Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2002-01-14
2004-07-13
O'Connor, Cary E. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
Reexamination Certificate
active
06761723
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of spinal surgery. More specifically, this invention relates to apparatuses for creating cavities in vertebral bodies and in intervertebral discs located between the vertebral bodies. This invention also relates to methods for creating such cavities. Once the cavities are created with the apparatuses and according to the methods of the present invention, an intervertebral prosthetic device, designed to replace a damaged intervertebral disc, can be implanted in the cavities. Moreover, the implanted device may be used in vertebral body fusion or in reconstruction of mobile discs through spinal arthroplasty (i.e., disc replacement).
The human spine is a flexible structure comprised of twenty-five vertebrae. Intervertebral discs separate and cushion adjacent vertebrae. The intervertebral discs act as shock absorbers and allow bending between the vertebrae.
An intervertebral disc comprises two major components: the nucleus pulposus and the annulus fibrosis. The nucleus pulposus is centrally located in the disc and occupies 25-40% of the disc's total cross-sectional area. The nucleus pulposus usually contains 70-90% water by weight and mechanically may function like an incompressible hydrostatic material. The annulus fibrosis surrounds the nucleus pulposus and resists torsional and bending forces applied to the disc. Thus, the annulus fibrosis serves as the disc's main stabilizing structure. A healthy disc relies on the unique relationship of the nucleus and annulus to one another. The top and bottom surfaces of intervertebral discs abut vertebral body endplates.
Individuals with damaged or degenerated discs often experience significant pain. The pain results, in part, from instability in the intervertebral joint due to a loss of hydrostatic pressure in the nucleus pulposus, which leads to a loss of disc height and altered loading of the annulus fibrosis.
A conventional treatment for degenerative disc disease is spinal fusion. In one such surgical procedure, a surgeon removes the damaged natural disc and then fuses the two adjacent vertebral bodies into one piece. The surgeon fuses the vertebral bodies by grafting bone between the adjacent vertebrae and sometimes uses metal rods, cages, or screws to hold the graft in place until the graft heals. Other fusion procedures do not require surgical removal of the disc.
Although spinal fusion may alleviate pain associated with degenerative disk disease, it also results in loss of motion at the fused vertebral joint. Lack of motion at the fused site puts abnormal loads on the adjacent discs above and below the fusion. This additional pressure may cause the adjacent discs to degenerate and produce pain, thereby recreating the problem which originally existed. To remedy the problems associated with spinal fusion, various prosthetic devices were developed to replace the damaged disc with a suitable biomechanical equivalent.
Existing prosthetic devices have met with limited success in reproducing the biomechanics of a natural disc. For example, U.S. Pat. No. 4,759,769 to Hedman et al. discloses a synthetic disc having upper and lower plates hinged together. Although the hinged disc allows forward bending between adjacent vertebrae, the hinged disc does not allow axial compression or lateral flexion. Nor does it allow axial rotation of the vertebral column at the site of the implant. Therefore, the Hedman et al. device lacks many of the biomechanics of a natural disc.
Likewise, the prosthetic disc device disclosed in U.S. Pat. No. 4,309,777 to Patil does not replicate natural motion between adjacent discs. The Patil device includes two cups, one overlapping the other and spaced from the other by springs. The cups move only in a single axial dimension. Thus, the Patil device does not enable natural flexion of the spine in any direction. In addition, the highly constrained motion of the Patil device can lead to high device/tissue interface stresses and implant loosening.
Many synthetic devices connect to the vertebral bodies by conventional mechanical attachments, such as pegs or screws, which are known to loosen under cyclic loading conditions. Other synthetic devices use plastic or elastomeric components which, over a lifetime, produce debris from wear and possible unknown side effects.
In response to these and other known problems associated with synthetic prosthetic disc devices, U.S. Pat. No. 5,827,328 to Buttermann, which is incorporated herein by reference in its entirety, discloses an intervertebral synthetic prosthetic device designed to replace the biomechanical functionality of a failing intervertebral disc. One embodiment of the Buttermann device includes a first fixation member for implantation in a first vertebral body, a second fixation member for implantation in a second vertebral body adjacent the first vertebral body, and a compressible member that is positioned between the first and second fixation members. The Buttermann device overcomes the aforementioned problems with synthetic devices.
SUMMARY OF THE INVENTION
There is a need for improved apparatuses and methods by which cavities can be created in vertebral bodies and in an intervertebral disc. Once the cavities are created, an intervertebral prosthetic device designed to replace a damaged intervertebral disc, such as the one described in U.S. Pat. No. 5,827,328, can be implanted in the cavities.
In one aspect of the present invention, a cutting guide is provided for use in removing bone from a vertebral body. The cutting guide includes a sidewall that defines an internal cavity. In addition, the sidewall has (i) a first edge to face toward and to contact a vertebral body in at least three points and (ii) a second, opposite edge to face away from the vertebral body. The first edge includes at least two concave portions and at least one convex portion oriented generally perpendicular to the at least two concave portions.
The sidewall of the cutting guide may be comprised of four walls arranged to form a rectangular cross-section. At least one of the four walls may include a hole extending from the first edge to the second edge to receive a fastener therethrough. Further, the first edge of the sidewall may be concave along a first of the four walls and along an opposite second of the four walls, and it may be convex along a third of the four walls and along an opposite fourth of the four walls. The concave first edge along the first wall may be a mirror image of the concave first edge along the second wall. Similarly, the convex first edge along the third wall may be a mirror image of the convex first edge along the fourth wall. Moreover, although the concave and convex edges may each comprise one smooth surface, they also may be formed by a plurality of adjacent surfaces.
In another aspect of the invention, a chisel guide is provided for use in cutting bone of a vertebral body. The chisel guide includes a first block member to be positioned adjacent the vertebral body and a second block member connected to the first block member. The second block member has a channel, formed on one side thereof, which terminates at the first block member.
In one embodiment of the chisel guide, the first block member and the second block member may be formed as one integral piece. Further, the second block member may extend beyond the perimeter of the first block member in at least one dimension to form a shoulder with the first block member. For example, the second block member may have a width greater than the width of the first block member such that the second block member forms a pair of opposed shoulders with respect to the first member.
Another aspect of the invention relates to a cutting guide and chisel guide combination for use in removing bone from a vertebral body. The combination includes a cutting guide having a sidewall defining an internal cavity. The sidewall, in turn, has a first edge to face toward and to contact a vertebral body in at least three points and a second, opposite edge to face away from t
Buttermann Glenn Robin
Cooper Doug Wayne
Dynamic Spine, Inc.
Foley & Lardner
Melson Candice C.
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