Abstract:
A modular implant for stabilizing the relative motion of spinal vertebrae comprises at least two pairs of plates which connect to two adjacent spinous processes, a spacer configured to be positioned between the spinous processes, and a fastener which pivotably connects to the plates and the spacer. The spacer is interchangeable and may comprise a variety of materials, each providing a different level of elasticity to the spinous processes. Relative motion between vertebrae can also be controlled by varying the surface configuration of the plates and by varying threading of the fastener. Several implants may be linked to provide stabilization across multiple vertebral levels, and the relative motion provided at each vertebral level may differ. A method for revising the implant is provided which comprises accessing the implant and replacing the spacer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the following, which is incorporated herein by reference: 
     Pending prior U.S. Provisional Patent Application No. 60/803,594, filed May 31, 2006 by T. Wade Fallin et al., which carries Applicants&#39; docket no. MLI-57 PROV, and is entitled SYSTEM AND METHOD FOR SEGMENTALLY MODULAR SPINAL PLATING. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates generally to spinal orthopedics, and more specifically, to posterior implants designed to dynamically stabilize or immobilize one or more spinal motion segments. 
     2. The Relevant Technology 
     Orthopedic medicine provides a wide array of implants that can be attached to bone to alleviate various pathologies. Due to the degeneration of spinal tissues, it can be desirable to dynamically stabilize, or even immobilize, adjacent vertebral levels. Unfortunately, currently available implants are often usable only to treat a very narrow range of pathologies. Many such devices are also bulky, difficult to implant, or difficult to revise. There is a need in the art for posterior spinal implants capable of providing dynamic stabilization at a desired level of stiffness so that a variety of pathologies can be treated via first implantation or revision. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. 
         FIG. 1  is a posterior view of a segmentally modular spinal plating system fixed to a portion of the spine. 
         FIG. 2  is a posterior view of the segmentally modular spinal plating system of  FIG. 1 , which includes a spacer assembly, a pair of straight plates, a pair of jogged plates, and three fasteners. 
         FIG. 3  is a perspective view of the spacer assembly of  FIG. 2 . 
         FIG. 4  is a perspective view of the straight plates of  FIG. 2 . 
         FIG. 5  is a perspective view of the jogged plates of  FIG. 2 . 
         FIG. 6  is a posterior view of a partial assembly of one straight plate of  FIG. 4  joined by a fastener to one jogged plate of  FIG. 5 . 
         FIG. 7  is a posterior view of the partial assembly of  FIG. 6 , joined to the spacer assembly of  FIG. 3 . 
         FIG. 8  is a posterior view of the partial assembly of  FIG. 7 , joined to an additional straight plate and an additional jogged plate. 
         FIG. 9  is a posterior perspective view of the segmentally modular spinal plating system of  FIG. 1 . 
         FIG. 10  is a posterior perspective view of a two-level segmentally modular spinal plating system fixed to a portion of the spine. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to systems and methods for stabilizing the relative motion of spinal vertebrae. Those of skill in the art will recognize that the following description is merely illustrative of the principles of the invention, which may be applied in various ways to provide many different alternative embodiments. 
     Referring to  FIG. 1 , a posterior view illustrates a segmentally modular spinal plating system  10  affixed to a portion of the lumbar spine. The system  10  comprises a non-threaded straight plate  12 , a singly-threaded straight plate  13 , a non-threaded jogged plate  14 , a doubly-threaded jogged plate  15 , and a spacer assembly  16 . The straight plates  12 ,  13  lie on both lateral sides of the spinous process  2  of the lower vertebra, and are connected by a fastener  18  which passes through the non-threaded straight plate  12 , through the spinous process  2 , and through the singly-threaded straight plate  13 . The jogged plates  14 ,  15  lie on both lateral sides of the spinous process  4  of the adjacent vertebra above and are connected by a fastener  20  which passes through the non-threaded jogged plate  14 , through the spinous process  4  and through the doubly-threaded jogged plate  15 . Between the two spinous processes  2 ,  4 , the spacer assembly  16  is connected to both of the straight plates  12 ,  13  and both of the jogged plates  14 ,  15  by a fastener  22 . The fastener  22  lies transverse to the spinal column on an axis about which the plates can pivot; this axis extends along the medial/lateral direction (i.e., left-to-right when viewing  FIG. 1 ). 
     Referring to  FIG. 2 , an enlarged posterior view illustrates the segmentally modular spinal plating system  10  in more detail. The two straight plates  12 ,  13  are secured by a fastener  18 . The two jogged plates  14 ,  15  are secured by a fastener  20 . “Jogged plates” refers to plates which are not planar between two ends, but are non-planar or bent between two ends. The straight plates  12 ,  13  and the jogged plates  14 ,  15  are linked together by the spacer assembly  16 . In the embodiment depicted in  FIG. 2 , the spacer assembly  16  includes a spacing member  40  and a rim cap  42 . The spacer assembly  16  is threaded on the fastener  22 . In alternative embodiments, the spacer assembly  16  is a one-piece unitary construct. In the embodiment depicted, the fasteners  18 ,  20 ,  22  are threaded bolts. In alternative embodiments, the fasteners  18 ,  20 ,  22  need not be threaded bolts but could be non-threaded bolts, bolts with nuts, screws, pins, or rivets, among others. 
       FIG. 3  illustrates the spacer assembly  16  in an enlarged perspective view. The spacing member  40  is generally tubular in form; however, the shape of the spacing member  40  is such that it best conforms to the morphology of the area on the spinous processes  2 , 4  which it contacts and can be other non-circular, more organic, bone conforming shapes. The spacing member  40  has an outer end  44  and an inner end  46 . The outer end  44  is wider in diameter than the rest of the spacing member  40 , and forms a flange-like shape along a rim  48 . A radial spline  50  occupies an outer interface surface  49  of the rim  48 . A bore  52  extends through the longitudinal center of the spacing member  40 . The outer cylindrical wall of the spacing member is a bearing surface  54 . 
     The rim cap  42  is generally flat and circular, and has an inner side  56  and an outer interface side  58 . Depressed into the inner side  56  is a concavity  64 . A diameter of the concavity  64  is sized to hold the inner end  46  of the spacing member  40 . A radial spline  60  (not visible in  FIG. 3 ) occupies an outer interface surface  59  of the outer side  58 . A bore  62  runs through the center of the rim cap  42 . 
     When implanted as part of the segmentally modular spinal plating device  10 , the spacing member  40  (particularly the bearing surface  54 ) and the rim cap  42  come in contact with the sides and outer edge of the spinous processes  2 ,  4  as seen in  FIG. 1 . To serve different stabilization purposes, the spacing member  40  and rim cap  42  may be composed of a variety of materials. If dynamic stabilization is desired, the spacing member  40  and rim cap  42  can be composed of a semi-rigid, elastically compliant biocompatible polymer such as polyurethane or the spacing member  40  may be designed with spring elements (not shown) that allow flexibility and compressibility of the spacer assembly  16  when it is loaded by the spinous processes  2  and  4 . If stabilization is desired, the spacing member  40  and rim cap  42  can be composed of a substantially rigid biocompatible materials including metals such as titanium, cobalt chromium alloys, stainless steel alloys or the like or other substantially rigid materials such as PEEK, Ultra High Molecular weight polyethylene (UHMWPE), Delrin, ceramics, or other biocompatible structural engineering polymers or ceramics. If fusion is desired, the spacing member  40  and rim cap  42  may be composed of natural or synthetic bone material. Finally, if completely dynamic movement is desired, the device  10  may be implanted without a spacer  40  and rim cap  42 , and with a non-threaded rod replacing the fastener  22 . 
     Referring to  FIG. 4 , an enlarged view shows the non-threaded straight plate  12  and the singly-threaded straight plate  13 . The two straight plates  12 ,  13  are substantially identical to each other in shape and are symmetrical from side to side. The only difference between the straight plates  12 ,  13  is whether or not the bores in the plates are threaded. Each straight plate  12 ,  13  has a substantially planar, elongated elliptical shape with an outer facing side  72  and an inner facing side  74 . The center of each straight plate  12 ,  13  is a planar member  76 , which is terminated at one longitudinal end by a first annulus  78 . A non-threaded bore  80  perforates the first annulus  78 . An outer facing radial spline  82  is an outer interface surface  79  of the first annulus  78 , and an inner facing radial spline  84  is on an inner interface surface  81  of the first annulus  78 . 
     The opposite longitudinal end of the planar member  76  is terminated by a second annulus  88 . On the non-threaded straight plate  12 , a non-threaded bore  90  perforates the second annulus  88 . On the singly-threaded straight plate  13 , a threaded bore  96  perforates the second annulus  88 . An outer facing radial spline  92  is on an outer interface surface  89  of the second annulus  88 , and an inner facing radial spline  94  is an inner interface surface  91  of the second annulus  88 . Because the non-threaded straight plate  12  has two non-threaded bores  80 ,  90 , and is otherwise symmetrical, it may be turned side to side or end to end prior to assembly in the device  10 . However, the singly-threaded straight plate  13  has one non-threaded bore  80  and one threaded bore  96 . Thus, it may be turned side to side but not end to end to be properly assembled in the device  10 . 
       FIG. 5  displays the two jogged plates  14 ,  15 . As with the straight plates  12 ,  13 , the jogged plates  14 ,  15  are identical to each other except for the threading of the bores. Each jogged plate  14 ,  15  has an outer facing side  102  and an inner facing side  104 . A central jogged member  106  terminates at one longitudinal end at a first annulus  108 . On the non-threaded jogged plate  14 , a non-threaded bore  110  perforates the first annulus  108 . On the doubly-threaded jogged plate  15 , a threaded bore  116  perforates the first annulus  108 . On both jogged plates  14 ,  15  an outer facing radial spline  112  is on an outer interface surface  109  of the first annulus  108 , and an inner facing radial spline  114  is on an inner interface surface  111  of the first annulus  108 . 
     The opposite longitudinal end of the jogged member  106  is terminated at a second annulus  118 . On the non-threaded jogged plate  14 , a non-threaded bore  120  perforates the second annulus  118 . On the doubly-threaded jogged plate  15 , a threaded bore  126  perforates the second annulus  118 . On each jogged plate  14 ,  15 , an outer facing radial spline  122  is on an outer interface surface  119  of the second annulus  118 , and an inner facing radial spline  124  is on an inner interface surface  121  of the second annulus  118 . Because of the non-planar configuration of the jogged plates, the jogged plates  14 ,  15  cannot be turned side to side or end to end but must be specifically oriented to be properly assembled in the system  10 . 
       FIGS. 6 through 9  show the steps in assembly of the device  10 .  FIG. 6  depicts the fastener  22  with the non-threaded straight plate  12  and the non-threaded jogged plate  14 . During assembly, first the non-threaded jogged plate  14  is placed onto the fastener  22 . A threaded shaft  32  of the fastener  22  is placed through the bore  120  of the second annulus  118 , from the outer facing side  102  to the inner facing side  104 . The non-threaded jogged plate  14  is slid along the shaft  32  until the second annulus  118  contacts a fastener head  34 . 
     Following placement of the non-threaded jogged plate  14  as described above, the non-threaded straight plate  12  is put onto the fastener  22 . The bore  80  on the first annulus  78  is slid along the threaded shaft  32 , until the first annulus  78  contacts the non-threaded jogged plate  14 . At this point, the inner radial spline  124  of the non-threaded jogged plate  14  engages with the outer radial spline  82  of the non-threaded straight plate  12 , causing the plates  12 ,  14  to releasably lock into place relative to one another. The interaction of the radial splines  124 ,  82  allows for very precise adjustment to obtain the desired length of the device  10 . During the implantation process, the angle at which the plates  12 ,  14  engage may be adjusted by pulling the plates apart, rotating one plate or another around the shaft  32  until the desired position of the plates about the axis is found, then pushing the plates  12 ,  14  back together so that the radial splines  82 ,  124  engage. Because the bores  80 ,  120  of the plates  12 ,  14  are not threaded, they can freely rotate around the shaft  32  until locked into place by meshing the splines. Adjusting the angle of the plates  12 ,  14  about the axis adjusts the length of the device  10 . The axis is defined by interaction between the bores of the plates and the outer surface of the fastener shaft  32 . 
       FIG. 7  illustrates the addition of the spacer assembly  16  to the partial assembly depicted in  FIG. 6 . The bore  52  of the spacer member  40  is slid onto the threaded shaft  32  of the fastener  22 . The spacer member  40  is slid onto the fastener  22  until the outer radial spline  50  of the spacer member  40  engages with the inner radial spline  84  of the non-threaded straight plate  12 . The rim cap  42  is then slid onto the fastener  22 . The bore  62  of the rim cap  42  is slid onto the threaded shaft  32  of the fastener  22 , until the concavity  64  fits over the inner end  46  of the spacer member  40 . Alternatively, the spacer member  40  and the rim cap  42  may first be press fit or threaded together, with the inner end  46  fitting into the concavity  64 , and then slid as a single piece onto the fastener  22 . 
     Referring to  FIG. 8 , the singly-threaded straight plate  13  and the doubly-threaded jogged plate  15  are shown as added to the partial assembly depicted in  FIG. 7 . The non-threaded bore  80  of the first annulus  78  on the singly-threaded straight plate  13  is slid onto the threaded shaft  32  (not visible) of the fastener  22 . When the first annulus  78  contacts the rim cap  42 , the inner radial spline  84  of the singly-threaded straight plate  13  engages with the outer radial spline  60  on the rim cap  42 . In the manner described above, during implantation the singly-threaded straight plate  13  may be rotated around the threaded shaft  32  until the desired position about the axis is achieved, before the meshing of the splines  60 ,  84  releasably locks the singly-threaded plate  13  into place. 
     The doubly-threaded jogged plate  15  is the last plate to be added to the assembly. The threaded bore  126  on its second annulus  118  is screwed onto the threaded shaft  32 , until the inner radial spline  124  engages with the outer radial spline  82  on the singly-threaded straight plate  13 . As with plates  12  and  14 , plates  13  and  15  may be adjusted about axis until the desired angle and length for the device  10  is found. 
       FIG. 9  depicts the system  10  as fully assembled, with the fasteners  18  and  20  in place. Before the fasteners  18 ,  20  are added, the partially assembled system  10  is placed on the spine so that the spacing member  40  is between the spinous processes  2 ,  4  of the vertebrae. The two first annuli  108  of the jogged plates  14 ,  15  extend in a cephalad direction on either side of the upper spinous process  4 . The two second annuli  88  of the straight plates  12 ,  13  extend in a caudal direction on either side of the lower spinous process  2 . The threaded shaft  24  of the fastener  18  passes through the non-threaded bore  90  of the non-threaded straight plate  12 , through the spinous process  2  of the lower vertebra, then screws into the threaded bore  96  of the singly-threaded straight plate  13 . The engagement of the threads on the threaded shaft  24  with the threads in the threaded bore  96  tightens the fastener  18  in place. Similarly, the threaded shaft  26  of the fastener  20  passes through the non-threaded bore  110  of the non-threaded jogged plate  14 , through the spinous process  4  of the upper vertebra, then screws into the threaded bore  116  of the doubly-threaded jogged plate  15 . The engagement of threads on the threaded shaft  26  with the threads in the threaded bore  116  tightens the fastener  20  into place. In the embodiment depicted, fasteners  18  and  20  pass through the spinous processes  2  and  4  to fasten the plates to the spinous processes. However, in other embodiments, other means of attachment may be used to fasten the plates to the spinous processes, such as bands, clamps, cables, wire, and sutures, among others. 
       FIG. 10  illustrates a two-level segmentally modular spinal plating system  210  fixed in place in a portion of the spine. The system  210  comprises a single level system  10 , plus two additional non-threaded straight plates  12 , an additional singly-threaded straight plate  13 , a doubly-threaded straight plate  17 , an additional spacer assembly  16 , and two additional fasteners. A non-threaded straight plate  12  and the doubly-threaded straight plate  17  are added to the upper level of the single level system  10 , and connect the single level system  10  to an additional fastener  22 . The fastener  22  retains the non-threaded straight plate  12 , a second non-threaded straight plate  12 , a spacer assembly  16 , a singly-threaded straight plate  13 , and the doubly-threaded straight plate  17 . The spacer assembly  16  fits between the spinous processes  4  and  6 . A final fastener  18  retains one non-threaded straight plate  12  and the singly-threaded straight plate  13 . When a two level system  210  is utilized, the two spacer assemblies  16  may be composed of like material to provide similar stabilization between all involved vertebrae, or the two spacer assemblies  16  may be of different materials to provide different types of stabilization between the different vertebrae. The two level system  210  enables stabilization between three vertebrae; additional levels may be added if desired, again with interchangeable spacer assemblies  16 . 
     The embodiments depicted in  FIGS. 1 through 10  utilize a threaded bolt for each of the fasteners  18 ,  20 ,  22 , and plates  12 ,  13 ,  14 ,  15  with bores that are threaded or not threaded. An alternative embodiment could have bolt fasteners that are shallowly threaded along most of the shaft, and deeply threaded at the end of the shaft. In this alternative, all the bores of the plate could be threaded, but only the plates that connect at the end of the shaft (the outermost plates) would threadably engage the shaft (where the shaft is deeply threaded) and tighten onto the fastener. In yet another alternative, the plates need not be threaded at all but a threaded nut could be added on the end of the threaded fastener shaft to tighten all the components together. 
     Another alternative embodiment (not shown) does not have radial splines on the outer or inner interface surfaces of the plates or other means of regulating movement between the plates. This allows for dynamic movement between the plates since the interface between the plates is not restricted by any mechanism that prevent rotation or sliding between the plates. Plates according to this alternative embodiment, when used in conjunction with a more elastically compliant spacer, allow for more dynamic movement between vertebrae. 
     Another embodiment (not shown) permits dynamic movement between the plates, as in the embodiment of the preceding paragraph, and also provides resilient force, for example, via the addition of springs, to stabilize such dynamic movement. For example, torsional springs (not shown) may be registered on the plates  12 ,  14 , on the plates  13 ,  15 , or at the junctions between both pairs of plates  12 ,  14 ,  13 ,  15 . In the alternative, damping force may be applied to the motion between the plates  12 ,  14 ,  13 ,  15 , for example, through the use of a frictional yet movable interface (not shown) such as frictional coatings on the various interface surfaces of the plates  12 ,  14 ,  13 ,  15 , or a sealed chamber containing a viscous fluid and a damper that moves through the fluid in response to relative rotation between the plates  12 ,  14 ,  13 ,  15  (not shown). These are merely examples; those of skill in the art will recognize that many other mechanisms may be used to provide resilient force, damping force, or some combination of the two between the plates  12 ,  14 ,  13 ,  15  to control relative motion between the spinous processes  2 ,  4 . 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. It is appreciated that various features of the above-described examples can be mixed and matched to form a variety of other alternatives, each of which may have different plates, spacer assembly or threading system according to the invention. As such, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.