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Talus


Type

irregular

Description

The talus is the second largest and most proximal tarsal bone. It consists of a cuboid body, a distally directed neck capped by a convex, oval head, a proximolateral facet for the fibular malleolus, and a proximal trochlea for the tibia.

Etymology

This word is the Latin term for the ankle bone. Roman soldiers commonly made die (plural of dice) from the ankle bones of the horse. They called these die a taxillus. This term, later shortened to talus, became the name of the ankle bone. In comparative anatomy the talus is called the astragalus. Astragalos is the Greek term used for die made of the second cervical vertebra of sheep. As the Romans followed the Greeks, but making their die from the heel bones, the term astragalos transferred to the ankle bone also.

Articulations

The talus articulates with four bones: tibia, fibula, calcaneus, and navicular. The dorsal pulley-like trochlear surface articulates with the distal end of the tibia. A lateral extension of this surface forms an articular facet with the fibular malleolus. A convexly oval head articulates distally with the proximal end of the navicular bone. On its plantar surface the head forms two ovoid articular surfaces with the calcaneus, the larger posterior one articulating with sustentaculum tali. The plantar surface of the talar body forms a concave rectangular surface of articulation with the mid-dorsal surface of the calcaneus.

Ossification

The talus ossifies from a single centrally located center. Ossification usually begins in the sixth month but may begin as early as the fifth month of fetal life. Occasionally the posterior tubercle will ossify from a separate center that may not fuse with the rest of the bone. When this occurs, the result is a triangular bone called the os trigonum.

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