Biomechanical Determinants of Anterior Cruciate Ligament Stress in Individuals Post–ACL Reconstruction During Side-Cutting Movements

This cross-sectional laboratory-based study investigates the stress characteristics of the anterior cruciate ligament (ACL) during side-cutting using a knee finite element (FE) model and identifies biomechanical factors influencing ACL stress. Kinematics and ground reaction forces (GRF) were collected from eight participants (age: 30.3 ± 5.3 years; BMI: 25.6 ± 2.4 kg/m²; time since surgery: 12.8 ± 1.2 months) one year post-ACL reconstruction during side-cutting tasks. A knee FE model incorporating time-varying knee angles, knee forces, and femoral translation was developed to simulate the knee biomechanics. The relationships between ACL stress and lower limb biomechanics were analyzed. The results indicated the highest stress concentrations at the femoral attachment during the early landing phase. Posterior femoral displacement relative to the tibia was significantly correlated with peak ACL equivalent stress (r = 0.89, <i>p</i> = 0.003) and peak ACL shear stress (r = 0.82, <i>p</i> = 0.023). Peak ACL equivalent stress also showed positive correlations with posterior GRF (r = 0.77, <i>p</i> = 0.025) and knee extension moments (r = 0.71, <i>p</i> = 0.049). In contrast, peak ACL shear stress exhibited a significant negative correlation with hip extension moment (r = -0.80, <i>p</i> = 0.032). This study identified key biomechanical factors affecting ACL stress, highlighting the roles of femoral displacement, knee extension moments, and ground reaction forces, while demonstrating a negative relationship with hip extension moments.