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Plantar interosseous muscles

The plantar interosseous muscles are three small intrinsic muscles located in the fourth (deepest) muscular layer of the sole of the foot. They lie between the metatarsal bones and play a key role in adducting the third, fourth, and fifth toes toward the second toe, stabilizing the toes during walking, running, and balance.

They work in conjunction with the dorsal interosseous muscles (which abduct the toes) and contribute significantly to maintaining the transverse and longitudinal arches of the foot.

Synonyms

  • Plantar interossei

  • Adductor muscles of the lateral three toes

Origin, Course, and Insertion

  • Origin: Bases and medial sides of the third, fourth, and fifth metatarsals

  • Course: Each muscle runs forward between the metatarsal bones, deep to the long flexor tendons and lumbricals

  • Insertion: Medial side of the bases of the proximal phalanges of the third, fourth, and fifth toes and into the extensor expansions

Tendon Attachments

  • Each muscle ends in a short tendon inserting onto the medial base of its respective proximal phalanx

  • Tendons merge with fibrous expansions of the extensor digitorum longus tendons, assisting in toe flexion and extension balance

Relations

  • Superficial (dorsal): Dorsal interosseous muscles and metatarsals

  • Deep (plantar): Adductor hallucis (transverse head) and plantar aponeurosis

  • Medial: Lumbrical muscles and flexor tendons

  • Lateral: Lateral plantar vessels and nerve branches

  • Posterior: Deep plantar arch and intermetatarsal spaces

Nerve Supply

  • Lateral plantar nerve (deep branch, roots S2–S3), a terminal branch of the tibial nerve

Arterial Supply

  • Plantar metatarsal arteries from the deep plantar arch

  • Additional supply from lateral plantar artery branches

Venous Drainage

  • Plantar venous network, draining into deep plantar veins and then into the posterior tibial vein

Function

  • Toe adduction: Adduct the third, fourth, and fifth toes toward the second toe (axis of the foot)

  • Toe stabilization: Maintain alignment of the lateral toes during stance and propulsion

  • Arch support: Reinforce the transverse and longitudinal arches of the foot

  • Balance and propulsion: Provide fine motor control during gait and balance activities

Clinical Significance

  • Atrophy: Common in neuropathies (e.g., tibial or lateral plantar nerve lesions), leading to toe splaying

  • Intermetatarsal bursitis: May mimic interosseous muscle inflammation on MRI

  • Overuse injury: Pain or swelling between metatarsal heads in runners or dancers

  • Entrapment: Compression of the deep branch of the lateral plantar nerve may weaken the interossei

  • Surgical relevance: Important for reconstructive procedures and plantar incisions

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity, distinct fascicular pattern

    • Surrounding fat: bright, defining intermetatarsal spaces clearly

    • Pathology (atrophy or denervation): increased fatty replacement, appearing hyperintense on T1

  • T2-weighted images:

    • Normal muscle: intermediate-to-low signal, slightly darker than on T1

    • Acute edema, strain, or inflammation: hyperintense signal replacing normal architecture

    • Chronic denervation: low-to-intermediate signal with fatty infiltration

  • STIR:

    • Normal muscle: intermediate-to-dark signal intensity

    • Pathology: bright hyperintense signal indicating muscle edema, inflammation, or acute denervation

    • Useful for detecting subtle intermetatarsal inflammation or soft-tissue edema

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark, homogeneous muscle appearance

    • Pathologic: bright hyperintense areas along muscle belly or intermetatarsal space suggesting strain or inflammatory process

    • Clearly defines perimuscular fluid and bursitis between metatarsal heads

  • T1 Fat-Sat Post-Contrast:

    • Normal: uniform, mild muscle enhancement

    • Myositis or neuritis: focal or diffuse enhancement

    • Chronic atrophy or fibrosis: minimal or peripheral enhancement

CT Appearance

Non-Contrast CT:

  • Muscles appear as soft-tissue density structures between metatarsal bones

  • Fat planes between muscles and metatarsals are clearly visible

  • Chronic pathology: atrophy or fatty infiltration may appear as decreased density

  • Calcifications or ossifications (rare) may occur post-trauma or in chronic inflammation

Post-Contrast CT (standard):

  • Normal muscle: homogeneous enhancement

  • Pathologic findings: focal enhancement or swelling in inflammation or infection

  • Useful for visualizing deep plantar abscesses, mass lesions, or foreign bodies within intermetatarsal spaces

MRI images

Plantar interosseous muscles axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Plantar interosseous muscles coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Plantar interosseous muscles coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

Plantar interosseous muscles ct axial image