Kinematics of Ankle Joint Motion
Assuming the foot is in a completely unloaded state where it can move freely, two simultaneous movements of the talus relative to the lower leg occur during dorsiflexion.
These two movements are a rolling motion in the forward direction and a sliding motion in the backward direction (Figure A). Among these complex movements, the existence of the backward sliding motion causes the talus to perform rotational motion accompanied by only a limited range of forward translational motion.
These two movements are a rolling motion in the forward direction and a sliding motion in the backward direction (Figure A). Among these complex movements, the existence of the backward sliding motion causes the talus to perform rotational motion accompanied by only a limited range of forward translational motion.
Figures A and B illustrate the tension state of the calcaneofibular ligament during the backward sliding of the talocalcaneal segment. Due to these biomechanical characteristics, all collateral ligaments, which gradually tighten as the talus translates backward, experience an increase in tension as dorsiflexion progresses.
At maximum dorsiflexion, all soft tissue structures capable of transmitting plantarflexion torque, including the posterior joint capsule and Achilles tendon, are placed in a stretched state. A clinically significant point here is that full dorsiflexion of the ankle is often restricted following a lateral ankle sprain. Thus, one of the primary therapeutic approaches to address this restriction could be the application of passive joint mobilization techniques to the talocrural joint.
When applying this technique, clinicians should specifically focus on translating the talus and foot in a posterior direction relative to the lower leg. Correct application of this posterior sliding technique is essential to reproduce the natural kinematic patterns of dorsiflexion in the talocrural joint.
During plantarflexion, the talus exhibits a complex motion pattern of rolling backward while simultaneously sliding forward (Figure B). In this process, certain collateral ligaments, gradually tightened by the forward translational motion of the talus, experience a continuous increase in tension as plantarflexion progresses.
As shown clearly in Figure B, the anterior talofibular ligament exhibits significant tension at maximum plantarflexion. Additionally, although not directly visible in the figure, the tibionavicular fibers of the deltoid ligament also display considerable tension in full plantarflexion. Along with the tension in these ligaments, plantarflexion imposes significant stretching forces on the dorsiflexor muscle group and the anterior joint capsule.