Anterior cruciate ligament rupture during a cognitively demanding change-of-direction task in football: biomechanical insights from a laboratory injury.

BACKGROUND: In laboratory-based injury risk assessments, there is always a small and not entirely avoidable risk of injury to participants. This case report describes an anterior cruciate ligament (ACL) re-rupture of a female participant during the approach run of a stimulus-response change-of-direction (COD) task. METHODS: Marker-based kinematic data from the injury trial were compared with 14 successful trials of the same participant. These trials included unanticipated CODs in response to an opponent's kicking action with varying cognitive demands, including one trial under identical high-demand conditions involving a feint. The participant approached at a speed of 4.08 m/s and the feint was initiated 475 ms before the injury step. RESULTS: The injury trial differed from the non-injury trials in terms of a markedly prolonged flight phase preceding initial contact in combination with deviations in lower-limb and trunk kinematics during the flight phase and the step before. These deviations exceeded the participant's typical movement range observed during the non-injury trials and included temporally pre-shifted flexion-extension patterns at the knee and hip, a more extended trunk at initial contact, an altered pelvic drop, and reduced ankle inversion. During the injury stance phase, pronounced hip adduction, knee abduction and ankle eversion were observed. CONCLUSIONS: The findings substantiate previously theorized mechanisms of non-contact ACL injury and show in a within-subject comparison that critical proximal and distal kinematic deviations at the trunk and lower limbs arise already during the preparatory phase. The occurrence after an opponent's feint further suggests and highlights the importance of a neurocognitive contribution for ACL injuries. TRIAL REGISTRATION: The study protocol was preregistered on Open Science Framework ( https://doi.org/10.17605/OSF.IO/4Z5R8 ).