SPONTANEOUS SYNOVITIS IN WISTAR RATS

Spontaneous synovitis has been detected in the stifle joints of contro l Wistar rats in 4-wk and 2-yr toxicity studies, and a specific site w as found to be predisposed to synovitis. The incidence of synovitis wa s 27.5% for males in the 4-wk study and 40.0% for males and 16.0% for females in the 2-yr study. The severity was not increased with aging. The degenerative changes, including chondroid metaplasia of the crucia te Ligaments of the stifle and/or the surrounding connective tissue at the border of the cruciate ligaments of the stifle, were present even in younger animals, and moreover there was a good correlation between synovitis and chondroid metaplasia of the cruciate ligaments of the s tifle and the surrounding connective tissue at the border of the cruci ate ligaments of the stifle. Vascular changes, including the developme nt of fibrin-containing thrombi, were observed in the surrounding conn ective tissue at the border of the cruciate Ligaments of the stifle. I t is speculated that the pathogenesis of the observed synovitis reflec ts joint instability that induces mechanical damage of the synovium.