Knee And Limb Loading Asymmetries Differ Between Tasks After ACL Reconstruction

While the prevalence of loading asymmetries in those with ACL reconstruction during gait and hopping independently is well documented, the extent to which limb differences manifest over time and across task difficulty remains uncertain. PURPOSE: The purpose of this study was to identify limb differences in lower extremity loading during gait and hopping in individuals 9 and 18 months after ACL reconstruction. METHODS: Twenty-seven individuals (14 F; Height: 1.7 ± .1 m; Mass: 73.9 ± 10.8 kg) who underwent ACL reconstruction completed testing 9.1 ± .5 m (9 M) and 18.1 ± .6 m (18 M) after surgery. 3D motion capture and force plates were used to assess bilateral kinetics during over ground walking and single and triple hop for distance. Limb differences (ACL – nonACL) were calculated for peak knee extension moments (pKEM) and peak vertical ground reaction forces (vGRF) for each task and timepoint. 2x3 (time x task) repeated measures ANOVA and Bonferroni post hoc comparisons were used to compare limb differences. RESULTS: A time x task interaction was noted for pKEM (p = .001), but not vGRF (p = 0.66). At 9 M and 18 M the pKEM difference was larger for SLH (9 M: p < .001; 18 M: p = .013) and TH (9 M: p < .001; 18 M: p < .001) compared to gait, but differences were not noted between SLH and TH at either time (9 M: p = 1.00; 18 M: p = .30). pKEM limb difference was larger at 9 M compared to 18 M for both SLH (p < .001) and TH (p = .001), but not gait (p = .17). A main effect of task (p < .001) but not time (p = .24) was noted for vGRF. vGRF limb differences were lower during gait compared to SLH (p < .001) but not different from TH (p = .08). The vGRF limb differences were greater during SLH compared to TH (p = .027). CONCLUSION: Knee underloading persists during hopping 9 and 18 months after surgery, and was evident during hopping but not gait, suggesting task difficulty can impact loading after ACL reconstruction. As individuals return to sport it may be critical to assess loading during a variety of tasks to identify lingering abnormalities. - 9 M 18 M Gait Single Leg Hop Triple Hop Gait Single Leg Hop Triple Hop pKEM -0.050 ± 0.88 -0.483 ± 0.30 -0.518 ± 0.34 -0.027 ± 0.08 -0.243 ± 0.35 -0.313 ± 0.32 vGRF -0.017 ± 0.04 -0.257 ± 0.30 -0.126 ± 0.29 -0.015 ± 0.02 -0.186 ± 0.24 -0.064 ± 0.18 Between limb differences; Negative numbers indicate ACL values are lower than NonACL values Supported by: NIH NICHD R01HD093626