US Patent 7033396 Shoulder or hip prosthesis facilitating abduction

The prosthesis of this invention comprises a humeral or femoral component presenting a concave articulation surface, and an intermediate component presenting first and second convex articulation surfaces intended to cooperate respectively with said concave articulation surface of the humeral or femoral component and with a concave glenoid or cotyloid articulation surface. The locus of the instantaneous centers of rotation of the first convex articulation surface, with respect to the concave humeral or femoral articulation surface, and the locus of the instantaneous centers of rotation of the second convex articulation surface on the glenoid or cotyloid surface, are located on either side of the first surface.