Extensor digitorum brevis muscle

Origin and insertion

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 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.

Relations

The extensor digitorum brevis is covered by the deep dorsal fascia of the foot, which is continuous with the inferior extensor retinaculum, one of the origin points of the extensor digitorum brevis. During dorsiflexion, the belly of the muscle forms a small elevation that can be seen and palpated anteriorly to the lateral malleolus. As it courses over the dorsum of the foot, the muscle is partly covered by the tendons of fibularis tertius and extensor digitorum longus muscles. 

In addition, the most medial tendon of extensor digitorum brevis crosses the dorsalis pedis artery over the calcaneocuboid joint, and the lateral tarsal artery over the navicular bone. The lateral tarsal artery runs laterally underneath extensor digitorum brevis and supplies it. The muscle also courses over the lateral terminal branch of deep fibular (peroneal) nerve.

Innervation

The extensor digitorum brevis muscle is supplied by the lateral terminal branch of deep fibular (peroneal) nerve, which arises from the L5 and S1 spinal nerves.

Blood supply

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.

Function

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. 

Now that you have learned the functions of extensor digitorum brevis, you can now check out the functions of other muscles of the foot using the following resources: