Cervical disc replacement

An articulating joint implant for use in the cervical spine, comprising:

• a first element having an upper surface for seating against a lower endplate surface of a superior vertebral body and a lower articulating surface, which lower articulating surface includes a saddle surface that is defined by a concave arc having a constant radius of curvature A about an axis perpendicular to an anterior-posterior plane of a spinal column, and a convex arc having a constant radius of curvature B about an axis perpendicular to a lateral plane of the spinal column;
• and
• a second element having a lower surface for seating against an upper endplate surface of an inferior vertebral body and an upper articulation surface, which upper articulation surface includes a saddle surface that is defined by a convex arc having a constant radius of curvature C about the axis perpendicular to the anterior-posterior plane of the spinal column and a concave arc having a constant radius of curvature D about the axis perpendicular to the lateral plane of the spinal column;
• wherein the saddle surface of the first element and the saddle surface of the second element are nestable with one another and articulatable against one another in flexion/extension in an anterior-posterior plane of the spinal column and in lateral bending in a lateral plane of the spinal column, respectively, without their vertebral body contact surfaces moving in directions directed away from one another along the longitudinal axis of the spinal column.