Which projection is used to assess the sacrum's articulation with the ilia?

• A. Lateral sacrum projection
• B. AP oblique pelvis
• C. Pelvic oblique or AP axial sacrum with pelvic oblique as indicated to evaluate SI joints.
• D. AP pelvis with sacroiliac joint view

Answer: (C)

To see how the sacrum connects to the ilia, you need a projection that presents the sacroiliac joints in profile with minimal overlap. Oblique pelvic views accomplish this by rotating the pelvis about 45 degrees, which opens the SI joints and allows you to assess joint space, alignment, and any disruption. That pelvic oblique (Judet) approach is the standard way to visualize the sacrum–ilia articulation. If a true oblique pelvis can’t be obtained, an AP axial sacrum view can be taken with the pelvis obliqued to still evaluate the SI joints, which is why that combined description is appropriate. A lateral sacrum view or a plain AP pelvis without obliquity doesn’t open or profile the SI joints as effectively, so they’re not as useful for assessing the sacrum’s articulation with the ilia.