An Uncommon Mass in The Distal Ulna; A Case of Atypical Osteoid Osteoma

Osteoid osteoma (OO) is a benign osteoblastic tumor that commonly occurs in the diaphysis of long bones but is rarely found in peri-articular locations, particularly the wrist. This case report describes a 19-year-old female who presented with chronic wrist pain lasting two years, accompanied by nocturnal exacerbation and tenderness over the distal ulna. Imaging revealed a radiolucent lesion with a nidus, leading to a diagnosis of OO, later confirmed histologically following surgical excision. Differential diagnoses such as ulnar impingement syndrome, triangular fibrocartilage complex (TFCC) injuries, aneurysmal bone cyst (ABC), and giant cell tumor (GCT) were considered and ruled out through clinical and radiological findings. The patient experienced significant pain relief and regained full wrist function postoperatively. This report emphasizes the rarity of OO in the distal ulna and the importance of advanced imaging and a thorough differential diagnosis in managing persistent wrist pain.