bone spacer.  
           [0015]    The procedure as would be undertaken with the use of the laminoplasty fixation system is described as follows. An open door laminoplasty entails creating a gutter at the junction of the lamina and medial aspect of the facet on both sides with the use of a drill. On the side of the laminoplasty opening, the drilling is carried through into the canal or the opening completed with a small kerrison rongeur. At the other side, the inner cortex at the lamina and facet junction is not drilled. The lamina at the open end is elevated and the spinous process pushed away in order to create a greenstick osteotomy and allow for the laminoplasty decompression. Typically, atleast one centimeter of distraction between the lamina and the facet provides for a good spinal decompression. In order to maintain the position of the lamina, the pre-contoured bicortical allograft of appropriate size is positioned between the lamina and the facet. Stabilization at each level is then undertaken with placement of the pre-designed plate with the curved ends to allow one end to secure to the lamina with a screw and the other end to the facet. Alternatively, the bone graft pre-attached to the plate can also be used to provide laminar fusion in the fixed position. In situations where laminoplasty stabilization without the use of a fusion graft is desired, the plate with added appendages to secure the displaced lamina is used.  
           [0016]    Another variation on the open door laminoplasty is the expansive laminoplasty most suited for the thoracolumbar spine. In this method, the lamina on either side at the junction of the facets are drilled and opened. A lateral spinal canal recess decompression and/or foraminotomy is undertaken and the lamina replaced with bone graft/plate construct on both sides.  
           [0017]    A trap door or double door laminoplasty is created by drilling on each side at the laminar and later mass junction the outer laminar cortex and sparing the inner laminar cortex. The spinous process is resected and a midline gutter is also created which extends through the inner cortex which can be opened with a small kerrison rongeur. The lamina on either side are lifted and opened creating a greenstick osteotomy on each side. In order to maintain the decompressed position of the lamina, a plate alone or a bone graft/plate construct is placed. The plate can either be fixated with screws to the lamina or the facets. For situations where laminar stabilization without the use of a fusion graft is desired, the plate with appendages in the middle is used.  
           [0018]    While the inventions described here are specific, any variations to the described embodiments falls within the scope of the current invention and the protection granted therein. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a cross section of the vertebra  
         [0020]    [0020]FIG. 2 is a top view of the bone graft  
         [0021]    [0021]FIG. 3 is a side view of one embodiment of the bone graft  
         [0022]    [0022]FIG. 4 is a cross section of the vertebra following open door laminoplasty with one embodiment of the bone graft  
         [0023]    [0023]FIG. 5 is a side view of another embodiment of the bone graft  
         [0024]    [0024]FIG. 6 is a cross section of the vertebra following open door laminoplasty with another embodiment of the bone graft  
         [0025]    [0025]FIG. 7 is a top view of one embodiment of the plate  
         [0026]    [0026]FIG. 8 is a top view of another embodiment of the plate  
         [0027]    [0027]FIG. 9 is a side view of the plates  
         [0028]    [0028]FIG. 10 is a top view of the graft and plate construct  
         [0029]    [0029]FIG. 11 is a side view of one embodiment of the construct  
         [0030]    [0030]FIG. 12 is a cross section of the vertebra with the graft and plate construct in place  
         [0031]    [0031]FIG. 13 is a side view of another embodiment of the construct  
         [0032]    [0032]FIG. 14 is a cross section of the vertebra with the graft and plate construct in place  
         [0033]    [0033]FIG. 15 is a cross section of the vertebra with expansive laminoplasty  
         [0034]    [0034]FIG. 16 is a cross section of the vertebra following double door laminoplasty with one embodiment of the bone graft  
         [0035]    [0035]FIG. 17 is a cross section of the vertebra following double door laminoplasty with another embodiment of the bone graft  
         [0036]    [0036]FIG. 18 is a top view of one embodiment of the graft and plate construct  
         [0037]    [0037]FIG. 19 is a side view of the construct  
         [0038]    [0038]FIG. 20 is a cross section of the vertebra with the graft and plate construct in place  
         [0039]    [0039]FIG. 21 is a top view of another embodiment of the graft and plate construct  
         [0040]    [0040]FIG. 22 is a side view of the construct  
         [0041]    [0041]FIG. 23 is a cross section of the vertebra with the graft and plate construct in place  
         [0042]    [0042]FIG. 24 is top view of another embodiment of the plate  
         [0043]    [0043]FIG. 25 is a side view of the plate  
         [0044]    [0044]FIG. 26 is a cross section of the vertebra with plate in place  
         [0045]    [0045]FIG. 27 is a side view of another embodiment of the plate  
         [0046]    [0046]FIG. 28 is a cross section view of the vertebra with the plate in place  
         [0047]    [0047]FIG. 29 is a top view of another embodiment of the plate  
         [0048]    [0048]FIG. 30 is a side view of the plate  
         [0049]    [0049]FIG. 31 is a top view of another embodiment of the plate  
         [0050]    [0050]FIG. 32 is a side view of the plate  
         [0051]    [0051]FIG. 33 is a cross section of the vertebra with one embodiment of the plate in place  
         [0052]    [0052]FIG. 34 is a cross section of the vertebra with another embodiment of the plate in place 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0053]    A top view of a vertebra is illustrated in FIG. 1 with vertebral body  1 , facet  2 , junctions of the facet and lamina  3  and  6 , lamina  4 , spinous process  5 , and spinal canal  7 .  
         [0054]    In one embodiment of the bone fusion device as illustrated in FIGS. 2 and 3, the device has a rectangular configuration with a top surface  9 , longitudinal edge  8 , side edge  10 , and grooved edges  10  and  11  to allow securement to the lamina and facet.  
         [0055]    For the open-door technique of laminoplasty, a bicortical opening at the junction of the lamina and facet on one side and a unicortical groove  6  on the other side with a greenstick fracture is created for the laminar displacement as illustrated in FIG. 4. A bone fusion graft  8  is placed between the facet  2  and lamina  4  to maintain the repositioned shape of the laminoplasty that provides decompression of the spinal canal  7 .  
         [0056]    In another embodiment of the bone fusion device with a longitudinal side  12  and top surface  13  as illustrated in a side view in FIG. 5, the edges at the ends are shouldered with superior cuffs  14  and  16  and edge  15 . Following the open-door laminoplasty, as depicted in FIG. 6, the bone fusion device rests between the lamina  4  on one side and facet  2  on the other and the shouldered ends  14  and  16  prevent migration of the graft into the spinal canal  7 .  
         [0057]    A plate is also used following the laminoplasty to stabilize and fuse the displaced lamina in the decompressed position. The plate has a top surface  20  with several bone screw receiving holes as illustrated in FIG. 7. Screw holes at the ends  17  and  19  secure the plate to the lamina on one side and the facet on the other. Screw hole  18  in the center of the plate can be used to secure the bone graft to the plate. In another embodiment of the plate as seen in FIG. 8, there are bone receiving screw holes  21  and  22  throughout the plate  23 . As illustrated in FIG. 9, the plates have curved ends to conform to the anatomy of the lamina following the open door laminoplasty technique with a top surface  20  and upward curved end  24  for facet fixation and downward curved end  25  for laminar fixation.  
         [0058]    In order to simplify the technique of laminoplasty and provide laminar fusion as well as stabilization, a pre-assembled construct with the plate attached to the bone fusion device is used as illustrated in FIGS. 10, 11, and  13 . The plate has a top surface  27  with a curved edge pointing superiorly  30  and inferiorly  31 . The bone screw holes at the both ends  28  and  29  allow the plate to be secured to the bone with screws. The bone fusion graft  26  has notches at the ends  32  as seen in FIG. 11, whereas in another embodiment in FIG. 13, the bone fusion graft  33  has shouldered ends  35  with a superior cuff  34 . The plate and fusion device construct is placed as seen in FIGS. 12 and 14 following an open-door laminoplasty. The bone fusion devices either  26  or  33  rest between the facet  2  and lamina  4  with the plate  27  secured to the lamina with a screw  37  and to the facet with a screw  36 .  
         [0059]    For the expansive laminoplasty technique as illustrated in FIG. 15, the plate and bone fusion construct is used on both sides. On one side, the bone graft  38  rests between the facet  42  and lamina  43  with the plate  39  securing the construct, whereas on the other side, the bone graft  40  rests between the facet  44  and lamina  45  with the plate  41  securing the construct.  
         [0060]    The trap door laminoplasty technique as shown in FIGS. 16 and 17 involves removal of the spinous process and creation of unicortical laminoplasty grooves  46  and  47  at the junction of the lamina and facet on both sides. The displaced lamina are then maintained in that position with a bone fusion construct  8  or  12 . In one embodiment of the bone graft and plate construct for use in this laminoplasty technique as illustrated in FIGS. 18 and 19, the plate with a top surface  51  has downward angled ends  52  and  53  and is attached to the bone graft  50 . The plate has bone screw receiving holes  48  and  49  that allow fixation of the plate to the lamina on both sides. FIG. 20 illustrates the construct in place with the laminar grooves  46  and  47 , bone graft  50  and the plate  51  with bone screws  62  and  63  securing the construct to the lamina.  
         [0061]    In another embodiment of the bone graft and plate construct for the trap door laminoplasty technique as illustrated in FIGS. 21 and 22, the plate has a top surface  59  with bone screw holes  54  and  58  for fixation to the facets and screw holes  55  and  57  for further fixation to the lamina if needed. The plate also has curved ends  60  and  61  contoured for fixation to the facets. The bone fusion device  56  is attached to the plate in the center. FIG. 23 illustrates the construct in place with the bone graft  56 , plate  59  and the plate fixated to the facets through bone screws  64  and  65 .  
         [0062]    For the technique of open-door laminoplasty, stabilization without laminar fusion can also be undertaken with the use of the plates as illustrated in FIGS. 24, 25, and  27 . The plate has a top surface  66  with bone screw holes at the ends  67  and  68 . The ends have a superiorly angled curve at one end  69  and inferiorly angled at the other  70 . In one embodiment as seen on the side view in FIG. 25, there is an inferiorly pointing curved hook  72  to engage the lamina at one end and a straight appendage  71  pointing inferiorly at the other end to secure to the facet. In another embodiment of the plate as seen in FIG. 27, there is only one appendage pointing inferiorly  72  at the end prior to the downward curvature of the plate. The implanted construct is seen in FIGS. 26 and 28. The plate is secured to the lamina  4  via bone screw  37  and facet  2  via bone screw  36 . The hook  72  secures the lamina in the displaced laminoplasty position. As seen in FIG. 26, the additional straight appendage  71  at the facet end allows the plate to rest on the facet  2 .  
         [0063]    For the trap-door technique of laminoplasty, stabilization without laminar fusion is undertaken with the use of the plates alone. In one embodiment of the plate as illustrated in FIGS. 29 and 30, the plate has a top surface  73  and screw holes at both ends  74  and  75 . The appendages  75  and  76  secure the displaced lamina and the curvatures at both ends  74  and  77  allows attachment to the lamina. The implanted plate is shown in FIG. 33 with bone screws  87  and  88  securing it to the lamina on both sides.  
         [0064]    In another embodiment as illustrated in FIGS. 31 and 32, the plate is curved at the ends  83  and  86 . The plate has a top surface  82  with bone screw holes  79  and  80  for laminar fixation and holes  78  and  81  for facet fixation on both sides. The appendages  84  and  85  secure the displaced lamina. The implanted plate is shown in FIG. 34 with bone screws  87  and  88  securing it to the facets on both sides.  
       REFERENCES  
       [0065]    [0065]                                                 U.S. Patent Documents                                    6080157   Jun. 27, 2000   Cathro           6241771   Jun. 5, 2001   Gresser