The extensor hallucis brevis is technically the medial portion of the extensor digitorum brevis, providing a short intrinsic extensor to the great toe that supplements the EHL. Its small muscle belly on the dorsolateral foot contributes to the EDB muscle mass palpable there. EHB atrophy is a sensitive early indicator of L5 nerve root or deep peroneal nerve compromise because it is an exclusively intrinsic muscle dependent on the nerve for its entire motor supply.
| Origin | Anterior calcaneus, considered the medial portion of the extensor digitorum brevis |
|---|---|
| Insertion | Dorsal surface of the base of the proximal phalanx of the great toe |
| Nerve Supply | Deep peroneal nerve (L5, S1) |
| Blood Supply | Dorsalis pedis artery |
| Actions | Extension of the great toe MCP joint; Assists the EHL in great toe dorsiflexion |
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It supplements the EHL in extending the great toe MTP joint, important during the swing phase of gait for toe clearance and during balance activities requiring active toe extension.
EHB atrophy is assessed clinically by comparing the dorsolateral foot bulk between sides and is an early, sensitive sign of L5 radiculopathy because intrinsic foot muscles denervate before the larger tibialis anterior. The EHB contributes to the Babinski response alongside the EHL when the plantar surface is stroked.
The EHB forms the medial portion of the rounded dorsolateral foot muscle mass and is distinguished from the main EDB by its course toward the great toe, becoming firm during isolated great toe extension.
Early L5 or deep peroneal nerve compromise producing EHB atrophy detectable as asymmetric dorsolateral foot wasting before tibialis anterior weakness becomes clinically apparent.
