Extensor digitorum brevis

At a glance

English

Extensor digitorum brevis

Latin (TA2)

Extensor brevis digitorum

System

Muscle

Region

Lower limb

Side

Paired, left and right

Inserts on

The middle phalanx of fourth finger of foot and middle phalanx of third finger of foot

About the extensor digitorum brevis

Extensor digitorum brevis is the only muscle on the dorsum of the foot, apart from its medial slip, extensor hallucis brevis, with which it is often counted as one muscle. It forms the soft, slightly bulging mass felt just in front of the lateral malleolus, which can be mistaken for swelling after an ankle injury.

It arises from the upper and outer surface at the front of the calcaneus, just ahead of the fibularis brevis groove, and from the inferior extensor retinaculum's stem and the interosseous talocalcaneal ligament nearby. The belly runs forwards and inwards across the dorsum, beneath the long extensor's tendons, and divides into slips. The most medial slip, extensor hallucis brevis, goes to the big toe. The others become slender tendons for toes two, three and four; each joins the outer edge of the long extensor tendon to the same toe near the metatarsophalangeal joint, and their fibres then share the long tendon's extensor expansion over the phalanges.

The muscle helps lift the toes at the metatarsophalangeal joints and, through the expansion, at the interphalangeal joints. It works with the long extensor and steadies the toes when the ankle is fully dorsiflexed and the long tendon is slack. The little toe receives no slip, so only the long extensor raises it.

Its nerve is the lateral terminal branch of the deep fibular nerve, carrying fibres mainly from L5. Because the muscle is easy to see and feel, testing its contraction or recording from it helps in finding an L5 root lesion or damage to the deep fibular nerve. The dorsalis pedis artery runs beneath its medial part, crossed by the tendon of extensor hallucis brevis.

Attachments, action and supply

Origin

Upper lateral surface of the front of the calcaneus, the inferior extensor retinaculum and the interosseous talocalcaneal ligament.

Insertion

Outer sides of the long extensor tendons to toes two, three and four, and through their extensor expansions the middle and distal phalanges.

Action

Extends toes two to four at the metatarsophalangeal and interphalangeal joints, assisting extensor digitorum longus.

Nerve supply

Deep fibular nerve, lateral terminal branch (L5, S1).

Blood supply

Lateral tarsal artery from the dorsalis pedis, with the perforating branch of the fibular artery and the anterior lateral malleolar artery.