Examining the validity of selected measures of foot type: a preliminary study.

The rationale that subtalar joint position, reflected by calcaneal alignment, determines foot morphology was used to formulate an approach to examination of the validity of three measures of "foot type": the Staheli Arch Index, the Chippaux-Smirak Index, and navicular height. Each measure was calculated in five positions, progressively inverting from a reference position of maximal comfortable eversion. Pearson product moment correlations (Staheli Arch Index: r = 0.5; Chippaux-Smirak Index: r = 0.6; and navicular height: r = 0.8) indicated that each measure progressively increased with inversion. The change in calcaneal position required to produce significant changes in each measure was investigated using analysis of variance with Scheffé post hoc analysis. This analysis revealed that changes of 15 degrees and 20 degrees were required to produce significant differences in Chippaux-Smirak Index and Staheli Arch Index scores, respectively, threatening their validity. Navicular height was sensitive to smaller changes of 10 degrees and thus displays greater sensitivity to changes in calcaneal position than the footprint parameters tested.