A knee prosthesis including a tibial component for mounting to the proximal end of a tibia, and a femoral component for mounting to the distal end of a femur. At least the face surface of the medial condylar portion of the femoral component may be preferably substantially congruent with the face surface of a medial cavity in the upper surface of the tibial component so that substantially complete surface-to-surface contact between the face surface of the medial cavity in the upper surface of the tibial component and the face surface of the medial condylar portion of the femoral component is provided throughout a significant portion of the range of flexion of the knee joint. The tibial component may include a base member, an articular bearing member movably positioned on the upper surface of the base member, and structure for restricting the movement of the lateral portion of the articular bearing member relative to the base member to allow a swinging motion thereof relative to the medial portion of the articular bearing member.