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Portrait of Talus

Anatomy · Bones

Talus

The ankle bone (astragalus)

Foot · hindfoot · tarsal bones

The talus, or ankle bone, is the second largest tarsal bone and the link between the leg and the foot. Its dome-shaped upper surface, the trochlea, sits between the tibia and fibula in the ankle joint; below it rests on the calcaneus, and in front its head meets the navicular. It receives the whole weight of the body from the tibia and passes it to the heel and forefoot, yet no muscle inserts on it, and much of its surface is covered in cartilage.

How to spot them

  • ▸Irregular bone made of a body, a short neck and a rounded head, sitting on top of the calcaneus
  • ▸Upper surface (trochlea) is pulley-shaped and wider in front, locked between the two malleoli in the ankle mortise
  • ▸Head faces forward and inward, meeting the navicular; underneath, a deep groove (sulcus tali) separates two facets for the calcaneus
  • ▸Articulates with four bones (tibia, fibula, calcaneus, navicular); no muscle or tendon inserts on it, and about 70% of its surface is articular cartilage

What to know

The bone that takes the whole weight of the body from the leg and passes it down to the heel and the forefoot, at the top of the foot's longitudinal arches

Talus — the keystone between the leg and the foot.

Its dome-shaped, wedge-like upper surface locks between the two bony prominences of the ankle, forming a hinge-type joint

Talus — the trochlea in the ankle (talocrural) joint.

It articulates with four other bones, yet no muscle inserts on it, and some 70 per cent of its surface is covered in cartilage

Talus — it has ligaments but no muscular attachments.

Its neck fractures when a pilot's foot is thrust upward by the rudder bar in a crash, giving a fracture an aviation name

Talus — 'aviator's astragalus'.

Its blood supply comes in from below and behind and runs retrograde, so a displaced break of its neck may leave the body of the bone to die

Talus — avascular necrosis after talar neck fracture (Hawkins classification).

It is also known by a Greek name meaning a knucklebone or die, from the game pieces of the ancient world

Talus — the astragalus.

A groove on its underside forms, with the bone below, a small canal called the sinus tarsi, and the bone touches the tibia, fibula, heel bone and boat-shaped bone

Talus — the sulcus tali; it articulates with tibia, fibula, calcaneus and navicular.

A fracture of its outer projection, classically in snowboarders, is often mistaken for an ankle sprain

Talus — the lateral process fracture, 'snowboarder's ankle'.

Key ideas

  • Weight is carried from the tibia to the talus, and then divided: backwards to the calcaneus (heel) and forwards through the navicular, cuneiforms and metatarsals to the ball of the foot.
  • Its blood supply is fragile: the vessels enter the neck and the sinus tarsi and run backwards into the body, so a displaced neck fracture can cut off the body, causing avascular necrosis.
  • The body of the talus is wider in front than behind, so the ankle is most stable when the foot is dorsiflexed and the wider part is wedged between the malleoli.

Quick-fire facts

  • •It is the second largest of the seven tarsal bones and the most proximal; only the calcaneus is larger.
  • •It has no muscular attachments, but many ligamentous ones; about 70% of its surface is covered in articular cartilage.
  • •It has three parts: a body (with the trochlea for the tibia and side facets for the malleoli), a neck and a head (for the navicular).
  • •It articulates with the tibia, fibula, calcaneus and navicular; the subtalar joint below allows inversion and eversion, the ankle (talocrural) joint above allows dorsiflexion and plantarflexion.
  • •The 'aviator's astragalus' is a fracture of the talar neck, so called from early aeroplane crashes (the term dates from about 1919) in which the rudder bar was driven upwards into the pilot's foot.
  • •The Hawkins classification (1970) grades talar neck fractures by displacement and predicts the risk of avascular necrosis; a subchondral lucency ('Hawkins sign') at six to eight weeks indicates that the body is still vascularised.
  • •The Latin talus means ankle; the Greek astragalos means knucklebone or die, and the sheep talus was used as a die in Greek and Roman games.
  • •The os trigonum, a small accessory ossicle behind the talus, is present in a minority of people (figures of roughly 7–25% are quoted) and can cause posterior ankle impingement in dancers.

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