New techniques to establish the subtalar joint's functional axis

A new technique to establish the functional subtalar joint axis in live models is presented. Previous studies had a poor reference to the body planes because they relied on cadaver bone models and were not referenced to actual live function. The lower value for the function axis is due to the response of the midtarsal joint and forefoot to loading and ground reactive forces. The techniques were applied to the clinical setting by establishing a reference line on lateral RCSP radiographs and calculating the actual axis to this reference line. The axis deviated from the reference line by a small range (4 degrees) and can be corrected by reference to the calcaneal inclination angle for high or low angular differences. This simple technique can be used clinically to determine axial changes that may be required for surgical procedures and for evaluating the effect of orthosis control.