ACL biomechanical risk factors on single-leg drop-jump: a cohort study comparing football players with and without history of lower limb injury

Background. The maximum knee valgus angle (KVA) and minimum knee flexion angle (KFA) have been identified as risk factors for non-contact anterior cruciate ligament (ACL) injury. The present study investigated whether a recent history of lower limb injury in professional male football players can affect KVA and KFA during a single-leg vertical drop-jump (SLVDJ). Methods. Twenty-one professional male football players performed a SLVDJ. The participants were divided into two groups depending on the history of a lower limb injury within the previous 12 months. Two-dimensional video analysis was used to investigate maximum KVA and minimum KFA using Kinovea software. Results. There were statistically significant differences between the injured and uninjured football players during the jump with the least ground contact time in KVA (t = 2.123, df = 19, p = 0.047) and KFA (t = 2.530, df = 19, p = 0.020), and in the mean KVA (t = 2.359, df = 19, p = 0.029) and KFA (t = 2.157, df = 19, p = 0.044). Conclusion. Football players who sustained a lower limb injury within the previous 12 months landed with increased KVA and decreased KFA at initial contact as compared to players without history of lower limb injury within the last 12 months.