Unusual Presentation of Post-traumatic Distal Radioulnar Synostosis Following a Nondisplaced Distal Ulna Fracture: A Case Report.

Post‑traumatic radioulnar synostosis is an uncommon but potentially disabling complication of forearm injuries, typically associated with high‑energy trauma or fractures involving both forearm bones. We report an unusual case of distal radioulnar synostosis developing after conservative treatment of an isolated, nondisplaced distal ulna fracture. The patient presented 1 year after injury with severe restriction of forearm rotation. Imaging revealed a distinctive acetabular‑like configuration, in which hypertrophic ulnar callus induced a concave periosteal remodeling of the distal radius, resulting in a pathological pseudo‑articulation rather than a simple linear osseous bridge. Surgical excision of the synostosis was performed, followed by pronator quadratus muscle interposition and postoperative indomethacin prophylaxis. Full restoration of forearm rotation was achieved intraoperatively and was maintained at 6‑month follow‑up without evidence of recurrence. This case expands the recognized radiographic spectrum of distal radioulnar synostosis and highlights the importance of early recognition and comprehensive surgical management.