Extensor Carpi Ulnaris

Clinical Notes

• ECU is innervated by the posterior interosseous nerve (PIN). In PIN palsy, ECU is affected along with extensor digitorum — the result is loss of ulnar deviation during wrist extension (wrist deviates radially via intact ECRL) and loss of finger extension at the MCP joints.

• A consistent contributor to conditions/lateral-epicondylitis — as part of the common extensor origin, ECU is loaded with every gripping and wrist extension activity. Lateral epicondylitis rarely involves only one muscle — the entire common extensor group is typically affected.
• ECU tendinopathy — overuse tendinopathy at the 6th dorsal compartment on the ulnar wrist. Common in racquet sports (tennis, badminton) from repetitive forehand and backhand motions. Presents as localized pain at the dorsal-ulnar wrist that worsens with resisted ulnar deviation. The tendon can also sublux from its groove during supination-pronation, producing a painful snapping sensation.
• ECU subluxation — the tendon can dislocate from the 6th dorsal compartment groove, particularly in athletes. A palpable snap during forearm rotation at the ulnar-dorsal wrist suggests subluxation — refer for further assessment.

• In clients with lateral elbow pain, ECU is tender along its full length but especially at the common extensor origin and the proximal muscle belly. It is part of the "lateral elbow pain complex" and is rarely treated in isolation.
• In clients with ulnar wrist complaints, the ECU tendon at the 6th dorsal compartment is often tender and thickened. Compare bilaterally — the normal side should be non-tender with a smooth tendon glide.

• Responds well to longitudinal stripping along the ulnar-posterior forearm from the lateral epicondyle to the wrist. Cross-fiber friction at the common extensor origin treats ECU alongside the other extensors.
• The 6th dorsal compartment tendon can be treated with specific cross-fiber friction at the dorsal-ulnar wrist — effective for chronic tendinopathy but requires precise localization.

• The ulnar styloid process lies immediately adjacent to the 6th dorsal compartment — do not apply friction directly on the bony styloid tip, which can be tender.
• The dorsal cutaneous branch of the ulnar nerve crosses the ulnar wrist area superficially — sustained heavy pressure over the dorsal-ulnar wrist can irritate this sensory branch, producing numbness on the dorsal hand.

• ECU has a dual role as extensor and ulnar deviator — it partners with FCU for pure ulnar deviation (canceling out each other's flexion/extension components). When treating ulnar wrist pain, always check both ECU and FCU. They share the ulnar deviation function and both refer pain to the ulnar wrist, but from different sides — ECU from the dorsal compartment, FCU through the pisiform.