Patent ID: 6994728

Claim:
A method for replacing at least a portion of an intervertebral disc in a spinal column, comprising: removing the portion of the intervertebral disc from the spinal column; and inserting an apparatus for replacing the portion of-the intervertebral disc, the apparatus comprising a first member having a first vertebral contact surface for engagement with an endplate of a first of the vertebral bones in the spinal column, and a first articulation surface, the entirety of the first articulation surface being a single saddle surface that is defined by a concave arc having a substantially constant radius of curvature A about an axis perpendicular to leading and trailing ends of the first member and a convex arc having a substantially constant radius of curvature B about an axis perpendicular to lateral sides of the first member; the apparatus further comprising a second member having a second vertebral contact surface for engagement with an endplate of a second of the vertebral bones in the spinal column, and a second articulation surface, the entirety of the second articulation surface being a single saddle surface that is defined by a convex arc having a substantially constant radius of curvature C about an axis perpendicular to leading and trailing ends of the second member and a concave arc having a substantially constant radius of curvature D about an axis perpendicular to lateral sides 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, and wherein the first and second articulation surfaces are operable to engage one another to permit flexion and extension in the anterior-posterior plane of the spinal column, lateral bending in the lateral plane of the spinal column, and axial rotation through a range of angles without permitting the vertebral bones to substantially move in directions directed away from one another along a longitudinal axis of the spinal column.