Tendon Sheath of the Extensor Carpi Ulnaris, Posterior View

Description

Seen from the posterior aspect of the distal forearm and wrist, the extensor carpi ulnaris (ECU) tendon runs longitudinally along the dorsoulnar border, deep to the extensor retinaculum and within its synovial tendon sheath. The sheath encloses the tendon as it courses toward the base of the fifth metacarpal, with the ulnar head and styloid region lying medially and the dorsal carpal surface and metacarpals positioned distal to the retinacular band. Extensor digitorum and extensor digiti minimi tendons sit more centrally and radially in the dorsal compartments, while the ECU occupies the sixth extensor compartment adjacent to the ulna. A tight space. This posterior view matters because the ECU sheath and subsheath act as a stabilizing sling where the tendon changes direction across the distal ulna, a common site of painful snapping and instability in athletes and manual workers. Supination, ulnar deviation, and wrist extension can precipitate ECU subluxation when the subsheath tears, and tenosynovitis may follow repetitive loading or inflammatory arthropathy. For surgeons, the relationship between the ECU tendon, its fibro-osseous tunnel under the extensor retinaculum, and the ulnar groove frames decisions around retinacular repair, subsheath reconstruction, and ulnar-sided wrist exposure. Use this artwork in upper-limb anatomy teaching to clarify the extensor compartments and the concept of synovial tendon sheaths, or in hand surgery and sports medicine materials discussing ulnar-sided wrist pain, ECU tendinopathy, and post-traumatic instability. It also suits textbooks and patient-facing diagrams explaining why a focal, retinaculum-confined process can produce motion-related crepitus and swelling at the dorsoulnar wrist. Anatomical accuracy verified by SciePro's Medical Advisory Board.