US Patent 7108719 Joint prosthesis

In a joint prosthesis with a base piece for anchoring in the bone, a collar piece articulated thereon and defining a collar axis, and a collar extension on the collar piece situated on the collar axis, an articulation space is formed on the base piece. An articulation head of the collar piece is disposed therein. The joint prosthesis further includes a head cap disposed on the collar extension and at least one pressure piece for pressing the articulation head against the base of the articulation space. The pressure piece and the base piece can be connected. In a joint prosthesis of this kind, the pressure piece includes a pressure disc with a passage opening for the collar extension.