In an AP oblique projection of the sacroiliac joints with the patient in an RPO position, which side will be demonstrated with the SI joint open?

In an AP oblique projection of the sacroiliac joints with the patient in an RPO position, which side will be demonstrated with the SI joint open?

• A. Nearest side to the IR
• B. Farthest side from the IR
• C. Both sides equally
• D. The side adjacent to the table

Answer: (B)

The key idea is that in an AP oblique view of the sacroiliac joints, rotating the patient so the joint of interest is on the far side from the image receptor reduces superimposition and lets that joint appear open. In an RPO position, the side farthest from the image receptor is the left side, so the left sacroiliac joint will be demonstrated with an open joint. Therefore, the open SI joint is the farthest side from the IR.

The key idea is that in an AP oblique view of the sacroiliac joints, rotating the patient so the joint of interest is on the far side from the image receptor reduces superimposition and lets that joint appear open. In an RPO position, the side farthest from the image receptor is the left side, so the left sacroiliac joint will be demonstrated with an open joint. Therefore, the open SI joint is the farthest side from the IR.