[Computer-assisted analysis of the kinematics of the upper ankle joint].

Usually the upper ankle joint is described as a typical hinge though it had been often remarked that the axis of rotation moves considerably with regard to the angular adjustment between the tibia and the trochlea tali. In the present study the relation between the movements in the upper ankle joint and the geometry of the lateral ligaments was analysed. The contours and elected landmarks of 6 dissected ankle joints were measured using a digitizer which allowed the computerized scanning of motion x-rays. In addition the proximal and distal insertion planes of the lateral ligaments were registered. Mathematical procedures were applied on the experimental data to predict the kinematic principles. The model of an hinged joint could not reproduce the motion curve which was actually found. Using the model of a link chain with four pivots, which was determined by the course of the talofibular and the calcaneofibular ligament, a good correlation with the experimental results was evident. This model implies a rotary and gliding component in the movement of the tibia against the trochlea tali. Beside the correspondence with the data of the present study the model allows an easy explanation of many other well known morphologic phenomena of the upper ankle joint for which a stringent interpretation was not yet available.