Intra-articular osteoid osteoma of the humerus with synovitis simulating chronic monoarthritis of the elbow in a recreational tennis player

We present a case of intra-articular osteoid osteoma of the humerus simulating chronic monoarthritis of the elbow in an 18-year-old male right-handed recreational tennis player. CT revealed a well-defined nidus in the coronoid fossa. Microscopic examination of the synovium showed a lymphofollicular synovitis that resembled the synovitis in rheumatoid arthritis.