Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-03-30
2002-07-02
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S017110
Reexamination Certificate
active
06413278
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a prosthetic system, and more particularly to mechanical and biological spinal prostheses, as well as a method and apparatus for inserting the prostheses between vertebrae of a spine.
Degenerative disease of the spine, which is caused by stresses imposed on the spine by trauma and normal loading, as well as genetics and other factors, results in abnormal motion between vertebrae beyond normal limits. Eventually, if uncorrected, the degenerative processes can lead to pain, deformity, musculoskeletal dysfunction and neurologic dysfunction. When other measures fail to alleviate these symptoms, surgical intervention is required.
Typically, the surgical intervention involves implanting mechanical and/or biological prostheses between affected vertebrae of the spine to immobilize the affected vertebrae and eventually fuse them together. Mechanical prostheses restore anatomical curvature to the spine, prevent deformity from progressing and immobilize the vertebrae to promote fusion of the vertebrae. Biological prostheses are sometimes used, alone or in combination with mechanical prostheses, to promote bone growth between the vertebrae, thereby facilitating fusion of the vertebrae. The biological protheses are generally made of bone harvested from the patient or some other donor.
According to a principle known as Wolff's Law, bone growth is stimulated and directed by loading the bone which occurs naturally as a person moves. For instance, growth of bone through biological prostheses may be stimulated by loading the prostheses. However, conventional mechanical prostheses are relatively rigid and do not permit the biological prostheses to be loaded in a natural manner due to “stress shielding”. As a result, bone growth is not stimulated when biological prostheses and conventional mechanical prostheses are used in combination. Accordingly, the efficacy of the prosthetic system is reduced when biological and conventional mechanical prostheses are used together.
Biological prostheses conduct and direct bone growth from exposed recipient bone. When biological prostheses are implanted between vertebrae, bone grows inward from the facing surfaces of the vertebrae adjacent the biological prosthesis, eventually growing together and fusing the vertebrae. As will be appreciated by those skilled in the art, the speed at which the bone grows and the overall success of the prosthetic system is greatly affected by the surface area of the vertebrae exposed to the biological prosthesis. However, many prior art mechanical prostheses contact the adjacent vertebrae over large areas and prevent the biological prostheses from contacting the vertebral surfaces. Thus, bone growth is inhibited, thereby reducing the efficacy of the prosthetic system.
Further, many conventional biological prostheses are composed only of fragments of bone. One desirable aspect of these “dry” prostheses is that they stay in position between vertebrae. However, it is sometimes desirable to add liquid to the prostheses. For instance, liquid growth factors are added to the biological prostheses for stimulating bone growth. However, the liquid additives make the prostheses highly flowable. As a result, available biological protheses containing growth factors frequently flow out from position between the vertebrae, thereby reducing their efficacy.
In addition, conventional mechanical prostheses and the conventional tools used to implant them have relatively wide profiles, requiring large portions of the discs or surrounding structures and tissues such as pedicles, facets and ligaments to be removed before the prosthesis can be inserted. However, experience has shown that the more material removed from around the vertebrae, the more the trauma and the greater the chance for instability and failure of the surgery. Further, the wide profiles of conventional prostheses and tools increase the likelihood of permanent injury to the spinal cord and nerve roots, especially when the prostheses are inserted in the upper spine.
SUMMARY OF THE INVENTION
Among the several objects of the present invention may be noted the provision of a method and apparatus which correct and relieve pain associated with segmental instability of the spine; the provision of such a method and apparatus which limit the motion of adjacent vertebrae of a spine; the provision of such a method and apparatus which facilitate fusion of adjacent vertebrae; the provision of such a method and apparatus which promote bone and blood vessel growth between adjacent vertebrae; the provision of such a method and apparatus which minimize the risk of injury to the surrounding vertebrae and structures; and the provision of such a method and apparatus which permit introduction of a fluid biological prosthesis having sufficient viscosity to remain in position between vertebrae.
Briefly, the present invention includes a surgical method of inserting a prosthetic system between first and second vertebrae spaced by a disc to limit motion between and to facilitate fusion of the first and second vertebrae. The method comprises the steps of exposing the first and second vertebrae and the disc, excising at least a portion of the disc from between the first and second vertebrae, and scraping the cartilage from facing surfaces of the vertebrae to expose the facing surfaces. The method also includes the steps of spacing the first and second vertebrae by a selected distance and simultaneously cutting grooves in the facing surfaces of the vertebrae using a cutting tool having opposing blades. A mechanical prosthesis is anchored in the grooves cut in the facing surfaces of the vertebrae so that the prosthesis extends between the vertebrae and limits motion between the vertebrae. In addition, the method includes the step of packing bone graft material between the vertebrae and around the mechanical prosthesis to promote bone growth between and facilitate fusion of the vertebrae.
In another aspect, the present invention includes a spinal prosthesis for insertion during surgery in a space between first and second vertebrae of a spine of a patient. The prosthesis comprises a central support sized and shaped for insertion between the first and second vertebrae. The support has a height measured between a top and a bottom approximately equal to a selected spacing between the vertebrae. The prosthesis also includes upper and lower flex members extending from the top and bottom of the central support, respectively, for engaging the first and second vertebrae. The upper and lower members have a stiffness sufficiently small to permit the members to flex elastically toward each other under loading from the vertebrae.
In yet another aspect, the invention includes a spinal prosthesis comprising a central support, as well as upper and lower anchors positioned at the top and bottom of the support, respectively, for anchoring the support between the first and second vertebrae. Each anchor includes a sharp edge for holding the anchor in position with respect to the respective vertebra.
In still another aspect, the present invention includes a spinal prosthesis comprising a central support and at least one stiffener extending from the support for strengthening the support to inhibit flexing thereof.
In addition, the present invention includes a set of surgical instruments for inserting a prosthetic system between first and second vertebrae to limit motion between and/or to facilitate fusion of the vertebrae. The set of instruments comprises a spacer for positioning the first and second vertebrae in a selected orientation and spacing the vertebrae by a selected distance. The spacer has a tapered tip for facilitating insertion of the spacer between the vertebrae and opposing surfaces for engaging facing surfaces of the vertebrae thereby to position and space them. The set of instruments also includes a cutting tool having opposing blades for cutting grooves simultaneously in the facing surfaces of the first and second vertebrae and a guard adapted
Snow Bruce
Sonnenschein Nath & Rosenthal
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