Stiff Landings Are Associated With Increased ACL Injury Risk in Young Female Basketball and Floorball Players: Letter to the Editor

Dear Editor: The recent study published in The American Journal of Sports Medicine (AJSM) entitled ‘‘Stiff Landings Are Associated With Increased ACL Injury Risk in Young Female Basketball and Floorball Players’’ by Leppänen et al is a highly interesting read. The stated purpose of the study was to ‘‘investigate selected biomechanical characteristics as potential risk factors for ACL [anterior cruciate ligament] injuries in young female basketball and floorball players. ’’ The authors tested whether 6 selected kinematic and kinetic variables were associated with future ACL injuries in a cohort of 171 young female athletes. In addition, the authors appeared to assess whether the drop vertical jump (DVJ) test could be used as a screening test to predict injuries with sufficient accuracy (see Conclusion). I congratulate the authors for performing this timely and important study. These authors’ findings demonstrated high consilience and corroboration with a prior larger 2005 AJSM study that examined a much greater number of biomechanical and neuromuscular variables that were potential risk factors from 205 athletes during the DVJ test. Although this new AJSM study significantly modified the methodology for the DVJ test (eg, no target set at the maximum vertical jump height appears to have been used), the results were quite similar in both direction and magnitude. Strikingly, in both studies, ‘‘stiff landing’’ was ‘‘predictive’’ of the risk for future ACL injuries, as the vertical groundreaction force (vGRF) was 20% versus 24% higher and the knee flexion range of motion (kROM) approximately 8 versus 6 lower in the ACL-injured group versus the uninjured group, respectively. The final model in the 2005 AJSM study identified multiple combined independent variables that predicted an ACL injury, including peak knee abduction angle, peak knee abduction moment, peak hip adduction moment, and kROM and vGRF, which were quite similar in direction and magnitude to the Leppänen et al findings. However, the authors subsequently incorrectly interpreted their findings as revealing ‘‘that these measures cannot predict injury with sufficient accuracy. ’’ The last 2 variables alone (kROM and vGRF) may be used to stratify the ACL injury risk in this new cohort of athletes. Even stronger models might be built that include multiple combinations of ‘‘stiff landing’’ and ‘‘valgus’’ factors. As such, this study may be strong evidence for the use of the DVJ test as a stratification tool for ACL injury risk. These authors should be congratulated for their outstanding work; however, they would be well served to repeat their study using more similar and stringent methodologies, which may lower the excessive variation that they observed in their measures, and reanalyze the data using a more rigorous and inclusive multivariate logistic regression analysis with models that include multiple combinations of ‘‘stiff landing’’ and ‘‘valgus’’ factors that trended similarly to the prior 2005 study and also approached significance in the current study. The authors would also likely observe higher correlation in these variables if the correlations within the injured and uninjured groups were examined separately.