[Osteoid osteoma of the femur neck with synovitis simulating chronic monoarthritis of the hip].

The authors report a case of subperiosteal osteoid osteoma of the femoral neck in a 14 year-old girl presenting as chronic hip monoarthritis with narrowed coxofemoral joint space and non specific histological synovitis. They analyse the synovitis which is associated with some osteoid osteomas (hip, elbow, knee, ankle bones) emphasizing the "pseudo-arthritis of the hip" picture and insist that all cases of unexplained chronic monoarthritis of the hip should suggest subperiosteal osteoid osteoma of the neck.