ECU runs in its own sixth extensor compartment and plays a critical role in DRUJ stability by providing dorsal support. Its subsheath and retinaculum anchor the tendon to the ulna, maintaining its position during forearm rotation.
| Origin | Lateral epicondyle — common extensor origin, and posterior border of the ulna |
|---|---|
| Insertion | Base of the fifth metacarpal |
| Nerve Supply | Posterior interosseous nerve (C7, C8) |
| Blood Supply | Posterior interosseous artery |
| Actions | Extends the wrist; Adducts the wrist (ulnar deviation); Stabilises the DRUJ in rotation |
|---|
ECU tendinopathy and subsheath tears produce ulnar wrist pain. ECU subluxation from its groove occurs with the wrist in supination-ulnar deviation (racquet sport position). Dynamic ultrasound is used to demonstrate ECU subluxation. ECU stability restoration involves retinacular repair or reconstruction.
Palpated at the dorsal ulnar wrist during resisted wrist extension with ulnar deviation.
ECU tendon subluxation from its sixth extensor compartment groove in the supination-ulnar deviation position, producing painful snapping on the dorsal ulnar wrist, managed by retinacular repair.
