Superoxide dismutase activity in arthropathy: its role and measurement in the joints.

The electron spin resonance (ESR) method was used to measure the superoxide dismutase (SOD) activity in synovial fluids from the knee joints of 73 patients with rheumatoid arthritis (RA), and the results were compared with those of 50 patients with osteoarthritis (OA) and posttraumatic arthritis (PA). The SOD activity in RA and OA knee joint fluids was higher than in the control patients with PA. Patients with moderate RA (grade III or IV according to Larsen's classification of rheumatoid knee radiographs) showed higher SOD activities in joint fluids than patients with early (grade I or II) and terminal (grade V) stages of RA. Our results suggest that the SOD activity in joint fluids is a valid index of articular destruction and repair.