For an AP projection of the knee, where should the central ray be directed?

For an AP projection of the knee, the central ray should be directed ½ inch distal to the apex of the patella. This specific positioning is crucial for accurately visualizing the knee joint, as it ensures that the central ray is centered on the knee joint space itself. The apex of the patella serves as a reliable anatomical landmark, aiding in consistent and reproducible radiographic positioning.

By directing the central ray ½ inch below the apex, the radiograph captures the joint of the knee properly, preventing issues such as magnification of the patella or misalignment of the femur and tibia in the image. This positioning technique is vital for diagnosing any knee-related conditions, as it clearly shows the joint space and related structures, allowing for better assessment and interpretation by healthcare professionals.