Effect of pregnancy on joint contracture in the rat knee.

As there is evidence that ligamentous laxity is affected by the female hormones, we hypothesized that hormonal changes occurring during pregnancy could have a therapeutic role in preventing the development of a joint contracture. Knee joint contractures were created in pregnant and nonpregnant rats. After 2 wk of immobilization, the degree of contracture was measured with structural properties of the medial collateral and anterior cruciate ligaments and the pubic symphysis. Although not statistically significant, there was a general trend toward reduced contracture in pregnant compared with nonpregnant rats. Cutting the posterior capsule significantly decreased contracture for both the pregnant and nonpregnant groups, confirming the contribution of capsular structures to contracture. Ultimate loads of the medial collateral and anterior cruciate ligaments significantly decreased after immobilization compared with control, but there was no significant effect due to pregnancy. Stiffness and ultimate load of the pubic symphysis were not significantly different between pregnant and nonpregnant groups. The trend toward reduced contracture with pregnancy points toward a possible therapeutic role for female hormones in the prevention of postoperative and/or posttraumatic joint contracture.