Abductor hallucis: origin, insertion, action and innervation

The abductor hallucis is the muscle along the inner border of the sole, running from the heel bone to the base of the big toe. It pulls the great toe away from the second toe, helps hold up the medial arch, and is supplied by the medial plantar nerve (S2-S3).

Where it is

Run your thumb along the inside of your foot, from the heel to the ball of the big toe. The soft, fleshy ridge under the arch is the abductor hallucis. It is the most medial muscle of the first layer of the sole, the superficial layer just under the plantar aponeurosis, alongside the flexor digitorum brevis and the abductor digiti minimi.

The muscle forms a soft roof over the start of the sole. Behind the medial malleolus, the tendons of the tibialis posterior, the flexor digitorum longus and the flexor hallucis longus, plus the tibial nerve and the posterior tibial vessels, pass under the flexor retinaculum. They then slip deep to the abductor hallucis to enter the sole. The back end of the muscle is therefore the doorway of the sole on the inner side.

Hallux is the Latin word for the big toe; hallucis means "of the big toe". See the bones it spans on bones of the foot.

Origin and insertion

• Origin: the medial process of the calcaneal tuberosity of the calcaneus, the flexor retinaculum at the ankle, and the plantar aponeurosis.
• Insertion: the medial side of the base of the proximal phalanx of the great toe, by a tendon that joins the medial head of the flexor hallucis brevis and its sesamoid bone.

Its tendon runs along the inner side of the first metatarsal, so the muscle spans almost the whole length of the medial arch.

What it does

1. Abduction of the great toe: it moves the big toe toward the midline of the body, away from the second toe. In the foot, the reference line for abduction runs through the second toe.
2. Flexion of the great toe: it helps bend the big toe at the metatarsophalangeal joint.
3. Supporting the medial arch: stretched between the heel and the big toe, it acts like a tie that resists flattening of the arch when you stand or push off.

It is active when the foot balances on uneven ground and during push-off in walking.

Innervation and blood supply

The abductor hallucis is supplied by the medial plantar nerve (S2-S3), the larger terminal branch of the tibial nerve. The medial plantar nerve runs forward in the sole between this muscle and the flexor digitorum brevis.

Its blood comes from the medial plantar artery, which travels with the nerve.

How to remember it

• Hallux, hallucis, big toe: any muscle with "hallucis" in its name acts on the great toe.
• Medial edge, medial nerve: the muscle on the inner edge of the sole takes the medial plantar nerve, the mirror image of the abductor digiti minimi on the outer edge.
• The doorway muscle: everything that turns the corner behind the medial malleolus goes under the abductor hallucis to reach the sole.
• Second toe is the midline: abduction in the foot means away from the second toe, so the big toe abducts by moving toward the other foot.

Test yourself in the leg and foot quiz.

Frequently asked questions

What does the abductor hallucis do?

It abducts the great toe at the metatarsophalangeal joint, helps flex it, and supports the medial longitudinal arch.

What nerve supplies the abductor hallucis?

The medial plantar nerve, from roots S2 and S3.

Where does the abductor hallucis originate?

From the medial process of the calcaneal tuberosity, the flexor retinaculum and the plantar aponeurosis.

Which layer of the sole is the abductor hallucis in?

The first, most superficial layer, on its medial side.

Sources

• OpenStax, Anatomy and Physiology 2e, 11.6 Appendicular muscles of the pelvic girdle and lower limbs
• OpenStax, Anatomy and Physiology 2e, 8.4 Bones of the lower limb
• Z-Anatomy, the libre 3D atlas of anatomy