The influence of foot abduction on differences between two-dimensional and three-dimensional rearfoot motion.

The advantage of a three-dimensional over a two-dimensional approach to rearfoot analysis has been questioned in the past. The purpose of this study was to examine differences in typical rearfoot variables obtained using a two-dimensional analysis compared with a three-dimensional approach. In addition, the influence of foot placement angle on these differences was assessed. Two- and three-dimensional rearfoot kinematics were collected from 18 recreational runners. Two-dimensional values for eversion at toe-off and time to peak eversion were found to be significantly different from the three-dimensional results. Differences between two-dimensional and three-dimensional variables were magnified with increased toe-out. Differences between eversion values were found to be minimal when the foot was abducted between 7 and 10 degrees. The premise that excessive pronators have more pronounced toe-out was not supported by this study. Results suggest that caution should be exercised when assessing two-dimensional rearfoot motion in subjects with excessive toe-out.