Talus

The talus has a head, neck and body. The superior surface of the body, the trochlea, is a pulley-shaped articular surface gripped by the malleoli in the ankle mortise; it is wider anteriorly than posteriorly, so the ankle is most stable in dorsiflexion (wide part wedged in the mortise) and less stable in plantarflexion — when most sprains occur. The body also bears medial and lateral malleolar facets and, posteriorly, the posterior process with medial and lateral tubercles separated by a groove for the flexor hallucis longus tendon.

The inferior surface has three facets (posterior, middle, anterior) for the calcaneus at the subtalar joint, separated by the sulcus tali, which with the calcaneal sulcus forms the sinus tarsi and tarsal canal (interosseous talocalcaneal ligament). The rounded head projects forward and medially to articulate with the navicular and the plantar spring ligament — forming the keystone of the medial longitudinal arch.

Because no muscles attach to it and most of its surface is articular, the talus has a precarious retrograde blood supply entering mainly through the neck and the sinus tarsi (branches of the posterior tibial, dorsalis pedis and fibular arteries).