Delayed Palmar Ulnar Head Dislocation After Malunion of Distal Radius Fracture

Abstract Traumatic palmar dislocation of the ulnar head at the distal radioulnar joint (DRUJ) is a known injury; however, palmar dislocation secondary to chronic DRUJ instability is relatively uncommon, with few studies reporting its occurrence. We report a case of palmar dislocation of the ulnar head that occurred during daily activity, long after the malunion of a distal radius fracture (DRF). A 70-year-old woman presented with pain in her left hand after carrying a ladder with both hands. Clinical examination revealed the disappearance of the dorsal prominence of the left ulnar head, accompanied by painful protrusion of the palmar side. Radiography and computed tomography confirmed palmar dislocation of the ulnar head. After infiltration anesthesia, the dislocation was reduced with a snapping sound by applying traction, pronation, and palmar pressure to the ulnar head under fluoroscopic guidance. Following the reduction, the DRUJ did not redislocate during pronation or supination. The patient had undergone conservative treatment for DRF 18 years prior. Postreduction radiography showed a malunion of DRF with a 19-degree radial inclination and a -8-degree palmar tilt (dorsal tilting). Magnetic resonance imaging revealed T2 high-intensity regions at the triangular fibrocartilage complex (TFCC) attachment site. For conservative management, the elbow joint was splinted with the forearm in a pronated position for 3 weeks. Additionally, a long wrist support was used during activities for 3 months, and the patient was advised to prevent supination movements. One year after the onset, redislocation has not occurred. Considering that the dislocation occurred while holding a ladder, this nontraumatic event was likely caused by a combination of factors, including malunion after DRF, TFCC injury, and mechanical loading in a supinated wrist position.