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Dorsal interosseous muscle of hand

The dorsal interosseous muscles (DIs) are four bipennate intrinsic muscles located between the metacarpal bones of the hand. They are responsible for abduction of the fingers away from the midline (the third digit), and play a key role in fine motor control, grip stability, and balance between flexor and extensor forces across the metacarpophalangeal (MCP) joints.

Each muscle arises by two heads from adjacent sides of neighboring metacarpals, converging into a common tendon that inserts into the proximal phalanx and extensor expansion. They are the most powerful intrinsic abductors of the fingers, aiding in coordinated hand movements, especially during grasp and object manipulation.

Synonyms

  • Dorsal interossei of the hand

  • Interosseus dorsalis manus

  • Dorsal metacarpal muscles

Origin, Course, and Insertion

  • Origin: Each muscle arises by two heads from the adjacent sides of the metacarpal bones:

    • First DI: Between the 1st and 2nd metacarpals

    • Second DI: Between the 2nd and 3rd metacarpals

    • Third DI: Between the 3rd and 4th metacarpals

    • Fourth DI: Between the 4th and 5th metacarpals

  • Course: The fibers pass dorsally and converge into a tendon directed toward the base of the proximal phalanx.

  • Insertion:

    • First DI: Lateral side of the index finger

    • Second & Third DIs: On opposite sides of the middle finger

    • Fourth DI: Lateral side of the ring finger

    • Each tendon joins the dorsal digital expansion of the extensor mechanism.

Relations

  • Dorsally: Dorsal fascia of the hand and extensor tendons

  • Ventrally: Deep palmar arch, palmar interossei, and lumbricals

  • Laterally and medially: Adjacent metacarpal bones

  • Superficial to: Metacarpal shafts and interosseous membranes

Tendon Attachments

  • Each dorsal interosseous tendon merges with the extensor expansion at the base of the proximal phalanx.

  • The tendons contribute to finger extension at interphalangeal joints and flexion at the MCP joints.

  • Tendinous slips blend with the lateral bands of the extensor hood.

Nerve Supply

  • Deep branch of the ulnar nerve (C8–T1)

Arterial Supply

  • Dorsal metacarpal arteries (branches of the dorsal carpal arch)

  • Deep palmar arch provides minor contributions via perforating branches

Function

  • Abduction: Abduct the index, middle, and ring fingers away from the midline (3rd digit)

  • Flexion: Assist in flexion at the metacarpophalangeal (MCP) joints

  • Extension: Aid in extension of interphalangeal joints via extensor hood

  • Grip stabilization: Balance flexor and extensor muscle forces during grasp

  • Fine motor control: Essential for coordinated precision tasks such as writing and pinching

Clinical Significance

  • Ulnar nerve palsy: Causes loss of finger abduction (“claw hand” deformity)

  • Muscle atrophy: Wasting of dorsal interossei is a hallmark of intrinsic hand muscle weakness

  • Trauma or compartment syndrome: May lead to ischemic necrosis of interosseous compartments

  • Infections: Deep space infections can spread between intermetacarpal spaces

  • Imaging relevance: MRI helps in detecting muscle atrophy, fibrosis, denervation, or compartmental infection

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity with visible fascicular texture

    • Adjacent fat planes: bright, outlining individual muscle bellies

    • Atrophy: increased intramuscular fat signal (bright)

    • Fibrosis or scarring: low signal intensity

  • T2-weighted images:

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

    • Pathology: bright hyperintense areas in edema, myositis, or partial tear

    • Muscle tendons: low signal linear bands merging into extensor expansions

  • STIR:

    • Normal muscle: intermediate-to-dark

    • Pathologic changes (strain, inflammation, or denervation): bright hyperintense signal within affected interosseous space

    • Very sensitive for acute edema and compartment inflammation

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: intermediate-to-dark signal

    • Abnormal: focal bright signal intensity representing edema or inflammation

    • Denervation: diffuse bright signal initially, followed by fatty infiltration (bright on T1) in chronic stages

  • T1 Fat-Sat Post-Contrast:

    • Normal: homogeneous mild enhancement

    • Myositis or abscess: focal or diffuse enhancement with adjacent fascial enhancement

    • Chronic scarring: peripheral or patchy enhancement with central low-signal fibrosis

CT Appearance

Non-Contrast CT:

  • Muscles appear as soft-tissue densities between metacarpals

  • Individual dorsal interossei separated by thin fat planes

  • Bony landmarks (metacarpal shafts and dorsal cortex) well visualized

  • Pathology:

    • Muscle atrophy: decreased bulk, increased surrounding fat attenuation

    • Calcification: seen in chronic myositis or post-trauma

    • Abscess or hematoma: focal low-density lesion

Post-Contrast CT (standard):

  • Normal: homogeneous mild enhancement of muscle

  • Inflammation or infection: localized or diffuse hyperenhancement

  • Neoplasm or granuloma: focal mass-like enhancing lesion

  • Useful in evaluating soft-tissue swelling, abscess, and foreign body reactions

MRI images

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

MRI images

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

CT images

dorsal interosseous muscles of hand xt axial image