SN6 SHORT NOTE 5M ★ High-yield

Describe the ankle joint with its ligaments and stability. Add a note on ankle sprain.

Anatomy · 1st Professional — Pre-Clinical

Definition

The ankle (talocrural) joint is a synovial hinge joint between the lower ends of the tibia and fibula above and the trochlea of the talus below.

The tibia and fibula form a mortise that grips the talus
Uniaxial — permits only dorsiflexion and plantar flexion

Ligaments

Ligament	Parts	Function
Medial (deltoid) ligament	Tibionavicular, tibiocalcanean, anterior and posterior tibiotalar	Very strong; resists eversion; so strong that it avulses the medial malleolus rather than tearing
Lateral ligament	Anterior talofibular, calcaneofibular, posterior talofibular	Weaker; resists inversion. The anterior talofibular is the weakest and most commonly torn
Inferior tibiofibular	Anterior, posterior and interosseous	Holds the mortise together — a syndesmosis

Stability and the Close-packed Position

The trochlea of the talus is wider IN front than behind
In dorsiflexion the wider part is gripped in the mortise → the joint is close-packed and most stable
In plantar flexion the narrower part lies in the mortise → the joint is loose and least stable
This is why sprains occur in plantar flexion and inversion — walking downstairs, stepping off a kerb, or landing from a jump

Movements and Muscles

Movement	Muscles	Nerve
Dorsiflexion	Tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius	Deep peroneal
Plantar flexion	Gastrocnemius, soleus, tibialis posterior, flexor hallucis longus, flexor digitorum longus, peronei	Tibial

Inversion and eversion occur at the subtalar and transverse tarsal joints, not at the ankle — a point often confused
Inversion — tibialis anterior and posterior; eversion — peroneus longus and brevis

Retinacula and Relations

Behind the medial malleolus, from front to back — Tibialis posterior, flexor Digitorum longus, posterior tibial Artery, tibial Nerve, flexor Hallucis longus
Mnemonic — "Tom, Dick And Nervous Harry"
These pass beneath the flexor retinaculum in the tarsal tunnel
In front — beneath the extensor retinacula, the anterior tibial vessels and deep peroneal nerve lie between extensor hallucis longus and extensor digitorum longus

Applied Aspects

Pott fracture — a fracture-dislocation of the ankle from forced eversion; classified by the number of malleoli involved (unimalleolar, bimalleolar, trimalleolar)
Ottawa ankle rules determine whether a radiograph is needed after injury, reducing unnecessary imaging
Tarsal tunnel syndrome — compression of the tibial nerve beneath the flexor retinaculum, the lower-limb equivalent of carpal tunnel syndrome
Rupture of the tendo calcaneus — sudden pain "like being kicked", a palpable gap, and a positive Simmonds (Thompson) test — squeezing the calf fails to plantarflex the foot
Talus has no muscular attachments and a retrograde blood supply, so fracture of its neck risks avascular necrosis of the body

All questions in Lower Limb

Every Anatomy chapter →