Extensor Digitorum Brevis Muscle – Nerve Supply, Function

The Extensor Digitorum Brevis Muscle (sometimes EDB) is a muscle on the upper surface of the foot that helps extend digits 2 through 4. The extensor digitorum brevis (also extensor digitorum brevis muscle, latin: musculus extensor digitorum brevis) is a muscle of the upper surface (dorsum) of the foot that aids in extending the second, third and fourth digits of the foot.

Structure

The muscle originates from the forepart of the upper and lateral surface of the calcaneus (in front of the groove for the peroneus brevis tendon), from the interosseous talocalcaneal ligament and the stem of the inferior extensor retinaculum. The fibres pass obliquely forwards and medially across the dorsum of the foot and end in four tendons. The medial part of the muscle, also known as extensor hallucis brevis, ends in a tendon that crosses the dorsal pedis artery and inserts into the dorsal surface of the base of the proximal phalanx of the great toe. The other three tendons insert into the lateral sides of the tendons of extensor digitorum longus for the second, third and fourth toes.

• Origin: Dorsal surface of the calcaneus
• Insertion: The base of the proximal phalanx of digits two through four
• Action: Extend the toes
• Blood Supply: Dorsalis pedis
• Innervation: Deep peroneal nerve

Origin and Insertion of Extensor Digitorum Brevis Muscle

The extensor digitorum brevis is a thin muscle of the foot that originates from three locations:

• anterior part of the superolateral surface of calcaneus,
• the talocalcaneal interosseous ligament,
• the stem of the inferior extensor retinaculum of the ankle.

The muscle belly divides into 4 slips and respective tendons that pass anteromedially, from the lateral side towards the medial side of the foot. The most medial slip and tendon of extensor digitorum brevis usually constitute a distinct muscle named extensor hallucis brevis. The lateral 3 tendons also course anteriorly over the tarsal and metatarsal bones, to insert at the lateral aspect of the tendons of extensor digitorum longus.

Extensor digitorum brevis (EDB muscle) is subject to significant variation. At times, the muscle is conjoined with the adjacent dorsal interossei muscles of the foot. The extensor digitorum brevis can also give off an additional tendon for the fifth digit, or accessory slips for the talus and navicular bones. It can even have one or more tendons absent.

Nerve Supply of Extensor Digitorum Brevis Muscle

Nerve supply: lateral terminal branch of Deep Peroneal Nerve (deep fibular nerve) (proximal sciatic branches L4-L5, but most clinically relevant L5 with L4/L5 spinal disc herniation causing L5 lesion). Same innervation of Extensor Hallucis Brevis

Blood Supply of Extensor Digitorum Brevis Muscle

The extensor digitorum brevis muscle is richly vascularized. Its proximal blood supply originates from the anterior perforating branch of the fibular artery and the anterior lateral malleolar artery, a branch of the anterior tibial artery.

More distally, the muscle receives blood supply from the dorsalis pedis artery and its branches, such as lateral tarsal arteries, arcuate artery, dorsal metatarsal arteries (first, second, third), proximal and distal perforating arteries and dorsal digital arteries to the medial four toes.

Functions of Extensor Digitorum Brevis Muscle

Extensor digitorum brevis extends the first four digits at the metatarsophalangeal joint and assists in extending the second, third and fourth digits at the interphalangeal joint. The fifth digit, lacking any insertion from extensor digitorum brevis, can only be raised by the long extensor.

The lack of direct bony attachments confines extensor digitorum brevis to help other muscles perform their actions. Most importantly, it assists extensor digitorum longus to extend the second, third and fourth toes at the corresponding distal interphalangeal joints. Additionally, these two muscles cooperate to aid the lumbrical muscles of the foot to extend the same interphalangeal joints.

The most medial tendon of extensor digitorum brevis (extensor hallucis brevis) extends the great toe at the metatarsophalangeal joint. In conclusion, extensor digitorum brevis works in unison with other muscles to raise the toes off the ground when walking or running.

References

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