The Effect of Gender-Related Differences in Knee Morphology on Peak ACL Strain During Repeated Simulated Pivot Landings: An In Vitro Investigation

Anterior cruciate ligament (ACL) injuries are associated with considerable morbidity, including the development of knee osteoarthritis. A smaller ACL cross-sectional volume and a steeper lateral tibial slope have been associated with increased ACL injury risk. A knowledge gap exists as to why adolescent females have a 2- to 8-fold greater ACL injury rate than males, and whether the human ACL is susceptible to a fatigue failure under repeated loading. This dissertation tests the research hypotheses that (1) the female ACL exhibits greater peak strain than the male ACL during a two-times body weight (2*BW) simulated pivot landing because of a smaller ACL cross-sectional area and steeper lateral tibial slope, and (2) the ACL is susceptible to fatigue failure under repeated 3 - 4*BW simulated pivot landings.;Ten male and 10 female knees from age- and size-matched donors were subjected to 3T MR imaging to measure ACL cross-sectional area and lateral tibial slope. Each knee was loaded into a custom testing apparatus which delivered a standardized 2*BW compound impulsive load (compression force, knee flexion moment, internal tibial torque and muscle forces). The quadriceps' resistance to rapid stretch was modeled using a novel non-linear spring. The 3-D tibiofemoral kinematics and kinetics, muscle forces, and anteromedial ACL relative strain were recorded for 100 ms. Females ACLs exhibited 95% greater peak strain than male ACLs during the pivot landing, and ACL cross-sectional area and lateral tibial slope explained 59% of the variance in peak ACL strain. These results suggest an individual's knee morphology can predispose them to an ACL injury.;Using similar methods and 10 pairs of knees, the human ACL exhibited fatigue failure under repetitive 3*BW and 4*BW pivot landings. The larger the applied cyclic loading, and the smaller the ACL cross-sectional area, the fewer cycles it took for the ACL to fail. Finally, in 12 female knees increasing quadriceps tensile stiffness by 33% reduced peak ACL strain by 16%, thereby reducing the risk for injury.;Future interventions should target the magnitude and frequency of pivot landing loading cycles and screen for high-risk knee morphologies in order to reduce ACL injury risk.