Stress reinforced artificial joint prostheses

#The present invention relates to prosthetic devices, and more particularly, is directed to artificial joint prostheses utilizing a graphite substrate and a pyrolytic carbon coating.

#The use of prosthetic devices for repair or replacement of bone structure in a living body is well known. Conventional prosthetic devices have been constructed from metals, ceramics, and plastics, depending upon the intended application. Many conventional artificial prostheses for artificial joint reconstruction, such as knee joint prostheses like that of U.S. Pat. No. 3,869,731, consist of a metallic articulating joint element, and a mating, ultra-high molecular weight polyethylene articulating joint element. A principal problem of these prostheses is caused by wear and/or cold-flow (creep) of the high molecular weight polyethylene component upon prolonged usage at the local levels which exist in the skeletal system.

#Metallic joint components have a high modulus of elasticity and do not flex in harmony with the bone in which they are implanted; instead, they concentrate stress in portions of the remaining, lower modulus bone, particularly at the metal-bone interface.

#Accordingly, it is an object of the present invention to provide improved joint prostheses. It is a further object to provide joint prostheses elements which have increased resistance to tensile stress resulting from skeletal load forces. These and other objects of the invention will be readily apparent from the following detailed description and the accompanying drawings of which:

#FIG. 1 is a perspective anterior view of an artificial knee prostheses having a compression ring reinforced tibial component;

#FIG. 2 is a top view of the tibial component of the prosthesis of FIG. 1;

#Generally, the present invention is directed to functional artificial joint prosthesis elements for prolonged or permanent implantation in a living body.

#The joint prosthesis elements of the present invention generally comprise an artificial graphite substrate having a predetermined shape adapted for articulating function, and having a modulus of elasticity in the range of that of natural living bone. A particularly preferred form of graphite for use as a substrate material is polycrystalline graphite, and an example of such a graphite is the polycrystalline graphite sold under the trade name POCO-AXF graphite having density of about 1.9 gm/cm, an average crystalline size of about 300 Angstroms, an isotropy of nearly 1.0 on the Bacon scale (BAF), and a modulus of elasticity of about 1.7.times.10.sup.6 psi.

#The substrate will also generally be suitably shaped for appropriate skeletal attachment, and is provided with a dense, isotropic pyrolytic carbon coating on the graphite substrate. The joint prosthesis elements of the present invention further comprise a high modulus metallic band in compressively loaded relationship with the perimeter of carboncoated joint element adjacent its articulating joint surface and in a plane generally perpendicular to the loading axis of the joint element.