Cervical disc replacement

1. An apparatus for replacing at least a portion of an intervertebral disc in a spinal column, comprising:

a first member having a first vertebral contact surface for engagement with an endplate of a first vertebral bone in the spinal column, and having a first articulation surface; and

a second member having a second vertebral contact surface for engagement with an endplate of a second vertebral bone in the spinal column, and having a second articulation surface, wherein:

an intervertebral disc space is defined substantially between the first and second endplates of the first and second vertebral bones, and

each of the first and second articulation surfaces having a toroidal saddle shaped surface, and the articulation surfaces are sized and shaped to engage one another when the first and second members are disposed in the intervertebral disc space to enable the first and second vertebral bones to articulate in at least one of flexion, extension, and lateral bending, wherein the engaging articulation surfaces include opposing constant radius of curvature surfaces that are non-congruent.

2. The apparatus of claim 1 , wherein the second articulation surface is defined by at least one bearing surface for engaging respective portions of the first articulation surface when the first and second members are disposed in the intervertebral disc space to enable the first and second vertebral bones to articulate in at least one of flexion, extension, and lateral bending.

3. The apparatus of claim 1 , wherein each of the saddle shaped articulation surfaces is defined by at least one bearing surface that cooperates to engage respective portions of the other articulation surface when the first and second members are disposed in the intervertebral disc space to enable the first and second vertebral bones to articulate in at least one of flexion, extension, and lateral bending.

4. The apparatus of claim 3 , wherein the at least one bearing surface defines a contiguous saddle shaped articulation surface.

5. The apparatus of claim 1 , wherein the toroidal saddle shaped articulation surfaces comprise:

the first articulation surface including a concave arc having a radius of curvature A about a first axis substantially perpendicular to an anterior-posterior plane of the spinal column, and a convex arc having a radius of curvature B about a first axis substantially perpendicular to a lateral plane of the spinal column; and

the second articulation surface including a convex arc having a radius of curvature C about a second axis substantially perpendicular to the anterior-posterior plane of the spinal column, and a concave arc having a radius of curvature D about a second axis substantially perpendicular to the lateral plane of the spinal column.

6. The apparatus of claim 1 , wherein the first and second articulation surfaces are sized and shaped to engage one another when the first and second members are disposed in the intervertebral disc space to enable the first and second vertebral bones to at least axially rotate relative to one another through a range of angles.

7. The apparatus of claim 1 , wherein the first and second articulation surfaces are sized and shaped to engage one another when the first and second members are disposed in the intervertebral disc space to enable the first and second vertebral bones to axially rotate relative to one another through a range of angles without substantially displacing the first and second vertebral bones away from one another.

8. The apparatus of claim 7 , wherein the first and second articulation surfaces are sized and shaped such that the first and second vertebral bones are substantially displaced away from one another at axial rotations outside the range of angles.