Arobotic system was developed to assess the mechanical functions of human knee joints under the physiological condition. The system consists of a six-axis articulated manipulator, a universal force sensor, custom-made fixation devices for a femur and a tibia, and a personal computer. Mechanical function of a human knee joint was assessed by the external force when the tibia was displaced against the femur from the physiological neutral position. The neutral position, where the external force was eliminated, was able to be formed by the force control of the manipulator. Eleven sets of normal human bilateral knee joints were subjected for the measurements. The anterior stiffness of normal knee joint was similar to the contralateral knee joint. One knee including the reconstructed anterior cruciate ligament was subjected and compared with the contralateral healthy knee joint. The anterior stiffness of the former was less than that of the later.
