Patent ID: 6972038

Claim:
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 a first articulating surface, the entirety of the first articulating surface being a single saddle surface that is defined by a concave arc having a substantially constant radius of curvature A about a first axis perpendicular to an axis passing through leading and trailing ends of the first member and a convex arc having a substantially constant radius of curvature B about a first axis perpendicular to an axis passing through lateral ends of the first member; a second member having a second vertebral contact surface for engagement with an endplate of a second vertebral bone in the spinal column, and a second articulating surface in contact with the first articulating surface, the entirety of the second articulating surface being a single saddle surface that is defined by a convex arc having a substantially constant radius of curvature C about a first axis perpendicular to an axis passing through leading and trailing ends of the second member and a concave arc having a substantially constant radius of curvature D about a second axis perpendicular to an axis passing through lateral ends of the second member, wherein the constant radius of curvature A is non-congruent with the constant radius of curvature C and the constant radius of curvature B is non-congruent with the constant radius of curvature D; an intervertebral disc space is defined substantially between the first and second endplates of the first and second vertebral bones; and the first and second members are operable to articulate relative to one another, when disposed in the intervertebral disc space, about at least one of: (i) a first center of rotation for at least one of flexion and extension that is located above the first and second articulating surfaces, and (ii) a second center of rotation for lateral bending that is located below the first and second articulating surfaces.