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.

Three-dimensional measurement of rearfoot motion during running.

Excessive ranges of motion during running have been speculated to be connected to injuries to the lower extremities. Movement of the foot and lower leg has commonly been studied with two-dimensional techniques. However, differences in the alignment of the longitudinal axis of the foot with the camera axis will produce measurement errors for projected angles of the lower extremities. A three-dimensional approach would not have this limitation. The purpose of this study is to present a three-dimensional model for calculation of angles between lower leg and foot, lower leg and ground, and foot and ground, and to compare results from treadmill running derived from this model with results derived from a two-dimensional model for different alignment angles between foot axis and camera axis. A two camera Selspot system was used to obtain three-dimensional information on motion of the studied segments. It was found that several two-dimensional variables measured from a posterior view are very sensitive to the alignment angle between the foot and the camera axis. Some variables change as much as 1 degrees for every 2 degrees of change of the alignment angle. The large influence of rotations other than the measured one in two-dimensional measurements makes advisable the use of a three-dimensional model when studying motion between foot and lower leg during running.