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The talus (/ ˈ t eɪ l ə s /; Latin for ankle [1] or ankle bone; [2] pl.: tali), talus bone, astragalus (/ ə ˈ s t r æ ɡ ə l ə s /), or ankle bone is one of the group of foot bones known as the tarsus. The tarsus forms the lower part of the ankle joint. It transmits the entire weight of the body from the lower legs to the foot. [3]
Its weakest part (i.e., the part most liable to yield from overpressure) is the joint between the talus and navicular, but this portion is braced by the plantar calcaneonavicular ligament a.k.a. spring ligament, which is elastic and is thus able to quickly restore the arch to its original condition when the disturbing force is removed.
The calcaneus is also modified, forming a heel for the attachment of the Achilles tendon. Neither of these adaptations is found in reptiles, which have a relatively simple structure to both bones. [3] The fifth distal tarsal disappears relatively early in evolution, with the remainder becoming the cuneiform and cuboid bones.
Enumerated from the medial side, the four canals which it forms transmit the tendons of the tibialis posterior and flexor digitorum longus muscles; the posterior tibial artery and tibial nerve, which run through a broad space beneath the ligament; and lastly, in a canal formed partly by the talus, the tendon of the flexor hallucis longus.
The synovial membrane between the second and third cuneiforms behind, and the second and third metatarsal bones in front, is part of the great tarsal synovial membrane. Two prolongations are sent forward from it, one between the adjacent sides of the second and third, and another between those of the third and fourth metatarsal bones.
Between these superior articulations and the equivalents on the talus is the tarsal sinus (a canal occupied by the interosseous talocalcaneal ligament). [ citation needed ] At the upper and forepart of the medial surface of the calcaneus, below the middle talar facet, there is a horizontal eminence, the talar shelf (also sustentaculum tali ). [ 2 ]
The sinus tarsi located in the hindfoot, it is contained by the calcaneus, talus, talocalcaneonavicular joint, and the bottom of the subtalar joint. [1] There are five ligamentous structures present inside it: the intermediate, medial, and lateral roots of the inferior extensor retinaculum; the cervical ligament, and the interosseous talocalcaneal ligament.
Tarsal tunnel syndrome is the most commonly reported nerve entrapment of the ankle. It is analogous to carpal tunnel syndrome in the wrist. It is caused by compression of the tibial nerve underneath the flexor retinaculum of the foot. [1] People with tarsal tunnel syndrome have pain in the plantar aspect of the foot mostly at night.