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First dorsal interosseous muscle of foot

The first dorsal interosseous muscle of the foot is one of four dorsal interossei and lies in the fourth (deepest) muscular layer of the sole. It occupies the first intermetatarsal space, between the first and second metatarsal bones. It is the largest and most robust of the dorsal interossei, contributing significantly to the stability and control of the first metatarsophalangeal (MTP) joint and lateral movement of the second toe.

This muscle is crucial during gait and balance, maintaining transverse metatarsal arch integrity and assisting in fine motor control of the forefoot. It functions in abduction of the second toe away from the midline of the foot and stabilization of the first web space during push-off.

Synonyms

  • First dorsal intermetatarsal muscle

  • Dorsal interosseous pedis I

Origin, Course, and Insertion

  • Origin: Adjacent sides of the first and second metatarsal shafts (bipennate muscle)

  • Course: Fibers converge into a strong tendon that passes distally and slightly dorsally along the first intermetatarsal space

  • Insertion:

    • Medial side of the base of the proximal phalanx of the second toe

    • Also contributes fibers to the dorsal digital expansion of the second toe

Tendon Attachments

  • The tendon blends with the extensor expansion of the second toe, aiding in coordinated toe movements

  • Provides a stabilizing slip to the first metatarsophalangeal joint capsule

  • Acts in conjunction with lumbricals and other interossei for dynamic toe alignment

Relations

  • Superiorly: Dorsal interosseous fascia and extensor tendons of the foot

  • Inferiorly: Plantar interosseous layer and plantar metatarsal vessels

  • Medially: First metatarsal bone

  • Laterally: Second metatarsal bone

  • Posteriorly: Deep plantar arch and branches of lateral plantar nerve and artery

Nerve Supply

  • Lateral plantar nerve, deep branch (from tibial nerve, roots S2–S3)

Arterial Supply

  • Dorsal metatarsal arteries (from the arcuate artery and deep plantar branch of dorsalis pedis)

  • Additional contribution from deep plantar arch

Venous Drainage

  • Dorsal venous arch and deep plantar venous plexus, draining into the anterior tibial and posterior tibial veins

Function

  • Abduction of the second toe: Moves the second toe away from the foot’s midline (imaginary line through the second toe)

  • Assists in flexion of the proximal phalanx at the MTP joint

  • Assists in extension of the middle and distal phalanges via the dorsal digital expansion

  • Stabilizes the first intermetatarsal space during propulsion

  • Supports the transverse arch of the foot

Clinical Significance

  • Muscle strain or denervation: May occur from repetitive forefoot stress or lateral plantar nerve entrapment

  • Atrophy: Seen in chronic neuropathy (e.g., diabetic neuropathy, tarsal tunnel syndrome)

  • Forefoot deformities: Weakness contributes to hallux valgus or splaying of metatarsals

  • Imaging relevance: Important in evaluating neuropathic muscle atrophy, plantar nerve lesions, or intermetatarsal bursitis

MRI Appearance

  • T1-weighted images:

    • Muscle: intermediate signal intensity with fine fascicular pattern

    • Surrounding fat: bright, outlining the muscle belly in the first intermetatarsal space

    • Pathology: fatty atrophy appears as increased T1 signal replacing muscle fibers

  • T2-weighted images:

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

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

    • Chronic atrophy: overall volume loss with fatty replacement (bright on T1, dark on T2)

  • STIR:

    • Normal muscle: intermediate-to-dark signal intensity

    • Pathology: hyperintense signal in acute myositis, muscle strain, or neuropathic edema

    • Useful for detecting early inflammatory or ischemic changes

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark signal

    • Pathologic: focal or diffuse bright hyperintensity from edema or denervation

    • Best for subtle intermetatarsal soft-tissue edema and early neuropathy detection

  • T1 Fat-Sat Post-Contrast:

    • Normal: uniform mild enhancement

    • Inflamed muscle or perimuscular tissue: focal or diffuse enhancement

    • Chronic atrophy: poor enhancement with fatty replacement

CT Appearance

Non-Contrast CT:

  • Muscle: homogeneous soft-tissue density occupying the first intermetatarsal space

  • Distinguishable from interosseous fascia and adjacent metatarsal cortices

  • Chronic atrophy: reduced bulk, replaced by fat density

  • Calcifications: possible in chronic myositis ossificans or post-trauma

Post-Contrast CT (standard):

  • Normal muscle: uniform, moderate enhancement

  • Inflammation or infection: increased enhancement with indistinct margins

  • Atrophy or fibrosis: reduced or patchy enhancement

  • CT useful in assessing osseous margins of metatarsals and adjacent intermetatarsal bursae

MRI image

First dorsal interosseous muscle of foot muscle coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

First dorsal interosseous muscle of foot muscle coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

First dorsal interosseous muscle of foot AXIAL CTIMAGE