Motion preserving artificial intervertebral disc device

A motion preserving implant having first and second bearing members and a biasing member disposed therebetween operable to provide resistance to the translation of the bodies with respect to one another. An intervertebral implant having first and second bearing members, a translatable member, a resilient connection between the translatable member and one of the bearing members to allow for relative motion therebetween and bearing surfaces of the translatable member and the other bearing member to allow complex, natural motion between the bearing members. A spinal implant having upper and lower bodies and an articulation surface that allows for polyaxial articulation and translation through a concave articulation surface having a first radius of curvature and a second radius of curvature in at least one plane, and a convex articulation surface having the first radius of curvature in the same plane.