Cervical disc replacement

An intervertebral implant comprising:

• a first member having a first toroidal saddle shaped articulation surface including a first concave arc extending between leading and trailing ends of the first articulation surface and a first convex arc extending between first and second lateral sides of the first articulation surface;
• and
• a second member having a second toroidal saddle shaped articulation surface including a second convex arc extending between leading and trailing ends of the second articulation surface and a second concave arc extending between first and second lateral sides of the second articulation surface,
• wherein the first concave arc has a radius that is greater than the radius of the second convex arc, and the first and second articulation surfaces are adapted to engage one another during flexion, extension and lateral bending.

An intervertebral implant comprising:

• a first member having a first articulation surface that is defined at least by a concave arc having a radius of curvature A about a first axis, and by a convex arc having a radius of curvature B about a second axis substantially perpendicular to the first axis;
• and
• a second member having a second articulation surface that is defined at least by a convex arc having a radius of curvature C about a third axis, and by a concave arc having a radius of curvature D about a fourth axis substantially perpendicular to the third axis, said radius of curvature A being greater than said radius of curvature C,
• wherein the first member has a first center of rotation that remains below said articulating surfaces during flexion/extension and a second center of rotation that remains above the articulation surfaces during lateral bending.