Patent ID: 7455694

Claim:
A total hip prosthesis comprising a cup 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 co-operate with said inner bearing surface to allow free movement therein, and having a flat cordal lower surface parallel to the plane of an equator of the ball, the ball-shaped head outer surface being ball-shaped at all locations spaced from the flat cordal lower surface; and in which the inner bearing surface has at least two equally spaced extension portions which extend beyond the diametrical equator toward the mouth of the cup, and two or more portions extending below the diametrical equator and between the extension portions, the surfaces of which are relieved by being curved in a radial direction parallel to the equator 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 the ball-shaped head across the opposite curved relieved portion and then rotating ball head to a position in which the flat on the ball head faces the mouth of the cup and the ball head is held in the cup by the extension portions which extend beyond the said diametrical equator.