Cervical interbody device

[0001] 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.

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] The inventive spacer assembly can be used to replace either a surgically removed disk (diskectomy) or vertebra (corpectomy).

[0015] 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.

[0016] 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.

[0017] 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 110a and 112a, 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.

[0018] 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.

[0019] 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.

[0020] 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'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.

[0021] 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 310a and 312a 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 310a and 312a 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. 310a), while the posterior side of each ridge (e.g. side 323) forms an angle greater than 90 degrees with the plane (e.g. 310a) 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.

[0022] 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 410a and 412a 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 410b, 412b which define openings 410c, 412c 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 410b, 412b so as to abut the vertically adjacent vertebrae (not shown) above and below end pieces 410, 412. The spaces 410c, 412c permit the solid bone to fuse and heal with the adjoining vertebrae.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.