Intra-articular osteoid osteoma of the lower extremity: diagnostic problems.

We report five cases of intra-articular osteoid osteoma. Physical findings of osteoid osteoma vary with the site of the tumor. Juxta- and intra-articular osteoid osteomas present various atypical and nonspecific features. They are recorded both for their rarity and for the unusual clinical and roentgenographic findings that may delay diagnosis or induce misdiagnosis. Specialized imaging techniques may hasten diagnosis, but only an accurate clinical history, with a high index of suspicion, can allow for a proper diagnosis. When the diagnosis is suspected, we suggest that the most sensitive test is a "three-phase" technetium-99m bone-scan followed by computerized tomographic-scanning. Detailed evaluation of the suspected area, using thin sections is required to prevent misinterpretation, especially in a diagnosis involving first sprain of an ankle. The following cases of intra-articular osteoid osteoma illustrate the problems encountered in their diagnosis.