Which one of the following projections requires the patient's knee to be placed on the lateral side?

The lateral foot projection requires the patient's knee to be placed on the lateral side. This positioning allows the foot to be oriented appropriately for the lateral view, which is crucial for accurately visualizing the bones and soft tissues of the foot. By placing the knee on the lateral side, the foot can be positioned perpendicular to the film or image receptor, ensuring that the necessary structures, such as the tarsal bones and metatarsals, are clearly depicted without overlap.

For the other options, they do not require the knee to be placed on the lateral side. The medial oblique foot projects the foot at an angle to visualize structures from a different perspective, while the anteroposterior (AP) ankle and oblique foot projections have their unique positioning requirements that focus on obtaining clear images without necessitating lateral knee positioning. Understanding the correct positioning for each type of projection is key in radiographic practices to ensure optimal imaging results.