Background and aims: Disruption of pronation magnitude and timing lead to knee Osteoarthritis, that it can be treated by lateral wedge insole under foot. There were inconsistent results that maybe arising from different inclination or used techniques. The aim of current study was to assess the effect of lateral wedge insole with different inclination using Principal Component Analysis (PCA).

Methods: 75 subjects were participated in this study. Lower limb kinematics was recorded at five conditions including, running with regular shoe, and regular shoe with 3°, 6°, 9° and 11° lateral wedge insole at rearfoot. Then, principal components (PCs) of pronation were calculated by PCA. Repeated measure ANOVA was used to evaluate the effect of lateral wedge insole on foot eversion and pronation index (PC1).

Results: The 9° and 11° lateral wedge conditions lead to significant increase in eversion angle. However, in addition to the 9° and 11° lateral wedge conditions, 6° lateral wedge showed significant differences with regular shoe. In addition to reported clinical results, the PCA method revealed that 6° lateral wedge insole has significant effects on foot mechanics.

Conclusion: The eversion angle could not exclusively present the foot pronation, and all of three movement planes should be considered for accurate results. The PCA method provides more accurate criteria for investigating pronation.