Reliability of the footwear total asymmetry score tool

Abstract

Both design and degradation of footwear contribute to mediolateral asymmetry of the inner-, mid- and outersole. Mediolateral asymmetry in footwear affects joint moments around the ankle, knee and hip and may contribute to lower limb injuries and the development of knee osteoarthritis. The aim of this study was to establish the reliability of an objective clinical assessment tool for measuring footwear asymmetry. We assessed the within-rater, between-rater and between-day reliability of the Footwear Total Mediolateral Asymmetry Score tool. Two novice and two expert raters assessed ten individual shoes varying in style, size and brand. The inner-, mid- and outersole thickness of each shoe was measured at 14 locations, while midsole hardness was assessed at four locations. Within-rater ICC(2,1), between-rater ICC(2,1),(2,2),(2,3) and between-day ICC(2,1),(2,2),(2,3) intraclass correlation coefficients were calculated for each measurement and for the total asymmetry scores of each shoe. Standard error of measurements (SEM) was determined for all footwear measurements and minimal detectable differences (MDD) were determined for between-day measurements. Within- and between-rater and between-day reliability of all measurements were poor to excellent (0.31–1.00). The MDD for rearfoot and forefoot total asymmetry scores was ≤1 mm, regardless of rater experience. Based on our findings, the footwear total asymmetry score tool is reliable for assessing the location and magnitude of mediolateral asymmetry in running shoes.