Intraepiphyseal location of an osteoid osteoma is extremely rare with few cases reported in the literature. They are often present with various atypical and nonspecific clinical features. Synovitis of adjacent joint is common and along with chronic inflammation could be misinterpreted as rheumatoid arthritis. Initial plain radiographs are often not diagnostic and further radiologic evaluation with CT scan is an essential part of diagnostic work-up. Repeated plain X-ray is very useful in making a correct diagnosis. Although the characteristic double density sign is usually absent in isotope scan in intra-articular osteoid osteoma, it plays an important role in localization of the nidus. We report a case with an intraepiphyseal osteoid osteoma without any signs of synovitis or growth disturbances. During the enbloc resection of nidus, we noticed no communication between the nidus and joint or physis in our cases. It seems that communication of nidus with joint space or growth plate is essential to allow mediators of inflammation pass to joint or growth plate and produce synovitis or growth disturbances, respectively.
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