Leg and ankle: compartments, nerves and ankle ligaments

1. Nerves of the leg

The common fibular nerve divides at the fibular neck: the deep fibular nerve runs to the front compartment (dorsiflexors) and the superficial fibular nerve to the lateral compartment (evertors) and the skin of the dorsum of the foot. The tibial nerve runs in the back with the posterior tibial artery.

Surgeon’s corner: A tight cast or a fracture of the fibular neck damages the common fibular nerve: foot drop. Test the first web space (deep fibular) and the dorsum of the foot (superficial fibular).

2. Arteries of the leg

The popliteal artery divides into the anterior tibial artery (through the interosseous membrane to the front, ending as dorsalis pedis) and the posterior tibial artery (behind the medial malleolus), which gives the fibular artery.

Surgeon’s corner: Feel the dorsalis pedis pulse lateral to the extensor hallucis longus tendon and the posterior tibial pulse behind the medial malleolus: always document them before and after reducing an ankle fracture.

3. Lateral ankle ligaments

Three ligaments hold the lateral malleolus to the talus and calcaneus: anterior talofibular (weakest, torn first in an inversion sprain), calcaneofibular, and posterior talofibular (strongest).

Surgeon’s corner: Anterior drawer test for the anterior talofibular ligament. Most sprains heal with functional treatment; chronic instability is repaired (Broström).

4. Superficial veins and sensory nerves

The great saphenous vein runs in front of the medial malleolus up the medial leg with the saphenous nerve. The small saphenous vein runs behind the lateral malleolus with the sural nerve.

Surgeon’s corner: The great saphenous vein in front of the medial malleolus is the classic emergency cut-down site. The sural nerve is at risk in Achilles tendon surgery and posterolateral ankle approaches.