Introduction Although the rate of anterior cruciate ligament (ACL) injury is low among children, it increases during adolescence, especially in girls. The injury typically occurs immediately after foot-ground contact during sports activities such as a cutting maneuver (CM). The knee frontal plane moment (KFM) has been implicated as a biomechanical risk factor, but it has not been extensively studied within the injury timeframe. The present study aimed to prospectively investigate sex-dependent changes in the KFM from pre-adolescence to adolescence during the first 70 ms of a CM task.

Methods A total of 293 handball and soccer players, aged 9–12 years, were recruited to perform a CM, where kinematic and kinetic data were obtained using marker-based motion capture and force plates. Those who continued sports participation (n=105) returned five years later to repeat the test procedure. A mixed-model analysis of variance (ANOVA) for repeated measures was used for statistical analysis of the KFM during the first 70 ms after foot-ground contact.

Results Overall, boys had significantly higher valgus KFM values than girls across both data collections (P=0.001). Also, a significant interaction between sex and age was observed, where girls and boys demonstrated respectively an increase and decrease in the valgus KFM values from pre-adolescence to adolescence age (13.8% increase vs. 10.6% decrease: P=0.001).

Conclusion The remarkable increase of KFM in adolescent athlete girls may, in part, play a role in their risk of ACL injury, although future studies need to assess the relationship between this increase and rate of ACL injuries.