Ankle Joint
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Direct answer
The ankle joint (talocrural joint) is a synovial hinge joint in which the trochlea and malleolar facets of the talus fit a mortise formed by the lower tibia, both malleoli and the inferior transverse tibiofibular ligament. Its strong medial deltoid ligament and weaker lateral ligaments allow dorsiflexion and plantar flexion, and inversion injuries in plantar flexion tear the anterior talofibular ligament first — the commonest ankle sprain.
What you must remember
- Type and bones: synovial hinge between the tibial plafond with both malleoli and the body of the talus; the lateral malleolus reaches lower and lies more posteriorly than the medial.
- Deltoid ligament (medial): strong and two-layered — superficial tibionavicular, tibiocalcaneal and posterior tibiotalar bands with a deep anterior tibiotalar band, running from the medial malleolus to the navicular, sustentaculum tali and talus.
- Lateral ligaments: anterior talofibular (weakest, torn first), calcaneofibular, and posterior talofibular (strongest).
- Movements: dorsiflexion of about 20 to 30 degrees and plantar flexion of about 40 to 50 degrees; the narrower posterior trochlea makes the joint least stable in plantar flexion, favouring inversion injury.
- Relations: in front — the long extensor tendons, the dorsalis pedis artery and the deep peroneal nerve; behind — tibialis posterior, flexor digitorum longus, the posterior tibial vessels and tibial nerve, and flexor hallucis longus (Tom, Dick and Harry).
- Blood and nerve supply: malleolar branches of the anterior tibial, dorsalis pedis and peroneal arteries; deep peroneal and tibial nerves by Hilton's law.
- Clinical importance: inversion sprains damage the lateral ligament complex; eversion forces may avulse the medial malleolus or disrupt the syndesmosis, producing Pott's, Tillaux and Maisonneuve patterns.
Common confusion
The ankle that rolls inward — inversion — damages the ligaments on the outer side, chiefly the anterior talofibular, not the deltoid. The deltoid is so strong that eversion forces fracture the medial malleolus instead of rupturing it. Remember also that the fibula transmits part of the load through the syndesmosis.
Exam-focused takeaway
For theory, draw the mortise with the three bones, label the deltoid and lateral ligaments, and add the anterior and posterior relations. In viva, expect the ligament torn in an inversion sprain, Tom, Dick and Harry behind the medial malleolus, and why plantar flexion predisposes to sprains. For spotters, identify the deltoid ligament and tarsal bones on specimens and ankle radiographs.
Frequently asked questions
What type of joint is the ankle?
A synovial hinge between the lower tibia and fibula (with the inferior transverse tibiofibular ligament) and the trochlea of the talus.
Name the ligaments of the ankle.
Medially the deltoid with superficial and deep parts; laterally the anterior talofibular, calcaneofibular and posterior talofibular ligaments.
Which ligament is torn first in a sprain?
The anterior talofibular ligament, because inversion injuries occur in plantar flexion when the talus is least stable.
What is Tom, Dick and Harry at the ankle?
From medial to lateral behind the medial malleolus — tibialis posterior, flexor digitorum longus, then the posterior tibial artery and tibial nerve, and finally flexor hallucis longus.
What are the movements and their range?
Dorsiflexion of about 20 to 30 degrees and plantar flexion of about 40 to 50 degrees around a transverse axis through the talus.
What is a Pott's fracture?
A fracture-dislocation of the ankle mortise, classically from forced eversion fracturing the fibula above the syndesmosis with avulsion of the medial malleolus or rupture of the deltoid.