What angle of tube tilt is used for an AP knee?

For an anteroposterior (AP) projection of the knee, a tube tilt of 5° cephalad is typically utilized to improve visualization of the joint space and maintain alignment with the anatomic structures of the knee. This slight angling of the tube helps to compensate for the natural curvature of the femur and the positioning of the knee, ensuring that the radiograph captures a clearer and more accurate image of the knee joint.

Using a 5° cephalad angle allows the X-ray beam to better penetrate and project through the knee, reducing distortion and superimposition of surrounding structures. This technique is particularly useful in knee imaging as it aids in achieving the best possible quality for assessment of any pathologies or injuries.

A flat angle of 0° may lead to inadequate visualization of the joint space, while a higher angle, such as 10° or 15° either cephalad or caudad, could further distort the anatomy and potentially misrepresent the condition of the knee joint. Thus, the specific choice of a 5° cephalad tilt makes it the optimal angle for an AP view of the knee.