Contributors To Stiffened Knee Gait In Individuals With ACL Reconstruction

Those who undergo anterior cruciate ligament reconstruction (ACLR) are at high risk for developing post-traumatic osteoarthritis (PTOA). Patients who develop PTOA within five years display “stiffened knee gait” (i.e., smaller sagittal knee moments) compared to those who do not develop PTOA. Smaller increases in the sagittal knee moment between 2-8 years post-ACLR are associated with greater knee cartilage thinning. Targeted biomechanical rehabilitation may improve stiffened knee gait, but biomechanical contributors to this phenomenon have not been identified. PURPOSE: To evaluate contributions of knee flexion angles, ground reaction forces, and activation of the quadriceps and hamstrings to knee extension moments during walking gait in those with ACLR. METHODS: Seventy-five volunteers with primary, unilateral ACLR walked overground at their preferred speed. Gait outcomes included the peak internal knee extension moment (PKEM), peak knee flexion angle (PKFA), knee flexion angle at heel strike, knee flexion displacement (KFD), peak vertical (vGRF) and posterior (pGRF) ground reaction force, mean preparatory and stance EMG amplitudes of the quadriceps and hamstrings, and quadriceps/hamstring EMG co-contraction index (CCI) in the ACLR limb. Simple partial correlations were evaluated between PKEM and the other biomechanical outcomes controlling for gait speed. Significant simple correlations were combined in a stepwise linear regression model (Block 1 = gait speed, Block 2 = significant predictors) to predict PKEM. RESULTS: Significant partial correlations were observed between PKEM and PKFA (r = 0.410, p = 0.031), KFD (r = 0.379, p = 0.003), vGRF (r = 0.406, p = 0.002), preparatory CCI (r = -0.246, p = 0.008), preparatory (r = 0.308, p = 0.019) and stance (r = 0.285, p = 0.030) vastus medialis EMG amplitude, and lateral hamstring EMG amplitude during stance (r = -0.264, p = 0.045). When combined via multiple regression, these outcomes explained 55.4% of the variance in PKEM (p < 0.001, R2 = 0.554), but only peak vGRF (p = 0.006) was a significant predictor. CONCLUSION: Multiple kinematic and kinetic outcomes contribute to stiffened knee gait following ACLR of which vGRF provides the dominant influence. Previous research has shown vGRF to be modifiable via gait retraining, which may improve this stiffened knee gait. U.S. Department of Defense Clinical and Rehabilitative Medicine Research Program, Neuromusculoskeletal Injuries Research Award (W81XWH-15-1-0287)