The opponens digiti minimi wraps around the fifth metacarpal to rotate and flex it at the CMC joint, deepening the palmar arch during grip. True opposition of the little finger to the thumb is a minor but important dexterity motion for fine pinch manipulation.
| Origin | Hook of the hamate and flexor retinaculum |
|---|---|
| Insertion | Entire medial border of the fifth metacarpal shaft |
| Nerve Supply | Deep branch of the ulnar nerve (C8, T1) |
| Blood Supply | Ulnar artery |
| Actions | Opposition of the little finger — CMC flexion, rotation, and abduction to face the thumb; Deepens the cup of the palm during grip |
|---|
The fourth and fifth metacarpal CMC joints have 15-20 degrees of flexion-extension mobility and the opponens digiti minimi drives the fifth metacarpal to cup the palm during cylindrical grip.
Opponens digiti minimi weakness is an early sign of ulnar deep branch compression at Guyon canal. Loss of hypothenar opposition flattens the medial palm and reduces cylindrical grip strength.
Deep to the ADM and FDMB and not individually palpable, but its contraction rotates the fifth metacarpal visibly during little finger opposition.
Deep ulnar branch compression disabling the opponens digiti minimi and flattening the palmar cup managed with decompression of Guyon canal.
