Extensor Pollicis Brevis Muscle Beneath the Skin, Posterior View

Description

Posterior forearm and dorsum of the hand are rendered with the skin removed to expose the extensor compartment over the radius and ulna, with the extensor pollicis brevis (EPB) emphasized along the dorsoradial forearm. Its short muscle belly lies distal to the lateral epicondylar region and courses obliquely toward the radial styloid, becoming a tendon that passes deep to the extensor retinaculum at the wrist. Distally, the EPB tendon tracks on the radial side of the dorsum of the hand toward the thumb, inserting on the base of the proximal phalanx and sitting close to abductor pollicis longus within the first dorsal compartment. Bony landmarks include the radial and ulnar shafts, the carpal bones, metacarpals, and phalanges, oriented in standard anatomical position. Clean relationships. EPB anatomy matters because its tendon shares a confined fibro-osseous tunnel where friction and synovial thickening produce De Quervain tenosynovitis, classically tender just proximal to the radial styloid and provoked by Finkelstein or Eichhoff maneuvers. Variations in EPB compartmentalization and insertion can explain incomplete symptom relief after first dorsal compartment release, and they influence surgical planning when you need to identify and protect the superficial branch of the radial nerve crossing the dorsoradial wrist. This posterior perspective also clarifies why EPB contributes to thumb metacarpophalangeal extension while extensor pollicis longus, running more ulnarly around Lister tubercle, dominates interphalangeal extension. Use this artwork in upper limb gross anatomy teaching, hand therapy education, and orthopedic or plastic surgery references that discuss radial-sided wrist pain and extensor retinaculum compartment releases. It also supports radiology and sonography materials for guiding probe placement over the first dorsal compartment and correlating tendon position with osseous landmarks on the dorsal radius. Anatomical accuracy verified by SciePro's Medical Advisory Board.