Tensions in the anterior and posterior cruciate ligaments of the knee during passive loading: predicting ligament loads from in situ measurements.

Cruciate ligament tensions were predicted for anteroposterior (AP) tibial translation at 20 degrees, 30 degrees, 80 degrees, and 90 degrees of knee flexion based on in vitro measurements from six cadaver knees. A three-dimensional trigonometric equation was derived to calculate cruciate ligament tension as functions of AP force applied to the tibia and knee flexion angle (KFA). AP forces less than or equal to 150 N were applied. Ligament tension increased with applied AP force. The relationship between ligament tension and applied AP force appeared linear, but a Hotteling's T2 test failed to demonstrate a linear relationship. Tensions in the anterior cruciate ligament (ACL) attained magnitudes of approximately equal to 140 N. Tensions in the posterior cruciate ligament (PCL) attained magnitudes of approximately equal to 220 N. An analysis was performed to determine the sensitivity of ligament tension to hypothetical errors in the experimentally measured parameters used to compute ligament tension. The new method we report can be used to determine tensions in the ligaments of the knee or other joints for various loading conditions.