Patent attributes
A hip prosthesis has a cup element having a part-spherical inner bearing surface and a spherical center through which the plane of a diametrical equator extends, and a ball shaped head which has a diameter to cooperate with the inner bearing surface to allow movement therein. The cup has a flat cordal lower surface parallel to the plane of an equator of the ball. The inner bearing surface has two or more equally spaced extension portions which extend beyond the diametrical equator towards the mouth of the cup. The surfaces of the two or more portions are relieved to enable the ball shaped head to be inserted into the cup by moving the flat on the ball across the face of one of the bearing surface extension portions and then rotating ball head to a position in which the flat on the ball head faces the mouth of the cup.
