Prediction of secondary ACL injury in female athletes using 2D video-based measurements obtained during dynamic tasks: a retrospective case–control study

OBJECTIVE: To determine if two-dimensional (2D) video-based angular measurements obtained during dynamic tasks predict secondary anterior cruciate ligament (ACL) injury in female athletes post-ACL reconstruction (ACLR). METHODS: Female athletes post-ACLR underwent 2D video assessment during six tasks (step down, drop jump, lateral shuffle, deceleration, triple hop and side-step-cut) before returning to sport. Reinjury status was determined via survey after returning to sport (N=345). Non-contact ACL reinjuries (n=23) were matched to non-injured athletes (n=57). Five 2D video-based surrogates of known risk factors for primary ACL injury (trunk-tibia angle, thigh angle, trunk lean, pelvis tilt, frontal plane projection angle (FPPA)) were measured from 2D videos across tasks. Reinjury cut-offs for the 2D angles were determined using receiver operating characteristic curves, and composite scores were calculated for each 2D surrogate, with higher scores indicating a high-risk movement across more tasks. Logistic regression, adjusted for confounders, assessed ACL reinjury risk for each composite score. Stepwise regression identified the strongest 2D predictor. RESULTS: Four of five 2D surrogate composite scores independently predicted ACL reinjury after adjusting for confounders. For each additional task in which an athlete demonstrated a high-risk movement, the odds of reinjury increased: trunk-tibia angle composite score (representing increased knee extensor relative to hip extensor moments; OR 1.75; 95% CI 1.24 to 2.47; p=0.001), thigh angle composite score (representing increased vertical ground reaction forces; OR 1.69, 95% CI 1.14 to 2.50, p=0.01), FPPA composite score (representing increased knee valgus moments; OR 2.29, 95% CI 1.13 to 4.65, p=0.02) and pelvis tilt composite score (representing increased pelvis drop; OR 1.85, 95% CI 1.16 to 2.95, p=0.01). The trunk-tibia angle composite score was selected as the strongest predictor. CONCLUSIONS: 2D surrogates of known three-dimensional risk factors for primary ACL injury can predict secondary ACL injury. These findings support developing a movement assessment using 2D video-based measurements to inform return to sport decisions and identify at-risk athletes following ACLR.