The opponens digiti minimi is the deepest hypothenar muscle, inserting along the entire fifth metacarpal shaft and rotating it medially to deepen the cup of the palm during power grip. Its action opposes the thumb from the little finger side, and together with the opponens pollicis it enables the cupped palm shape essential for gripping cylindrical objects such as tool handles. Its hook of hamate origin makes it vulnerable in hamate hook fractures.
| Origin | Flexor retinaculum and hook of the hamate |
|---|---|
| Insertion | Entire length of the ulnar border of the fifth metacarpal |
| Nerve Supply | Deep branch of the ulnar nerve (C8, T1) |
| Blood Supply | Ulnar artery |
| Actions | Opposition of the little finger — flexes and rotates the fifth metacarpal to deepen the palm cup; Assists in little finger MCP flexion |
|---|
By rotating the fifth metacarpal forward and medially it deepens the palmar cup and positions the little finger for opposition against the thumb, maximising grip circumference adaptability for different object sizes.
Opponens digiti minimi weakness from ulnar nerve palsy prevents full palm cupping and reduces grip efficiency for round objects. Hook of hamate fractures at the ODM origin cause ulnar-sided palm pain that worsens with grip and must be confirmed by CT as plain radiographs miss up to 30 percent of hook fractures.
The ODM is not directly palpable as a distinct muscle belly, but its function is assessed by the ability to cup the palm and rotate the little finger toward the thumb tip.
Stress fracture at the ODM and FDM origin from golf club or racket handle impact, producing hypothenar pain with grip reproduced by direct hamate hook palpation and confirmed by CT.
