Articulating disc implant

Abstract

An intervertebral disc implant for use in the spine including a first part ( 10 ) and a second part ( 20 ), wherein the first part and second part are configured as a joint prosthesis for the spine. The first part includes one of a concave or convex articulating surface ( 16 ) and the second part includes one of the other concave or convex articulating surface ( 26 ). One of the concave or convex articulating surfaces is preferably elliptically shaped in at least one direction and does not match and is different than one of the other concave or convex articulating surfaces.

1 . An intervertebral implant for insertion between a first and a second vertebrae, the implant comprising:
 an upper part including an upper surface sized and configured to contact an end plate of the first vertebra;   a lower part including a lower surface sized and configured to contact an end plate of the second vertebra;   a convex articulating surface operatively associated with one of the upper and lower parts and having a first radius of curvature in a first direction; and   a concave articulating surface operatively associated with the other one of the upper and lower parts so that the upper part is moveable with respect to the lower part, and the concave articulating surface has a first radius of curvature in the first direction;   wherein the first radius of curvature of the convex articulating surface is different than the first radius of curvature of the concave articulating surface in the same first direction.   
     
     
         2 . The intervertebral implant of  claim 1  wherein the convex articulating surface has a second radius of curvature in a second direction perpendicular to the first direction, and the concave articulating surface has a second radius of curvature in a second direction perpendicular to the first direction, and wherein the second radius of curvature of the convex articulating surface is the same as the second radius of curvature of the concave articulating surface in the same second direction. 
     
     
         3 . The intervertebral implant of  claim 1  wherein the convex articulating surface has a second radius of curvature in a second direction perpendicular to the first direction, and the concave articulating surface has a second radius of curvature in a second direction perpendicular to the first direction, and wherein the second radius of curvature of the convex articulating surface is different than the second radius of curvature of the concave articulating surface in the same second direction. 
     
     
         4 . The intervertebral implant of  claim 2  wherein the first direction is in the medial-lateral direction. 
     
     
         5 . The intervertebral implant of  claim 1  wherein the concave articulating surface is associated with the upper part. 
     
     
         6 . The intervertebral implant of  claim 1  wherein the convex articulating surface has a constant radius of curvature in the first direction. 
     
     
         7 . The intervertebral implant of  claim 6  wherein the concave articulating surface is substantially continuous with no flat spots and has a radius of curvature in the first direction that varies over its length. 
     
     
         8 . The intervertebral implant of  claim 1  wherein the concave articulating surface is in the shape of a partial oblate ellipsoid. 
     
     
         9 . The intervertebral implant of  claim 8  wherein the convex surface  15  is in the shape of a partial sphere. 
     
     
         10 . The intervertebral implant of  claim 1  wherein the concave articulating surface only contacts the convex articulating surface on an area comprising less than 50% of the area of the convex articulating surface. 
     
     
         11 . The intervertebral implant of  claim 10  wherein the concave articulating surface only contacts less than 25% of the convex articulating surface. 
     
     
         12 . The intervertebral implant of  claim 11  wherein the concave articulating surface only contacts less than 10% of the convex articulating surface. 
     
     
         13 . The intervertebral implant of  claim 1  wherein the convex articulating surface forms approximately line contact with the concave articulating surface. 
     
     
         14 . The intervertebral implant of  claim 1  wherein the concave articulating surface is in the shape of an ellipse wherein the first radius of curvature of the concave articulating surface varies over the concave articulating surface in the first direction and a second radius of curvature of the concave articulating surface in a second direction perpendicular to the first direction varies over the concave articulating surface. 
     
     
         15 . The intervertebral implant of  claim 14  wherein the convex articulating surface forms approximately point contact with the concave surface. 
     
     
         16 . The intervertebral implant of  claim 1 , wherein the upper part comprises a multi piece assembly and the lower part comprises a multi-piece assembly. 
     
     
         17 . The intervertebral implant of  claim 1 , wherein the first radius of curvature of the upper part is between about 1 mm and about 100 mm, and the second radius of curvature of the upper part is between about 1 mm and about 30 mm. 
     
     
         18 . The intervertebral implant of  claim 1 , wherein the upper articulating surface has an arc length between about 10 mm and about 15 mm, and the lower articulating surface has an arc length between about 10 mm and about 15 mm. 
     
     
         19 . The intervertebral implant of  claim 1 , wherein the concave articulating surface has a depth, the convex articulating surface has a height, and the depth of the concave articulating surface has a different value than the height of the convex articulating surface. 
     
     
         20 . The intervertebral implant of  claim 1 , wherein the concave articulating surface rolls on and along at least a portion of the convex articulating surface in at least the first direction. 
     
     
         21 . The interbertebral implant of  claim 1 , wherein the concave articulating surface rolls on and along at least a portion of the convex articulating surface in at least two directions. 
     
     
         22 . The intervertebral implant of  claim 1 , wherein the depth of the concave articulating implant has an apex, and the height of the convex articulating surface has an apex, wherein the concave articulating surface and the convex articulating surface are configured, sized and shaped so the concave apex is axially aligned and opposed by the convex apex when no forces are applied to the first and second parts. 
     
     
         23 . An intervertebral implant for insertion between a first and a second vertebrae, the implant comprising:
 an upper part including an upper surface sized and configured to contact an end plate of the first vertebra;   a lower part including a lower surface sized and configured to contact an end plate of a second vertebra;   a convex articulating surface operatively associated with one of the upper and lower parts; and   a concave articulating surface operatively associated with the other one of the upper and lower parts so that the upper part is moveable with respect to the lower part,   wherein the concave articulating surface has a different shape than and does not match with the convex articulating surface such that the entire concave articulating surface does not contact the convex articulating surface and the concave articulating surface rolls on the convex articulating surface in at least one direction whereby the axis of rotation of the concave articulating surface moves along the convex articulating surface.   
     
     
         24 . An intervertebral implant comprising:
 an upper part including an upper surface sized and configured to contact an end plate of an upper vertebra;   a lower part including a lower surface sized and configured to contact an end plate of a lower vertebra;   a convex articulating surface operatively associated with one of the upper and lower parts;   a concave articulating surface operatively associated with the other one of the upper and lower parts so that the upper part is moveable with respect to the lower part;   wherein one of the concave and convex articulating surfaces is elliptically shaped with a radius of curvature that varies in at least one direction and the other of the concave and convex surfaces is partially spherically shaped having a constant radius of curvature in the same at least one direction.   
     
     
         25 . The intervertebral implant of  claim 23  wherein the other of the convex and concave articulating surfaces is partially spherically shaped having a constant radius of curvature that is the same in all directions.