Atypical Intra-articular Osteoid Osteoma Mimicking Slipped Capital Femoral Epiphysis: A Rare Diagnostic and Therapeutic Challenge in a Pediatric Patient.

This case report describes a complex diagnostic challenge in a 10-year-old male presenting with persistent and progressively worsening hip pain. The initial clinical suspicion centered on slipped capital femoral epiphysis (SCFE), a common orthopedic condition in adolescents often associated with obesity and characterized by displacement of the femoral head at the growth plate. Standard radiographs suggested potential epiphyseal abnormalities, raising concerns for SCFE. However, subsequent advanced imaging revealed a 1 cm lytic lesion in the femoral neck with surrounding sclerosis, a classic radiologic feature of osteoid osteoma, thereby confirming the diagnosis. The patient underwent successful treatment with CT-guided radiofrequency ablation (RFA) with adjunctive perilesional cryotherapy and intraoperative nonsteroidal anti-inflammatory drug (NSAID) infusion, resulting in rapid pain relief and expedited recovery. This case underscores the diagnostic overlap between SCFE and osteoid osteoma, as both conditions can manifest with hip pain and restricted range of motion in pediatric patients. It emphasizes the critical role of advanced imaging modalities, such as magnetic resonance imaging (MRI) and computed tomography (CT), in distinguishing between these two entities, particularly when initial radiographs are inconclusive.