Which of the following should be demonstrated on a diagnostic AP knee radiograph?

• A. Symmetric femoral and tibial condyles
• B. The patella superimposed over the distal femur
• C. Open femorotibial joint space
• D. Patella lateral projection

Answer: (C)

The key idea here is that a diagnostic AP knee radiograph must clearly show the joint where the femur meets the tibia. That femorotibial joint space should be open, meaning you can see the distance between the articular surfaces without them being overlapped by bone or distorted by rotation. An open joint space allows proper assessment of the joint surfaces, alignment, and potential pathology such as effusion or early degenerative changes. If the joint space isn’t open, it’s hard to evaluate the knee accurately from this view.

Other aspects described by the options relate to different concerns or views. A true AP view should also aim for minimal rotation, which would help produce symmetric condyles, but the essential requirement for a diagnostic AP knee is an open femorotibial joint space. The lateral projection of the patella and additional patellar positioning aren’t part of this AP view’s goals, and the criterion of a specific patellar superimposition isn’t the primary diagnostic feature here.