The invention provides an apparatus comprising a prosthetic femoral head and a liner. The prosthetic femoral head has a truncated spherical body, a truncated surface, and a stem cavity. The liner has a liner cavity and a rim wherein said liner cavity comprises a greater-than-hemispherical concavity and said rim comprises at least one slot. The slot allows insertion of the prosthetic femoral head into the liner cavity at an insertion orientation and retaining the prosthetic femoral head in the liner cavity at orientations other than the insertion orientation.
