Extensor Pollicis Longus, Posterior View

Description

Arising from the posterior surface of the ulna and the adjacent interosseous membrane, the extensor pollicis longus (EPL) runs distally along the dorsal forearm, its muscle belly tapering into a long tendon as it approaches the wrist. Near the distal radius, the EPL tendon angles obliquely from ulnar to radial, wrapping around Lister’s tubercle (dorsal tubercle of the radius) before crossing the dorsum of the hand toward the thumb. On the dorsoradial aspect of the wrist, the tendon relates to the extensor retinaculum and neighboring extensor compartments, sitting medial to the abductor pollicis longus and extensor pollicis brevis tendons that form the lateral boundary of the anatomical snuffbox. Bony context typically includes the radius, ulna, carpal bones, first metacarpal, and thumb phalanges. This posterior trajectory matters because the EPL’s turn around Lister’s tubercle creates a predictable friction point and an anatomic pulley that concentrates stress during repetitive thumb extension. Attritional rupture at the level of the distal radius is a classic complication after nondisplaced distal radius fractures and can also follow inflammatory tenosynovitis or hardware irritation after volar plate fixation. Loss of active thumb interphalangeal extension is the clinical clue. It is simple to miss. Use this illustration to teach the extensor compartments of the wrist, the surface anatomy of the anatomical snuffbox, and the tendon course relevant to dorsal wrist injections, first dorsal compartment differential diagnosis, and thumb extensor repair or tendon transfer planning (often using extensor indicis proprius when EPL ruptures). It also fits cleanly into hand surgery operative manuals, orthopedic trauma discussions of distal radius fractures, and musculoskeletal ultrasound or MRI labeling exercises focused on the dorsal wrist tendons. Anatomical accuracy verified by SciePro's Medical Advisory Board.