Osteoid osteoma of the acetabulum: two cases.

We report two cases of osteoid osteoma of the acetabulum associated with severe chronic synovitis. The diagnosis is difficult and usually delayed because the acetabulum is a rare site for this tumor and clinical signs are nonspecific. Computed tomography (CT) scanning is the best diagnostic technique. An intraarticular surgical approach allows complete resection, but one case required spongy bone grafts. Postoperative results are excellent.