On the Mechanisms of Non-contact ACL Injury During a Simulated Jump Landing: Experimental and Theoretical Analyses

Abstract

Of the 350,000 ACL reconstructions performed annually in the U.S., 70% are due to “non-contact” injuries often due to pivot landing maneuvers. Because an ACL injury predisposes the individual to early onset knee osteoarthritis, mechanistic insights are needed into why these injuries occur so they can be better prevented in the future. A knowledge gap concerns the relative contributions of dynamic internal tibial torque and valgus moment in causing ACL strain under the large impulsive ground reactions and muscle forces typically experienced in vivo. The goal of this dissertation, therefore, was to investigate the effect of impulsive axial tibial torque, with and without frontal plane moment, on ACL strain during a realistic jump landing scenario. Human cadaveric knees were loaded with realistic muscle forces in a simulated pivot landing test scenario. Impulsive compression, flexion moment, internal or external tibial torque, and ab- or adduction moments were simultaneously applied to the knee while recording the 3-D knee loads, muscle forces, tibiofemoral kinematics, and anteromedial ACL relative strain. In addition, a dynamic 3-D biomechanical model of the knee was developed to further explore ACL injury mechanisms. The results show that internal tibial torque, rather than a knee abduction moment, causes the largest ACL strains during a jump landing. Furthermore, an internal tibial torque induces a 70% larger ACL strain than a similar magnitude of external tibial torque. The presence of either a knee ab- or adduction moment did not significantly alter these results. An insight provided by the knee model is that when the lateral tibial slope exceeds that of the medial tibial plateau, then an abduction moment augments coupled internal tibial rotation, thereby increasing ACL strain, even without medial knee joint opening. Finally, the model simulation found that a steeper lateral tibial slope compared to a medial tibial slope, a more valgus limb alignment, and a shallower medial tibial concavity all increase the ACL strain during a simulated landing.