The knee joint prosthesis has a section at the femur which forms a pair of condyle sliding surfaces (5). The tibia section has sliding surfaces (9), at a carrier plate (7) on a tibia plateau (8), working with the condyle surfaces. A coupling (10) holds the two sections together, with rotation on a rotary axis parallel to the shin bone. When the femur and tibia sections are aligned on the same ante posterior line, the load is transferred through a center zone (14) of the tibia sliding surfaces. When the two sections rotate against each other, each condyle surface remains in contact with its associated tibia sliding surface before or after the normal center contact zone. The condyle surface working with the tibia sliding surface sections has a constant curvature radius.
