Abstract: A knee prosthesis comprising a femur component defining a ball-like femoral condyle and a tibia component defining a cavity on its medial side corresponding to the ball-like condyle. The knee prosthesis enables pivoting of the tibia component about the medial side of the femur component as a function of the flexion angle ? as long as there is joint compression applied to the knee prosthesis as exemplified by muscle forces, weight, and ligament tensions, to enforce contact between the tibia component and the femur component. The geometries of the spherical load bearing surfaces of the medial tibia condyle and medial femur condyle provide the kinematic degrees of freedom and the geometric constraints required for proper guiding of the rolling and sliding surfaces of the femoral component and tibial component during articulation of the present knee prosthesis.

Abstract: A knee prosthesis for a knee joint with a medial ball-like femoral condyle and with a width “w” is characterized on the lateral compartment by:—a trace-line “Lt1” of contact points “Pt1” for the tibia component (2) as a predetermined curve (15) on a spherical surface “Sc1”, which has its centre at the centre Mb of the medial ball 1 and which has a radius in the range “Rc1”=0.65 w+/?0.25 w—a trace-line “Lt2” of common contact points “Pt2” at given flexion angles ? for a similar spherical surface “Sc2” attached to the femoral component with radius “Rc2”=Rc1, whereby at a given flexion angle ? there exists a plane “E1” through the centre Mb and the common contact point Pt1/Pt2, which contains the same guiding curves “Bi”, “Be” on the tibial and on the femoral components, “Bi” towards medial and “Be” towards lateral, both of which stay in a geometrically fixed relation to the common contact point Pt1/Pt2, and—guiding curves “Bi” and “Be”, which generate an enforced gilding and rolling movement in both directions.

Abstract: A knee prosthesis for a knee joint with a medial ball-like femoral condyle and with a width “w” is characterized on the lateral compartment by:—a trace-line “Lt1” of contact points “Pt1” for the tibia component (2) as a predetermined curve (15) on a spherical surface “Sc1”, which has its centre at the centre Mb of the medial ball 1 and which has a radius in the range “Rc1”=0.65w+/?0.25w—a trace-line “Lt2” of common contact points “Pt2” at given flexion angles ? for a similar spherical surface “Sc2” attached to the femoral component with radius “Rc2”=Rc1, whereby at a given flexion angle ? there exists a plane “E1” through the centre Mb and the common contact point Pt1/Pt2, which contains the same guiding curves “Bi”, “Be” on the tibial and on the femoral components, “Bi” towards medial and “Be” towards lateral, both of which stay in a geometrically fixed relation to the common contact point Pt1/Pt2, and—guiding curves “Bi” and “Be”, which generate an enforced gliding and rolling movement in both directions.