CorpusHuman Anatomy
SkeletalJoint

Ankle joint

Articulatio talocruralis

Also known as: talocrural joint, ankle, ankle mortise, deltoid ligament, ATFL

The hinge-type synovial joint between the trochlea of the talus and the mortise formed by the distal tibia and the medial and lateral malleoli. It permits dorsiflexion and plantarflexion of the foot.

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Overview

TypeHinge synovial (uniaxial)
Dorsiflexion / plantarflexion≈20° / ≈50°
Most stable positionDorsiflexion

The mortise is a deep socket: the inferior surface of the tibia forms the roof, the medial malleolus the medial wall and the lateral malleolus (fibula) the lateral wall, bound by the distal tibiofibular syndesmosis. The trochlea of the talus fits into it. Because the trochlea is wider anteriorly, the joint is most stable in dorsiflexion (close-packed), when the wide part wedges between the malleoli; in plantarflexion the narrower posterior part allows some side-to-side play — which is why most sprains occur in plantarflexion.

The capsule is thin anteriorly and posteriorly, reinforced by strong collateral ligaments. Medially, the fan-shaped deltoid (medial collateral) ligament has four parts — anterior tibiotalar, tibionavicular, tibiocalcaneal and posterior tibiotalar — and is so strong that eversion injuries often avulse the medial malleolus rather than tear it. Laterally, three separate, weaker bands: the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL) and the posterior talofibular ligament (PTFL).

Movements: dorsiflexion ≈20° (tibialis anterior, extensor hallucis/digitorum longus, fibularis tertius) and plantarflexion ≈50° (gastrocnemius, soleus, plantaris, tibialis posterior, flexor hallucis/digitorum longus, fibularis longus/brevis). Inversion and eversion occur at the subtalar and transverse tarsal joints, not at the ankle.

Location

Between the leg and the foot.

Parts & subdivisions

  1. Ankle mortise
    Tibial plafond + medial and lateral malleoli.
  2. Trochlea of talus
    Wider anteriorly — stable in dorsiflexion.
  3. Deltoid ligament
    Strong medial ligament: anterior and posterior tibiotalar, tibionavicular, tibiocalcaneal parts.
  4. Anterior talofibular ligament (ATFL)
    Weakest; first to tear in inversion sprains.
  5. Calcaneofibular ligament (CFL)
    Second to tear; spans the subtalar joint too.
  6. Posterior talofibular ligament (PTFL)
    Strongest lateral ligament; rarely torn.
  7. Distal tibiofibular syndesmosis
    AITFL, PITFL, interosseous ligament — holds the mortise together.

Anatomy

Innervation

Deep fibular and tibial nerves (also saphenous and sural branches).

Arterial supply

Malleolar branches of the anterior tibial, posterior tibial and fibular arteries.

Articulations

Distal tibia and fibula (malleoli) ↔ trochlea of the talus.

Ligaments

Deltoid ligament (medial); anterior talofibular, calcaneofibular and posterior talofibular ligaments (lateral); anterior and posterior inferior tibiofibular and interosseous ligaments (syndesmosis).

Function

  • Dorsiflexion and plantarflexion of the foot
  • Transmits body weight from the leg to the foot
  • Contributes to propulsion during gait

Clinical significance

Inversion ankle sprain

The commonest musculoskeletal injury: forced inversion of the plantarflexed foot tears the ATFL first, then the CFL. The Ottawa ankle rules (bone tenderness at the posterior edge/tip of either malleolus, navicular or 5th metatarsal base, or inability to bear weight for 4 steps) determine the need for an X-ray.

Ankle fractures

Pott (bimalleolar) and trimalleolar fractures from rotational forces; classified by Weber (A/B/C — level of the fibular fracture relative to the syndesmosis). Unstable fractures with talar shift require open reduction and internal fixation, as 1 mm of lateral talar shift reduces the contact area by ≈40%.

Achilles tendon rupture

Sudden pain "like being kicked" at push-off; palpable gap and a positive Simmonds/Thompson test (no plantarflexion on squeezing the calf).

Mnemonics

Structures behind the medial malleolus (anterior → posterior)

"Tom, Dick And Very Nervous Harry": Tibialis posterior, flexor Digitorum longus, posterior tibial Artery, Vein(s), tibial Nerve, flexor Hallucis longus.

Test yourself

The ankle joint is most stable in which position, and why?
  1. Plantarflexion, because the posterior talus is wider
  2. Dorsiflexion, because the anterior part of the talar trochlea is wider and wedges into the mortise
  3. Inversion, because the deltoid ligament is slack
  4. Eversion, because the lateral malleolus is shorter

Answer: Dorsiflexion, because the anterior part of the talar trochlea is wider and wedges into the mortise

The trochlea of the talus is wider anteriorly; in dorsiflexion this wide part fills the mortise between the malleoli (close-packed). In plantarflexion the narrow posterior part permits movement, so most sprains occur then.

In a typical inversion sprain of the ankle, which ligament is usually torn first?
  1. Deltoid ligament
  2. Calcaneofibular ligament
  3. Anterior talofibular ligament
  4. Posterior talofibular ligament

Answer: Anterior talofibular ligament

The anterior talofibular ligament is the weakest lateral ligament and is taut in plantarflexion, so it is the first to tear in inversion–plantarflexion injuries; the calcaneofibular ligament tears next; the posterior talofibular ligament is rarely involved.

More skeletal system questions

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.