Flexor pollicis longus is one of the muscles of the forearm. It arises from the anterior surface of the radius distal to the anterior oblique line and the neighbouring interosseous membrane.
It passes distally deep to the flexor retinaculum in a separate flexor sheath to the majority of the flexor tendons. It inserts into the volar base of the distal phalanx of the thumb.
Flexor pollicis longus is innervated by the anterior interosseous branch of the median nerve (C7,C8).
It acts to:
- flex the interphalangeal joint of the thumb
- flex the more proximal metacarpophalangeal and carpometacarpal joints of the thumb
- weakly flex the wrist joint