Which anatomy pair is primarily evaluated on the AP sacroiliac joints radiograph?

• A. The sacroiliac joints and L5-S1 disk space
• B. One sacroiliac joint
• C. The lumbar vertebrae
• D. The coccyx

Answer: (A)

The key idea is that this view is intended to visualize the sacroiliac joints and their immediate neighbor, the L5–S1 disk space. The sacroiliac joints are the focus because the projection is used to assess their alignment, symmetry, and joint-space width for signs of sacroiliitis, fracture, or other pathology. The L5–S1 disk space sits just above the sacrum and is included in the same exposure, providing important context about the lumbosacral junction and helping identify adjacent degenerative changes or alignment issues that could influence the appearance of the SI joints. While you may see other structures on the image, the primary evaluation on this view is the sacroiliac joints together with the L5–S1 disk space, rather than a single SI joint or more distant spinal anatomy.