Abductor hallucis

At a glance

English

Abductor hallucis

Latin (TA2)

Abductor hallucis

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the abductor hallucis

Abductor hallucis is one of the foot's intrinsic muscles, found in the first layer of the sole. It runs along the medial border and makes the soft bulge felt on the inner side of the foot below the ankle. Its inner surface lies directly under the skin and fascia, so it is easy to see and feel when the big toe is drawn away from the others.

The muscle arises from the medial process of the calcaneal tuberosity, from the flexor retinaculum that bridges the inside of the ankle, and from the plantar aponeurosis and the septum it shares with flexor digitorum brevis. Its belly is thick behind and thins as it passes forwards. It ends in a tendon that joins the medial head of flexor hallucis brevis and attaches to the medial side of the base of the big toe's proximal phalanx, with the medial sesamoid bone sitting in the common tendon.

Abductor hallucis moves the big toe away from the second toe and flexes it at the metatarsophalangeal joint. Few people can abduct the toe much, but the muscle matters more as a support: it stretches like a tie beam along the medial longitudinal arch and helps hold the arch up during standing and walking.

Near the heel the muscle covers the tarsal tunnel, the route by which the posterior tibial vessels and the tibial nerve and its plantar branches enter the sole. Its upper edge, where the medial and lateral plantar nerves pass under it, is a site where these nerves can be compressed, giving burning heel or arch pain. Its own supply comes from the medial plantar nerve, whose twigs enter along the muscle's upper border. In hallux valgus the big toe drifts outwards and the muscle slips under the joint, losing its abducting pull, which helps the deformity worsen.

Attachments, action and supply

Origin

Medial process of the calcaneal tuberosity, flexor retinaculum, plantar aponeurosis and the adjacent intermuscular septum.

Insertion

Medial side of the base of the big toe's proximal phalanx and the medial sesamoid, with the medial head of flexor hallucis brevis.

Action

Abducts and flexes the big toe at the metatarsophalangeal joint; supports the medial longitudinal arch.

Nerve supply

Medial plantar nerve, a branch of the tibial nerve (S2, S3).

Blood supply

Medial plantar artery and the first plantar metatarsal artery.