Extensor pollicis longus arises from the middle posterior ulna surface below abductor pollicis longus. It passes distally and radially. It inserts into the dorsal base of the distal phalanx of the thumb and on route uses the tubercle of the radius as a pulley.
It acts to extend the metacarpophalangeal joints and interphalangeal joints of the thumb.
Extensor pollicis longus is supplied by the posterior interosseous nerve (C7,C8), a branch of the radial nerve.
Spontaneous rupture may occur and it is thought to be secondary to ischaemia of the interosseous vessels or fraying of the tendon after a Colles' fracture or rheumatoid arthritis: 'thumb drop' may occur. Tendon transfer of extensor indicis may be required.