Apparatus for constraining a socket bearing in an artificial joint

Claim 1

A ball and socket joint for implanting in the body which comprises: a ball; a cup with a spherical cavity, said cup including first and second elements, the first element to be affixed to bone and the second element having associated therewith two spaced apart coaxial pin members which extend into the spherical cavity and whose common axis defines an axis of rotation, said second element being moveable with respect to the first element to provide a plurality of possible orientations for said axis of rotation, said cup having a projection in the form of an axially symmetric pin extending into the spherical cavity at the geometric pole of the cavity; and a bearing member surrounding a portion of the ball and rotatable within said spherical cavity about said coaxial pin members, the axis of rotation of the bearing member being the axis of rotation defined by the common axis of the pin members, said bearing member including an aperture for receiving the projection, said aperture having end walls and side walls, the projection and the aperture being sized so that the projection can be received in the aperture for each of the possible orientations of the axis of rotation, the rotation of the bearing being constrained by engagement of an end wall of the aperture with the projection.