Artificial facet joint

Abstract

A spinal facet prosthesis for a diseased or painful facet joint comprises a superior component and an inferior component. The superior component is roughly conical or pyramidal in form and is fastened to and over the distal tip of the inferior articular process of the diseased or painful facet joint. The inferior component is also roughly conical or pyramidal in form with one side elongated postero-medially and distally. The outer surface of the elongated side of the inferior component is of low friction, such as polished chromium coating or medical grade high-density polyethylene. The inferior component is fastened to and over the superior articular process of the diseased or painful facet joint. Each component is made of a biocompatible material. The inner surface of each component which is in contact with its respective articular process is coated with a porous coating to enhance the adhesion of each component to its respective articular process.

I claim: 
     
       1. A prosthetic device for implantation over a painful or otherwise damaged inferior articular process or .[.a.]. .Iadd.an adjacent .Iaddend.superior articular process, or both, .[.of.]. .Iadd.at the point where such processes interact within .Iaddend.a human spinal facet joint, .Iadd.the device .Iaddend.comprising, a .[.superior.]. component .[.roughly in the form of a hollow cone or pyramid with a rounded apex.]. .Iadd.having an outer surface adapted to .Iaddend.substantially .[.conforming.]. .Iadd.conform .Iaddend.to the size and shape of the .[.distal tip of the inferior.]. .Iadd.outer surface of said painful or otherwise damaged .Iaddend.articular process .[.so as to be a substantially matching fit over it;.]..Iadd., at least at the point where said painful or otherwise damaged articular process interacts with said adjacent articular process; and .Iaddend.   .[.an inferior component roughly in the form of a hollow cone or pyramid substantially conforming to the size and shape of the distal tip of the inferior articular process so as to be a substantially matching fit over it;   means for affixing said superior component to said distal tip of the inferior articular process;.].   means for affixing said .[.inferior.]. component to said .[.distal tip of the superior.]. .Iadd.painful or otherwise damaged .Iaddend.articular process.   
     
     
       2. The device of claim 1, wherein said .[.inferior.]. component has a concave and elongated exterior surface positioned in matching opposition to .[.the distal tip of the inferior.]. .Iadd.the outer surface of said mating .Iaddend.articular process so as to provide a bearing surface .[.to said distal tip along its path.]. as it moves .[.medially and inferiorly over said elongated surface.]. .Iadd.with respect thereto.Iaddend.. 
     
     
       3. The device of claim 2, wherein said elongated surface is smooth so as to reduce the resistance to .[.the.]. .Iadd.said .Iaddend.movement .[.of said inferior articular process over said inferior component.].. 
     
     
       4. The device of claim 2, wherein said elongated surface is coated with non-porous polished chrome. 
     
     
       5. The device of claim 2, wherein a layer of medical-grade high density polyethylene is firmly affixed to said elongated surface. 
     
     
       6. The device of claim 1, wherein said means of affixing said .[.superior.]. component .[.to said distal tip of the inferior articular process is.]. .Iadd.comprises .Iaddend.at least one screw passing through the apex of .[.the superior.]. .Iadd.said .Iaddend.component and into the underlying .[.distal tip of the inferior articular process.]. .Iadd.bone.Iaddend.. 
     
     
       7. The device of claim 1, wherein said means of affixing said .[.inferior.]. component .[.to said tip of the superior articular process is.]. .Iadd.comprises .Iaddend.at least two screws passing through the distal portion of .[.the inferior.]. .Iadd.said .Iaddend.component and into the underlying .[.distal tip of the superior articular process.]. .Iadd.bone.Iaddend.. 
     
     
       8. The device of claim 1, wherein said .[.device.]. .Iadd.component .Iaddend.is made of a biocompatible material. 
     
     
       9. The device of claim 1, wherein .[.the device.]. .Iadd.said component .Iaddend.is made of stainless steel. 
     
     
       10. The device of claim 1, wherein .[.the device.]. .Iadd.said component .Iaddend.is made of unalloyed titanium. 
     
     
       11. The device of claim 1, wherein .[.the device.]. .Iadd.said component .Iaddend.is made of a titanium-aluminum alloy. 
     
     
       12. The device of claim 1, wherein .[.the.]. .Iadd.said component includes an .Iaddend.inside .[.surfaces of said device are.]. .Iadd.surface .Iaddend.coated with a porous coating. 
     
     
       13. The device of claim 12, wherein the material of said porous coating is the same as the material of said .[.device.]. .Iadd.component.Iaddend.. 
     
     
       14. The device of claim .[.1.]. .Iadd.20.Iaddend., wherein said form of the inferior component has an incomplete side so as to form an open area in said inferior component so that said open area is superimposed over the spinal nerve at the superior articular process. 
     
     
       15. The device of claim 14, wherein said incomplete side is in the shape of a pedicle. 
     
     
       16. A prosthetic device for implantation over a painful or otherwise damaged inferior articular process .[.or a superior articular process, or both.]., of a human spinal facet joint, comprising, a superior component roughly in the form of a .[.hollow.]. cone or pyramid with a rounded apex .[.with a hole at the apex.]. .Iadd.adapted to .Iaddend.substantially .[.conforming.]. .Iadd.conform .Iaddend.to the size and shape of the distal tip of the inferior articular process .[.so as to be a substantially matching fit over it.]. .Iadd.to be repaired with said component.Iaddend..[.;.].   .[.an inferior component roughly in the form of an incomplete hollow cone or pyramid substantially conforming to the size and shape of the distal tip of the inferior articular process so as to be a substantially matching fit over it with one side having a smooth concave and elongated surface positioned in matching opposition to the distal tip of the inferior articular process and to provide a bearing surface to said distal tip along its path as it moves medially and inferiorly over said elongated surface with at least two holes in the distal portion of said elongated surface and with an open area adjacent to said elongated surface formed by an incomplete side in the shape of a pedicle.]..   
     
     
       17. The device of claim 16, wherein .[.the.]. .Iadd.said superior component includes an .Iaddend.inside .[.surfaces of the device are.]. .Iadd.surface .Iaddend.coated with a porous coating. .Iadd.18. The device of claim 1, wherein said component is a superior component..Iaddend..Iadd.19. The device of claim 18, wherein said superior component is roughly in the form of a hollow cone or pyramid with a rounded apex adapted to substantially conform to the size and shape of the distal tip of the inferior articular process so as to be a substantially matching fit over it..Iaddend..Iadd.20. The device of claim 1, wherein said component is a 
     
     
        inferior component..Iaddend..Iadd.21.  The device of claim 20, wherein said inferior component roughly in the form of a hollow cone or pyramid adapted to substantially conform to the size and shape of the distal tip of the superior articular process so as to be a substantially matching fit over it..Iaddend..Iadd.22. A prosthetic device for implantation over a painful or otherwise damaged inferior articular process of a human spinal facet joint, comprising: a superior component roughly in the form of a cone or pyramid with a rounded apex adapted to substantially conform to the size and shape of the distal tip of an inferior articular process to be repaired with said component..Iaddend..Iadd.23. In a human spinal facet joint wherein a portion of the outer surface of a superior articular process interacts with a portion of the outer surface of an inferior articular process, a method of relieving discomfort comprising the steps of:   installing a prosthetic device having an outer surface which replaces the outer surface of one or both of the superior and inferior articular processes, at least in the vicinity where said processes interact..Iaddend.