Which pattern is consistent with bilateral extension?

• A. Sacral bases shallow and ILAs deep
• B. Sacral bases deep and ILAs shallow
• C. Sacral bases deep and ILAs deep
• D. Sacral bases shallow and ILAs shallow

Answer: (A)

In bilateral extension, the sacrum as a whole moves into a more extended position, which changes how we feel the key landmarks on palpation. The sacral base becomes shallower because the top of the sacrum tilts forward, reducing the depth you sense there. At the same time, the inferior lateral angles (ILAs) appear deeper, as the sides of the sacrum come to sit more posteriorly relative to the ilia. This combination—shallow sacral base with deep ILAs—fits the pattern of bilateral extension.

If the sacral base were deep, or if the ILAs were shallow, that would correspond to different patterns (such as bilateral flexion or other sacral mechanics), so they don’t match bilateral extension.