The calcaneal facet of the posterior subtalar joint can be divided into two portions: an anterolateral portion and a posteromedial portion. The importance of this consideration is that the two portions of the facet do not lie in the same plane. This should be taken into consideration when interpreting radiographs of the subtalar joint. Measurements from 50 dry-bone specimens and radiographs of 10 cadaver specimens were taken. The radiographs were obtained after marking the posterior subtalar joint to demonstrate the corresponding site of each facet portion on radiographs. The posteromedial portion lies almost in the transverse plane, making an angle of approximately 40° with the anterolateral portion. Each radiographic projection was explained by demonstrating the orientation of markings applied to the specimens and correlated to the data derived from the angular measurements. A protocol of sequential radiographs that can be used to evaluate the posterior subtalar joint is proposed.
