CAMRT Radiography Practice Exam

What is required for a successful AP projection of the knee to visualize the joint space accurately?

1. The patient must remain still

2. The beam should be perpendicular to the film

3. The knee must be flexed at 30 degrees

4. The patient's heel must be placed flat

The correct answer is: The beam should be perpendicular to the film

To visualize the joint space accurately in an anteroposterior (AP) projection of the knee, it is essential that the X-ray beam is perpendicular to the film (or imaging receptor). This alignment ensures that the image captures the knee joint's true anatomy without distortion, which is critical for accurate evaluation and diagnosis. If the beam is not perpendicular, it can result in superimposition of surrounding structures or misrepresentation of the joint space, making interpretation challenging. While it is beneficial for the patient to remain still to avoid motion blur and for the knee to be in a specific position to enhance visualization, these factors do not directly influence the imaging geometry required for accurately depicting the joint space itself. Thus, ensuring that the beam is perpendicular is fundamental for achieving a clear and diagnostically valuable AP view of the knee.