The extensor hallucis brevis is the medial portion of the EDB, providing a short intrinsic extensor to the great toe supplementing the EHL. As an exclusively intrinsic foot muscle, it is a sensitive early indicator of L5 nerve root or deep peroneal nerve compromise — its selective atrophy before tibialis anterior weakness appears in L5 radiculopathy from the intrinsic muscle's total dependence on L5 through the deep peroneal nerve.
| Origin | Anterior calcaneus dorsal surface, considered the medial portion of the EDB |
|---|---|
| Insertion | Dorsal base of the great toe proximal phalanx |
| Nerve Supply | Deep peroneal nerve (L5, S1) |
| Blood Supply | Dorsalis pedis artery |
| Actions | Extension of the great toe MTP joint |
|---|
By extending the great toe MTP joint alongside the EHL it supports toe clearance during swing phase and contributes to the toe-off phase, and its wasting produces subtle great toe weakness that precedes the more obvious anterior compartment weakness in progressive neuropathy.
EHB atrophy is an early, sensitive sign of L5 nerve root compression or deep peroneal nerve palsy because intrinsic foot muscles denervate before the larger tibialis anterior. Comparison of dorsolateral foot bulk between sides identifies asymmetric EHB wasting. The Babinski response involves EHB and EHL contraction from the plantar surface stimulus in upper motor neurone lesions.
The EHB contributes to the rounded dorsolateral foot muscle mass medial to the main EDB, becoming firm during isolated great toe extension and distinguishable from EDB by its more medial course toward the great toe.
EHB atrophy appearing before anterior compartment weakness as an early sensitive indicator of L5 nerve root compression from lumbar disc herniation.
