Which finding would prompt using the sacrum rather than the ilium?

• A. Anterior rotation
• B. Posterior rotation >6 mm same side
• C. Bilateral neutral
• D. No rotation

Answer: (B)

Focusing on how to tell which bone is rotating in the pelvis, you identify sacral involvement when there is a clear, unilateral, posterior rotation on that side with a noticeable magnitude. A posterior rotation on one side greater than about 6 mm points to the sacrum as the primary rotating segment, rather than the ilium. In this pattern, the sacrum’s rotation creates a distinct asymmetry that stands out beyond typical ilial motion alone, so the sacrum becomes the treatment target.

If the finding were an anterior rotation, that would more likely indicate the ilium is the rotating component. Bilateral neutral or no rotation shows no unilateral sacral rotation to address, so the sacrum wouldn’t be the focus.