For the purposes of classification, it should be specified whether osteoarthritis (OA) of the knee is of unknown origin (idiopathic, primary) or is related to a known medical condition or event (secondary). Clinical criteria for the classification of idiopathic OA of the knee were developed through a multicenter study group. ____and radiographs were used to develop sets of criteria that serve different investigative purposes. In contrast to prior criteria, these proposed criteria utilize classification trees, or algorithms.

Clinical criteria for the classification of symptomatic idiopathic (primary) osteoarthritis (OA) of the hands were developed from data collected in a multi- center study. Patients with OA were compared with a group of patients who had hand symptoms from other causes, such as rheumatoid arthritis and the spondylarthropathies. Variables from the medical history, physical examination, laboratory tests, and radiographs were analyzed. All patients had pain, aching, or stiffness in the hands. Patients were classified as having clinical OA if on examination there was hard tissue enlargement involving at least 2 of 10 selected joints, swelling of fewer than 3 metacarpophalangeal joints, and hard tissue enlargement of at least 2 distal interphalangeal (DIP) joints. If the patient had fewer than 2 enlarged DIP joints, then deformity of at least 1 of the 10 selected joints was necessary in order to classify the symptoms as being due to OA. The 10 selected joints were the second and third DIP, the second and third proximal interphalangeal, and the trapeziometacarpal (base of the thumb) joints of both hands. Criteria derived using the "classification tree" method were 92% sensitive and 98% specific. The "traditional format" classification method required that at least 3 of these 4 criteria be present to classify a patient as having OA of the hand. The latter sensitivity was 94% and the specificity was 87%. Radiography was of less value than clinical examination in the classification of symptomatic OA of the hands.To promote uniformity in the reporting of the rheumatic diseases, the Diagnostic and Therapeutic Criteria Committee of the American College of Rheumatology established subcommittees to develop classification criteria. During the last decade, criteria for systemic sclerosis, Reiter's syndrome, systemic lupus er ythematosus, rheumatoid arthritis (RA), osteoart hri-

Little information is available regarding the long-term effects, if any, of running on the musculoskeletal system. We therefore compared the prevalence of degenerative joint disease among 17 male runners (mean age, 56 years; height, 180 cm [5 ft 11 in]; and weight, 73.02 kg [161 lb] with 18 male nonrunners (mean age, 60 years; height, 178 cm [5 ft 10 in]; and weight, 78 kg [171 lb]). Running subjects (53% marathoners) ran a mean of 44.8 km (28 miles)/wk for 12 years. Pain and swelling of hips, knees, ankles, and feet and other musculoskeletal complaints among runners were comparable with those among nonrunners. Radiologic examinations (for osteophytes, cartilage thickness, and grade of degeneration) also were without notable differences among groups. We did not find an increased prevalence of osteoarthritis among the runners. Our observations suggest, within the limits of our study, that long-duration, high-mileage running need not be associated with premature degenerative joint disease in the lower extremities.

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