QUANTIFICATION OF IN-VIVO PATELLOFEMORAL CONTACT FORCES BEFORE AND AFTER ACL TRANSECTION

Altered knee loading following anterior cruciate ligament (ACL) transe ction is believed to play an important role in initiating cartilage de generation. Changes of in vivo joint contact forces pre-and post-ACL t ransection have not been quantified to date. Consequently, it is not k nown how knee loading changes following ACL transection, and how it co ntributes to cartilage degeneration. The objective of this study was t o quantify in vivo patellofemoral contact forces in the cat knee prior to and up to nine days following uni-lateral ACL transection. Patello femoral contact forces were predicted using a planar three-force model with knee extensor forces and patellofemoral geometry as input. Patel lofemoral movements were expressed as functions of external knee kinem atics. Kinematics and knee extensor forces were measured in both hindl imbs before and after ACL transection during unrestrained locomotion. Following ACL transection, resultant patellofemoral contact forces wer e decreased by approximately 30% in the ACL-deficient hindlimbs. These results suggest that decreased loading in the ACL-deficient knees may initiate the early degenerative changes observed in cartilage of ACL- transected animals. It remains to be shown, if the general unloading o f the joint also results in locally decreased contact loads and altere d joint kinematics. Alterations of in vivo patellofemoral loading foll owing ACL transection have been quantified for the first time in this study. A next step will be to quantify the dynamic in vivo cartilage s tresses in intact and injured knees which may help to elucidate the ef fects of mechanical stimuli on cartilage metabolism. (C) 1998 Elsevier Science Ltd. All rights reserved.