Muscle · Lower limb
Extensor digitorum brevis: origin, insertion, action and innervation
The extensor digitorum brevis runs from the calcaneus to the tendons of toes 2 to 4. It extends those toes and is supplied by the deep fibular nerve.
Quick answer
- Latin name
- Musculus extensor digitorum brevis
- Origin
- Upper and outer surface of the front of the calcaneus, floor of the sinus tarsi and inferior extensor retinaculum
- Insertion
- Lateral sides of the extensor digitorum longus tendons of the second, third and fourth toes
- Action
- Extends the second to fourth toes at the metatarsophalangeal and interphalangeal joints
- Innervation
- Deep fibular nerve, lateral branch (L5-S1)
- Blood supply
- Lateral tarsal artery from the dorsalis pedis artery, with the arcuate artery and the perforating branch of the fibular artery
See it on the 3D body
The extensor digitorum brevis lit on the 3D leg and foot, as in the leg and foot quiz. Turn the body, peel the layers, tap any structure for its name.
The extensor digitorum brevis is a small, flat muscle on the top of the foot that runs from the calcaneus to the tendons of the second, third and fourth toes. It helps extend those toes and is supplied by the lateral branch of the deep fibular nerve (L5-S1).
Where it is
The top of the foot (the dorsum) has very little muscle: almost everything you see there is tendon. The extensor digitorum brevis and the extensor hallucis brevis are the only muscles that sit on the dorsum.
Its belly lies on the outer side of the dorsum, just in front of the lateral malleolus (the bony bump on the outside of the ankle). It lies under the long extensor tendons, which cross over it on their way to the toes. If you lift your toes hard, a soft bulge often appears in front of the outer ankle: that is the belly of this muscle. People sometimes mistake it for a swelling.
The muscle splits into small tendons that run forward and medially. Its most medial part goes to the big toe and is usually named separately as the extensor hallucis brevis, so the extensor digitorum brevis itself serves the second to fourth toes. The fifth toe gets no tendon from it. See the bones underneath on bones of the foot.
Origin and insertion
- Origin: the upper and outer surface of the front part of the calcaneus, the floor of the sinus tarsi (the tunnel between the talus and calcaneus) and the inferior extensor retinaculum.
- Insertion: three thin tendons that join the lateral sides of the extensor digitorum longus tendons of the second, third and fourth toes. Through those tendons it reaches the dorsal expansions over the phalanges.
So it does not attach directly to bone at its far end. It adds its pull to the long tendons, much like a helper tugging on the same ropes.
What it does
The extensor digitorum brevis extends the second, third and fourth toes at the metatarsophalangeal and interphalangeal joints. It assists the extensor digitorum longus, which does most of the work.
Because it starts on the calcaneus and does not cross the ankle, it acts on the toes alone and has no effect on the ankle joint. Its tendons run obliquely, from the outer side of the foot toward the toes, while the long tendons run straight down from the front of the ankle. You see both sets at work when you lift your toes off the floor while standing.
Innervation and blood supply
The extensor digitorum brevis is supplied by the lateral (terminal) branch of the deep fibular nerve (L5-S1). The deep fibular nerve runs down the front of the leg, crosses the ankle, and divides into a medial branch to the skin between the first and second toes and a lateral branch to this muscle.
Its blood comes from the lateral tarsal artery, a branch of the dorsalis pedis artery, helped by the arcuate artery and the perforating branch of the fibular artery.
How to remember it
- One fleshy mass on the dorsum: the top of the foot has a single muscle belly, shared with its big-toe part, the extensor hallucis brevis.
- Brevis starts in the foot: short muscles arise in the foot, long ones in the leg.
- Three toes, not four: the long extensor goes to toes 2 to 5. The short one goes to toes 2 to 4. The fifth toe is left out.
- The bump in front of the outer ankle: lift your toes and look for it.
Test yourself in the leg and foot quiz.
Frequently asked questions
What does the extensor digitorum brevis do?
It extends the second to fourth toes at the metatarsophalangeal and interphalangeal joints.
What nerve supplies the extensor digitorum brevis?
The lateral branch of the deep fibular nerve, from roots L5 and S1.
Where is the extensor digitorum brevis?
On the outer part of the top of the foot, just in front of the lateral malleolus, under the long extensor tendons.
What is the difference between the extensor digitorum brevis and longus?
The brevis lies on the foot and extends toes 2 to 4. The longus lies in the leg, extends toes 2 to 5 and also dorsiflexes the ankle.
