If sacral posterior rotation exceeds 6 mm on the same AS side, the leg check will appear:

• A. Long
• B. Equal
• C. Short
• D. Alternating

Answer: (C)

The key idea is how sacral motion in the sagittal plane affects the pelvis and how that shows up in a standing leg check. When the sacrum rotates posteriorly on one side, the pelvis on that side tilts in a way that makes the leg on that same side functionally shorter during the check. If the posterior rotation is substantial—beyond about 6 mm—the change is enough to be seen as a shorter leg on that side. That’s why the leg check will appear short on the side of the posterior sacral rotation. The other patterns—long, equal, or alternating—come from different sacral or pelvic motions (anterior rotation, minimal imbalance, or a mixed/changing pattern), not from a sacral posterior rotation exceeding 6 mm on the same side.