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Extensor Digitorum Brevis Third Slip

musculus extensor digitorum brevis (fasciculus tertius)

The third slip of extensor digitorum brevis inserts into the third toe, lying between the second and fourth slips. It is smaller than the second slip but contributes meaningfully to third toe extension, particularly during toe-off phase of gait.

Nerve: Deep peroneal nerve (L5, S1) Blood Supply: Arcuate artery Region: Foot & Ankle

Anatomical Data

Origin, Insertion & Supply

Origin	Dorsal surface of the calcaneus, central portion of EDB origin
Insertion	Dorsal surface of the proximal phalanx of the third toe and lateral EDL tendon to the third toe
Nerve Supply	Deep peroneal nerve (L5, S1)
Blood Supply	Arcuate artery

Biomechanics

Function & Actions

Actions	Extends the third MTP joint; Assists dorsiflexion of the third toe

Clinical Relevance

Clinical Notes

The third EDB slip is at risk during the third web space neuroma excision approach, where the dorsal incision passes through the EDB territory. EMG studies of individual EDB slips help localise deep peroneal nerve branch lesions within the foot. Selective atrophy of the EDB slips indicates deep peroneal nerve injury distal to the ankle.

Palpation

Palpated on the lateral dorsum of the foot between the second and fourth metatarsals during resisted third toe extension.

Pathology

Common Injuries & Conditions

Deep Peroneal Nerve Distal Lesion

Selective EDB atrophy from deep peroneal nerve injury at the dorsal foot level, producing third (and adjacent) toe extensor weakness without anterior compartment involvement.