Influence of Sex and Knee Joint Rotation on Patellofemoral Joint Stress through a Mathematical Modelling Study

Background: Females are two times as likely to experience patellofemoral pain syndrome (PFPS) than males; however, the reason for this sex difference remains unclear. Patellofemoral joint (PFJ) stress is believed to contribute to PFPS alterations through knee joint rotation alignment, but the influence of knee joint rotation conditions on PFJ stress is unclear. We aimed to investigate the influence of sex and knee joint rotation alignment on PFJ stress. Methods: Simulation ranges were set to knee joint flexion angles of 10°-45° (common to both sexes) and extension moments of 0-240 Nm (males) and 0-220 Nm (females). The quadriceps force and effective lever arm length at the quadriceps muscle were determined as a function of the knee joint flexion angle and extension moment. The PFJ contact area, which is specific to sex, and knee joint rotation was calculated from cadaver data, and PFJ stress was estimated. Results: In all knee joint rotation conditions, PFJ stress was higher in females than in males. Additionally, PFJ stress in males and females was the largest under neutral conditions compared with other rotation conditions. Conclusion: The results may be useful for understanding the underlying mechanisms contributing to the differences in PFPS in males and females.