Abductor digiti minimi of the foot: origin, insertion, action and innervation

The abductor digiti minimi of the foot is a long, narrow muscle along the outer border of the sole that runs from the heel bone to the base of the little toe. It moves the fifth toe away from the others and is supplied by the lateral plantar nerve (S2-S3).

Where it is

The muscles of the sole are arranged in four layers. The abductor digiti minimi belongs to the first layer, the most superficial one, just under the thick plantar aponeurosis. That layer has three muscles side by side:

• the abductor hallucis along the inner border,
• the flexor digitorum brevis in the middle,
• the abductor digiti minimi along the outer border.

It forms the soft, rounded lateral edge of the sole, the outer rim you see in a wet footprint. It runs along the underside of the fifth metatarsal, partly covering the tuberosity at its base, and helps fill out the outer side of the foot. Digiti minimi means "of the smallest digit". See the bones it crosses on bones of the foot.

Origin and insertion

• Origin: both the lateral and medial processes of the calcaneal tuberosity, at the underside of the calcaneus, plus the deep surface of the plantar aponeurosis and the septum that separates it from the flexor digitorum brevis.
• Insertion: the lateral side of the base of the proximal phalanx of the fifth toe, often together with the tendon of the flexor digiti minimi brevis.

On the way, some fibers usually attach to the tuberosity of the fifth metatarsal. Anatomists sometimes describe this slip as a separate small muscle.

What it does

1. Abduction of the fifth toe: it pulls the little toe outward, away from the second toe, at the metatarsophalangeal joint.
2. Flexion of the fifth toe: it helps bend the little toe at the same joint.
3. Supporting the lateral arch: like a bowstring from the heel to the front of the foot, it helps hold up the outer longitudinal arch when you stand.

In daily life, its support of the lateral arch during standing and walking matters more than moving the little toe.

Innervation and blood supply

The abductor digiti minimi is supplied by the lateral plantar nerve (S2-S3), a terminal branch of the tibial nerve. The first branch of the lateral plantar nerve, which runs across the heel to reach this muscle, is sometimes called the inferior calcaneal nerve.

Its blood comes from the lateral plantar artery, which runs across the sole with the nerve.

How to remember it

• Same name as in the hand: the hand has an abductor digiti minimi for the little finger. The foot has one for the little toe. Both run along the outer border.
• Lateral border, lateral nerve: the muscle on the outer edge of the sole takes the lateral plantar nerve.
• LAFF goes medial, the rest go lateral: the medial plantar nerve supplies only the first Lumbrical, the Abductor hallucis, the Flexor digitorum brevis and the Flexor hallucis brevis. Every other sole muscle, this abductor included, gets the lateral plantar nerve.
• Footprint edge: the outer rim of a footprint is where this muscle lies.

Test yourself in the leg and foot quiz.

Frequently asked questions

What does the abductor digiti minimi of the foot do?

It abducts the fifth toe at the metatarsophalangeal joint, helps flex it and supports the lateral arch of the foot.

What nerve supplies the abductor digiti minimi of the foot?

The lateral plantar nerve, from roots S2 and S3.

Which layer of the sole is the abductor digiti minimi in?

The first, most superficial layer, with the abductor hallucis and the flexor digitorum brevis.

Where does the abductor digiti minimi of the foot insert?

On the lateral side of the base of the proximal phalanx of the fifth toe.

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