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Second dorsal interosseous muscle of hand

The second dorsal interosseous muscle (2nd DI) is one of the four dorsal interossei muscles located in the intermediate (deep) layer of the dorsum of the hand. These muscles occupy the spaces between the metacarpal bones and play a crucial role in finger abduction, metacarpophalangeal (MCP) joint flexion, and interphalangeal (IP) joint extension through the extensor expansion.

The second dorsal interosseous muscle lies between the second (index) and third (middle) metacarpal bones. It arises by two heads from the adjacent sides of these metacarpals and inserts into the base of the proximal phalanx and extensor expansion of the middle finger. Functionally, it abducts the middle finger laterally toward the radial side.

Synonyms

  • Second interosseous dorsalis manus

  • Dorsal interosseous II

  • Second dorsal intermetacarpal muscle

Origin, Course, and Insertion

  • Origin: Adjacent sides of the second and third metacarpal bones (from the intermetacarpal space).

  • Course: Fibers converge dorsally toward the third metacarpal; form a central tendon that runs distally toward the MCP joint of the middle finger.

  • Insertion:

    • Primary: Base of the proximal phalanx of the middle finger on its radial side.

    • Secondary: Into the extensor expansion (dorsal digital expansion) of the same finger.

Relations

  • Dorsally: Dorsal aponeurosis and skin of hand.

  • Ventrally: Deep palmar interosseous fascia, adductor pollicis oblique head, and deep palmar arch.

  • Laterally: First dorsal interosseous muscle (between thumb and index finger).

  • Medially: Third dorsal interosseous muscle (between third and fourth metacarpals).

  • Superiorly (proximal): Deep branch of radial artery and tendon of extensor digitorum.

  • Inferiorly (distal): Extensor expansion and proximal phalanx of middle finger.

Tendon Attachments

  • Joins the extensor expansion on the dorsum of the proximal phalanx of the middle finger.

  • Blends with the lateral band of the extensor digitorum and lumbrical tendon.

  • Stabilizes the MCP joint capsule during finger abduction.

Nerve Supply

  • Deep branch of the ulnar nerve (C8–T1) — motor innervation to all dorsal interossei.

Arterial Supply

  • Dorsal metacarpal arteries (from dorsal carpal arch).

  • Additional contribution from deep palmar arch via perforating branches.

Function

  • Abduction: Abducts the middle finger toward the radial (lateral) side relative to the hand’s midline.

  • MCP joint flexion: Assists in flexing the metacarpophalangeal joint.

  • IP joint extension: Via extensor expansion, helps extend the interphalangeal joints.

  • Grip stabilization: Contributes to firm grasp and hand dexterity.

  • Fine motor control: Works in coordination with lumbricals and flexor tendons for precise finger movements.

Clinical Significance

  • Ulnar nerve lesions: Paralysis causes weakness in finger abduction and reduced dexterity (positive Froment’s and Egawa’s signs).

  • Intrinsic hand muscle wasting: Seen in chronic ulnar neuropathy or lower brachial plexus lesions.

  • Overuse or strain: Can occur in repetitive gripping or fine-motor activities.

  • Trauma: Deep lacerations between second and third metacarpals can damage muscle or its neurovascular bundle.

  • Imaging relevance: Important for evaluating ulnar neuropathy, muscle atrophy, and hand trauma.

MRI Appearance

  • T1-weighted images:

    • Muscle belly: intermediate signal intensity, clearly demarcated from surrounding fat (bright).

    • Tendinous insertion: low signal (dark) at proximal phalanx base and extensor expansion.

    • Chronic atrophy: shows volume loss and fatty replacement (bright on T1).

  • T2-weighted images:

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

    • Acute strain or inflammation: bright hyperintense areas within muscle belly or tendon.

    • Chronic fibrosis: low signal due to dense connective tissue.

  • STIR:

    • Normal muscle: intermediate-to-dark homogeneous signal.

    • Pathology: hyperintense signal in muscle belly with indistinct fascicular margins (myositis, edema, or partial tear).

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark, uniform muscle texture.

    • Pathologic: bright intramuscular signal denoting edema, strain, or denervation.

    • Very sensitive for subtle nerve-related muscle changes.

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: mild uniform enhancement.

    • Inflammation or denervation: patchy or diffuse enhancement.

    • Chronic scarring or fibrosis: little to no enhancement with low signal core.

CT Appearance

Non-Contrast CT:

  • Muscle: homogeneous soft-tissue density between second and third metacarpals.

  • Tendons: fine linear soft-tissue densities extending to base of proximal phalanx.

  • Chronic changes: fatty atrophy (lower density) or calcific myositis (high attenuation foci).

  • Useful in trauma for foreign body detection, muscle lacerations, or metacarpal fractures.

Post-Contrast CT (standard):

  • Normal muscle: homogeneous mild enhancement.

  • Inflammatory or post-traumatic changes: focal or diffuse enhancement in muscle belly or perimuscular fascia.

  • Helpful in differentiating infective myositis from post-traumatic edema or hematoma.

MRI images

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

MRI images

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

CT images

Second dorsal interosseous muscle ct image