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Fourth dorsal interosseous muscle of foot

The fourth dorsal interosseous muscle is the most lateral of the four dorsal interossei in the foot. It lies in the fourth intermetatarsal space, situated between the fourth and fifth metatarsal bones. Like all dorsal interossei, it functions primarily to abduct the toes (spreading them away from the second toe) and assist in metatarsophalangeal (MTP) joint flexion.

This small intrinsic muscle plays a stabilizing role in the lateral forefoot and contributes to fine motor control during gait, balance, and push-off. It is innervated by the lateral plantar nerve and forms part of the fourth (deepest) layer of plantar muscles, lying deep to the long flexor tendons.

Synonyms

  • Fourth dorsal intermetatarsal muscle

  • Dorsal interosseous IV

  • Lateral dorsal interosseous muscle

Origin, Course, and Insertion

  • Origin: Adjacent sides of the fourth and fifth metatarsal shafts

  • Course: Fibers run obliquely forward between the metatarsals toward the lateral aspect of the foot

  • Insertion: Lateral side of the base of the proximal phalanx of the fourth toe, blending with the extensor expansion and lateral MTP joint capsule

Tendon Attachments

  • The tendon of the fourth dorsal interosseous inserts onto the lateral base of the proximal phalanx of the fourth toe

  • It merges with the extensor expansion of the fourth digit and contributes to MTP joint stability during flexion and extension

  • The muscle’s insertion allows abduction of the fourth toe away from the midline (second toe)

Relations

  • Superiorly: Dorsal interosseous fascia and deep plantar arch

  • Inferiorly: Plantar interossei and oblique head of adductor hallucis

  • Medially: Third dorsal interosseous muscle

  • Laterally: Lateral plantar neurovascular bundle and fifth metatarsal shaft

  • Anteriorly: MTP joint capsule and extensor digitorum longus tendons

  • Posteriorly: Interosseous membrane and metatarsal bases

Nerve Supply

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

Arterial Supply

  • Dorsal metatarsal artery (branch of arcuate artery)

  • Deep plantar arch via perforating branches

Venous Drainage

  • Dorsal venous arch of the foot and deep plantar venous network, draining into the posterior tibial vein

Function

  • Abduction: Abducts the fourth toe away from the midline (second toe)

  • Flexion: Assists in flexion of the MTP joint

  • Extension: Helps extend the interphalangeal joints via the extensor expansion

  • Stabilization: Maintains toe alignment and balance during stance and propulsion

  • Dynamic control: Assists in lateral balance and weight distribution across metatarsal heads

Clinical Significance

  • Atrophy: Seen in chronic neuropathies such as tarsal tunnel syndrome or lateral plantar nerve entrapment

  • Muscle strain: Overuse or traumatic injuries can cause localized pain between the fourth and fifth metatarsals

  • Interosseous bursitis: Inflammation in intermetatarsal space may mimic Morton’s neuroma

  • Ischemic changes: Chronic pressure or compartment syndrome may cause selective interosseous edema

  • Imaging role: MRI is superior for detecting atrophy, denervation, edema, or small tears

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity with clear fascicular pattern

    • Surrounding fat: bright signal delineating muscle borders

    • Chronic atrophy: replaced by high signal fatty infiltration

  • T2-weighted images:

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

    • Pathology: bright hyperintense signal in cases of edema, strain, or denervation

    • Chronic fatty replacement: overall increased signal with atrophic volume loss

  • STIR:

    • Normal: intermediate-to-dark signal intensity

    • Pathology: bright hyperintense signal within or around the muscle indicating edema, inflammation, or nerve injury

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark homogeneous muscle signal

    • Pathologic: focal or diffuse bright signal areas from edema or partial tear

    • Best sequence to assess small interosseous muscle pathology and denervation changes

  • T1 Fat-Sat Post-Contrast:

    • Normal: homogeneous mild enhancement

    • Inflamed or denervated muscle: diffuse or patchy enhancement

    • Chronic atrophy: minimal enhancement with fatty replacement pattern

CT Appearance

Non-Contrast CT:

  • Muscle: soft-tissue density between fourth and fifth metatarsals

  • Borders well defined by interosseous fascia and adjacent fat planes

  • Chronic atrophy: visible as volume loss and fat density replacement

  • May show calcifications or ossifications in chronic trauma or myositis ossificans

Post-Contrast CT (standard):

  • Muscle enhances uniformly

  • Inflammatory or vascular lesions show focal increased enhancement

  • Useful for assessing postoperative changes, calcific enthesopathy, or space-occupying lesions in the intermetatarsal space

MRI images

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

CT image

Fourth dorsal interosseous muscle of foot ct axial