On the estimation of knee joint kinematics

Abstract

This paper presents the results of an experimental research protocol concerning the kinematics of the knee joint in vivo. The research was conducted using the VICON opto-electronic system. The angular kinematics of the femur relative to the tibia was evaluated by three successive finite rotations about floating axes: (1) axial rotation about the distal–proximal axis of the tibia; (2) varus–valgus angle and, finally, (3) flexion–extension about the medio–lateral axis of the femur. As one of the main objectives was to avoid skin motion artefact from the use of skin-markers, rigid structures were fixed onto the shank and the thigh segments. Tests of repeatability of the main protocol were conducted to verify the reliability of the measurements. The procedure had shown excellent repeatability of our measurements as far as the flexion–extension was concerned. However, the angles of varus–valgus and of the internal–external rotation were not as repeatable, possibly due to their comparatively smaller amplitudes, and then more sensitive to errors. The main study compared kinematics of young and healthy volunteer with those of an older healthy subject group. There, our research showed that there appeared to be a reduction of the amplitude of flexion–extension and a shifting of the tibia relative to the femur in direction of internal rotation in the older group compared to the younger.