Abstract
Data have been analysed from a retrospective review of 151 patients with monarthritis of more than 3 months' duration, usually involving the knee joint. The largest group, 49 patients (32%), had synovitis of unknown cause, 44 (29%) had synovitis probably associated with osteoarthrosis and 13 (9%) were diagnosable at presentation as having rheumatoid arthritis according to American Rheumatism Association (1959) criteria, which include serological and histological findings. There was only one case of tuberculous synovitis. Twelve of the thirteen patients diagnosed as rheumatoid arthritis developed involvement in other joints. In most other conditions, however, including synovitis of uknown cause, the prognosis was favourable, with either improvement or complete remission.