Which radiographic views of the calcaneus commonly use a 40 inch SID?

• A. Lateral calcaneus radiograph
• B. Plantodorsal axial calcaneus radiograph
• C. Lateral calcaneus radiograph and plantodorsal axial calcaneus radiograph
• D. AP calcaneus radiograph

Answer: (C)

Focusing on how distance affects image sharpness and magnification helps explain this. For the calcaneus, using a 40-inch source-to-image distance is the standard that yields a clear, undistorted view for two key projections. The lateral calcaneus radiograph is performed with the patient on their side and the beam aligned perpendicular to the calcaneus; at 40 inches, the size of the bone on the film is kept consistent and detail in the calcaneal body and subtalar joint is preserved. The plantodorsal axial calcaneus projection (beam directed along the long axis of the foot from plantar to dorsal) also benefits from a 40-inch SID because it minimizes distortion along the axial plane and allows a true representation of the calcaneal anatomy when the heel is angled toward the beam. The AP calcaneus view, while common in some settings, is not as consistently tied to a 40-inch standard across protocols, which is why the two views above are the ones typically associated with that SID.