The Ankle Joint

Articulating Surfaces

The ankle joint is formed by three bones; the tibia and fibula of the leg, and the talus of the foot:

The tibia and fibula are bound together by strong tibiofibular ligaments. Together, they form a bracket shaped socket, covered in hyaline cartilage. This socket is known as a mortise.

The body of the talus fits snugly into the mortise formed by the bones of the leg. The articulating part of the talus is wedge shaped – it is broad anteriorly, and narrow posteriorly:

• Dorsiflexion – the anterior part of the talus is held in the mortise, and the joint is more stable.
• Plantarflexion – the posterior part of the talus is held in the mortise, and the joint is less stable.

By TeachMeSeries Ltd (2025)

Fig 2
X-ray of a normal ankle joint. Note the bracket shaped socket formed by the tibia and fibula.

By TeachMeSeries Ltd (2025)

Fig 3
The talus. It is broad anteriorly, which strengthens the joint during dorsiflexion.

Ligaments

There are two main sets of ligaments, which originate from each malleolus.

Medial Ligament

The medial ligament (or deltoid ligament) is attached to the medial malleolus (a bony prominence projecting from the medial aspect of the distal tibia).

It consists of four ligaments, which fan out from the malleolus, attaching to the talus, calcaneus and navicular bones. The primary action of the medial ligament is to resist over-eversion of the foot.

Lateral Ligament

The lateral ligament originates from the lateral malleolus (a bony prominence projecting from the lateral aspect of the distal fibula).

It resists over-inversion of the foot, and is comprised of three distinct and separate ligaments:

• Anterior talofibular – spans between the lateral malleolus and lateral aspect of the talus.
• Posterior talofibular – spans between the lateral malleolus and the posterior aspect of the talus.
• Calcaneofibular – spans between the lateral malleolus and the calcaneus.

By OpenStax College [CC BY 3.0], via Wikimedia Commons

Fig 4
Ligaments of the ankle joint.

Neurovascular Supply

The arterial supply to the ankle joint is derived from the malleolar branches of the anterior tibial, posterior tibial and fibular arteries.

Innervation is provided by tibial, superficial fibular and deep fibular nerves.

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Clinical Relevance

Ankle Sprain

An ankle sprain refers to partial or complete tears in the ligaments of the ankle joint. It usually occurs via excessive inversion to a plantarflexed and weight-bearing foot.

The lateral ligament is more likely to be damaged for two main reasons:

• The lateral ligament is weaker than the medial ligament.
• The lateral ligament resists inversion.

The anterior talofibular ligament is the lateral ligament most at risk of irreversible damage.

Clinical Relevance

Pott’s Fracture-Dislocation

A Pott’s fracture is a term used to describe a bimalleolar (medial and lateral malleoli) or trimalleolar (medial and lateral malleoli, and distal tibia) fracture.

This type of injury is produced by forced eversion of the foot. It occurs in a series of stages:

• Forced eversion pulls on the medial ligaments, producing an avulsion fracture of the medial malleolus.
• The talus moves laterally, breaking off the lateral malleolus.
• The tibia is then forced anteriorly, shearing off the distal and posterior part against the talus.

By Steven Fruitsmaak [CC BY-SA 3.0], from Wikimedia Commons

Fig 5
Bimalleolar fracture of the ankle. 1 – Fibula, 2 – Tibia.