The subtalar angle: a proposed measure of rearfoot structure

The purpose of this study was to propose a new measure of rearfoot structure to further enhance the understanding of the function of the foot. Landmarks visible on sagittal plane radiographs were used to represent the approximate direction of the subtalar joint axis in the sagittal plane based upon descriptions from the literature of its orientation. Four landmarks were chosen, resulting in four calculated angles. One hundred lateral view radiographs were analyzed. The mean values ranged from 28.7 degrees to 47.7 degrees. These values are within the ranges reported from both cadaver and in vivo studies. Tests of repeatability of the measures resulted in intraclass coefficient values between 0.94 and 0.98, suggesting good reliability. All four angles correlated highly among each other (r = 0.88-0.97). Examination of the validity of any one of these measures is left to those who are able to accurately calculate the orientation of the subtalar joint axis.