Biomechanical alterations in the lower extremity associated with foot progression angle during gait in knee osteoarthritis

Objective. The net external knee adduction moment captured during gait is considered an indicator of medial tibio-femoral compressive loading. Reducing the magnitude of this moment is a primary goal of many suggested management strategies. This thesis addressed (i) the association between toe out foot progression angle during gait and the characteristics of the net external knee adduction moment for those with different severities of knee osteoarthritis (OA) and (ii) the immediate effect of altering foot progression angle on lower limb rotational kinematics and knee adduction moment in both asymptomatic controls and those with moderate knee OA. Design. Firstly, a cross-sectional analysis of an existing gait data set was performed. Fifty asymptomatic individuals, 46 patients with mild to moderate and 44 patients with severe knee OA were included. Discrete variable and principal component analysis were employed. Separate multiple regression models were used for each of the three group assignments to determine the association between the independent variables (Body Mass Index, Velocity and Foot Progression Angle) and the knee adduction moment. Secondly, ten patients with mild to moderate knee OA and 16 asymptomatic control subjects were recruited to determine the differences in the knee adduction moment and transverse plane angular displacement of the hip, knee and ankle between groups and between neutral, toe out and toe in gait conditions. Peak-to-peak angular displacement was used to describe the transverse plane movement in the lower extremity and principal component analysis was used to characterize the knee adduction moment waveforms captured during gait for each group and condition. Two-way analysis of variance models were used to test the dependent variables for main effects (group x condition) and interactions. Bonferonni post hoc testing (alpha = 0.05) was used to test all significant findings. Results. For the first study, FPA explained a significant amount of the variability associated with the shape of the knee adduction moment waveform for the asymptomatic and mild to moderate group (p<0.05), but not for the severe group (p>0.05). Walking velocity alone explained significant variance associated with the second peak and the shape of the knee adduction moment in the severe OA group (p<0.05). In the second study, both groups utilized a significantly greater (p<0.05) degree of transverse plane peak-to-peak angular hip rotation to modify their foot progression angle. A significantly reduced (p<0.05) transverse plane range of knee and hip motion, and a significantly greater knee adduction moment was found for those with mild to moderate OA compared to asymptomatic controls. In both groups, toe out gait produced (1) a reduction in the overall knee adduction moment and late stance magnitude and (2) increase in the early stance knee adduction moment magnitude (p<0.05). Conclusion. A self-selected toe out foot progression angle in asymptomatic controls and those with mild to moderate knee OA was associated with an altered knee adduction moment, directly implicated in medial knee compartment loading, whereas those with severe knee OA did not show this association. The features of the knee adduction moment waveform extracted by principal components analysis were related to the foot progression angle. The magnitude associated with the second peak of the knee adduction moment waveform was not related to foot progression angle. In the second study, voluntary foot progression angle modifications were produced primarily by alterations in transverse plane hip rotation for both the asymptomatic control subjects and those with mild to moderate disease. Voluntary toe out gait, while reducing the overall and late stance magnitude of the knee adduction moment waveforms in both groups, this modification also increased the initial stance knee adduction moment.