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Third dorsal interosseous muscle of foot

The third dorsal interosseous muscle is one of the four dorsal interossei located in the fourth (deepest) muscular layer of the foot. It occupies the intermetatarsal space between the third and fourth metatarsal bones, functioning as an intrinsic muscle responsible for abducting the third toe away from the midline of the second toe and assisting in flexion at the metatarsophalangeal (MTP) joint and extension at the interphalangeal (IP) joints.

Each dorsal interosseous muscle has two heads, originating from adjacent metatarsal shafts, converging into a single tendon that inserts into the extensor expansion and the base of the proximal phalanx. The third dorsal interosseous muscle is critical in toe stabilization during gait, maintaining transverse arch support, and coordinating with plantar interossei for fine digital balance.

Synonyms

  • Dorsal interosseus III

  • Third dorsal intermetatarsal muscle

  • Interosseous muscle between third and fourth metatarsals

Origin, Course, and Insertion

  • Origin: Adjacent sides of the third and fourth metatarsal bones

  • Course: Fibers run distally and converge into a narrow tendon within the third intermetatarsal space

  • Insertion: Lateral side of the base of the proximal phalanx of the third toe and into the dorsal digital expansion

Tendon Attachments

  • The tendon joins the extensor expansion of the third toe along with slips from the extensor digitorum longus

  • Helps coordinate digital extension during propulsion

  • Stabilizes the third MTP joint against lateral deviation during toe-off

Relations

  • Superiorly: Dorsal metatarsal vessels and deep plantar branches

  • Inferiorly: Plantar interosseous muscles

  • Medially: Second dorsal interosseous muscle

  • Laterally: Fourth dorsal interosseous muscle

  • Deep to: Dorsal intermetatarsal fascia and extensor tendons

Nerve Supply

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

  • Occasionally receives a communicating branch from the deep fibular (peroneal) nerve

Arterial Supply

  • Dorsal metatarsal artery (branch of arcuate artery from dorsalis pedis)

  • Small contributions from the deep plantar arch

Venous Drainage

  • Dorsal metatarsal veins, draining into the dorsal venous arch and then into the great and small saphenous veins

Function

  • Abduction: Abducts the third toe away from the second toe (foot’s midline)

  • Flexion: Flexes the MTP joint of the third toe

  • Extension: Assists in extending the interphalangeal joints

  • Arch support: Maintains the transverse arch during stance and propulsion

  • Digital balance: Works with plantar interossei to stabilize toes during gait

Clinical Significance

  • Interosseous atrophy: Seen in neuropathies (tibial or plantar nerve injury) and chronic disuse

  • Muscle strain: May occur in athletes, dancers, or runners with excessive toe abduction

  • Entrapment: Compression of the deep branch of the lateral plantar nerve causes intrinsic muscle weakness

  • Surgical relevance: Important landmark during Morton’s neuroma decompression and plantar neuroma excision

  • Imaging importance: MRI useful for evaluating intrinsic muscle pathology, denervation, or inflammation

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity, clearly separated from surrounding fat (bright on T1)

    • Tendons: low signal linear bands inserting into the extensor expansion

    • Atrophy: reduced bulk and increased fatty infiltration (hyperintense on T1)

    • Chronic neuropathy: high T1 signal due to fatty replacement

  • T2-weighted images:

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

    • Tendons: low signal (black), well-defined

    • Pathology (strain, inflammation): focal bright hyperintense areas within the muscle belly or at origin/insertion

    • Acute denervation: increased T2 signal due to muscle edema

  • STIR:

    • Normal muscle: intermediate-to-dark signal

    • Pathology: bright hyperintense areas indicating edema, strain, or active denervation

    • Excellent for detecting subtle muscle inflammation or post-traumatic changes

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark homogeneous signal

    • Muscle tear or strain: bright hyperintense foci at myotendinous junction

    • Chronic atrophy: dark muscle belly with adjacent fat infiltration

    • Useful for distinguishing acute edema (bright) from chronic fatty change (dark with fat-sat loss)

  • T1 Fat-Sat Post-Contrast:

    • Normal: uniform mild enhancement

    • Inflammation or infection: diffuse or patchy enhancement

    • Chronic fibrosis: minimal or rim enhancement around low-signal scar tissue

CT Appearance

Non-Contrast CT:

  • Muscle appears as a homogeneous soft-tissue density between the third and fourth metatarsals

  • Bony landmarks (metatarsal shafts, phalangeal bases) well visualized

  • Chronic denervation: visible volume loss or increased intermuscular fat density

Post-Contrast CT (standard):

  • Normal: uniform mild enhancement of the muscle belly

  • Inflammation or abscess: focal or rim enhancement with perimuscular fat stranding

  • Chronic atrophy: reduced volume, low attenuation, fatty replacement

MRI images

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

CT image

Third Dorsal Interosseous Muscle of Foot ct axial image