Talus

At a glance

English

Talus

Latin (TA2)

Os tali

System

Bone

Region

Foot

Side

Paired, left and right

Series

Tarsal bones

About the talus

The talus is the uppermost bone of the foot, sitting in the fork made by the lower ends of the leg bones, and resting on the calcaneus. It is the second largest tarsal bone. Every step passes the full weight of the body through it, down from the leg and then backwards to the heel and forwards to the rest of the foot. It is unusual in two ways: no muscle attaches to it, so its position is set entirely by the bones and ligaments around it, and a large share of its surface is covered with joint cartilage, leaving little room for vessels to enter.

It is described in three parts: a body behind, a head in front and a short neck between. The upper surface of the body is the trochlea, a pulley-shaped surface that fits under the tibia, with a large triangular facet on its outer side for the lateral malleolus and a smaller comma-shaped facet on its inner side for the medial malleolus. The trochlea is a few millimetres wider in front than behind, so the ankle is most stable when the foot is pulled up, wedging the wider part into the mortise, and looser when the foot points down. Behind the trochlea the posterior process carries medial and lateral tubercles, with a channel between them for the flexor hallucis longus tendon.

Below, the body has a large concave posterior facet for the calcaneus, and the head and neck carry middle and anterior facets; a deep groove between the posterior and middle facets, the sulcus tali, lines up with a matching groove on the calcaneus to form the tarsal sinus and canal, which the interosseous talocalcaneal ligament fills. The rounded head faces forwards and inwards and fits into the navicular, and its underside rests on the spring ligament. Together, these joints form the talocalcaneonavicular joint, a ball-and-socket that lets the foot turn in and out.

Because most vessels enter at the neck and the lower surface, a fracture of the neck can cut off blood to the body, which may then collapse; healing is slow and often needs long protection from weight. The lateral tubercle sometimes forms a separate small bone, the os trigonum, which can be pinched behind the ankle in dancers and footballers.

Function and supply

Function

Passes body weight from the leg into the foot and, through its upper and lower joints, lets the foot pull up and point down and turn in and out.

Nerve supply

Not innervated as a muscle is; the ankle and subtalar joints are supplied by branches of the deep fibular, tibial and sural nerves.

Blood supply

Branches of the posterior tibial artery (including the artery of the tarsal canal), the dorsalis pedis artery and the fibular artery's perforating branch, most of which enter at the neck and underside and run backwards into the body.