Effect of Pregnancy on Knee Joint Contracture in the Rat

ABSTRACT

OBJECTIVE: To study the effect of pregnancy on knee joint contracture in the rat, because the laxity of peripheral joint increases during pregnacy. METHOD: We evaluated the difference of contracture between the pregnant and non-pregnant female rats after 3 week of knee immobilization using a wire. The femorotibial angle at immobilization status was 30o. After immobilization, the femorotibial angle were measured using X-ray after removal of wire at 50 g and 100 g weighted state on the tibia. To study the change of fibroblast in immobilized knee joint ligament, immunohistochemical staining for actin was performed using alpha-smooth muscle actin antibody (DAKO, Denmark). RESULTS: The femorotibial angles were 116.7+/-9.2o and 97.3+/-18.0o after wire removal, in the immobilized pregnant and nonpregnant rats respectively. The femorotibial angles at 50 g and 100 g weighted state were 136.8+/-7.2o and 144.7+/-3.8o, respectively in the immobilized pregnant rats and 129.4+/-12.7o and 136.3+/-8.9o in the immobilized non-pregnant rats. The angles of pregnant group were significantly larger than those of non-pregnant group (p<0.05). In immobilized pregnant and non-pregnant rats, the alpha-smooth muscle actin was moderately expressed in fibroblast of anterior and posterior cruciate ligaments of the knee by immunohistochemistry, while there was no expression of alpha-smooth muscle actin in fibroblast of the ligaments in the non-immobilized knee. CONCLUSION: Joint contracture develops to a lesser degree in pregnant rats than in non-pregnant rats and alpha-smooth muscle actin is expressed in fibroblast of contractured knee ligaments.