This arises from the ulna just distal to abductor pollicis longus. Thus it extends higher into the forearm than extensor pollicis brevis. It extends more distally also into the thumb, being inserted into the base of the distal phalanx. Its long tendon changes direction as it hooks around the dorsal tubercle of the radius (Lister’s tubercle), whence it forms the ulnar boundary of the snuffbox. In this situation the tendon is supplied with blood by local branches of the anterior interosseous artery. Their occlusion after Colles’ fracture may lead to necrosis and spontaneous rupture of the tendon — hammer thumb. Such a rupture is not due to wearing through of the tendon as it grates over the fragments.
There is no extensor expansion on the thumb; the tendon of extensor pollicis longus is stabilized on the dorsum of the thumb by receiving expansions from abductor pollicis brevis and adductor pollicis.
Nerve supply of extensor pollicis longus:
By the posterior interosseous nerve (C7, 8).
Action of extensor pollicis longus:
It extends the terminal phalanx of the thumb, and draws the thumb back from the opposed position.