dorsalinterossei

Dorsal interossei are a group of four intrinsic hand muscles located between the metacarpal bones. They arise from the adjacent sides of metacarpals II–V and are traditionally numbered I to IV from the thumb side toward the little finger.

Each dorsal interosseous muscle inserts on the bases of the proximal phalanges and on the extensor expansions of the corresponding digits. Their primary action is to abduct the fingers away from the long axis of the hand (away from the middle finger), with additional roles in flexing the metacarpophalangeal joints and extending the interphalangeal joints via the extensor mechanism.

The dorsal interossei are innervated by the deep branch of the ulnar nerve (C8–T1). Their blood supply comes from branches of the deep palmar arch and the dorsal metacarpal arteries.

Functionally, these muscles contribute to finger abduction and to the refinement of grip, complementing the adducting palmar interossei. Injury or disease affecting the ulnar nerve can reduce dorsal interosseous strength, leading to impaired finger abduction and altered hand function. The dorsal interossei, together with the palmar interossei and other intrinsic hand muscles, play a key role in fine motor tasks and grip stability.