Medial head of flexor hallucis brevis

At a glance

English

Medial head of flexor hallucis brevis

Latin (TA2)

Caput mediale flexoris brevis hallucis

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the medial head of flexor hallucis brevis

Flexor hallucis brevis is a short muscle in the third layer of the sole that bends the great toe at its base. It starts as a single mass from the tarsal bones and then splits into two heads, medial and lateral, which lie side by side under the shaft of the first metatarsal. The tendon of flexor hallucis longus runs in the groove between them, protected as it travels forwards to the tip of the toe.

The common origin is from the plantar surface of the cuboid and the lateral cuneiform, with fibres from the tendon of tibialis posterior. The medial head runs forwards along the inner side of the first metatarsal and ends on the medial side of the base of the proximal phalanx of the great toe. Before it attaches, its tendon merges with that of abductor hallucis, so the two muscles share an insertion. The lateral head, in the same way, combines with adductor hallucis on the outer side.

A sesamoid bone sits in the tendon of each head under the head of the first metatarsal. The medial sesamoid, in this head, is usually the larger and bears much of the load passed through the ball of the foot when pushing off. The two sesamoids lift the tendons away from the joint, increasing their leverage, and they shelter the long flexor tendon that runs between them.

Acting with its partner, the medial head flexes the great toe at the metatarsophalangeal joint and helps it press firmly into the ground as the heel rises, which matters for balance and for the final push in walking and running. It is supplied by the medial plantar nerve and by branches of the medial plantar artery and first plantar metatarsal artery. Overload of the medial sesamoid, in dancers and runners, gives pain under the ball of the great toe, a condition known as sesamoiditis; the bone may also fracture or be split into two pieces from birth.

Attachments, action and supply

Origin

Plantar surface of the cuboid and lateral cuneiform, shared with the lateral head, and the tendon of tibialis posterior.

Insertion

Medial side of the base of the proximal phalanx of the great toe, through the medial sesamoid bone and blended with the abductor hallucis tendon.

Action

Flexes the great toe at the metatarsophalangeal joint.

Nerve supply

Medial plantar nerve (S1, S2).

Blood supply

Medial plantar artery and the first plantar metatarsal artery.