Spinal Implant With Elliptical Articulatory Interface

Abstract

A spinal implant prosthesis includes a pair of end plates for affixation to adjacent vertebral bone structures and respectively defining inter-engaged convex and concave articulatory surfaces of elliptical profile. These elliptical articulatory surfaces are elongated in an anterior-posterior direction, and are comparatively shorter in a medial-lateral direction. With this configuration, in response to angular displacement and/or axial rotation, the elliptical surfaces displace in a manner increasing the distance between the adjacent vertebral bone structures, thereby tensioning the prosthesis and producing counteracting forces which urge the components back toward a substantially centered or neutral position. In addition, in the preferred form, the anterior-posterior length of the concave articulatory surface in incrementally greater than the anterior-posterior length of the convex articulatory surface to accommodate a limited range of anterior-posterior translation.

What is claimed is: 
     
         1 . A spinal implant, comprising:
 a pair of implant components adapted for affixation respectively to adjacent vertebral structures and including inter-engageable articulatory bearing members;   said bearing members including a convex articulatory surface and a concave articulatory surface both defined by a generally elliptical profile shape in an anterior-posterior direction and a generally elliptical profile shape in a medial-lateral direction.   
     
     
         2 . The spinal implant of  claim 1  wherein said concave articulatory surface is incrementally elongated relative to said convex articulatory surface in the anterior-posterior direction. 
     
     
         3 . The spinal implant of  claim 2  wherein said concave articulatory surface substantially matches said convex articulatory surface in the medial-lateral direction. 
     
     
         4 . The spinal implant of  claim 1  wherein said convex and concave articulatory surfaces are each formed as a segment of an ellipsoid. 
     
     
         5 . The spinal implant of  claim 1  wherein said convex and concave surfaces are elongated in the anterior-posterior direction relative to the medial-lateral direction. 
     
     
         6 . The spinal implant of  claim 1  wherein said pair of implant components each include means for affixation to adjacent vertebral structures. 
     
     
         7 . A spinal implant, comprising:
 a pair of implant components adapted for affixation respectively to adjacent vertebral structures and including inter-engageable articulatory bearing members;   said bearing members respectively including convex and concave articulatory surfaces each defined by a generally elliptical profile shape in an anterior-posterior direction and a generally elliptical profile shape in a medial-lateral direction;   said convex and concave surfaces being elongated in the anterior-posterior direction relative to the medial-lateral direction; and   said concave articulatory surface being incrementally elongated relative to said convex articulatory surface in the anterior-posterior direction, and substantially matching each other in the medial-lateral direction.   
     
     
         8 . A spinal implant, comprising:
 a pair of implant components adapted for affixation respectively to adjacent vertebral structures and including inter-engageable articulatory bearing members;   said bearing members respectively including convex and concave articulatory surfaces of generally ellipsoid shape having an elongated major axis extending generally in an anterior-posterior direction; and   said concave articulatory surface being incrementally elongated relative to said convex articulatory surface in the anterior-posterior direction.