Using Finite Element Methods to Study Anterior Cruciate Ligament Injuries: Understanding the Role of ACL Modulus and Tibial Surface Geometry on ACL Loading.

Abstract

ACL injury, frequently encountered in sports, results in impaired gameplay, accruement of medical expenses and potential for long-term degenerative disease of the knee. More than 200,000 ACL injuries occur annually with the injury rate disproportionately higher in females. Many factors are implicated in this gender dimorphic behavior including ACL modulus and tibial surface geometry. The main objective was to determine if the effects of knee geometry and ligament properties manifest as externally measurable variables such as 3-D tibiofemoral kinematics, providing us with much needed insight into the mechanism of ACL loading and informing the potential for surveillance monitoring of knee kinematics to identify real-time injury risk. To achieve this goal, a finite element model was developed to simulate a single-leg landing by applying an impulsive load to the distal tibia recreating an experiment using cadaver knees by Oh (2011). A significant correlation (Pearson’s R = 0.861, p < 0.01) was found for the peak in ACL strain between 40ms and 70ms. The model was then used to predict knee kinematics and ACL strain resulting from a variation in ACL modulus and tibial surface geometry during simulated single-limb landing. The results indicate that ACL modulus had a significant effect on ACL strain. Additionally, a significant correlation (0.999) was observed between the peak ACL strain and peak anterior tibiofemoral acceleration. Tibial surface geometry examined through the effect of lateral tibial slope, medial tibial slope, and medial tibial depth had a significant effect on ACL strain. However, none of these parameters individually influenced the ACL strain. Additionally, peak ACL strain correlated with peak anterior acceleration (0.483), peak valgus angle (0.779) and peak internal rotation angle (0.678). Simulations examining the effect of ACL modulus and tibial surface geometry indicated a significant main effect of both factors. However no interaction effect was observed. A significant correlation was observed between the peak ACL strain with peak anterior tibiofemoral acceleration (0.979), peak valgus angle (0.458) and peak internal rotation angle (0.853). These findings support our hypothesis that differences in morphometric and ligament properties manifest as altered kinematics of the knee joint that correlate with ACL strain.