A new kinematic model for the study of the role of the anterior cruciate ligament (ACL) in human knee motion

Abstract

A six degree of freedom model was utilized to continuously measure the motions of loaded cadaveric human knees with unconstrained motion at the tibiofemoral joint through a range of motion from zero to 110 degrees of flexion. Several conditions were studied. Loading conditions were varied to simulate the natural body forces (i.e. the normal condition) and quadriceps-deficient condition. The range of motion in which the anterior cruciate ligament (ACL) is the primary restraint to anterior tibial translation was determined. The effect of ACL insufficiency on the kinematics of the human knee was investigated by comparing the kinematics of the knee specimens in the intact state with the kinematics obtained after the ACL was surgically severed. To simplify the complex kinematics of a six degree of freedom model, the motion of the instant center of the tibiofemoral joint for each specimen was estimated using the femoral transepicondylar pin reference point. The estimated motion of the instant center of the knees in the intact state and ACL deficient state was compared to empirical observations. The importance of the motion of the instant center was then determined in pathologic knee motion. Finally, the effect of total knee replacement on kinematics was investigated.