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Palmar Interossei Tendon hand

The palmar interossei tendons originate from the palmar interossei muscles—three intrinsic muscles on the palmar side of the hand responsible for finger adduction toward the middle finger. These tendons extend from the metacarpal shafts toward the proximal phalanges and extensor apparatus, inserting primarily into the bases of the proximal phalanges and the extensor expansion.

They play an essential role in precision grip, adduction, and fine motor coordination, strengthening the movements of the lumbricals and helping maintain finger stability during pinch and grasp. Their close relationship with the deep transverse metacarpal ligament and the extensor hood makes them clinically significant in tendon injuries, deformity correction, and intrinsic hand muscle dysfunction.

Synonyms

  • Volar interossei tendons

  • Palmar interosseous tendons

  • PI tendons

Origin, Course, and Insertion

Origin:

  • Tendons arise from the palmar interossei muscles, which originate on the palmar surfaces of the metacarpals:

    • First PI: ulnar side of index metacarpal

    • Second PI: radial side of ring finger metacarpal

    • Third PI: radial side of small finger metacarpal

Course:

  • Tendons pass forward and distally along the palmar aspect of their respective metacarpals

  • Travel deep to flexor tendons and lumbricals

  • Approach the proximal phalanx and extensor hood

Insertion:

  • Bases of the proximal phalanges on their adducting sides (index–ulnar; ring–radial; little–radial)

  • Extensor hood (dorsal expansion) to assist in MCP flexion and IP extension

Relations

  • Dorsally: Deep transverse metacarpal ligament and metacarpal heads

  • Palmarly: Flexor tendons and lumbricals

  • Laterally: Digital nerves and arteries

  • Medially: Adjacent interosseous compartments

Function

  • Adduction: Draw fingers toward the midline (middle finger)

  • Stabilization: Maintain MCP joint alignment and resist ulnar or radial deviation

  • Assist lumbricals: MCP joint flexion with simultaneous IP joint extension

  • Precision grip: Essential for fine digital control during writing, grasping, and pinching

Clinical Significance

  • Interosseous tendon tears: Rare but impair adduction and fine motor control

  • Intrinsic muscle imbalance: Contributes to claw hand or lumbrical-plus deformities

  • Surgical relevance: Important in tendon transfers and correction of deformities

  • Inflammatory thickening: May be visualized in inflammatory arthropathies

  • Trauma or laceration: Common on palmar aspect during deep cuts

MRI Appearance

T1-weighted images:

  • Tendon: Uniformly low signal (dark) as dense collagen

  • Muscle portions: Intermediate signal

  • Surrounded by bright palmar fat, highlighting tendon margins

  • Extensor hood insertion: Low-signal blending with dorsal expansion

T2-weighted images:

  • Tendon: Low signal (dark)

  • Muscle fibers: Intermediate-to-high signal compared to tendon

  • Clear separation from flexor tendons and lumbricals on sagittal/coronal planes

STIR:

  • Tendon: Low signal (dark band)

  • Muscle: Intermediate signal

  • High contrast between tendon and suppressed fat surrounding the metacarpals

MRI images

Palmar Interossei Tendon hand MRI axial image-img-00000-00000