Three-dimensional analysis of the talocrural and subtalar joints in single-limb stance.

A quasi-static three-dimensional model of the rear foot was developed to enable calculation of joint motion and net torque with respect to talocrural and subtalar joint axes. The functional behaviour of these joints was analysed during single-limb stance. Six female soccer players with unilateral functional instability of the ankle joint were examined. Recordings were performed both with eyes open and eyes closed. The rear-foot model was implemented into an optoelectronic motion analysis system together with a force plate. The subtalar torque precedes the angular movement by 0.1-0.2 s, indicating active postural corrections. Up to a certain limit of subtalar joint inversion, the external everting torque increases. If the inversion is further increased an external inverting torque is obtained. With eyes closed the amplitudes increased for joint motions, torques, centre of pressure trajectories, shear forces, and vertical forces. All events found with external inverting torques occurred when standing on the injured foot with the eyes closed.