The effects of wedged footwear on lower limb frontal plane biomechanics during running.

OBJECTIVE: Patellofemoral pain syndrome (PFPS), the most common running injury, has been associated with increased internal knee abduction angular impulses (KAAI). Wedged footwear can reduce these impulses during walking, but their effects during running are not well understood. The purpose of this study was to identify the effects of wedged footwear on KAAIs and describe the mechanism by which wedged footwear alters KAAIs during running. DESIGN: Controlled laboratory study. SETTING: Motion analysis laboratory. PARTICIPANTS: Nine healthy male subjects. INTERVENTIONS: Participants ran at a speed of 4 m/s with 7 different footwear conditions (3-, 6-, and 9-mm lateral wedges; 3-, 6-, and 9-mm medial wedges; neutral). MAIN OUTCOME MEASURES: Knee abduction angular impulses and 8 predictor variables were measured and compared by 1-way repeated measures analysis of variance (α = 0.05) with Bonferroni-adjusted 2-tailed paired t tests for post hoc analysis (α = 0.002). Correlation (α = 0.05) was used to determine the relationship between the mediolateral center of pressure to ankle joint center (COP-AJC) lever arm length and KAAIs. RESULTS: Laterally wedged conditions produced significantly lower KAAIs (P = 0.001) than medial wedge conditions. Peak knee abduction moments decreased (P = 0.001), whereas ankle inversion moments (P = 0.041) and the COP-AJC lever arms increased (P < 0.001) as wedges progressed from medial to lateral. KAAIs were negatively correlated with COP-AJC lever arm length (r = -0.50, P < 0.001). CONCLUSIONS: KAAIs are reduced with laterally wedged footwear because of lateral shifts in the center of pressure beneath the foot, which then increases ankle inversion moments and decreases peak knee abduction moments. Laterally wedged footwear may therefore offer greater relief to runners with PFPS than medially wedged footwear by reducing KAAIs.