Spinal prosthesis

A spinal prosthesis comprising:

• a first spinal attachment member attachable to a first posterior portion of a spinal structure;
• a second spinal attachment member attachable to a second posterior portion of the spinal structure, said first and second posterior portions being adjacent superiorly-inferiorly to one another;
• and
• a connector element attached to said first spinal attachment member, wherein an interface portion is rotatingly assembled on said second spinal attachment member and acts as a roller bearing therefor, and wherein said interface portion passes through an elongate aperture formed in said connector element so as to permit rotational and translational movement of said second spinal attachment member with respect to said connector element, wherein said rotational movement of said second spinal attachment member with respect to said connector element is about at least two different rotational axes, and wherein said second spinal attachment member comprises elongate members that extend outwards from opposite sides of said interface portion, wherein said elongate aperture is elongate along a first axis and has end faces that face in opposite directions along a second axis, and said interface portion has abutments spaced from the end faces of said elongate aperture, wherein said abutments define limits of movement of said interface portion.