Supernumerary extensor pollicis longus tendon masking an extensor pollicis longus rupture following non-surgical treatment of a distal radius fracture.

Extensor pollicis longus tendon pathology is a recognised complication following non-surgical treatment of non-displaced distal radius fractures. Tendon entrapment typically presents with pain, but preservation of thumb retropulsion during complete rupture results in loss of active thumb retropulsion and tenodesis effect. We present the case of a 52-year-old woman who developed extensor pollicis longus tendon entrapment with full active thumb extension following a non-displaced distal radius fracture. During her elective third dorsal compartment release, the extensor pollicis longus tendon was found to be completely ruptured and a rare supernumerary extensor pollicis longus tendon was found emerging from the fourth dorsal compartment. Gentle traction of this tendon resulted in thumb interphalangeal joint extension and simultaneous index finger metacarpophalangeal joint extension. An extensor indicis proprius to extensor pollicis longus tendon transfer was performed. At her final 6-month follow-up, she had painless full active thumb motion comparable to her contralateral side.