Extensor pollicis longus

Origin

The extensor pollicis longus is a critical muscle for thumb movements. It originates from the middle third of the posterior surface of the ulna and the adjacent interosseous membrane.

Course and insertion

The extensor pollicis longus muscle transitions into a long tendon that takes a distinctive course. Distally, this tendon passes obliquely around the dorsal (Lister's) tubercle of the radius, which serves as a crucial pulley. It then passes through the third dorsal extensor compartment of the wrist, beneath the extensor retinaculum. Continuing towards the thumb, the tendon crosses superficially over the extensor carpi radialis longus and brevis tendons. Importantly, it forms the medial border of the anatomical snuffbox. The tendon ultimately inserts onto the dorsal base of the distal phalanx of the thumb, typically via the dorsal aponeurosis, enabling independent thumb mobility.

Action

The primary functions of the extensor pollicis longus are to extend the interphalangeal and metacarpophalangeal joints of the thumb. Additionally, it assists in thumb retropulsion and abduction at the carpometacarpal joint.