What is the FFD for the external rotation of the shoulder?

The correct answer, which states that the focal film distance (FFD) for the external rotation of the shoulder is 40 inches, is based on standard radiographic practices. In this positioning, the patient’s arm is externally rotated to provide a clear view of the humeral head and the relationship to the glenoid cavity.

Using a FFD of 40 inches helps to reduce distortion of the image while simultaneously ensuring that sufficient detail is captured for accurate diagnosis. This distance is optimal for minimizing magnification effects while ensuring that the anatomy of the shoulder is well visualized. It aligns with standard protocols in radiography to maintain appropriate image quality.

Other distances are typically either too short, which can lead to distortion and insufficient detail, or too long, which might unnecessarily increase exposure and reduce image quality. Therefore, 40 inches is recognized as the standard FFD for this specific shoulder positioning to ensure clarity and accuracy in the diagnostic image.