Artificial Spinal Disc

Abstract

An artificial disc prosthesis is provided. The prosthesis of the present invention enables spinal segment alignment by having a variable height across its surface. The variable height is achieved by an asymmetric artificial nucleus or by at least one variable height end plate.

1 . A method for implanting an intervertebral disc prosthesis in a portion of a spine, the method comprising:
 securing a first vertebral contacting surface to a first vertebral body, the first vertebral contacting surface comprising at least one bone engagement feature;   securing a second vertebral contacting surface to a second vertebral body, the second vertebral contacting surface comprising at least one bone engagement feature;   positioning first, second, third and fourth bearing surfaces between the first and second vertebral contacting surfaces, at least one of the first and second bearing surfaces comprising a section inclined at a constant slope to provide a correction angle when the prosthesis is in a neutral position, each of the third and fourth bearing surfaces comprising a planar portion;   positioning the planar portions of the third and fourth bearing surfaces into surface contact with one another; and   positioning the inclined section to cross the coronal plane of the first and second vertebral bodies to urge the first and second vertebral contacting surfaces toward a relative anterior/posterior orientation that provides a preferred lordotic angle between the first and second vertebral bodies.   
     
     
         2 . The method of  claim 1 , wherein an anterior portion of the inclined section is higher than a posterior portion of the inclined section to correct lordosis, wherein the preferred lordotic angle is greater than zero. 
     
     
         3 . The method of  claim 1 , wherein the preferred lordotic angle is selected from the group consisting of 3 and 6 degrees. 
     
     
         4 . The method of  claim 1 , further comprising:
 securing a first end plate to the first vertebral body, wherein the first end plate comprises the first vertebral contacting surface, the first end plate further comprising the first bearing surface; and   positioning the first bearing surface to cooperate with the second bearing surface to urge the first and second vertebral contacting surfaces toward the anterior/posterior orientation.   
     
     
         5 . The method of  claim 4 , further comprising:
 securing a second end plate to the second vertebral body, wherein the second end plate comprises the second vertebral contacting surface, the second end plate further comprising the second bearing surface; and   positioning the second bearing surface to cooperate with the first bearing surface to urge the first and second vertebral contacting surfaces toward the anterior/posterior orientation.   
     
     
         6 . The method of  claim 2 , further comprising positioning a nucleus between the first and second vertebral contacting surfaces, the nucleus formed separately from the first and second vertebral contacting surfaces, wherein the nucleus comprises the first and third bearing surfaces. 
     
     
         7 . The method of  claim 6 , further comprising:
 securing a first end plate to the first vertebral body, the first end plate comprising the first vertebral contacting surface, securing a second end plate to the second vertebral body, the second end plate comprising the second vertebral contacting surface, wherein the first end plate comprises the second bearing surface and the second end plate comprises the fourth bearing surface;   positioning the second bearing surface to articulate with the first bearing surface of the nucleus, and   positioning the fourth bearing surface to articulate with the third bearing surface of the nucleus.   
     
     
         8 . The method of  claim 6 , wherein an anterior portion of the nucleus has a greater thickness than a posterior portion of the nucleus to correct lordosis, wherein the preferred lordotic angle is greater than zero. 
     
     
         9 . A method for implanting an intervertebral disc prosthesis in a portion of a spine, the method comprising:
 securing a first essentially flat vertebral contacting surface to a first vertebral body;   securing a second essentially flat vertebral contacting surface to a second vertebral body;   positioning a nucleus between the first and second vertebral contacting surfaces, a first bearing surface formed on the nucleus, a planar third surface formed on the nucleus opposite the first bearing surface; a first straight section formed on the first bearing surface, the first straight section having a constant non-zero slope oriented with respect to the planar third surface to provide a corrective angle;   positioning the first straight section to cross the coronal plane of the first and second vertebral bodies; and   positioning a second bearing surface to articulate with the first bearing surface such that the second bearing surface mates with the constantly sloped first straight section to urge the first and second vertebral contacting surfaces toward an orientation of the first vertebral contacting surface relative to the second vertebral contacting surface that provides a deformity correction across at least one axis.   
     
     
         10 . The method of  claim 9 , wherein the second bearing surface comprises a second straight section formed on the second bearing surface. 
     
     
         11 . A method for implanting an intervertebral disc prosthesis in a portion of a spine, the method comprising:
 securing a first end plate to a first vertebral body, the first end plate comprising a plurality of bone engagement features shaped to penetrate bone and a first bearing surface;   securing a second end plate to a second vertebral body, the second end plate comprising a plurality of bone engagement features shaped to penetrate bone and a planar second bearing surface; and   positioning a nucleus between the first and second end plates, the nucleus comprising a third bearing surface and a planar fourth bearing surface, the nucleus comprising an asymmetrical shape across a coronal plane of the first and second vertebral bodies;   positioning the third bearing surface to articulate with the first bearing surface, the asymmetrical shape urging the first and second endplates to remain in a relative orientation that provides a preferred lordotic angle between the first and second vertebral bodies, providing line contact between the first and third bearing surfaces when the first bearing surface is articulated relative to the third bearing surface in the anterior/posterior direction; and   positioning the fourth bearing surface to articulate with the second bearing surface to permit at least one of medial-lateral and anterior-posterior translation between the nucleus and the second end plate.   
     
     
         12 . The method of  claim 11 , wherein the fourth bearing surface comprises a second straight section. 
     
     
         13 . The method of  claim 11 , wherein an anterior portion of the nucleus has a greater thickness than a posterior portion of the nucleus to provide the preferred lordotic angle. 
     
     
         14 . The method of  claim 11 , further comprising positioning at least one stop member formed on one of the first and second end plates to abut the respective vertebral body to prevent the prosthesis from migrating from its intended position between the first and second vertebral bodies. 
     
     
         15 . The method of  claim 11 , wherein the second bearing surface comprises a trough larger than the fourth bearing surface in at least one of the anterior-posterior and medial-lateral dimensions to permit translation between the nucleus and the second end plate, wherein positioning the nucleus further comprises sliding the nucleus into the trough along an anterior-posterior direction.