Muscles of the foot: the dorsal muscles and the four plantar layers

The foot is moved by two sets of muscles. The extrinsic muscles arise in the anterior, lateral and posterior compartments of the leg and mainly produce eversion, inversion, plantar flexion and dorsiflexion of the foot. The intrinsic muscles lie within the foot itself and control finer movements, such as moving individual toes. (TeachMeAnatomy: The Muscles of the Foot.)

OpenStax describes the intrinsic muscles in two groups. The dorsal group is extensor digitorum brevis, and the plantar group consists of four layers, numbered from the most superficial. These muscles primarily support the foot and its arch and contribute to movements of the toes. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

The usual layer scheme is: first layer abductor hallucis, flexor digitorum brevis and abductor digiti minimi; second layer quadratus plantae and the lumbricals; third layer flexor hallucis brevis, adductor hallucis and flexor digiti minimi brevis; fourth layer the plantar and dorsal interossei. (Kenhub: Medial plantar muscles of the foot.)

All the plantar muscles are supplied by the medial or lateral plantar nerves, which are branches of the tibial nerve. The two dorsal muscles are supplied by the deep fibular nerve. (TeachMeAnatomy: The Muscles of the Foot.)

The dorsum of the foot (the top of the foot) has only two intrinsic muscles, extensor digitorum brevis and extensor hallucis brevis. Both arise from the calcaneus and the inferior extensor retinaculum and are supplied by the deep fibular nerve. Extensor hallucis brevis inserts on the base of the proximal phalanx of the great toe and extends it; it is often regarded as the medial part of extensor digitorum brevis. (TeachMeAnatomy: The Muscles of the Foot.)

Extensor digitorum brevis arises from the front of the upper lateral surface of the calcaneus, the talocalcaneal interosseous ligament and the stem of the inferior extensor retinaculum. It divides into four slips: the medial one is extensor hallucis brevis, and the lateral three join the lateral side of the extensor digitorum longus tendons for toes 2 to 4, helping to extend those toes. (Kenhub: Extensor digitorum brevis muscle.)

Extensor digitorum brevis lies under the deep fascia of the dorsum. Its fleshy belly can be seen and felt as a small soft bulge just in front of the lateral malleolus when the foot is dorsiflexed. Its medial tendon crosses the dorsalis pedis artery, and its nerve is the lateral terminal branch of the deep fibular nerve (L5, S1). (Kenhub: Extensor digitorum brevis muscle.)

Several tendons from the leg also cross the dorsum of the feet. Tibialis anterior, extensor hallucis longus, extensor digitorum longus and fibularis tertius all cross the front of the ankle: tibialis anterior to the medial cuneiform and first metatarsal, extensor hallucis longus to the great toe, extensor digitorum longus to the lateral four toes and fibularis tertius to the fifth metatarsal. (TeachMeAnatomy: Muscles in the Anterior Compartment of the Leg.)

The superior and inferior extensor retinacula, thick bands of connective tissue at the ankle, hold these tendons in place during dorsiflexion. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

The dorsal muscle of the great toe, in 3D. Extensor hallucis brevis.

The first layer is the most superficial, lying just under the plantar fascia. All three muscles run from the heel towards the toes. Abductor hallucis (musculus abductor hallucis) lies along the medial edge of the sole. It arises from the medial calcaneal tubercle, the flexor retinaculum and the plantar aponeurosis, inserts on the medial side of the base of the proximal phalanx of the great toe, and abducts and flexes the great toe. It is supplied by the medial plantar nerve. (TeachMeAnatomy: The Muscles of the Foot.)

Kenhub adds that abductor hallucis, like flexor hallucis brevis, helps support the longitudinal arch of the foot, so it does more than spread the big toe. (Kenhub: Medial plantar muscles of the foot.)

Flexor digitorum brevis lies in the centre of the sole. It arises from the medial calcaneal tubercle and the plantar aponeurosis and inserts on the middle phalanges of toes 2 to 5. It flexes the lateral four toes at the proximal interphalangeal joints and is supplied by the medial plantar nerve. (TeachMeAnatomy: The Muscles of the Foot.)

Abductor digiti minimi lies along the lateral edge of the sole. It arises from the calcaneal tuberosity and the plantar aponeurosis, inserts on the base of the proximal phalanx of the little toe, abducts and flexes the little toe and helps support the longitudinal arch. It is supplied by the lateral plantar nerve. (Kenhub: Lateral plantar muscles of the foot.)

The muscle along the inner edge of the sole, in 3D. Abductor hallucis.

The second layer is built around the tendons of flexor digitorum longus, which arrive from the leg. Quadratus plantae (also called flexor accessorius) arises from the medial and lateral plantar surfaces of the calcaneus and inserts into the flexor digitorum longus tendons. It assists flexor digitorum longus in flexing the lateral four toes and is supplied by the lateral plantar nerve. (TeachMeAnatomy: The Muscles of the Foot.)

The four lumbricals of the foot arise from the tendons of flexor digitorum longus and insert into the extensor hoods of toes 2 to 5. They flex the metatarsophalangeal joints and extend the interphalangeal joints. The most medial lumbrical is supplied by the medial plantar nerve and the lateral three by the lateral plantar nerve. (TeachMeAnatomy: The Muscles of the Foot.)

OpenStax summarises the same action: the lumbricals extend toes 2 through 5 at the interphalangeal joints. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

The muscle that straightens the pull of the long toe flexor tendons. Quadratus plantae (flexor accessorius).

Flexor hallucis brevis has two heads. TeachMeAnatomy gives the lateral head as arising from the plantar surfaces of the cuboid and lateral cuneiform and the medial head from the tendon of tibialis posterior. Both insert on the base of the proximal phalanx of the great toe and flex it at the metatarsophalangeal joint. (TeachMeAnatomy: The Muscles of the Foot.)

Kenhub notes that flexor hallucis brevis reaches the proximal phalanx through the two sesamoid bones under the head of the first metatarsal. Sources differ on its nerve: TeachMeAnatomy gives the medial plantar nerve for the whole muscle, while Kenhub gives the medial plantar nerve for the medial head and the lateral plantar nerve for the lateral head. (Kenhub: Medial plantar muscles of the foot.)

Adductor hallucis has an oblique head from the bases of metatarsals 2 to 4 and a transverse head from the plantar ligaments of the metatarsophalangeal joints. Both insert on the lateral side of the base of the proximal phalanx of the great toe. It adducts the great toe, supports the transverse arch and is supplied by the deep branch of the lateral plantar nerve. (TeachMeAnatomy: The Muscles of the Foot.)

Flexor digiti minimi brevis arises from the base of the fifth metatarsal and the long plantar ligament and inserts on the base of the proximal phalanx of the little toe, which it flexes at the metatarsophalangeal joint. A separate slip called opponens digiti minimi, inserting on the lateral border of the fifth metatarsal, is found in some people but not all. Both are supplied by the lateral plantar nerve. (Kenhub: Lateral plantar muscles of the foot.)

The deepest layer is the interossei, which lie between the metatarsals. The three plantar interossei arise from the medial sides of metatarsals 3 to 5 and insert on the medial sides of the proximal phalanges of toes 3 to 5. They adduct those toes and flex the metatarsophalangeal joints. (TeachMeAnatomy: The Muscles of the Foot.)

The four dorsal interossei each arise from the facing sides of two neighbouring metatarsals. The first inserts on the medial side of the proximal phalanx of the second toe; the second to fourth insert on the lateral sides of the proximal phalanges of toes 2 to 4. They abduct the toes and flex the metatarsophalangeal joints. All interossei are supplied by the lateral plantar nerve. Because the first and second dorsal interossei insert on opposite sides of the second toe, the toes spread apart and close together around a line through the second toe. (TeachMeAnatomy: The Muscles of the Foot.)

OpenStax describes the dorsal interossei as abducting and flexing the middle toes at the metatarsophalangeal joints. (OpenStax Anatomy and Physiology 2e, 11.6: Appendicular Muscles of the Pelvic Girdle and Lower Limbs.)

The plantar intrinsic muscles work together to stabilise the arches of the foot, while also moving the toes individually. The principal passive support of the longitudinal arch is the plantar aponeurosis, a thick deep fascia on the sole. (TeachMeAnatomy: The Muscles of the Foot.)

A study with fine-wire electrodes in abductor hallucis, flexor digitorum brevis and quadratus plantae showed that these muscles are active in walking and running. They lengthened slowly while the arch flattened under load and then shortened rapidly as the arch recoiled during push-off, and both their activity and length changes increased with speed. (Kelly LA, Lichtwark G, Cresswell AG. Active regulation of longitudinal arch compression and recoil during walking and running. J R Soc Interface. 2015.)

The same study found abductor hallucis active just before foot contact and early in stance, while flexor digitorum brevis and quadratus plantae peaked in mid-stance. The authors concluded that the intrinsic muscles work alongside the plantar aponeurosis, actively regulating foot stiffness according to the forces met during locomotion. (Kelly LA, Lichtwark G, Cresswell AG. Active regulation of longitudinal arch compression and recoil during walking and running. J R Soc Interface. 2015.)

The medial plantar nerve passes deep to abductor hallucis and can be compressed there. This causes aching, numbness and pins and needles over the medial sole. Repeated eversion, as in gymnastics, may contribute. (TeachMeAnatomy: The Muscles of the Foot.)

In tarsal tunnel syndrome the tibial nerve is compressed in the tarsal tunnel behind the medial malleolus, under the flexor retinaculum. It usually alters sensation over the sole, and in severe cases it causes weakness and wasting of the intrinsic foot muscles. (TeachMeAnatomy: The Tarsal Tunnel.)

Weakness of the ligaments and muscles of the sole often leads to foot deformities. One of the most common is hallux valgus (a bunion), in which the great toe deviates laterally towards the second toe and the first metatarsal is abnormally adducted. Rest, ice and pain relief ease the discomfort but do not correct the deformity; more serious cases may need surgery (bunionectomy). (Kenhub: Medial plantar muscles of the foot.)

A bunionette (tailor's bunion) is the equivalent on the little toe side: the fifth metatarsal head protrudes laterally and the little toe drifts towards the fourth toe. It is usually managed with rest, padding, wider shoes and medication, with surgery reserved for severe cases. (Kenhub: Lateral plantar muscles of the foot.)

Abductor digiti minimi of foot

A muscle along the lateral border of the sole of the foot.

Abductor hallucis

A muscle along the medial border of the sole of the foot.

Extensor hallucis brevis

A small muscle on the dorsum of the foot.

First lumbrical of foot

A small muscle in the sole arising from the flexor digitorum longus tendon to the 2nd toe.

First plantar interosseous of foot

A small muscle between the metatarsals on the sole of the foot.

Flexor accessorius

A muscle of the sole that assists the long toe flexor.

Flexor digiti minimi brevis of foot

A small muscle of the lateral sole.

Flexor digitorum brevis

A central muscle of the sole.

Fourth lumbrical of foot

A small muscle in the sole acting on the 5th toe.

Lateral head of flexor hallucis brevis

The lateral part of flexor hallucis brevis in the sole.

Medial head of flexor hallucis brevis

The medial part of flexor hallucis brevis in the sole.

Oblique head of adductor hallucis

The larger head of adductor hallucis in the sole.

Opponens digiti minimi of foot

An inconstant small muscle of the little toe, usually regarded as a deep slip of flexor digiti minimi brevis.

Second lumbrical of foot

A small intrinsic muscle of the sole attached to the flexor digitorum longus tendons.

Second plantar interosseous of foot

One of three plantar interossei, small muscles beneath the metatarsals in the fourth layer of the sole.

Third lumbrical of foot

A small intrinsic muscle of the sole attached to the flexor digitorum longus tendons.

Third plantar interosseous of foot

One of three plantar interossei, small muscles beneath the metatarsals in the fourth layer of the sole.

Transverse head of adductor hallucis

The transverse part of adductor hallucis in the sole.