The ankle joint bears the weight of the body. An understanding of ankle injuries depends on not only a thorough knowledge of the anatomy of the joint but also on the mechanism of force that caused the injury.

The proximal part of the joint, or mortise, is comprised of distal fibula and tibia. This fits on top of the talus, or plafond, the distal part of the joint. These three bones are bound together by three groups of ligaments. Bony stability is provided by the medial and lateral malleoli extending over the plafond. Ligamentous stability is provided by the lateral ligament complex, the medial deltoid ligament, and the syndesmosis. The lateral malleolus is attached to the anterior and posterior aspects of the talus and to the calcaneus, respectively, by the anterior talofibular, posterior talofibular, and the calcaneofibular ligaments. The medial collateral or deltoid ligament is a thick triangular band of tissue that originates on the medial malleolus. The superficial fibers insert on the navicular, the sustentaculum of the calcaneus, and the talus, while a deep set of fibers insert on the medial aspect of the talus. The syndesmosis is a group of four distinct ligaments that attach the distal fibula to the tibia just above the plafond (Fl9... .268-1. ).

The ankle joint is sometimes described as having a range of motion in only the plantar-dorsiflexion plane, however, a small degree of medial-lateral movement does occur. The four groups of muscles that serve the ankle joint are supplied by branches of the sciatic nerve. Dorsiflexion is accomplished by tibialis anterior, extensor digitorum longus, and extensor hallucis longus muscles that run over the anterior aspect of the joint. On the medial side of the joint, the tibialas posterior, flexor digitorum longus, and flexor hallucis longus run behind the medial malleolus and contribute to inversion of the joint. Laterally, running behind the distal fibula, the peroneous and brevis muscles contribute to eversion and plantar flexion. These two peroneal tendons share a common synovial sheath that is held in place by a groove on the posterior aspect of the lateral malleolus and the superior retinaculum. Plantar flexion is provided by the soleus and gastrocnemius muscles. The blood supply of the foot is served by branches of the popliteal artery.

Almost all injuries of the ankle joint are due to an abnormal motion of the talus within the mortise. Motion of the talus causes a stress on the malleoli and the ligaments, causing injury. If the injury allows shifting of the position of the talar dome within the mortise, then the injury has the potential to be unstable. Fractures above the plafond may be unstable, and injuries that cause disruption on both sides of the joint are unstable. Instability can result from a fracture of a malleolus and rupture of a ligament, fracture of both malleoli, or rupture of both ligaments.

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