rectangular socket. The ankle is composed of three joints: the talocrural joint (also called talotibial joint, tibiotalar joint, talar mortise, talar joint), the subtalar joint (also called talocalcaneal), and the Inferior tibiofibular joint. The joint surface of all bones in the ankle are covered with articular cartilage. The distances between the bones in the ankle are as follows: Talus - medial malleolus : 1.70 ± 0.13 mm Talus - tibial plafond: 2.04 ± 0.29 mm Talus - lateral malleolus: 2.13 ± 0.20 mm Decreased distances indicate osteoarthritis. Ligaments 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, and is attached at the medial malleolus of the tibia and connect in four places to the talar shelf of 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. Though it does not span the ankle joint itself, the syndesmotic ligament makes an important contribution to the stability of the ankle. This ligament spans the syndesmosis, i.e. 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 bony 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. Retinacula, tendons and their synovial sheaths, vessels, and nerves A number of tendons pass through the ankle region. Bands of connective tissue called retinacula (singular: retinaculum) allow the tendons to exert force across the angle between the leg and foot without lifting away from the angle, a process called bowstringing. The superior extensor retinaculum of foot extends between the anterior (forward) surfaces of the tibia