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:
RELATED U.S. APPLICATION DATA 
     This application is a continuation of U.S. application Ser. No. 10/299,624, which was filed on Nov. 19, 2002, and issued as U.S. Pat. No. 6,660,007 on Dec. 9, 2003, which was filed as a continuation of U.S. application Ser. No. 10/035,281 and filed on Jan. 3, 2002, now abandoned, and herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     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. 
     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. 
     A posterior approach has traditionally involved a simple laminectomy, laminectomy with facet fusion, or 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. 
     Laminoplasty either through open door or double door technique provides greater stability and range of motion when compared with laminectomy alone. This technique entails laminoplasty for decompression and fixation with a plate with or without laminar fusion. The principle behind laminar fixation is that it maintains the decompression following laminoplasty as well as the displaced lamina in a fixed position thereby providing stabilization also. 
     U.S. patent application Ser. No. 10/035,281 describes several laminar fixation plates with and without a bone fusion spacer that allow for lamina fixation and/or fusion. U.S. Pat. No. 6,660,007 describes laminoplasty plates for open door and double door techniques with a spacer in the middle to maintain the decompressed lamina position. 
     The present invention is an apparatus for use in either the open door or double door laminoplasty technique to stabilize the lamina in the spine thereby preserving the range of motion as well as maintaining stability. 
     SUMMARY OF THE INVENTION 
     The present invention relates a laminar fusion and fixation system following either open door or double door laminoplasty technique. This system with the spacer and plate reduces surgical time and simplifies laminar fixation and fusion if needed after laminoplasty. 
     In one embodiment the lamina fixation device consists of a plate angled at each end with a bone engaging appendage. The plate length can be variable with uniform width and thickness specific for the cervical, thoracic or lumbar spine. The angled ends of the plate allows screw placement in the lamina or spinous process on one side and the facet on the other side. The appendage shape can be straight, curved, or contoured with a notch to encase the lamina edge and allow securement to the lamina on one side and the lateral mass or facet on the other side. This implant is made of titanium or similar alloy with magnetic resonance imaging compatibility. 
     Alternatively, the implant is made of allograft bone, hydroxyapatite, or similar absorbable fusion material. The implant can also be made of a radiolucent material like polyaryletherketone or polyetheretherketone (PEEK). 
     In another embodiment the invention relates a laminar fusion and fixation system following laminoplasty. The invention comprises a plate made of titanium or similar alloy with magnetic resonance imaging compatibility which is contoured at the edges to allow fixation of the lamina and securement of the bone fusion spacer. The contoured design of the plate allows screw placement in the lamina and/or facets. The spacer longitudinal ends can be contoured with a notch to allow securement to the lamina on one side and the lateral mass or facet on the other side. The contoured end shape can be curved, straight, or any other shape to encase and secure the lamina or facet edge. The spacer can be made of allorgraft bone, autograft bone, xenograft bone, or a resorbable fusion material like hydroxyapatite which is eventually resorbed and replaced with autologous bone during the fusion process. 
     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. 
     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 both ends securing the graft to the lamina. 
     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, between 6-20 mm 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 laminar fixation plate with the attached bone fusion spacer is positioned between the lamina and the facet. The spacer maintains the displaced position of the lamina and the plates with the contoured ends secure the construct via screws to the lamina and facet. In another embodiment of the laminoplasty fixation device, the plate has appendages instead of a spacer perpendicular to the longitudinal plate axis which engage the lamina and the facet and increase the extent of the spinal canal space. 
     A trap door or double door laminoplasty is created by drilling on each side at the laminar and lateral mass junction the outer laminar cortex and sparing the inner laminar cortex. The spinous process is resected or split 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 contoured plate attached to a bone fusion spacer is placed in between the split lamina. The plate can either be fixated with screws to the lamina or the facets. In another embodiment, the plate has appendages instead of a spacer perpendicular to the longitudinal plate axis which engage the lamina and increase the extent of the spinal canal space. 
     A minimally invasive approach is undertaken with small incisions and serial dilation of the soft tissue along with splitting of the paraspinal muscles from the skin to the spine. A tubular port or any other shape retractor is then placed to maintain the exposure. The drilling of the lamina and, if needed, the spinous process is undertaken with this exposure using either an endoscope or a microscope magnification and subsequently the lamina are displaced to widen the spinal canal. A laminoplasty implant is then placed and secured to the lamina and facet. The tubular port is then removed and the skin incision closed. Intra-operative x-rays or a navigation system can be used to localize the spine level and confirm correct implant placement. 
     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 the spacer construct on both sides. 
     Embodiments of the laminoplasty implants also describe a spacer portion and one or more bendable lamina engagement portions in order to conform to the anatomy of a particular patient. The spacer portions and/or lamina engagement portions can also be pre-bent to accommodate patient anatomy based on anatomical considerations encountered during surgery. The spacer has open ends along the longitudinal plate axis and in other embodiments can also contain open top end to pack the spacer with bone fusion material after implantation and set expansion of the spacer. The bottom end of the spacer is solid and prevents any bone fusion material to migrate into the spinal canal. 
     Various embodiments and advantages of the current invention are set forth in the following detailed description and claims which will be readily apparent to one skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of one embodiment of the plate. 
         FIG. 2  is a side view of the plate. 
         FIG. 3  is a cross section of the vertebra following an open door laminoplasty with the plate shown in  FIG. 2  in place. 
         FIG. 4  is a side view of another embodiment of the plate. 
         FIG. 5  is a cross section of the vertebra following an open door laminoplasty with the plate shown in  FIG. 4  in place. 
         FIG. 6  is a top view of another embodiment of the plate. 
         FIG. 7  is a sectional side view of the plate. 
         FIG. 8  is a side view of another embodiment of the plate. 
         FIG. 9  is a side view of another embodiment of the plate. 
         FIG. 10  is a sectional side view of another embodiment of the plate. 
         FIG. 11  is a sectional side view of another embodiment of the plate. 
         FIG. 12  is a sectional side view of another embodiment of the plate. 
         FIG. 13  is a sectional side view of another embodiment of the plate. 
         FIG. 14  is a sectional side view of another embodiment of the plate. 
         FIG. 15  is a sectional side view of another embodiment of the plate. 
         FIG. 16  is a top view of another embodiment of the plate. 
         FIG. 17  is a side view of the plate. 
         FIG. 18  is a top view of another embodiment of the plate. 
         FIG. 19  is a side view of the plate. 
         FIG. 20  is a cross section of the vertebra following a trap door laminoplasty with the plate shown in  FIG. 17  in place. 
         FIG. 21  is a cross section of the vertebra following a trap door laminoplasty with the plate shown in  FIG. 19  in place. 
         FIG. 22  is a side view of another embodiment of the plate. 
         FIG. 23  is a sectional side view of the plate. 
         FIG. 24  is a side view of another embodiment of the plate. 
         FIG. 25  is a side view of another embodiment of the plate with a spacer. 
         FIG. 26  is a top view of the device shown in  FIG. 25 . 
         FIG. 27  is a sectional side view of the device taken along line A in  FIG. 26 . 
         FIG. 28  is a top view of another embodiment of the unitary plate and spacer device. 
         FIG. 29  is a side view of the device. 
         FIG. 30  is a sectional side view of the device. 
         FIG. 31  is a top view of another embodiment of the unitary plate and spacer device. 
         FIG. 32  is a side view of the device. 
         FIG. 33  is a sectional side view of the device. 
         FIG. 34  is a side view of another embodiment of the plate with a spacer. 
         FIG. 35  is a top view of another embodiment of the plate with a spacer. 
         FIG. 36  is sectional side view taken along line B in  FIG. 35 . 
         FIG. 37  is a cross section of the vertebra following a trap door laminoplasty with the device shown in  FIG. 35  in place. 
         FIG. 38  is a top view of another embodiment of the unitary plate and spacer device. 
         FIG. 39  is a side view of the device. 
         FIG. 40  is a sectional side view of the device. 
         FIG. 41  is a side view of another embodiment of the plate with a spacer. 
         FIG. 42  is a top view of another embodiment of the plate with a spacer. 
         FIG. 43  is sectional side view taken along line C in  FIG. 35 . 
         FIG. 44  is a cross section of the vertebra following a trap door laminoplasty with the device shown in  FIG. 42  in place. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The technique of open-door laminoplasty stabilization without laminar fusion undertaken with the use of the plates is illustrated in  FIGS. 1-5 . The plate has a top surface  1  with bone screw holes at the ends  2  and  3 . The ends have an upward angle at one end  4  and downward angle at the other  5 . In one embodiment as seen on the side view in  FIG. 2 , there is a hook appendage  7  perpendicular to the plate to engage the lamina at one end and a straight appendage  6  at the other end to secure to the facet. In another embodiment of the plate as seen in  FIG. 4 , there is only one appendage  7  at the end prior to the downward angle of the plate. The implanted construct is seen in  FIGS. 3 and 5 . The plate is secured to the lamina  11  via bone screw  10  and facet  8  via bone screw  9 . The hook  7  secures the lamina in the displaced laminoplasty position. As seen in  FIG. 3 , the additional straight appendage  6  at the facet end allows the plate to rest on the facet  8 . 
     In another embodiment, the plate  12  as shown in  FIG. 6  comprises a lamina engaging portion with screw hole  13  and facet engaging portion with multiple screw holes. The plates can have straight appendages  15  and  16  prior to the angle at both sides as shown in  FIG. 7 , a straight appendage  17  on the facet side as shown in  FIG. 17 , a straight appendage  18  on the lamina side as shown in  FIG. 9 , a curved appendage  19  at the lamina side and a straight appendage  20  at the facet side as shown in  FIG. 10 , curved appendages  21  and  22  prior to the angle at both sides as shown in  FIG. 11 , a curved appendage only 23 at the lamina side as shown in  FIG. 12 , or a curved appendage  24  at the facet side as shown in  FIG. 13 . 
     In another embodiment as shown in  FIG. 14 , the plate has a central portion  25 , a lamina engaging end  30  and a facet engaging end with screw holes  28 . The lamina engaging end  30  has a hook extension  26  which engages the lamina end into the space  27 . The facet engaging end also has a perpendicular extension  29 . In a variation of the above embodiment as seen in  FIG. 15 , comprising of a lamina engaging end  32  and a facet engaging end  31  without an appendage. Other embodiments of the plate can comprise of spikes or clamps at the lamina or facet bone engaging ends with or without screw placement. 
     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. 16 and 17 , the plate has a top surface  33  and screw holes at both ends  34  and  35 . The appendages  36  and  37  secure the displaced lamina and the curvatures at both ends  38  and  39  allow attachment to the lamina. The implanted plate is shown in  FIG. 20  with bone screws  51  and  52  securing it to the lamina on both sides. 
     In another embodiment as illustrated in  FIGS. 18 and 19 , the plate is curved at the ends  47  and  48 . The plate has a top surface  44  with bone screw holes  41  and  42  for laminar fixation and holes  40  and  43  for facet fixation on both sides. The appendages  45  and  46  secure the displaced lamina. The implanted plate is shown in  FIG. 21  with bone screws  53  and  54  securing it to the facets on both sides. 
     The trap door laminoplasty implant can comprise of straight or curved appendages.  FIGS. 22 and 23  illustrates the implant with a central portion  55  and angled ends  56  and  57  with screw holes  60  and  61  for fixation to the lamina. The appendages  58  and  59  in the middle are straight.  FIG. 24  illustrates the implant with curved appendages  62  and  63 . Other embodiments of the implant can also comprise of hook shaped appendages to secure the lamina ends. 
     In one embodiment of the trap door laminoplasty fusion device as illustrated in  FIGS. 25-27 , the device has a spacer in the middle  64 , an end  65  that engages with the facet, and an end  66  that engages with the displaced lamina edge. The plates at the distal ends are angled upwards  67  at one end with screw holes  69  to allow fixation to the facet via a screw and angled downwards  68  with screw holes  70  to allow fixation to the lamina via a screw. The spacer  64  in the middle is attached to the plate with a screw through the screw hole  71 . The spacer is made of a fusion material like allograft bone, autograft bone, xenograft bone, bone morphogenic protein, or hydroxyapatite to fuse the lamina in the fixed position provided by the device. 
     In another embodiment of the trap door laminoplasty fusion device as illustrated in  FIGS. 28-30 , the device has a spacer in the middle with a top surface opening  79 , one end  74  that engages with the facet, and another end  73  that engages with the lamina. The plate is angled upwards  76  at one end with screw holes  78  to allow fixation to the facet via a screw and angled downwards  75  at the other end with screw hole  77  to allow fixation to the lamina via a screw. The spacer in the middle is hollow  80  with a top contiguous with the plate. The hollow spacer has open ends  73  and  74 . The spacer can be packed with a fusion material like allograft or autograft bone, bone morphogenic protein, or hydroxyapatite to fuse the lamina to the facet in the fixed position provided by the device. The spacer has a partial or complete opening  79  at the top to allow for packing of the bone fusion material and a solid floor  81  to prevent migration of the fusion material into the spinal canal. 
     In one embodiment of the open door laminoplasty fusion device as illustrated in  FIGS. 31-33 , the device has a spacer  89  in the middle with a top surface opening  82 , one end  83  and another end  84  that engage with the lamina. The plate is angled downwards  85  and  86  at both ends with screw holes  87  and  88  to allow fixation to the lamina via a screw. The spacer  89  in the middle is hollow  90  with a top contiguous with the plate. The hollow spacer has open ends  83  and  84 . The spacer can be packed with a fusion material like allograft or autograft bone, bone morphogenic protein, or hydroxyapatite to fuse the lamina in the fixed position provided by the device. The spacer has a partial or complete opening  82  at the top to allow for packing of the bone fusion material and a solid floor  91  to prevent migration of the fusion material into the spinal canal. 
     In another embodiment of the open door laminoplasty fusion device as illustrated in  FIG. 34 , the device has downward angled distal ends  92  and  94  and a bone fusion spacer  93  in the middle attached to the central plate portion  31  with a biocompatible adhesive. 
     In another embodiment as shown in  FIGS. 35-37 , the plate at the distal ends is angled with screw holes  96  and  98  to allow fixation to the lamina via screws. The spacer  93  in the middle is attached to the plate with a screw through the central plate screw hole  97 . The spacer ends  99  and  100  engage the lamina ends. The spacer is made of a fusion material like allograft bone, autograft bone, or bone morphogenic protein. The open door laminoplasty technique as shown in  FIG. 37  involves removal of the spinous process and creation of unicortical laminoplasty grooves  101  and  102  at the junction of the lamina and facet on both sides. The displaced lamina are then maintained in that position with the device with a spacer in the middle secured to the plate with the bone screw  105 . The fusion device also has plates with bone screw receiving holes that allow fixation of the plate with bone screws  103  and  104  securing the device to the lamina. 
     In another embodiment of the open door laminoplasty fusion device as illustrated in  FIGS. 38-40 , the device has a spacer  106  in the middle with a top surface opening  107 , one end  108  and another end  109  that engage with the lamina. The plate has a lazy L-shape  110  and  111  on both sides with screw holes  112  and  113  to allow fixation to the facets via a screw. The spacer  106  in the middle is hollow with a top contiguous with the plate. The hollow spacer has open ends  108  and  109 . The spacer can be packed with a fusion material like allograft or autograft bone, bone morphogenic protein, or hydroxyapatite to fuse the lamina in the fixed position provided by the device. The spacer has a partial or complete opening  107  at the top to allow for packing of the bone fusion material and a solid floor  114  to prevent migration of the fusion material into the spinal canal. 
     In another embodiment of the laminoplasty fusion device for the open door laminoplasty technique as illustrated in  FIGS. 41-44 , the device has a spacer in the middle  117  and ends  115  and  116  that engage with the facet with screws. The plates at the distal ends are angled both ends with screw holes  119  and  120 . The spacer  64  in the middle is attached to the plate  118  either with a biocompatible adhesive as shown in  FIG. 41  or a screw placed through the central plate hole  121 . The spacer is made of a fusion material like allograft bone, autograft bone, xenograft bone, bone morphogenic protein, or hydroxyapatite to fuse the lamina in the fixed position provided by the device. The plate also has screw holes  122  and  123  if needed for screw placement into the lamina.  FIG. 44  illustrates the lamina fusion device in place following an open door laminoplasty. The displaced lamina are then maintained in that position with a lamina fixation device with a spacer in the middle  117  with the plate fixated to the facets through bone screws  124  and  125 . 
     The length of the plates as well as the spacer can vary depending on the laminar displacement desired by the surgeon with either the open door or trap door laminoplasty technique. 
     The laminoplasty plates can be made of metal, polymers, ceramics, composites, and/or any bio-compatible material with sufficient strength to maintain the open position of the divided lamina. The plates can be constructed of titanium or titanium alloy for MRI imaging compatibility. It could also be made of a bio-absorbable material (polyesters, poly amino acids, polyanhydrides, polyorthoesters, polyurethanes, polycarbonates, homopolymers, copolymers of poly lactic acid and poly glycolic acid, copolyesters of e-caprolactone, trimethylene carbonate, and para-dioxanone), or allograft or xenograft bone that is absorbed by the body over time once the divided lamina have fused. Alternatively, it could be made of a radiolucent material (polyetheretherketone), plastic, or a combination of plastic and metal to reduce CT and MRI imaging artifact. 
     The laminoplasty plates can be of a unitary construction, such that the spacer portion, lamina engaging portions and/or the facet engaging portions can be integral or formed from a single piece of material. Alternative embodiments contemplate that the components of the laminoplasty plate can be non-integral, and can be attached to and/or coupled to other components of laminoplasty plate. 
     The spacer can be made of any bio-compatible material, including autograft, allograft or xenograft, and can be resorbable or non-resorbable in nature. Bone fusion material can include demineralized bone matrix, bone morphogenic protein, hydroxyapatite, and combinations thereof. Resorbable materials can include polylactide, polyglycolide, tyrosine-derived polycarbonate, polyanhydride, polyorthoester, polyphosphazene, calcium phosphate, hydroxyapatite, bioactive glass, and combinations thereof. Further examples of non-resorbable materials are non-reinforced polymers, carbon-reinforced polymer composites, PEEK (polyetheretherketone), and PEAK (polyaryletherketone) composites, shape-memory alloys like nitinol, titanium, titanium alloys, cobalt chrome alloys, stainless steel, ceramics and combinations thereof and others as well. 
     While the present invention has been described in conjunction with preferred embodiments and methods, it is intended that the description and accompanying drawings shall be interpreted as only illustrative of the invention. It is evident that those skilled in the art may make numerous uses and modifications of and departures from the specific embodiments described herein without departing from the inventive concept.