Extensor Pollicis Longus Under the Skin, Posterior View

Description

Running obliquely across the dorsal distal forearm, the extensor pollicis longus muscle belly gives way to a long tendon that passes from the posterior ulna and interosseous membrane toward the radial side before descending to the thumb. Proximally it lies deep to extensor digitorum and extensor carpi ulnaris, then becomes superficial under the skin as it approaches the wrist, where the extensor retinaculum and the bony contours of the distal radius and ulna provide clear landmarks. At the dorsum of the wrist the tendon angles around Lister’s tubercle (dorsal radial tubercle) to enter the third extensor compartment, then continues distally toward the base of the distal phalanx of the thumb, forming the ulnar border of the anatomical snuffbox. Key neighbors. Extensor pollicis brevis and abductor pollicis longus sit more radial in the first compartment. This posterior superficial presentation matters because the extensor pollicis longus is a common culprit in dorsal wrist and thumb extension complaints, and its pulley-like turn around Lister’s tubercle explains both its mechanical advantage and its vulnerability. After a nondisplaced distal radius fracture, delayed attritional rupture of the EPL tendon can occur at the level of the third compartment, and clinicians often localize tenderness or crepitus here in tenosynovitis. The oblique course also helps you distinguish EPL from extensor digitorum on exam and on ultrasound, where dynamic thumb extension makes the tendon stand out against the dorsal carpal bones. Use this illustration in upper limb anatomy teaching to reinforce extensor compartment organization, the anatomical snuffbox boundaries, and tendon surface anatomy used for palpation and injection landmarks. It also fits hand surgery, sports medicine, and radiology publications covering EPL rupture, dorsal compartment tenosynovitis, and post-traumatic wrist pain patterns. Anatomical accuracy verified by SciePro's Medical Advisory Board.