Abstract:
An interbody spacer assembly includes a pair of end pieces spaced apart by a connector extending between them. The end pieces extend generally parallel to the end plates of adjoining vertebral bodies. Fasteners connect the end pieces to the vertebral bodies. Bone graft material or solid bone can be placed in the interior space defined by the end pieces and connector, which bone graft material or solid bone eventually fuses together and to the adjoining end plates through the end pieces.

Description:
This invention relates to cervical spine supports, and, in particular, to a device that acts as a spacer between cervical vertebral bodies so that bone graft material inserted within the device can fuse and replace pathological bone removed surgically. 
   BACKGROUND OF THE INVENTION 
   It is known in the prior art to use cage-like spacers made of titanium mesh in tube shapes between vertebrae to provide support to the cervical spine. Spacers are needed when either the vertebrae or disk are removed for pathological reasons due to injury or disease. One such spacer  10  is shown in  FIGS. 6 and 7 . Such prior art spacers are typically formed from a mesh  12  rolled into a tube extending longitudinally for the length of the removed vertebrae or disk. Rings  14  on both ends  16 ,  18  are intended to reinforce the mesh and maintain the desired diameter of the spacer and also connect to adjacent vertebrae with screws  20 . Spacer  10  is filled with granular bone tissue which eventually fuse or graft together and with the healthy tissue above and below the spacer. The spacer maintains the granular bone tissue in place until the graft is complete. The prior art spacers are difficult to install between existing vertebrae and difficult to satisfactorily fill with such bone tissue. The corrugated ends  22  of the mesh often catch adjoining tissue as the spacer is being implanted between the desired vertebrae. The reinforcing rings  14  tend to collapse into the adjacent vertebrae and damage them, i.e., subsidence. The granular bone tissue placed within the mesh tends to fall out of the mesh during the positioning process, and the mesh makes it difficult to refill the spacer with additional bone tissue. Gaps between the bone tissue inside the cage often result, which cannot be readily detected or remedied. Consequently, the grafting process is slowed or results in a weakened graft or incomplete fusion and malalignment due to these gaps. 
   Consequently, a need exists for, and it is an object of this invention to provide, an improved cervical interbody device that is easier to install between cervical vertebral bodies and results in a stronger and more reliable graft. 
   SUMMARY OF THE INVENTION 
   According to the present invention, a spacer assembly is provided for use in spinal surgeries. The spacer assembly comprises two end pieces for interfacing with the end plates of adjacent vertebrae. Each end piece is generally disk-like in form and includes an inner surface facing the interior of the spacer and an outer surface facing the adjacent vertebrae. Each end piece has attached thereto a flange that extends longitudinally and exteriorly of the end piece. The end pieces are spaced and reinforced by one or more connectors. The spacer assembly engages the adjacent vertebral disks by engaging each flange with the adjacent vertebrae to couple the assembly and vertebrae together. The spacer assembly defines an interior region that is filled with morselized bone graft, structural bone graft, biologic fusion materials, or solid bone to fuse together and with the adjacent vertebrae, thereby replacing pathological bone or disk material removed surgically. 
   In a preferred embodiment, the end pieces are contoured to conform to the spinal cord. The end pieces are further designed to promote bone growth into the adjacent areas by, for instance, including apertures or an opening between the interior region and the vertebrae. 
   The inventive spacer assembly can be used to replace either a surgically removed disk (diskectomy) or vertebra (corpectomy). 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front perspective view of the invention implanted in the spine. 
       FIG. 2  is a side perspective view of the invention with the surrounding spine tissue partially cut-away. 
       FIG. 3  is a perspective view of second embodiment of the invention. 
       FIG. 4  is a perspective view of a third embodiment of the invention not yet implanted in the spine. 
       FIG. 5  is a partial side elevation view of an end piece of the embodiment of  FIG. 4  which is not yet positioned in the spine as viewed along line  5  of  FIG. 4 . 
       FIG. 6  is a top perspective view of a prior art spacer. 
       FIG. 7  is a side perspective view of a prior art spacer. 
       FIG. 8  is a perspective view of a fourth embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As seen in  FIGS. 1 ,  2 , the inventive spacer assembly  100  includes an upper end piece  110  and a lower end piece  112  with connector  118  therebetween. The assembly  100  is located between the vertebral bodies of a spine  116  during surgery to maintain the vertebrae in a spaced-apart configuration. End pieces  110 ,  112  of the present invention are substantially parallel to the adjoining surfaces (often referred to as “end plates”) of the vertebral bodies  128 ,  129  and are shaped and dimensioned to closely match the cross-sectional shape and dimensions of the end plates. 
   Connectors  118  comprise one or more rigid or semi-rigid posts for maintaining a desired distance between the end pieces  110 ,  112 . For example, titanium posts  118 , as seen in  FIGS. 1 and 2 , maintain the spacing between the end pieces so that granular bone material can be inserted between the end pieces in the interior region  114  defined by the assembly  100 . The connectors  118  may be of equal length or they may be of different lengths. For example, if the anterior connectors (i.e. those farthest from the spinal cord  140 ) are longer than the posterior connectors (i.e. those closest to the spinal cord  140 ), lordosis can be maintained or restored. When the connectors are not of equal lengths, the end pieces are not parallel to each other, and that non-parallel relationship would be preferred in most cases to accommodate the natural curvature of the spine. 
   The end pieces  110 ,  112  are approximately disk-shaped to conform to the cross-sectional shape of the end plates of the adjacent vertebrae. The exterior surfaces  110   a  and  112   a , respectively, of end pieces  110  and  112  interface with the end plates of adjacent vertebrae  128 ,  129 . The end pieces are preferably contoured at  132 ,  134  to avoid compressing or otherwise affecting the spinal cord  140 . 
   The interior region  114  between end pieces  110 ,  112  is substantially open around its circumference, and it can be easily filled with bone graft tissue to fuse to vertebral bodies  128 ,  129  of spine  116 . The end pieces  110 ,  112  contain apertures  126  extending through their thickness to allow the bone graft tissue to grow through the end pieces and into the adjacent vertebrae, and thereby providing direct contact between the bone graft tissue and the adjoining vertebrae. 
   The end pieces  110 ,  112  have attached flanges  142 ,  144  projecting perpendicularly and exteriorly away from the end pieces  110 ,  112 , respectively, and the flanges  142 ,  144  are located circumferentially around an anterior portion of the end pieces  110 ,  112 , respectively. The flanges act as stops to engage the assembly in proper position relative to the spine. They also prevent retropulsion or compression of the spinal cord, which can occur if the assembly were to slide too far into the spine toward the spinal cord  140  or otherwise shift out of place. The flanges have holes  150 ,  152  for receiving screws  136 ,  138  of the type customarily used in spine surgeries. These screws  136 ,  138  are screwed into the adjacent vertebral bodies  128 ,  129  respectively, preferably with commonly available locking mechanisms, to secure the spacer assembly in place relative to the spine. Alternatively, screws could be located through apertures in the end pieces and directly into the vertebrae. Preferably, the screws are inserted through the flange at an angle toward or away from the adjoining end piece, rather than parallel thereto, to increase the stability of the device and reduce the possibility of inadvertent displacement. 
   A second embodiment of the invention is shown in  FIG. 3 . The spacer assembly  200  includes a pair of end pieces  210 ,  212  spaced apart by a connector  220 . The connector  220  is in the form of a contoured wall that connects the end pieces at their peripheries where the end pieces are likewise contoured, i.e. at  232 ,  233 . This embodiment also includes a mesh  221  that partially but does not entirely surround interior region  214  between the end pieces where the bone graft tissue is located and spans the distance between the end pieces. This mesh  221  is preferably located at the anterior side of assembly  200  and helps retain the bone graft tissue and prevent it from dislodging during implantation of the assembly  210 . The mesh is held in place relative to the rest of assembly  210  by screws  236 ,  238  extending through the mesh, through holes  250 ,  252  of flanges  242 ,  244 , and finally into the adjacent vertebrae. Thus, the mesh can be installed after the bone graft tissue is positioned. Like the first embodiment, end pieces  210 ,  212  each include multiple apertures  226  to permit the bone graft tissue in region  214  to fuse with the adjacent vertebrae. The remaining region  214  is not surrounded by mesh because a patient&#39;s muscle tissue along the spine will partially enclose the area  214 . Preferably, mesh  221  has an arcuate width that is slightly larger than the arcuate width of flanges  242 ,  244 . The connector  220  is located at the posterior side of the assembly, closest to the spinal cord, where it protects the spinal cord from the bone graft tissue. This embodiment can be supplemented with anteriorly-located connectors in the form of posts, such as those shown in  FIGS. 1 ,  2 ,  4 , if desired for additional strength. 
   A third embodiment of the invention appears in  FIGS. 4 ,  5 . This embodiment is a spacer assembly  300  that is essentially the same as the first embodiment, except that the exterior surfaces  310   a  and  312   a  of end pieces  310  and  312 , respectively, are roughened or formed with alternating ridges  315  and valleys  317 . The ridges are angled relative to the planes of surfaces  310   a  and  312   a  so that the peak  319  of each ridge  315  is on the anterior side (i.e. farthest from the spinal cord) of the ridge. Stated differently, the ridges are slanted so that the anterior side of each ridge (e.g. side  321 ) forms an angle less than 90 degrees with the plane of the exterior surface of the end piece (e.g.  310   a ), while the posterior side of each ridge (e.g. side  323 ) forms an angle greater than 90 degrees with the plane (e.g.  310   a ) of the exterior surface of the end piece. This arrangement permits the assembly  300  to easily slide laterally in the direction of arrow A between the spaced vertebrae  328 ,  329 , while also resisting lateral movement in the opposite direction away from the spaced vertebrae. This helps prevent inadvertent dislocation of the assembly away from the desired position between the vertebrae. 
   A fourth embodiment of the invention is shown in  FIG. 8 . In this embodiment, the spacer assembly  400  includes a pair of U-shaped end pieces  410 ,  412  which are spaced apart by a connector  420 . The connector is the form of a contoured wall that connects the end pieces at their peripheries where the end pieces are closed and likewise contoured, i.e. at  432 ,  433 . The end pieces include alternating ridges  415  and valleys  417 , which are angled relative to the planes of exterior surfaces  410   a  and  412   a  of end pieces  410  and  412 , respectively, similar to the ridges, valleys and planes of the third embodiment ( FIG. 5 ). The U-shaped end pieces each have a pair of arms  410   b ,  412   b  which define openings  410   c ,  412   c  between the arms. These openings communicate with open interior region  414 , which is between end pieces  410 ,  412  and partially bounded by connector  420 . This embodiment is therefore adapted to receive solid, whole pieces of bone (not shown) rather than bone graft pieces. The solid bone can be inserted into region  414  and between arms  410   b ,  412   b  so as to abut the vertically adjacent vertebrae (not shown) above and below end pieces  410 ,  412 . The spaces  410   c ,  412   c  permit the solid bone to fuse and heal with the adjoining vertebrae. 
   The end pieces and flanges are desirably composed of titanium or a bioabsorbable material, but they may also be composed of other rigid materials such as other metals and plastics. There is no need for adjuvant fixation, such as with a plate or another device to stabilize the position of the assembly. 
   The end pieces, flanges and connectors can be formed integrally, or they can be modular. A modular construction more easily permits the use of different size end pieces in the same assembly, as well as different length connectors. 
   The present invention has been described in connection with cervical vertebral bodies, but the same invention could be applied to the thoracic and lumbar spine by simply varying the shapes and dimensions of the components to correspond to the shapes and dimensions of the thoracic and lumbar vertebrae. 
   It should be recognized that, while the invention has been described in relation to a preferred embodiment, those skilled in the art may develop a wide variation of structural details without departing from the principles of the invention. Accordingly, the appended claims are to be construed to cover all equivalents falling within the scope and spirit of the invention.