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Foot Muscles (Intrinsic)

Here we'll learn about the four layers of plantar foot muscles and the single layer of dorsal foot muscles.

Plantar Foot Muscles

These muscles are responsible for toe flexion, adduction, and abduction, and for maintenance of the arches of the foot.

The plantar aponeurosis is a thick layer of connective tissue that supports the arch of the foot; distally, it gives rise to the fibrous sheaths of the digits. The fibrous sheaths of the toes are like tunnels on the plantar side of the digits that hold the tendons in place.

Clinical Correlation: Overuse, such as from running, can lead to inflammation of the aponeurosis and a painful condition called plantar fasciitis. Pain is typically worse after sitting/sleeping. Point tenderness is at the medial tubercle of the calcaneus, where the aponeurosis attaches.

Layer 1 - Most Superficial

Abductor digiti minimi arises from the medial and lateral processes of the calcaneal tuberosity and extends along the lateral side of the foot; it inserts on the proximal phalanx of digit 5.

As its name suggests, abductor digiti minimi abducts the little toe (minimi means little).

Flexor digitorum brevis arises from the medial process of the calcaneal process and the plantar aponeurosis, aka the plantar fascia. Distally, show that the tendons of flexor digitorum brevis split to insert on both sides of the middle phalanx of digits 2-5.

Recall that flexor digitorum longus is a muscle of the deep compartment of the posterior leg; its tendons pass deep to, and then through, the tendons of flexor digitorum brevis.

Abductor hallucis arises from the medial process of the calcaneal tuberosity and inserts on medially on the proximal phalanx of digit 1, the great toe (hallucis refers to the great toe).

Layer 2

The two muscles of this layer are attached to the tendons of flexor digitorum longus, so we show it, first. The main tendon wraps under the foot from the medial side of the ankle and gives rise to 4 long tendons that insert on the distal phalanges of digits 2-5.

Quadratus plantae has two heads that arise from the medial and lateral aspects of the calcaneus and merge to form a quadrilateral muscle that inserts on the lateral side of the tendon of flexor digitorum longus.

Four lumbricals arise from the tendons of flexor digitorum longus and insert medially on digits 2-5 on the proximal phalanges and extensor expansions (aka, extensor hoods).

Notice that the first lumbrical is unipennate (muscle fibers attach to one side of tendon), and lumbricals 2-4 are bipennate (muscle fibers attach to both sides of a central tendon); the lumbricals are often described as "worm-like."

The lumbricals have complex actions on the lateral 4 digits: They flex the proximal phalanges and extend the middle and distal phalanges. Collectively, these actions stabilize and coordinate toe movements during walking.

Layer 3

Flexor digiti minimi brevis arises from the base of metatarsal 5 and inserts on the proximal phalanx of digit 5.

Flexor hallucis brevis arises from the medial side of the foot as two heads from the cuboid and lateral cuneiform; the two heads merge to form a single belly, and then split again to insert on each side of the proximal phalanx of digit 1 (the great toe).

Be aware that sesamoid bones are located in each tendinous insertion of flexor hallucis brevis.

Two heads of adductor hallucis:

The transverse head arises from the plantar ligaments of the metatarsophalangeal joints and inserts on the first digit, on the lateral side of the proximal phalanx. The oblique head arises from the bases of metatarsals 2-4 and inserts with the transverse head.

Layer 4 - Deepest

Dorsal and plantar interossei muscles; both sets of muscles flex the metatarsophalangeal joints in addition to their specific and opposing actions.

4 dorsal interossei muscles are bipennate and arise from the adjacent metatarsals; they insert on the bases of the proximal phalanges of digits 2-5 and into the dorsal expansions. Notice that two dorsal interossei insert on digit 2.

The Dorsal interossei ABduct the toes; we can remember this with the acronym DAB.

3 plantar interossei are unipennate and arise from the medial sides of the associated metatarsals and insert on the proximal phalanges of digits 3-5 and the dorsal expansions.

Plantar interossei ADduct the toes; we can remember this with the acronym PAD.

Dorsal Foot Muscles

Extend the toes.

Extensor digitorum brevis arises from the superolateral surface of the calcaneus and sends tendons to insert into the extensor hoods of digits 2-4.

The extensor hoods are expansions of the tendons of foot extensor muscles that splay over the phalanges.

Extensor hallucis brevis arises medial to extensor digitorum brevis and inserts, via its own tendon, on the proximal phalanx of digit 1.

Though we've shown them separately here, extensor hallucis brevis is sometimes considered a medial portion of extensor digitorum brevis.

Foot Muscles (Intrinsic)

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