The three-dimensional kinematics and flexibility characteristics of the human ankle and subtalar joints- Part I: Kinematics

The in-vitro, three dimensional kinematic characteristics of the human ankle and subtalar joint were investigated in this study. The tests were conducted on fifteen fresh amputated lower limbs and consisted of incrementally displacing the foot with respect to the shank while the motion of the articulating bones was measured through a three dimensional position data acquisition system. From the results of this investigation it was concluded that: the range of motion of the foot-shank complex in any direction (dorsiflexion/plantarflexion, inversion/eversion and internal rotation/external rotation) is larger than that of either the ankle joint or the subtalar joint; large kinematic coupling values are present at the foot-shank complex in inversion/eversion and in internal rotation/external rotation. However, only a slight amount of coupling was observed to occur in dorsiflexion/plantarflexion; neither the ankle joint nor the subtalar joint are acting as ideal hinge joints with a fixed axis of rotation; motion of the foot-shank complex in any direction is the result of rotations at both the ankle and the subtalar joints. However, the contribution of the ankle joint to dorsiflexion/plantarflexion of the foot-shank complex is larger than that of the subtalar joint and the contribution of the subtalar joint to inversion/eversion is larger than that of the ankle joint; the ankle and the subtalar joints have an approximately equal contribution to internal rotation/external rotation movements of the foot-shank complex.