Mice after ovariectomy (OVX) displayed a significantly more severe disease than sham-operated mice. (a) The mice were observed twice weekly for frequency of arthritis. They were considered arthritic when they displayed signs of arthritis in one joint for two consecutive assessments, or arthritis in more than one joint. (b) Severity of arthritis was evaluated twice weekly. Severity was graded 1 to 3 in each paw (maximum 12 points per mouse). Open circles, sham (n = 18); filled circles, ovariectomy (n = 15). *P < 0.05; **P < 0.01; ***P < 0.001. CII, type II collagen.