ECU Subluxation

Definition

Instability of the extensor carpi ulnaris tendon out of its groove on the distal ulna after disruption of the ECU subsheath.

Anatomy

• Sixth dorsal compartment, held in the ulnar groove by a fibro-osseous subsheath
• Subsheath lies deep to the extensor retinaculum and forms part of the TFCC
• Tendon least stable in supination, flexion and ulnar deviation

Aetiology

• Forced supination, flexion and ulnar deviation
• Tennis, especially the non-dominant wrist in a two-handed backhand
• Golf and rugby league injuries

Classification

• Inoue and Tamura Type A. Subsheath ruptured ulnarly, lying superficial to the tendon
• Type B. Subsheath ruptured radially, lying in the groove beneath the tendon
• Type C. Periosteal stripping from the ulna forming a false pouch

Clinical Features

• Painful snapping on the dorsoulnar wrist during forearm rotation
• Tendon subluxes ulnarly and volarly in supination and relocates in pronation
• ECU synergy test positive with associated tendinopathy

Investigations

• Dynamic ultrasound shows subluxation during rotation
• MRI for subsheath tears and associated TFCC injury

Differential Diagnosis

• ECU tendinopathy
• TFCC tears
• Ulnar impaction syndrome
• DRUJ instability
• Dorsal ulnar wrist ganglion

Management

• Long arm cast. Acute injury, wrist in pronation and radial deviation for about 6 weeks
• Subsheath repair. Direct suture for Type B tears
• Subsheath reconstruction. Extensor retinaculum flap for Type A tears
• Periosteal reattachment. Type C false pouch
• Groove deepening. Added when the ulnar groove is shallow

Complications

• Recurrent instability
• Dorsal sensory branch of the ulnar nerve injury
• Loss of supination after reconstruction

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 19 October 2026.