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 30^o. 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 α-smooth muscle actin antibody (DAKO, Denmark).

Results: The femorotibial angles were 116.7⁑9.2^o and 97.3⁑18.0^o 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⁑7.2^o and 144.7⁑3.8^o, respectively in the immobilized pregnant rats and 129.4⁑12.7^o and 136.3⁑8.9^o 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 α-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 α-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 α-smooth muscle actin is expressed in fibroblast of contractured knee ligaments.

Keywords :Joint contracture, Pregnancy, α-smooth muscle actin, Fibroblast