A joint prosthesis particularly useful in total knee replacement, and capable of providing controlled motion about three axes corresponding to the capabilities of a normal knee. A dual centered pivot with contacting arcuate support blocks provides for a combination of rotational and translational movement during knee bending movements. Axial rotation of the femur (upper leg) relative to the tibia (lower leg) is also possible through the normal range of movements, and a bias toward the neutral position is provided to signal the patient that such rotation exists. Flexure or bending of the joint in an axis transverse to the normal knee axis is also provided with a resilient bias toward the aligned orientation. The joint is secured to the bone structure by self tapping connector screws. The connector screws are locked in place by outrigger screws. The entire knee joint is enclosed in a flexible encapsulating cover to prevent damage to adjacent tissues and contamination of body fluids.