US Patent 8491661 Knee joint prosthesis

A knee joint endoprosthesis is provided with a simplified construction. The knee joint endoprosthesis consists of a femur component and a tibia component which comprise cooperating joint surfaces that are in contact with one another. A rotation guide arrangement is provided for forcing the femur component and the tibia component to rotate relative to each other about a medial center of rotation upon a flexure of the knee joint endoprosthesis. The rotation guide arrangement comprises a first guide element having a first guidance surface and a second guide element having a second guidance surface which cooperates with the first guidance surface. The tibia component comprises the first guide element and the femur component comprises the second guide element. The first guidance surface defines a first radius of curvature and the second guidance surface defines a second radius of curvature. The first and second radii of curvature are identical.