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Dorsal interosseous muscles

The dorsal interosseous muscles (DI) are four bipennate muscles located in the four intermetatarsal spaces of the foot. They form part of the fourth (deepest) muscular layer, lying between the metatarsal bones. Each muscle acts to abduct the toes away from the second digit, which serves as the reference axis of the foot.

The dorsal interossei contribute to toe abduction, stabilization of the metatarsophalangeal (MTP) joints, and assist in flexion of the MTP joints and extension of the interphalangeal (IP) joints. These muscles are critical for balance, lateral stabilization, and the fine control of toe movement during gait.

Synonyms

  • Dorsal interossei of the foot

  • Intermetatarsal muscles

  • Abductors of the toes

Origin, Course, and Insertion

  • Origin: Adjacent sides of the metatarsal bones (from the first to the fifth)

  • Course: Fibers pass anteriorly and converge toward the dorsal aponeurosis and proximal phalanges

  • Insertion:

    • First dorsal interosseous: Medial side of the proximal phalanx of the second toe

    • Second to fourth dorsal interossei: Lateral sides of the proximal phalanges of the second, third, and fourth toes

Tendon Attachments

  • Each muscle forms a short tendon that inserts into the base of the proximal phalanx and the dorsal digital expansion

  • The tendons blend with the extensor digitorum longus and brevis tendons to assist in IP joint extension

Relations

  • Dorsally: Extensor digitorum longus and brevis tendons

  • Plantarly: Plantar interosseous muscles and deep plantar vessels

  • Laterally: Lateral plantar nerve and artery branches

  • Medially: Deep plantar arch and metatarsal shafts

  • Anteriorly: Proximal phalanges and dorsal aponeurosis

Nerve Supply

  • Lateral plantar nerve (deep branch), root values S2–S3

  • Occasionally, the first dorsal interosseous may receive a contribution from the deep fibular nerve

Arterial Supply

  • Dorsal metatarsal arteries (branches of the arcuate artery)

  • Plantar metatarsal arteries (from the deep plantar arch)

Venous Drainage

  • Dorsal venous arch and deep plantar venous network, draining into the posterior tibial and fibular veins

Function

  • Abduction: Moves the toes (2nd–4th) away from the second toe (midline of the foot)

  • Flexion: Flexes MTP joints

  • Extension: Assists in extension of interphalangeal joints through dorsal expansion

  • Stabilization: Maintains digital alignment during stance and gait

  • Balance: Aids in lateral stability during propulsion and uneven ground contact

Clinical Significance

  • Weakness or atrophy: Seen in neuropathies involving the lateral plantar nerve

  • Overuse injury: Chronic strain in runners or dancers causing dorsal forefoot pain

  • Compartment syndrome: May cause ischemic damage due to deep plantar space compression

  • Nerve entrapment: Lateral plantar nerve or deep plantar branch irritation causes weakness and clawing deformity

  • Surgical relevance: Important landmark during plantar neurolysis or intermetatarsal fasciotomy

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity with distinct fascicular pattern

    • Tendons: low signal (dark lines) inserting near proximal phalanges

    • Fatty tissue between interossei: bright signal delineating muscle borders

  • T2-weighted images:

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

    • Pathology (strain, edema): focal or diffuse hyperintense signal

    • Tendons remain dark unless inflamed, when they may show mild hyperintensity

  • STIR:

    • Normal muscle: intermediate-to-dark signal

    • Pathology: bright hyperintensity representing edema or inflammatory change

    • Excellent for detecting muscle strain or early denervation

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: intermediate-to-dark homogeneous signal

    • Pathology: bright hyperintense regions indicating inflammation, contusion, or partial tear

    • Useful for identifying small foci of myositis or perimuscular fluid

  • T1 Fat-Sat Post-Contrast:

    • Normal: uniform mild enhancement

    • Inflammation or myositis: diffuse or patchy enhancement

    • Chronic denervation: minimal enhancement with fatty atrophy (high T1 signal pre-contrast)

CT Appearance

Non-Contrast CT:

  • Muscles: homogeneous soft-tissue density between metatarsal bones

  • Tendons: small linear densities inserting onto bases of proximal phalanges

  • Chronic changes: calcifications or mild atrophy in long-standing denervation

  • Fat planes: well-defined between interossei and metatarsal shafts

Post-Contrast CT (standard):

  • Normal: mild homogeneous enhancement

  • Inflammatory or ischemic changes: increased focal enhancement

  • Useful for detecting compartmental lesions, chronic fibrosis, or space-occupying processes in the dorsal intermetatarsal space

MRI images

Dorsal interosseous muscles AXIAL cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

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

MRI images

Dorsal interosseous muscles AXIAL cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

MRI images

Dorsal interosseous muscles AXIAL cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00003

CT image

Dorsal interosseous muscles AXIAL CT IMAGE