Which pattern describes sacral dysfunctions on a horizontal axis?

• A. Unilateral shear
• B. Bilateral flexion/extension
• C. Horizontal axis dysfunction
• D. Anterior torsion

Answer: (B)

Sacral motion can run around different axes, and a horizontal axis runs left to right through the sacrum. When the sacrum moves around this axis as a unit, both sides shift in the same direction. That bilateral, symmetric movement is what we call bilateral flexion or bilateral extension. In these patterns, the motion is organized about the horizontal axis, affecting the entire sacrum rather than just one side.

Unilateral shear and anterior torsion involve asymmetry or rotation about oblique axes, not a clean bilateral move on a horizontal axis, so they don’t describe the horizontal-axis pattern. The label “horizontal axis dysfunction” points to the axis itself rather than the bilateral flexion/extension movement, so the best match for a horizontal-axis pattern is bilateral flexion/extension.