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Portrait of Ankle joint

Anatomy · Joints & cartilage

Ankle joint

A mortise-and-tenon hinge

Lower limb · leg to foot

The ankle (talocrural) joint is a hinge between the talus and a bony socket, the mortise, formed by the lower ends of the tibia and fibula. It allows only dorsiflexion and plantarflexion; the side-to-side tilting of the foot, inversion and eversion, occurs at the subtalar joint just below. The medial deltoid ligament is very strong, but the lateral ligaments are weaker and are the ones most often sprained.

How to spot them

  • ▸The medial malleolus (tibia) and lateral malleolus (fibula) clasp the sides of the talus
  • ▸The talus is the only bone in the foot with no muscle attached, and it is wider in front than behind
  • ▸A fan-shaped deltoid ligament on the medial side; three separate lateral ligaments on the outside
  • ▸The Achilles tendon passes behind it to the heel

What to know

A hinge joint whose socket is a mortise formed by the ends of two leg bones, gripping the top of the talus

Ankle joint — the talocrural joint.

The joint permits only two movements, dorsiflexion and plantarflexion; inversion and eversion happen just below it

Ankle joint — the subtalar joint is responsible for tilting.

The commonest sprain is an inversion injury that tears the anterior talofibular ligament first

Ankle joint — lateral ligament sprain.

A fan-shaped ligament on the medial side, so strong that a bone often breaks before it tears

Ankle joint — the deltoid ligament.

Radiographs are requested after injury by a set of rules named after a Canadian city: bone tenderness at the malleoli and inability to bear weight

Ankle joint — the Ottawa ankle rules.

Key ideas

  • Stability depends on the mortise: because the talus is wider in front, the joint is most stable in dorsiflexion and least stable in plantarflexion.

Quick-fire facts

  • •OpenStax: the talocrural (ankle) joint is a uniaxial hinge that only allows dorsiflexion or plantarflexion of the foot.
  • •The lateral malleolus is the lower end of the fibula and the medial malleolus is the lower end of the tibia.
  • •The medial (deltoid) ligament is stronger than the lateral ligaments; the anterior talofibular ligament is the one most often torn in inversion sprains.
  • •The talus is wider anteriorly, so the joint is most stable in dorsiflexion.
  • •Pott's fracture is a fracture-dislocation of the ankle involving the malleoli; it is named after Percivall Pott.
  • •The Ottawa ankle rules help decide whether an X-ray is needed after injury.

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Sources