Plantar interossei muscles

At a glance

English

Plantar interossei muscles

Latin (TA2)

Musculi interossei plantares

System

Muscle

Region

Lower limb

Side

Paired, left and right

Arises from

The fifth metatarsal bone and fourth metatarsal bone

Inserts on

The proximal phalanx of fifth finger of foot and proximal phalanx of fourth finger of foot

About the plantar interossei muscles

The plantar interossei are three slender muscles in the deepest, fourth layer of the sole, lying beneath the spaces between the metatarsal bones. Each sits on the plantar side of the third, fourth or fifth metatarsal and serves the toe of that same bone. They work alongside the four dorsal interossei, which lie higher in the intermetatarsal spaces, and together the two sets control spreading and closing of the toes.

Unlike the dorsal muscles, which arise from two neighbouring bones and are bipennate, each plantar interosseous is unipennate and springs from only one metatarsal. The origin is the base and medial side of the shaft of the third, fourth or fifth metatarsal. Each belly runs forwards, its tendon passing above the deep transverse metatarsal ligament and below the axis of the metatarsophalangeal joint. It ends on the medial side of the base of the proximal phalanx of the same toe and sends a slip into the dorsal extensor expansion. Because each muscle stays on its own ray, none crosses to a neighbouring toe.

Movements of the toes are judged against a line through the second toe. The plantar interossei pull the third, fourth and fifth toes towards that line, which is adduction, so they close the spread toes. Running below the joint axis, they also help flex the metatarsophalangeal joints, and through the extensor expansions they help keep the interphalangeal joints straight. With the dorsal interossei they brace the front of the foot and support the transverse arch when standing on the toes.

All three are supplied by the deep branch of the lateral plantar nerve, which arises from the tibial nerve, and they receive blood from the plantar metatarsal arteries of the deep plantar arch. Weakness of the small foot muscles, as in some nerve disorders, lets the long flexors and extensors pull unopposed and contributes to clawing of the lesser toes.

Attachments, action and supply

Origin

Base and medial side of the third, fourth and fifth metatarsals, one muscle to each bone.

Insertion

Medial side of the base of the proximal phalanx of the third, fourth and fifth toes, and their dorsal extensor expansions.

Action

Adduct the third to fifth toes towards the second toe, assist flexion at the metatarsophalangeal joints and help support the transverse arch.

Nerve supply

Deep branch of the lateral plantar nerve (S2, S3).

Blood supply

Plantar metatarsal arteries from the deep plantar arch.