In an AP oblique projection of the sacroiliac joints, which side from the IR is opened to view the SI joint?

• A. The farthest side from the IR
• B. The nearest side to the IR
• C. Both sides are opened
• D. Neither side opens any joint

Answer: (A)

In an AP oblique projection of the sacroiliac joints you want the joint of interest to lie in a plane that minimizes overlapping pelvic bones and lets the joint space be seen clearly. Rotating the patient so that the side away from the image receptor is the one you’re viewing accomplishes this. The SI joint on the far side from the IR is opened because this orientation brings that joint into its best profile while reducing superimposition from the ilium and sacrum.

That’s why the farthest side from the image receptor is the side opened. The near side would still be overlapped by adjacent pelvic structures, and opening both sides or neither side would not provide the targeted, clear view of a single SI joint.