The adductor pollicis is the most powerful intrinsic muscle of the hand, generating the key pinch force between the thumb pulp and the lateral index finger. Froment's sign (the patient uses the FPL to flex the thumb IP joint for pinch because the adductor pollicis is paralysed) indicates ulnar nerve palsy. The web space between the first and second metacarpals is the adductor pollicis origin, and deep space hand infections commonly track along the adductor pollicis.
| Origin | Capitate and bases of the second and third metacarpals; Palmar shaft of the third metacarpal |
|---|---|
| Insertion | Medial (ulnar) sesamoid and medial base of the thumb proximal phalanx |
| Nerve Supply | Deep branch of the ulnar nerve (C8, T1) |
| Blood Supply | Deep palmar arch and first palmar metacarpal artery |
| Actions | Thumb adduction (drawing the thumb toward the second metacarpal); Thumb MCP flexion assistance; The primary pinch muscle — generates the force for key pinch between thumb and index finger |
|---|
Froment's sign (thumb IP flexion during lateral pinch) indicates adductor pollicis paralysis from ulnar nerve palsy. Jeanne's sign (MCP hyperextension during lateral pinch) occurs concurrently. Adductor pollicis reconstruction using the ring finger FDS tendon transfer (Bunnell) or a split ECRB restores key pinch in permanent ulnar palsy.
The adductor pollicis forms the bulk of the first web space, palpable as the thick muscle between the first and second metacarpals during resisted thumb adduction.
Loss of key pinch from adductor pollicis denervation in ulnar nerve palsy producing Froment and Jeanne signs managed with tendon transfer.
