INTRODUCTION: ACL-reconstructed (ACL-R) patients exhibit side-to-side asymmetries in movement and loading patterns after surgery, some of which are predictive of a secondary ACL injury. These asymmetries have not been fully assessed in healthy athletes. PURPOSE: To quantify side-to-side symmetry in secondary injury predictors in healthy athletes and compare these metrics to those measured in previous cohorts of ACLR patients, as well as to assess differences in these metrics between two landing tasks and between sexes. METHODS: 60 healthy recreational athletes performed seven trials of a stop-jump task and seven trials of a single-leg hop for distance on each limb. The kinematics and kinetics of the first landing of the stop-jump and the landing of the singleleg hop were analyzed with a 10-camera motion analysis system (240Hz) and 2 embedded force plates (1920Hz). Limb symmetry indices (LSIs) were calculated for each variable and compared between subject groups, tasks, and sexes with Wilcoxon Signed Rank tests (p<0.05). RESULTS: Control subjects exhibited asymmetry in hop distance (p=0.006). ACL-R subjects displayed greater asymmetry in knee flexion variables, peak forces, and peak knee extension moments during the bilateral landing (p<0.001) and in hop distance (p<0.001). Control subjects showed greater asymmetry in knee flexion variables during the single-leg hop (p<0.001). Males and females showed similar symmetry in both tasks. CONCLUSIONS: Symmetry cannot be assumed in control subjects in all metrics. Asymmetries are more prevalent in ACL-R athletes than in healthy controls. Future work will continue to examine the usefulness of each metric in assessing ACL-R rehabilitation.
Keywords:
ACL; Biomechanics; Landing; Symmetry; Kinematics; Kinetics; Motion Capture; Athletes; Sports