Intra-articular osteoid osteoma at the elbow mimicking arthritis: a case report.

Osteoid osteomas are benign, typically intracortical lesions most often affecting the diaphysis of long bones. Nocturnal pain and characteristic symptoms that are relieved by administration of non-steroidal anti-inflammatory drugs (NSAIDs) are present and can help in the diagnosis of osteoid osteoma. We report a case of 18-year-old boy with an osteoid osteoma in the olecranon fossa with an atypical clinical manifestation. The initial manifestation was arthritis-like symptoms such as local heat, motion pain rather than pain at rest, and limited range-of-motion. Notably, NSAIDs were not effective at all for relieving his symptoms. Magnetic resonance imaging showed bone marrow edema around the elbow joint. The symptoms were resistant to conservative treatments, and thus, surgical resection was required. Histopathological examination showed that the lesion consisted of woven bones and osteoid tissues that anastomosed with each other. Combined with a tumor size that was less than 2 cm, clinicopathologically, the tumor was diagnosed as an osteoid osteoma. The pain was immediately relieved after the operation, and range-of-motion recovered at 2 months postoperatively. At 1 year after the surgery, the patient did not exhibit recurrence of the tumor or exacerbation of elbow pain and had a full range of elbow motion. Osteoid osteoma should be considered for the differential diagnosis of arthritis of the elbow in patients who are adolescents and young adults, which is the peak age of onset for osteoid osteoma.