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Palmar interosseous muscles of hand

The palmar interosseous muscles (interossei palmares) are a group of three small intrinsic muscles located in the deep layer of the hand, within the intermetacarpal spaces on the palmar side. Their primary action is adduction of the fingers toward the midline (the axis of the third digit). These muscles play a key role in precision grip, fine digital control, and stabilization of the metacarpophalangeal (MCP) joints during flexion and extension.

They are part of the interosseous group along with the four dorsal interossei, but unlike the dorsal set (which abduct), the palmar interossei adduct — summarized by the mnemonic “PAD” (Palmar ADduct).

Synonyms

  • Interossei palmares

  • Volar interosseous muscles

  • Palmar adductors of the fingers

Number and Location

  • Three muscles are typically present (sometimes four if a small one is associated with the thumb).

  • Located in the second, fourth, and fifth intermetacarpal spaces.

  • Absent on the radial side of the middle finger (axis of hand motion).

Origin, Course, and Insertion

  • Origin:

    • Each muscle arises from the metacarpal shaft of the metacarpal corresponding to the finger it adducts —

      • 1st palmar interosseous: medial side of 2nd metacarpal

      • 2nd palmar interosseous: lateral side of 4th metacarpal

      • 3rd palmar interosseous: lateral side of 5th metacarpal

  • Course:

    • Fibers pass distally, running along the sides of the metacarpals toward the proximal phalanges.

    • Tendons blend with the extensor expansion (dorsal digital expansion) and joint capsule at the MCP joint.

  • Insertion:

    • Base of the proximal phalanx and the extensor expansion of digits 2, 4, and 5.

Relations

  • Superficial: Lumbrical muscles and deep palmar fascia

  • Deep: Metacarpal bones and interosseous spaces

  • Medially/Laterally: Adjacent dorsal interossei

  • Distally: Extensor expansion and tendons of the extensor digitorum

  • Proximally: Deep palmar arch and deep branch of ulnar nerve

Nerve Supply

  • Deep branch of the ulnar nerve (C8, T1) — motor branch supplying all interossei.

Arterial Supply

  • Deep palmar arch (from radial artery)

  • Perforating branches from the palmar metacarpal arteries

Function

  • Finger adduction: Move digits 2, 4, and 5 toward the middle finger axis.

  • MCP joint flexion: Assist in flexing the metacarpophalangeal joints.

  • IP joint extension: Via insertion into the extensor expansion, help extend interphalangeal joints.

  • Grip stabilization: Provide fine motor control and stabilize the MCP joints during pinching and grasping.

  • Assist lumbricals: In coordinated finger flexion-extension during precision movements.

Clinical Significance

  • Ulnar nerve palsy: Causes weakness or loss of finger adduction; positive card test (Froment’s sign).

  • Intrinsic muscle wasting: Seen in chronic neuropathy; intermetacarpal spaces become hollow.

  • Tendon injuries: May affect extensor expansion continuity.

  • Ischemic or compartment syndromes: Rare but can involve interosseous muscle edema.

  • Surgical importance: Important landmarks during deep palmar arch exposure, tendon repair, or decompression surgeries.

MRI Appearance

  • T1-weighted images:

    • Muscle bellies: Intermediate signal intensity, clearly separated by bright intermuscular fat.

    • Tendons: Low signal (dark).

    • Perimuscular fascia: Thin, dark rim separating each interosseous compartment.

    • Fatty infiltration in chronic denervation appears hyperintense.

  • T2-weighted images:

    • Normal muscle: Intermediate-to-low signal, slightly darker than on T1.

    • Tendons: Low signal (dark).

    • Pathology: Edema or myositis shows bright hyperintense signal within muscle belly.

    • Atrophy: Muscle thinning with high signal fatty replacement.

  • STIR:

    • Normal muscle: Intermediate-to-dark signal intensity.

    • Pathology: Hyperintense signal in acute inflammation, strain, or compartment edema.

    • Excellent for early detection of denervation or trauma-related edema.

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: Intermediate-to-dark signal with clear fascicular texture.

    • Acute injury or inflammation: Bright hyperintensity within affected interosseous compartments.

    • Ideal for detecting soft-tissue edema, post-traumatic changes, or small hematomas.

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: Mild uniform enhancement.

    • Inflamed or injured areas: Focal or diffuse enhancement of muscle belly and fascial planes.

    • Chronic scarring: Minimal or rim-like enhancement with low-signal fibrosis.

CT Appearance

Non-Contrast CT:

  • Muscles: Appear as soft-tissue density structures between metacarpal shafts.

  • Tendons: Denser linear bands within palmar intermetacarpal spaces.

  • Bones: Surrounding metacarpals clearly defined with cortical margins.

  • Pathology: Muscle atrophy appears as reduced volume with increased perimuscular fat density; calcifications are rare.

Post-Contrast CT (standard):

  • Muscles: Enhance homogeneously in normal cases.

  • Inflammation or infection: Focal or diffuse enhancement with fascial thickening.

  • Tumors or vascular lesions: Well-defined enhancing masses within deep palmar compartment.

  • Excellent for evaluating post-traumatic hematoma, fibrosis, or deep-space abscess in the hand.

MRI images

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

MRI images

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

CT images

Palmar interosseous muscles of hand ct axial image