Flexor digitorum brevis

At a glance

English

Flexor digitorum brevis

Latin (TA2)

Flexor brevis digitorum

System

Muscle

Region

Lower limb

Side

Paired, left and right

Inserts on

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

About the flexor digitorum brevis

Flexor digitorum brevis occupies the centre of the sole in its most superficial muscle layer, resting on the plantar aponeurosis and firmly bound to its central band. On each side lie abductor hallucis and abductor digiti minimi. A thin layer of fascia separates its deep surface from the lateral plantar nerve and vessels.

It begins as a narrow tendon on the calcaneal tuberosity's medial process, and also takes fibres from the aponeurosis and from the septa beside it. Its belly runs forwards and divides into tendons for toes two to five. Near the base of each proximal phalanx a tendon splits in two, letting the matching flexor digitorum longus tendon pass through; the halves then rejoin to form a grooved bed for the long tendon, and part again to fix on both sides of the middle phalanx. The pattern copies the superficial finger flexor of the forearm, so this muscle is in effect its counterpart in the foot.

The muscle flexes the lesser toes at their metatarsophalangeal and proximal interphalangeal joints, but not at the distal joints, which only the long flexor reaches. With the plantar aponeurosis it acts as a tie along the sole, supporting the longitudinal arches during standing and stiffening the foot for push-off.

The slip to the little toe is often thin or missing and may be replaced by a tiny muscle springing from quadratus plantae or the long tendon. Its close attachment to the aponeurosis means it is often involved in heel pain at the calcaneal origin, as in plantar fasciitis. It is supplied by the medial plantar nerve.

Attachments, action and supply

Origin

Calcaneal tuberosity (medial process), the aponeurosis's central band and adjacent intermuscular septa.

Insertion

Both sides of the middle phalanges of the second to fifth toes, by split tendons.

Action

Flexes the lesser toes at the metatarsophalangeal and proximal interphalangeal joints; supports the longitudinal arches.

Nerve supply

Medial plantar nerve (S2, S3).

Blood supply

Medial and lateral plantar arteries, plantar metatarsal arteries and plantar digital arteries.