What position should the knee be in during the plantodorsal axial calcaneus projection?

In the plantodorsal axial calcaneus projection, the knee should be in an extended position. This positioning is essential to ensure that the calcaneus (heel bone) is properly aligned for optimal imaging. When the knee is extended, it allows the foot to be dorsiflexed to a 90-degree angle, which is necessary to project the heel accurately on the film or digital sensor. This projection evaluates the calcaneus for fractures or other pathologies and requires the foot and ankle to be in a configuration that maximizes visualization of the bone structures.

In contrast, if the knee were flexed, it could lead to foreshortening of the calcaneus on the image, hindering the assessment of the heel structure. A slightly flexed position might not achieve that ideal 90-degree dorsiflexion necessary for proper imaging either. Lastly, the seated choice is not suitable because it does not provide the necessary position of the limb for the imaging technique required for the calcaneus projection.