The extensor digitorum brevis is a small muscle on the dorsolateral foot arising from the calcaneus and running obliquely to the lateral extensor tendons of the middle three toes. Its muscle belly is the visible rounded mass on the dorsolateral foot that is often mistaken for a ganglion or cyst by patients when it becomes oedematous after a lateral ankle sprain. The most medial portion extending to the great toe is called the extensor hallucis brevis.
| Origin | Anterior calcaneus (superolateral surface, dorsal to the sinus tarsi) |
|---|---|
| Insertion | Bases of the proximal phalanges of toes 2, 3, and 4 via the lateral sides of the long extensor tendons |
| Nerve Supply | Deep peroneal nerve (L5, S1) |
| Blood Supply | Dorsalis pedis artery |
| Actions |
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By pulling the middle toes obliquely it assists toe extension and provides a medial direction of pull that complements the straightening action of the long extensors.
EDB hypertrophy from adaptive changes in drop foot, Charcot-Marie-Tooth disease, or peroneal nerve palsy can produce a visible dorsal foot mass that is easily confirmed on ultrasound. EDB muscle belly swelling after lateral ankle sprains is a common source of confusion with a ganglion cyst. An absent EDB muscle, identifiable clinically by the absent dorsolateral foot bulk and confirmed on ultrasound, localises L5 and S1 nerve root or deep peroneal nerve lesions.
The EDB muscle belly is palpable as the rounded mass on the dorsolateral foot just distal to the lateral malleolus, becoming firm during active toe extension particularly of toes 2, 3, and 4.
Avulsion of the EDB origin from the anterior calcaneus during forceful dorsiflexion inversion, producing dorsolateral foot pain that must be distinguished from anterior process calcaneal fracture and lateral ankle ligament injury.
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