The extensor hallucis longus runs between the tibialis anterior and extensor digitorum longus in the anterior compartment of the leg, its tendon crossing the ankle under the extensor retinaculum to reach the great toe. It is an important dorsiflexor and the key muscle for testing the L5 nerve root, with EHL weakness being one of the most sensitive clinical signs of L5 radiculopathy from a lumbar disc herniation.
| Origin | Middle half of the medial surface of the fibula and adjacent interosseous membrane |
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| Insertion | Dorsal surface of the base of the distal phalanx of the great toe |
| Nerve Supply | Deep peroneal nerve (L4, L5, S1) |
| Blood Supply | Anterior tibial artery |
| Actions | Extension of the great toe; Dorsiflexion of the ankle; Assists inversion of the foot |
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Its great toe extension allows foot clearance during swing phase of gait and its ankle dorsiflexion contribution assists tibialis anterior. When tibialis anterior is paralysed, the EHL often hypertrophies to compensate and can produce a characteristic cockup deformity of the great toe.
EHL weakness is the most clinically sensitive indicator of L5 nerve root compression, making great toe dorsiflexion strength testing a routine part of the lumbar spine neurological examination. EHL tendinopathy on the dorsal foot from shoe pressure is an overuse injury in runners and hikers. The EHL tendon is also at risk during distal tibial or talar neck fracture surgery.
The EHL tendon is the most prominent structure visible on the dorsal foot during active great toe extension, running from the ankle toward the great toe and clearly visible in lean individuals during resisted dorsiflexion.
Overuse inflammation on the dorsal foot from direct shoe pressure or repetitive loading, producing dorsal foot pain reproduced by resisted great toe extension and worsening with running.
Compression of the L5 nerve root producing EHL weakness as the most sensitive early sign, identified clinically by comparing great toe extension strength bilaterally.
