Muscle · Lower limb
Flexor digitorum brevis: origin, insertion, action and innervation
The flexor digitorum brevis runs from the calcaneus to the middle phalanges of toes 2 to 5. It flexes those toes and is supplied by the medial plantar nerve.
Quick answer
- Latin name
- Musculus flexor digitorum brevis
- Origin
- Medial process of the tuberosity of the calcaneus, plantar aponeurosis and intermuscular septa
- Insertion
- Both sides of the middle phalanges of the second to fifth toes
- Action
- Flexes the lateral four toes at the proximal interphalangeal joints, then at the metatarsophalangeal joints; supports the arches
- Innervation
- Medial plantar nerve (S2-S3)
- Blood supply
- Medial and lateral plantar arteries, plantar metatarsal and plantar digital arteries
See it on the 3D body
The flexor 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 flexor digitorum brevis is a flat muscle in the middle of the sole that runs from the heel bone to the middle phalanges of the second to fifth toes. It bends those toes at their proximal interphalangeal joints and is supplied by the medial plantar nerve (S2-S3).
Where it is
Peel away the thick plantar aponeurosis from the sole and the flexor digitorum brevis is the first muscle you see, right in the center. It is the middle muscle of the first layer of the sole, with the abductor hallucis on its inner side and the abductor digiti minimi on its outer side. Its superficial surface is fused with the plantar aponeurosis near the heel, so the two are hard to separate.
The muscle runs forward from the heel and divides into four tendons, one for each of the lateral four toes. Deep to it lie the tendons of the flexor digitorum longus, which head for the same toes. The slip to the fifth toe is small and is often missing.
The arrangement copies the hand. In the forearm, the flexor digitorum superficialis has tendons that split to let the deeper profundus tendons pass. In the foot, the flexor digitorum brevis plays the superficialis role and the flexor digitorum longus plays the profundus role. See the bones under it on bones of the foot.
Origin and insertion
- Origin: the medial process of the calcaneal tuberosity of the calcaneus, the central part of the plantar aponeurosis, and the septa that separate it from its neighbors.
- Insertion: near the base of each toe, every tendon splits into two slips. The flexor digitorum longus tendon passes through the gap, and the two slips reunite and attach to both sides of the middle phalanx of toes 2 to 5 (see the phalanges of the foot).
This split is why the muscle is sometimes called "perforated": its tendons are pierced by the long flexor tendons.
What it does
- Flexion of the lateral four toes: it bends toes 2 to 5 at the proximal interphalangeal joints, the middle joint of each toe.
- Flexion at the metatarsophalangeal joints: by continuing to pull, it also bends the toes at the ball of the foot.
- Supporting the arches: running from the heel to the toes along the sole, it helps hold up the longitudinal arch and stiffen the foot during push-off.
It does not reach the distal phalanges, so it cannot bend the tips of the toes. That job belongs to the flexor digitorum longus.
Innervation and blood supply
The flexor digitorum brevis is supplied by the medial plantar nerve (S2-S3), a terminal branch of the tibial nerve. The nerve runs forward between this muscle and the abductor hallucis.
Its blood comes from the medial and lateral plantar arteries, with branches from the plantar metatarsal and plantar digital arteries near the toes.
How to remember it
- Brevis bends the middle: the short flexor stops at the middle phalanx; the long flexor goes on to the distal phalanx.
- Foot copy of the superficialis: split tendons, middle phalanges, superficial position. If you know the hand, you know this muscle.
- Center of layer one: abductor hallucis, flexor digitorum brevis, abductor digiti minimi, from medial to lateral.
- LAFF: it is one of the four sole muscles supplied by the medial plantar nerve, with the first lumbrical, the abductor hallucis and the flexor hallucis brevis.
Test yourself in the leg and foot quiz.
Frequently asked questions
What does the flexor digitorum brevis do?
It flexes the second to fifth toes at their proximal interphalangeal joints and then at the metatarsophalangeal joints. It also helps support the arches.
What nerve supplies the flexor digitorum brevis?
The medial plantar nerve, from roots S2 and S3.
Where does the flexor digitorum brevis insert?
On both sides of the middle phalanges of the four lateral toes, after each tendon splits around a flexor digitorum longus tendon.
What is the difference between the flexor digitorum brevis and longus?
The brevis lies in the sole and bends the middle joint of toes 2 to 5. The longus starts in the leg and bends the tips of the same toes.
