The invention relates in general to a medical device structured to serve as a replacement for damaged, diseased, pathologic, degenerated or ruptured intervertebral discs, and more particularly to such a device which is self-centering and maintains the proper spatial relationship between adjacent vertebrae while allowing for movement of the adjacent vertebrae in a manner similar to and consistent with the range and type of motion found prior to pathology, degeneration or rupture.
In addressing the problems of pathologic, degenerated or ruptured intervertebral discs, the solutions have generally focused on immobilizing the adjacent vertebrae by fusion or replacement of the damaged disc with a prosthetic disc, where the prothesis is designed to allow for some motion between the adjacent vertebrae. A successful disc replacement requires a prosthetic device which remains properly positioned between the vertebrae, maintains the vertebrae in proper spaced relation, allows for a range of motion while maintaining proper alignment of the spine and vertebrae in the frontal and sagittal plane during such motion, is biocompatible and is of sufficient durability to withstand loading cycles of up to 100 million or more.
There have been numerous patents issued in this field. Some patents involve replacement discs composed of a compressible or elastic material, some involve discs comprising matrices to enhance bone growth into the discs, some involve discs composed of both rigid and non-rigid materials, and some involve rigid discs. Of the later type, some are designed to remain detached from the adjacent vertebrae while others are designed for direct connection to the vertebrae. Multi-component replacement discs are known where the plural components are free to move relative to each other. The major drawback from the known devices is that the range, angle and type of movement does not properly mimic the natural range, angle and type of motion found in the actual human disc, while maintaining proper frontal and sagittal alignment of the spine.
It is an object of the replacement intervertebral disc of the present invention to provide a device which substitutes for a human disc and successfully replicates the range, angle and type of movement between the adjacent vertebrae, where the disc is composed of a durable, rigid, biocompatible material of high fatigue strength so as to withstand millions of loading cycles without failure or degradation. It is a further object to provide such a disc having two generally convex surfaces which generally correspond to the disc being replaced and the concave shape of adjacent vertebrae, where the maximum dimension between the two convex surfaces is not central to the main body of the disc, where the disc is self-centering to preclude disc impingement into the spinal canal, and where proper intervertebral spacing is maintained by joining the two opposing convex surfaces by a generally vertically oriented wall member. It is a further object to provide such a disc where the convex surfaces are not in parallel relationship so as to better replicate the configuration of a human disc and proper spinal alignment.