A socket bearing for implantation in a patient's body as part of a ball and socket joint is provided. The joint includes a ball portion and a socket portion. The ball portion includes a ball connected to a neck, and the socket portion includes two spaced-apart coaxial pin members which engage the socket bearing and allow the bearing to rotate in the assembled joint. The inner surface of the bearing forms a cavity for receiving the ball, and the outer surface includes two spaced-apart, cylindrically-shaped surfaces for receiving the pin members. The bearing can encompass either more than half or less than half of the ball, so that in the assembled joint, the ball is either physically constrained or not physically constrained within the bearing.