Sex-based differences in knee ligament biomechanics during robotically simulated athletic tasks

ACL injury rates are greater in female athletes than their male counterparts. As female athletes are at increased risk, it is important to understand the underlying mechanics that contribute to this sex bias. The purpose of this investigation was to employ a robotic manipulator to simulate male and female kinematics from athletic tasks on cadaveric specimens and identify sex-based mechanical differences relative to the ACL loading. It was hypothesized that simulations of female motion would generate the higher loads and ligament strains associated with in vivo ACL injury risk than simulations of male motion. A 6-degree-of-freedom robotic manipulator articulated cadaveric lower extremity specimens from 12 donors through simulations of in vivo kinematics recorded from male and female athletic tasks. Simulation of female kinematics exhibited lower peak lateral joint force during the drop vertical jump and lower peak anterior and lateral joint force and external joint torque during the sidestep cut (P<0.05). Peak ACL strain during a drop vertical jump was 6.27% and 6.61% for the female and male kinematic simulations, respectively (P=0.86). Peak ACL strain during a sidestep cut was 4.33% and 7.57% for female and male kinematic simulations respectively (P=0.21). For the tasks simulated, the sex-based loading and strain differences identified were unlikely to have a significant bearing on the increased rate of ACL injures observed in female athletes. Additional perturbation may be necessary to invoke the mechanisms that lead to higher rates of ACL injury in female populations.