3D kinematics of noncontact and indirect contact ACL injuries in elite male football players

Purpose: Our primary goal was to deepen the understanding of the mechanisms leading to anterior cruciate ligament (ACL) injuries by reconstructing the three-dimensional (3D) joint kinematics of ACL injuries that occurred in professional male football matches. In particular, we aimed to compare the time courses of trunk and injured limb joint angles between noncontact and indirect contact injury mechanisms. Methods: In this cross-sectional observational study, we analysed a total of 27 cases (18 noncontact, 9 indirect contact). Whole-body 3D kinematics preceding and during ACL injuries was reconstructed using the Model-Based Image-Matching technique, implemented in Blender. For each injury, television footage from multiple perspectives (≥2, nine frames per view) were used, and Euler's joint angles across all the anatomical planes were extracted. The joint angle time courses of both the trunk and the injured limb, comprising 12 waveforms in total, were compared between injury mechanisms and Statistical Parametric Mapping was used to detect significant clusters. Results: Compared to noncontact injuries, indirect contact cases showed a lower hip abduction (−16°, p = 0.003), knee internal rotation (~3°, p < 0.001) at the initial contact with the ground, and ankle dorsiflexion (~7°, p = 0.035) at instants before the initial ground contact. These differences resulted from the player's adaptation to the sudden (yet variable) mechanical perturbation due to the contact with the opponent. Conclusion: Mechanical interactions with other players impact segmental kinematics before and during ACL injuries in professional male football. These findings reinforce the importance of considering the sport-specificity of mechanisms in injury prevention. Level of Evidence: Level IV.