Mechanical Factors Contributing to Altered Knee Extension Moment during Gait after ACL Reconstruction: A Longitudinal Analysis

PurposeThis study aimed to comprehensively examine the extent to which knee flexion angle at initial contact, peak knee flexion angle, and vertical ground reaction force (vGRF) contribute to knee extension moments during gait in individuals with anterior cruciate ligament (ACL) reconstruction.MethodsOverground gait biomechanics were evaluated in 26 participants with ACL reconstruction at three time points (about 2, 4, and 6 months after the surgery). Knee flexion angle at initial contact, peak knee flexion angle, peak vGRF, and peak knee extension moment were calculated for each limb during the early stance phase of gait for all three time points. A change score from baseline (time point 2 - time point 1 and time point 3 - time point 1) along with limb symmetry values (ACL - non-ACL limb values) was also calculated for these variables. Multiple linear regressions utilizing classical and Bayesian interference methods were used to determine the contribution of knee flexion angle and vGRF to knee extension moment during gait.ResultsPeak knee flexion angle and peak vGRF positively contributed to knee extension moment during gait in both the reconstructed (R-2 = 0.767, P < 0.001) and nonreconstructed limbs (R-2 = 0.815, P < 0.001). Similar results were observed for the symmetry values (R-2 = 0.673, P < 0.001) and change scores (R-2 = 0.731-0.883; all P < 0.001), except that the changes in knee flexion angle at initial contact also contributed to the model using the change scores in the nonreconstructed limb (time point 2 - time point 1: R-2 = 0.844, P < 0.001; time point 3 - time point 1: R-2 = 0.883, P < 0.001). Bayesian regression evaluating the likelihood of these prediction models showed that there was decisive evidence favoring the alternative model over the null model (all Bayes factors >1000). Standardized beta coefficients indicated that changes in knee flexion angle had a greater impact (>2x) on knee extension moments than vGRF at both time points in both limbs (beta(vGRF) = 0.204-0.309; beta(kneeflexion) = 0.703-0.831).ConclusionsThe findings indicate that both knee flexion angle and peak vGRF positively contribute to altered knee extension moments during gait, but the contribution of knee flexion angle is much greater than vGRF. Therefore, treatment strategies targeting these variables may improve knee loading after ACL reconstruction.