Early Quadriceps Weakness Is Linked To Aberrant Vertical Ground Reaction Force Gait Profiles Post-ACL Reconstruction

PURPOSE: Quadriceps weakness following anterior cruciate ligament reconstruction (ACLR) is hypothesized to contribute to the development of persistent aberrant limb loading (i.e., vertical ground reaction forces; vGRF) during gait post-ACLR, which is associated with osteoarthritis development and poor functional outcomes. However, there is limited evidence that early diminished quadriceps strength is linked to persistent changes in limb-loading gait profiles. We aimed to determine if early quadriceps strength loss (between preoperative [pre-op] to 4 months and preop to 6 months post-ACLR) is associated with vGRF magnitudes at the 1st peak, 2nd peak, and midstance during gait at 6 months post-ACLR. METHODS: We collected data from 43 participants with primary unilateral ACLR (56% female and 44% male, 22.2 ± 4.8 yrs; 72.2 ± 13.7 kg; 1.74 ± .09 m). Maximal voluntary isometric quadriceps contractions (normalized to body mass) were collected for each limb, pre-op and at 4 and 6 months post-ACLR. Quadriceps strength changes were calculated as the change between the injured limb at 4 and 6 months post-ACLR divided by the pre-op uninjured limb. vGRF was collected at 4 and 6 months post-ACLR at a self-selected walking speed, and the 1st and 2nd vGRF peaks and minimum vGRF at midstance were extracted. Pearson product moment correlation coefficients were computed to determine the associations between percent changes in quadriceps strength and vGRF measures. RESULTS: Decreases in quadriceps strength between pre-op to 4 and pre-op to 6 months post-ACLR were associated with lower 2nd peak vGRF magnitudes 6 months post-ACLR (r = 0.31, p = 0.05 and r = 0.37, p = 0.02, respectively). When controlling for walking speed with a partial r, decreases in strength at 6 months (ρxy.z = 0.32, p = 0.05) were still associated with lower 2nd peak vGRF at 6 months post-ACLR, while decreases in strength at 4 months were not associated with 2nd peak vGRF (ρxy.z = 0.28, p = 0.08). There were no statistically significant correlations between strength and the 1st vGRF peak or midstance vGRF. CONCLUSION: The association between early quadriceps weakness and the 2nd vGRF peak suggests that greater quadriceps strength is important for developing sufficient propulsion during late stance phase, which may be linked to better locomotion and functional outcomes. Supported by: Arthritis Foundation