The opponens pollicis is the deepest thenar muscle and the one most responsible for the medial rotation component of thumb opposition that rotates the thumb tip to face the other finger tips. Its name describes its defining action. It is the muscle that makes human precision grip possible, and its loss from median nerve paralysis reduces the hand to a crude hook grip.
| Origin | Flexor retinaculum and trapezium |
|---|---|
| Insertion | Entire length of the lateral border of the first metacarpal |
| Nerve Supply | Recurrent branch of the median nerve (C8, T1) |
| Blood Supply | Superficial palmar arch |
| Actions | Opposition of the thumb — combines flexion, abduction, and medial rotation of the first metacarpal to bring the thumb pad to face the finger pads |
|---|
By rotating the first metacarpal medially while flexing and abducting it, the opponens produces the combined motion of opposition that brings the thumb pad into precise contact with each fingertip, a uniquely primate movement.
Opponens pollicis weakness is tested by asking the patient to touch the tip of the little finger with the thumb tip while the examiner resists the movement or tries to break the O formed by the thumb and little finger. Surgical opposition restoration using the flexor digitorum superficialis tendon transfer (Bunnell opposition transfer) is performed when median nerve palsy produces permanent loss of opposition.
The opponens pollicis is palpable deep to the APB, best appreciated with deep thumb pressure into the thenar eminence during resisted thumb opposition.
Loss of opposition from median nerve injury producing inability to bring the thumb tip to the fingertips, severely limiting hand function and requiring opposition tendon transfer if nerve recovery is not expected.
