Intra-articular osteoid osteoma.

The joint is a relatively rare localization for osteoid osteoma. The location of the tumor and the concomitant synovitis-explain the peculiarity of the clinical features, which makes differential diagnosis with inflammatory diseases of the joint difficult. The authors report the results of three cases of intra-articular osteoid osteoma in which it was possible to determine the levels of prostaglandin (PGE2) and prostacyclin (PGI2), which are synthesized by the tumoral tissue. The increased production of these substances, which can reach up to 70 times their production in normal tissue, explain both the character of the pain and the origin of the synovitis which is so commonly found in this kind of tumor. The results of this study confirm the ability of the neoplastic tissue to produce high quantities of mediators of inflammation and enable the authors to formulate a theory as to the pathogenesis of the concomitant reactive synovitis observed in cases of intra-articular osteoid osteoma.