An in vitro biomechanical evaluation of anterior-posterior motion of the knee. Tibial displacement, rotation, and torque

We tested the anterior-posterior motion of nine normal cadaver knees in zero to 90 degrees of flexion using a specially designed apparatus. This apparatus applied a dynamic anterior-posterior force to each knee and measured the resulting tibial displacement, rotation, and torque. In the intact knee, an anterior force produced an internal tibial torque and internal tibial rotation, while a posterior force produced an external torque and external rotation. Anterior-posterior displacement increased by 30 per cent when the tibia was allowed to rotate freely about its neutral rotation position. Isolated section of the anterior cruciate ligament produced more than double the amount of anterior displacement without affecting posterior displacement. Isolated section of the posterior cruciate ligament produced almost triple the amount of posterior displacement without affecting anterior displacement. After cutting either the anterior or the posterior cruciate ligament, the resulting internal or external secondary tibial rotation disappeared. It appears, therefore, that the anterior and posterior cruciate ligaments are the primary restraints to motion in the anterior and posterior directions as well as the causes of internal and external tibial rotation during anterior and posterior motion. Clinical Relevance: Clinical evaluation of the knee requires the measurement of relative femoral-tibial motion resulting from an applied force. Cadaver experiments are a useful means by which quantitative measurements of the motion can be made. Through the selective cutting of various ligament structures, alterations in the motion of the normal knee can be studied and the appropriate characteristics can be defined. In this investigation, we found that in knees with insufficiency of the cruciate ligaments the greatest increases in anterior and posterior displacement occurred at 30 and 75 degrees of flexion, respectively. Concomitantly a drastic loss of tibial rotation also occurred, suggesting that this characteristic must not be ignored when evaluating stability of the knee.