Imaging Report With Radiologic Criteria for Differentiation: Avulsion Fracture or Os Triquetrum Secundarium?

Accessory ossicles of the wrist are uncommon bone variants that can be mistaken for avulsion fractures, potentially leading to unnecessary tests, procedures, and radiation exposure. We report a case of a 19-year-old male who presented after a motor vehicle collision with bilateral wrist pain and swelling. Radiographs of the right wrist were normal. Imaging of the left wrist demonstrated a small, oval ossicle located between the triquetrum and the ulnar styloid process. The ossicle displayed smooth cortical margins, a preserved cortical-medullary ratio, and a distinct radiolucent gap from adjacent carpal bones, features consistent with an os triquetrum secundarium (OTS). The patient denied prior wrist trauma, and no changes in the normal range of motion in the wrists were established. The diagnosis was reached by correlating the clinical history with radiographic findings. Conservative management, including immobilization, nonsteroidal anti-inflammatory drugs, cryotherapy, and physiotherapy, resulted in complete symptom resolution within two weeks. This case underscores the importance of including OTS in the differential diagnosis of ulnar-sided wrist pain and suspected avulsion fractures, applying established imaging criteria to avoid misdiagnosis, and favoring nonoperative treatment when there is no associated triangular fibrocartilage complex injury.