The sprained ankle: ligaments, tendons and nerves of the ankle and foot

1. The ankle mortise and the bones you must palpate

The upper ankle joint is a mortise: the tibia (with the medial malleolus) and the fibula (lateral malleolus, which reaches lower) clasp the dome of the talus. The dome is wider in front, so the joint is most stable in dorsiflexion and loosest in plantarflexion, when most sprains happen. Below it, the lower ankle (subtalar) joint lets the heel tilt in and out.

Surgeon’s corner: Ottawa ankle rules: X-ray only if there is pain in the malleolar zone with bone tenderness at the posterior edge or tip of either malleolus (lower 6 cm), or inability to take four steps; foot X-ray if the base of the 5th metatarsal or the navicular is tender. Sensitivity close to 100% for clinically relevant fractures.

2. Inversion sprain: the lateral ligaments tear in order

With the foot plantarflexed and inverted, the anterior talofibular ligament (ATFL) is taut and almost vertical: it tears first (about two thirds of sprains are isolated ATFL tears). With more force the calcaneofibular ligament (CFL) goes as well; the strong posterior talofibular ligament (PTFL) tears only in dislocations.

Surgeon’s corner: Examine 4–5 days after the injury, when swelling and pain have settled: the anterior drawer test (ATFL) and the talar tilt test (CFL) are then far more reliable. Grade I–III sprains are treated functionally: short protection in a brace, early weight bearing, then proprioceptive and peroneal training. Surgery (Broström repair) only for chronic instability.

3. High ankle sprain: the syndesmosis

Above the joint, the distal tibia and fibula are bound by the syndesmosis: the anterior inferior tibiofibular ligament (AITFL), the posterior one with its deep transverse part, and the interosseous ligament continuing as the interosseous membrane. External rotation of the foot (football, skiing) forces the talus to push the fibula away and tears it.

Surgeon’s corner: Pain above the joint line, a positive squeeze test (compressing tibia and fibula at mid-calf hurts at the ankle) and pain on external rotation. Recovery takes twice as long as a lateral sprain. Always palpate the whole fibula up to the knee: a medial injury with a high fibular fracture is a Maisonneuve injury and needs fixation.

4. Eversion: the deltoid ligament

On the medial side the fan-shaped deltoid ligament runs from the medial malleolus: superficially to the navicular (tibionavicular) and the sustentaculum tali (tibiocalcaneal), deeply to the talus (posterior tibiotalar). It is far stronger than the lateral ligaments; isolated tears are rare.

Surgeon’s corner: Medial pain after a "sprain" means a more severe injury: look for a lateral malleolus fracture (Weber B) and measure the medial clear space on a weight-bearing or stress view (> 4–5 mm = deltoid torn = unstable ankle).

5. Not every sprain is the ankle: Chopart and the 5th metatarsal

The same twist can injure the midfoot. The bifurcate ligament (calcaneonavicular and calcaneocuboid limbs) sits about 2 cm in front of the ATFL and can avulse the anterior process of the calcaneus. Fibularis brevis inserts on the base of the 5th metatarsal and can pull it off.

Surgeon’s corner: Palpate point by point: ATFL, CFL, bifurcate ligament, base of the 5th metatarsal, navicular. A tuberosity avulsion (zone 1) is treated in a hard-soled shoe; a Jones fracture (zone 2) heals poorly and is often fixed in athletes.

6. The peroneal tendons: the dynamic lateral ligament

Fibularis (peroneus) longus and brevis run in a groove behind the lateral malleolus, held by the superior peroneal retinaculum. They evert the foot and are the active guard against inversion: brevis inserts on the 5th metatarsal, longus crosses under the cuboid to the 1st metatarsal and medial cuneiform.

Surgeon’s corner: Pain and clicking behind the malleolus after a sprain suggest a peroneal tendon tear or dislocation (retinaculum torn), often missed. Peroneal strengthening and balance training after every sprain halve the risk of re-injury.

7. Behind the medial malleolus: tendons, artery and tibial nerve

From front to back behind the medial malleolus: tibialis posterior, flexor digitorum longus, the posterior tibial artery and veins with the tibial nerve, and flexor hallucis longus ("Tom, Dick And Very Nervous Harry"). Under the flexor retinaculum this is the tarsal tunnel; the nerve then divides into the medial and lateral plantar nerves.

Surgeon’s corner: Feel the posterior tibial pulse halfway between the malleolus and the Achilles tendon. A "sprain" in which the patient cannot push off may be an Achilles rupture: do the Thompson test (squeeze the calf, the foot should plantarflex).

8. Nerves at risk around the ankle

The superficial fibular nerve pierces the fascia about 10–12 cm above the lateral malleolus and crosses the front of the ankle to the dorsum of the foot. The sural nerve runs behind the lateral malleolus with the small saphenous vein. The deep fibular nerve and the dorsalis pedis artery run in front, under the extensor tendons, to the first web space.

Surgeon’s corner: A severe inversion sprain can stretch the superficial fibular nerve (numbness on the dorsum of the foot). It is also at risk from the anterolateral arthroscopy portal and lateral approaches; plantarflex and invert the foot to see it under the skin before you cut.