ACL Forces and Knee Kinematics Produced by Axial Tibial Compression During a Passive Flexion-Extension Cycle

Application of axial tibial force to the knee at a fixed flexion angle has been shown to generate ACL force. However, direct measurements of ACL force under an applied axial tibial force have not been reported during a passive flexion-extension cycle. We hypothesized that ACL forces and knee kinematics during knee extension would be significantly different than those during knee flexion, and that ACL removal would significantly increase all kinematic measurements. A 500N axial tibial force was applied to intact knees during knee flexion-extension between 0 degrees and 50 degrees. Contact force on the sloping lateral tibial plateau produced a coupled internal + valgus rotation of the tibia, anterior tibial displacement, and elevated ACL forces. ACL forces during knee extension were significantly greater than those during knee flexion between 5 degrees and 50 degrees. During knee extension, ACL removal significantly increased anterior tibial displacement between 0 degrees and 50 degrees, valgus rotation between 5 degrees and 50 degrees, and internal tibial rotation between 5 degrees and 15 degrees. With the ACL removed, kinematic measurements during knee extension were significantly greater than those during knee flexion between 5 degrees and 45 degrees. The direction of knee flexion-extension movement is an important variable in determining ACL forces and knee kinematics produced by axial tibial force. (C) 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.