Co-Variation Structure of Established Risk Factors in Athletes with Non-Contact ACL Injury: A Principal Component Analysis

Background: Several risk factors have been identified for knee anterior cruciate ligament (ACL) injuries. Yet, their contributions still raise questions when attempting to identify at-risk populations with whom they are associated. Objectives: The purpose of this study was to identify combinations of characteristics in athlete populations at risk of non-contact ACL injuries using principal component analysis. Methods: From a cohort of 161 sports practitioners aged 28.6 ± 8 years who had presented a non-contact ACL injury, five risk factors were assessed on the healthy contralateral knee: passive knee alignment (valgus and recurvatum), knee laxity (KT-1000 test), and isokinetic hamstring strength at 60°/s and at 180°/s. Female sex, age and BMI were considered as individual risk factors. The profile of the population at risk of non-contact ACL injury was determined using a principal component analysis. Results: A total of 31% of the patients were females, 34% were under 24 years old, and 63% had a BMI > 22.5 Kg/m2. The knee axis was valgus in 37% and recurvatum in 80%. An anterior–posterior laxity ≥ 4 mm was present in 38% of the cases. Weakness of the hamstring was present at 60°/s (<1.3 Nm/kg) and 180°/s (<1.0 Nm/kg) in 49% and 54% of the cases, respectively. The principal component analysis explained only 61% of the variance in non-contact ACL injury. Three profiles of the population could be identified: “female with dynamical factors” (knee valgus and weakness of the hamstring strength), “male with physiological factors” (old age and high BMI), and “knee morphology” (valgus, recurvatum and laxity). Conclusions: In the absence of a comparison with a non-injured population, combinations of the potential factors associated with non-contact ACL injuries have been identified, and three independent populations could be at risk.