Which structures should be visible on a diagnostic AP SI joints radiograph?

• A. Both sacroiliac joints and the open intervertebral disk space between L5 and S1
• B. Only one sacroiliac joint
• C. The aorta and inferior vena cava
• D. The coccyx

Answer: (A)

In AP sacroiliac joints imaging, you need to see both sacroiliac joints and the open intervertebral disk space between L5 and S1. Seeing both SI joints bilaterally allows you to compare them for symmetry and identify any unilateral abnormalities such as fractures or sacroiliitis. The L5–S1 disk space being open indicates the pelvis is properly oriented with minimal rotation, which is essential for an accurate view of the SI joints and to avoid misinterpreting overlapping structures. The aorta and inferior vena cava aren’t the structures of interest for this projection, and the coccyx isn’t the target area for evaluating the sacroiliac joints, so they aren’t required in this view.