Position of the subtalar joint axis and resistance of the rearfoot to supination.

Determination of the position of the subtalar joint axis is being more widely used clinically to facilitate the prescription of foot orthoses and the understanding of foot function, but clinical determination of the axis has not been widely investigated. The aim of this study was to determine the relationship between clinical determination of the subtalar joint axis and the amount of force needed to supinate the foot. The transverse plane position of the subtalar joint axis was determined in 47 subjects. The sagittal plane orientation of the subtalar joint axis was determined using the relative amounts of forefoot adduction and abduction obtained when the rearfoot was supinated and pronated. The amount of force needed to supinate the foot was measured using a device designed to measure resistance to supination. The only two parameters that were correlated to supination resistance of the rearfoot were body weight (r = 0.52) and the perpendicular distance from the fifth metatarsal head to the subtalar joint axis (r = 0.59). The model on which determination of the subtalar joint axis is based may not be valid, but it might help determine how much force is needed to supinate a foot using foot orthoses.