Movement of the ankle is directed in part by the tibialis anterior, a muscle that originates in the upper two-thirds of the lateral surface of the tibia (thick and fleshy above, tendinous below) and inserts into the medial cuneiform of the ankle and first metatarsal bones of the foot. Its acts to dorsiflex and invert the foot . It also allows for the ankle to be inverted giving the ankle horizontal movement allowing for some cushion if the ankle were to be rolled. The tibialis anterior functions to stabilize the ankle as the foot hits the ground during the contact phase of walking (eccentric contraction) and acts later to pull the foot clear of the ground during the swing phase (concentric contraction). It also functions to 'lock' the ankle, as in toe-kicking a ball, when held in an isometric contraction. Essentially, the movements of tibialis anterior are dorsiflexion and inversion of the ankle. However, actions of tibialis anterior are dependent on whether the foot is weight bearing or not (closed or open kinetic chain). When the foot is on the ground the muscle helps to balance the leg and talus on the other tarsal bones so that the leg is kept vertical even when walking on uneven ground.
The peroneus longus (also known as fibularis longus) is a superficial muscle in the lateral compartment of the leg, and acts to evert and plantarflex the ankle. It is attached proximally to the head of the fibula and its 'belly' runs down most of this bone. It becomes a tendon that goes posteriorly around the lateral malleolus of the ankle, then continues under the foot to attach to the medial cuneiform and first metatarsal. The peroneus longus and brevis plantarflex the ankle (in conjunction with the tibialis posterior) while antagonizing the tibialis anterior and peroneus tertius, which are dorsiflexors of the foot .
The ankle joint is bound by the strong deltoid ligament and three lateral ligaments: the anterior talofibular ligament, the posterior talofibular ligament, and the calcaneofibular ligament. The deltoid ligament supports the medial side of the joint. It is attached at the medial malleolus of the tibia and connects to the calcaneus, calcaneonavicular ligament, the navicular tuberosity, and to the medial surface of the talus. The anterior and posterior talofibular ligaments support the lateral side of the joint from the lateral malleolus of the fibula to the dorsal and ventral ends of the talus. The calcaneofibular ligament is attached at the lateral malleolus and to the lateral surface of the calcaneus. Although it does not span across the ankle joint itself, the syndesmotic ligament makes an important contribution to the stability of the ankle. This ligament spans the syndesmosis, which is the term for the articulation between the medial aspect of the distal fibula and the lateral aspect of the distal tibia. An isolated injury to this ligament is often called a high ankle sprain. The boney architecture of the ankle joint is most stable in dorsiflexion. Thus, a sprained ankle is more likely to occur when the ankle is plantar-flexed, as ligamentous support is more important in this position. The classic ankle sprain involves the anterior talofibular ligament (ATFL), which is also the most commonly-injured ligament during inversion sprains. Another ligament that can be injured in a severe ankle sprain is the calcaneofibular ligament.