Biomechanical but not timed performance asymmetries persist between limbs 9 months after ACL reconstruction during planned and unplanned change of direction

Whilst anterior cruciate ligament injury commonly occurs during change of direction (CoD) tasks, there is little research on how athletes execute CoD after anterior cruciate ligament reconstruction (ACLR). The aims of this study were to determine between-limb and between-test differences in performance (time) and joint kinematics and kinetics during planned and unplanned CoD. One hundred and fifty-six male subjects carried out 90 maximal effort, planned and unplanned CoD tests in a 3D motion capture laboratory 9 months after ACLR. Statistical parametric mapping (2 x 2 ANOVA; limb x test) was used to identify differences in CoD time and biomechanical measures between limbs and between tests. There was no interaction effect but a main effect for limb and task. There was no between-limb difference in the time to complete both CoD tests. Between-limb differences were found for internal knee valgus moment, knee internal rotation and flexion angle, knee extension and external rotation moment and ankle external rotation moment with lower values on the ACLR side (effect size 0.72-0.5). Between tests differences were found with less contralateral pelvis rotation, distance from centre of mass to the ankle in frontal plane, posterior ground reaction force and greater hip abduction during the unplanned CoD (effect size 0.75-0.5). Findings demonstrated that kinematic and kinetic differences between limbs are evident during both CoD tests 9 months after surgery,despite no statistical differences in performance time. Biomechanical differences between tests were found in variables, which have previously been associated with ACL injury mechanism during unplanned CoD.