Extensor Pollicis Longus Muscle Beneath the Skin, Posterior View

Description

Posterior superficial anatomy of the male forearm and hand is rendered with the extensor pollicis longus (EPL) muscle belly highlighted against the radius and ulna, its fibers arising from the posterior ulnar shaft and adjacent interosseous membrane. From a proximal, medial origin the muscle courses distally and laterally, narrowing into a tendon that traverses the dorsal wrist toward the thumb. At the hand, the tendon tracks to the base of the distal phalanx of digit I, forming the ulnar, medial border of the anatomical snuffbox as it angles obliquely across the dorsum. Bony landmarks of the carpus, metacarpals, and phalanges provide reference for tendon direction and thumb alignment. EPL matters because its tendon makes a sharp turn around Lister tubercle on the distal radius within the third dorsal compartment, a mechanical arrangement that explains both efficient thumb interphalangeal extension and a classic site of attrition. Rupture after nondisplaced distal radius fracture or following chronic tenosynovitis presents with sudden loss of active thumb IP extension and difficulty elevating the thumb off a flat surface. This posterior perspective also helps clarify why dorsal wrist pain can localize near the third extensor compartment, distinct from first-compartment De Quervain disease involving abductor pollicis longus and extensor pollicis brevis. A clean landmark. Use this artwork in upper limb anatomy teaching to connect forearm compartment organization to thumb mechanics, or in hand surgery and orthopaedics materials discussing dorsal compartment pathology, distal radius fracture complications, and tendon transfer planning. It also suits radiology and ultrasound education when correlating the EPL course with Lister tubercle and the anatomical snuffbox on physical exam. Anatomical accuracy verified by SciePro's Medical Advisory Board.