What is the focal film distance (FFD) for the internal rotation of the shoulder?

The focal film distance (FFD), also known as the source-to-image distance (SID), plays a crucial role in obtaining high-quality radiographic images. For the internal rotation of the shoulder, a standard FFD is typically set at 40 inches. This distance is selected to optimize the image quality by allowing for a balance between magnification and detail resolution.

Setting the FFD to 40 inches helps minimize distortion and improve the clarity of the shoulder anatomy being imaged, such as the humeral head, glenoid cavity, and surrounding soft tissues. This standardization is important in radiographic practices to ensure that images are consistent and diagnostically useful.

While other FFDs could demonstrate varying characteristics, such as increased magnification or reduced detail at shorter distances, or excessive elongation at longer distances, 40 inches is widely accepted due to its effectiveness in producing clear, usable images for diagnostic interpretation.