When in a right posterior oblique (RPO) position, which side is demonstrated on an anteroposterior (AP) oblique projection of the sacroiliac (SI) joint?

In a right posterior oblique (RPO) position, the orientation of the patient's body is such that the right posterior aspect is closest to the imaging plate. When taking an anteroposterior (AP) oblique projection of the sacroiliac (SI) joint, this positioning technique allows the radiologist to visualize the far side of the SI joint.

When in RPO, the left sacroiliac joint is the one that is furthest away from the image receptor. This results in better visualization of the left sacroiliac joint, as it is not obscured by the patient's body. The angles and positioning enable the radiographer to obtain a clearer image of the left SI joint, contrasting it effectively with the right SI joint, which is projected closer to the imaging area and may appear overlaid or less distinct.

Understanding this positioning is critical for interpreting images accurately and ensuring that the correct anatomy is visualized in an AP oblique projection, maximizing the effectiveness of the imaging process in clinical settings.