Ligaments and articular contact guide passive knee flexion

The aim of this study was to test the hypothesis that the coupled features of passive knee flexion are guided by articular contact and by the isometri c fascicles of the ACL, PCL and MCL. A three-dimensional mathematical model of the knee was developed, in which the articular surfaces in the lateral and medial compartments and the isometric fascicles in the ACL, PCL and MCL were represented as five constraints in a one degree-of-freedom parallel s patial mechanism. Mechanism analysis techniques were used to predict the pa th of motion of the tibia relative to the femur. Using a set of anatomical parameters obtained from a cadaver specimen, the model predicts coupled int ernal rotation and ab/adduction with flexion. These predictions correspond well to measurements of the cadaver specimen's motion. The model also predi cts posterior translation of contact on the tibia with flexion. Although th is is a well-known feature of passive knee flexion, the model predicts more translation than has been reported from experiments in the literature. Mod elling of uncertainty in the anatomical parameters demonstrated that the di screpancy between theoretical predictions and experimental measurement can be attributed to parameter sensitivity of the model. This study shows that the ligaments and articular surfaces work together to guide passive knee mo tion. A principal implication of the work is that both articular surface ge ometry and ligament geometry must be preserved or replicated by surgical re construction and replacement procedures to ensure normal knee kinematics an d by extension, mechanics. (C) 1998 Elsevier Science Ltd. All rights reserv ed.