Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-10-04
2002-09-10
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S064000
Reexamination Certificate
active
06447544
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to interbody spinal fusion implants, and in particular to spinal fusion implants configured to restore and maintain two adjacent vertebrae of the spine in correct anatomical angular relationship.
2. Description of The Related Art
Both the cervical and lunbar areas of the human spine are, in a healthy state, lordotic such that they are curved convex forward. It is not uncommon that in degenerative conditions of the spine that lordosis is lost. This effectively shortens the spinal canal which decreases its capacity. Further, the absence of lordosis moves the spinal cord anteriorly where it may be compressed against the posterior portions of the vertebral bodies and discs. Finally, such a loss of lordosis disturbs the overall mechanics of the spine which may cause cascading degenerative changes throughout the adjacent spinal segments.
The surgical treatment of those degenerative conditions of the spine in which the spinal discs are in various states of collapse, and out of lordosis, commonly involves spinal fusion. That is the joining together of adjacent vertebrae through an area of shared bone. When the shared bone is in the area previously occupied by the intervertebral disc that is referred to as an interbody fusion. Further history in this regard is provided in application Ser. No. 08/263,952 entitled Artificial Spinal Fusion Implants (“Parent Application”) incorporated herein by reference.
The Parent Application taught the use of artificial spinal fusion implants that were capable of being placed between adjacent vertebrae, and which implants were capable of containing and providing fusion promoting substances including bone at the fusion site. These devices were further capable of restoring the height of the disc space and of supporting the spine, and were self-stabilizing as well as being stabilizing to the spinal area where implanted.
SUMMARY OF THE INVENTION
The present invention is directed to interbody spinal fusion implants having a structural configuration that provides for the maintaining and creating of the normal anatomic angular relationship of two adjacent vertebrae of the spine to maintain and create spinal lordosis. The spinal fusion implants of the present invention are sized to fit within the disc space created by the removal of disc material between two adjacent vertebrae and conform wholly or in part to the disc space created. The spinal fusion implants of the present invention have upper and lower surfaces that form a support structure for bearing against the end plates of the adjacent vertebrae. In the preferred embodiments, the upper and lower surfaces are disposed in a converging angular relationship to each other such that the implants of the present invention have an overall “wedged-shape” in an elevational side view. The angular relationship of the upper and lower surfaces places and maintains the vertebrae adjacent to those surfaces in an angular relationship to each other, creating and maintaining the desired lordosis.
The implants of the present invention may have surface irregularities to increase their surface area, and/or to further engage the adjacent vertebrae and to enhance stability. The lordotic implants of the present invention may have surface irregularities that are uniform in height along the longitudinal axis of the upper and lower vertebrae engaging surfaces, or may increase in height from one end of the implant to the other. That is, the implant body and the surface formed and the projections may be similarly wedged. The outer contour of the surface projections may be more or less rectangular while the underlying implant may be wedge-shaped; or the reverse wherein the underlying implant body is more or less rectangular while the contour of the surface projections are wedge-shaped from one end of the implant to the other.
The implants of the present invention have various faces which may be curved so as to conform to the shape of the vertebral surfaces adjacent to the area of the disc removal. Specifically the upper and/or lower surfaces may be convex, and/or the front and/or rear surfaces may be convex. The surfaces of the implants of the present invention may have openings which may or may not pass all the way through them, and a central chamber in communication to the surface through holes. The openings may be of random sizes, and/or shapes, and/or distributions. The implants themselves may be composed of materials, and/or have surface treatments, to encourage microscopic bone ingrowth into the implants.
In the performing of a posterior lumbar interbody fusion, it is not possible to replace the removed portions of the disc, if a total nuclear discectomy has been performed, with a single large implant as the delicate dural sac containing the spinal cord, and the nerve roots cover at all times at least some portion of the posterior disc space. As set forth in the Parent Application, the use of “modular implants” is appropriate in such cases. The modular implants being approximately as long as the depth of the disc material removed, but being considerably narrower, such that they can be introduced into the disc space from the posterior aspect to either side of the dural sac, and then aligned side to side within the disc space so that a number of them each having a length consistent with the depth of the disc removed in that area would in combination have a width equal to the width of the disc material removed.
The modular implants of the present invention may be generally wedge-shaped and may have upper and lower surfaces conforming to the contours of the vertebral endplates, which contours include but are not limited to being relatively flat or convex. As the disc spaces in the lumbar spine are generally lordotic, said implants in the preferred embodiment would be taller anteriorly, that is at the implant's insertion end, and less tall posteriorly, that is at the implant's trailing end. To introduce an implant that is taller at its insertion end than the space available at the posterior aspect of the disc space, even when that disc space is optimally distracted, is problematic.
The modular implants of the present invention provide two solutions to the problem. In the first embodiment, the modular implants may have a reduced size at their insertion end, including but not limited to a bullet nose, a convexity, and a chamfer to a smaller front surface. This then provides that the implant has an area small enough to be introduced into the posterior aspect of the disc space when the disc space is adequately distracted and the contour of that specialized leading portion of the implant is such that it then allows for a ramping up of the adjacent vertebrae relative to the implant as the implant is advanced forward into the disc space.
The implants of the present invention provide a second solution to this same problem. In the preferred embodiment of the modular implant, the implant is again wedge-shaped in the side elevational view and is taller at its insertion end than at its trailing end. flowever, the implant incorporates at its trailing end a means for engaging insertion instrumentation such as the box and threaded opening configuration disclosed in the Parent Application. Since in the preferred embodiment these implants are wedge-shaped in the side elevational view when upright but are generally rectangular when viewed from the top plan view, these implants are therefore designed to be introduced into the disc space on their side such that the side walls of the implants are adjacent to the end plates of the adjacent vertebrae. The implants have a side-to-side dimension that is less than the dimension through the insertion end of the implant when upright. It is possible to easily insert these implants with them on their side and then to use the insertion instrument engaged to the implant to rotate the implants ninety degrees into the fully upright position, once they have been fully inserted. Once inserted, the upper and lower sur
Chattopadhyay Urmi
Isabella David J.
Martin & Ferraro LLP
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