The ADM is the most lateral hypothenar muscle, forming the medial border of the hand and abducting the little finger. It is used clinically as an EMG target to confirm ulnar nerve integrity since it is one of the first intrinsic muscles to show denervation in ulnar neuropathy at the wrist (Guyon canal) or elbow (cubital tunnel).
| Origin | Pisiform and pisohamate ligament |
|---|---|
| Insertion | Ulnar side of the proximal phalanx base of the little finger |
| Nerve Supply | Deep branch of the ulnar nerve (C8, T1) |
| Blood Supply | Ulnar artery |
| Actions | Abduction of the little finger; MCP joint flexion assistance; Assists in opposition of the little finger to the thumb |
|---|
Little finger abduction by the ADM spreads the hand for grip stabilisation and contributes to the cup shape of the palm during catching activities.
ADM denervation produces visibly absent medial hand bulk in advanced ulnar neuropathy. The muscle is tested by resisted little finger abduction. Its EMG changes are used to localise ulnar neuropathy — preserved ADM function with intrinsic weakness localises to a distal ulnar lesion sparing the motor branch to ADM.
The ADM forms the medial hypothenar eminence, palpable from the pisiform to the fifth MCP joint.
ADM weakness and atrophy from ulnar nerve compression at Guyon canal or cubital tunnel, confirmed by EMG and managed with decompression.
