The third palmar interosseous adducts the little finger from its naturally abducted position toward the ring finger. It is the most ulnar of the palmar interossei and works against the hypothenar abductor digiti minimi to control little finger alignment. The three hand palmar interossei form the PAD group (Palmar ADduct) in the mnemonic PAD-DAB.
| Origin | Radial side of the fifth metacarpal (unipennate) |
|---|---|
| Insertion | Radial base of the proximal phalanx of the little finger and extensor hood |
| Nerve Supply | Deep branch of the ulnar nerve (C8, T1) |
| Blood Supply | Third palmar metacarpal artery |
| Actions | Adducts the little finger toward the middle finger axis; Assists MCP flexion and IP extension of the little finger |
|---|
The third palmar interosseous is the most commonly assessed of the three in clinical ulnar nerve testing, as little finger adduction (Wartenberg's sign — inability to adduct the abducted little finger) is a reliable early sign of ulnar neuropathy. Its denervation produces the characteristic little finger abduction posture in ulnar claw hand. Along with abductor digiti minimi, it controls the little finger's transverse alignment during grip.
Palpated on the radial border of the fifth metacarpal during resisted little finger adduction toward the ring finger.
Involuntary little finger abduction from third palmar interosseous weakness in ulnar neuropathy, creating the characteristic little finger gap that catches on trouser pockets and is one of the first functional complaints in ulnar nerve palsy.
