Quantification of in vivo patellofemoral contact forces before and after ACL transection.

Altered knee loading following anterior cruciate ligament (ACL) transection is believed to play an important role in initiating cartilage degeneration. Changes of in vivo joint contact forces pre- and post-ACL transection have not been quantified to date. Consequently, it is not known how knee loading changes following ACL transection, and how it contributes to cartilage degeneration. The objective of this study was to quantify in vivo patellofemoral contact forces in the cat knee prior to and up to nine days following uni-lateral ACL transection. Patellofemoral contact forces were predicted using a planar three-force model with knee extensor forces and patellofemoral geometry as input. Patellofemoral movements were expressed as functions of external knee kinematics. Kinematics and knee extensor forces were measured in both hindlimbs before and after ACL transection during unrestrained locomotion. Following ACL transection, resultant patellofemoral contact forces were 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 of the joint also results in locally decreased contact loads and altered joint kinematics. Alterations of in vivo patellofemoral loading following ACL transection have been quantified for the first time in this study. A next step will be to quantify the dynamic in vivo cartilage stresses in intact and injured knees which may help to elucidate the effects of mechanical stimuli on cartilage metabolism.