Intra-articular Osteoid Osteoma of the Femoral Neck Mimicking Inflammatory Hip Disease: A Case Report and Review of the Literature.

Osteoid osteoma is a benign osteogenic tumor that predominantly affects the long bones of young adults. Intra-articular involvement of the femoral neck is uncommon and may present with atypical clinical features, often leading to a delayed diagnosis. We report the case of a 30-year-old woman presenting with chronic right hip pain of two years' duration, characterized by nocturnal exacerbation and partial relief with nonsteroidal anti-inflammatory drugs (NSAIDs). Initial evaluation raised suspicion of inflammatory hip disease; however, laboratory investigations were unremarkable. Subsequent CT revealed a well-defined 10 × 8 mm nidus in the inferomedial subcapital region of the right femoral neck, establishing the diagnosis of intra-articular osteoid osteoma. The patient underwent CT-guided percutaneous excision with complete pain relief, and histopathological examination confirmed the diagnosis. Intra-articular osteoid osteoma of the femoral neck represents a particular diagnostic challenge because its clinical presentation may be atypical, and inflammatory joint disease may initially be considered. MRI findings in intra-articular osteoid osteoma can be nonspecific, as reactive synovitis, joint effusion, and bone marrow edema may obscure the nidus, as reported in the literature. CT remains particularly useful for identifying the nidus when the diagnosis is uncertain. To place this case in context, we performed a narrative review of previously published reports on intra-articular and femoral neck osteoid osteoma, focusing on the clinical presentation, diagnostic pitfalls, imaging findings, and management strategies.