In a posterior torsion sacral dysfunction, which axis is typically involved?

• A. It is on an oblique axis
• B. It is on a horizontal axis
• C. It involves bilateral flexion
• D. It does not involve sacral motion

Answer: (A)

The key idea is that sacral torsions rotate around an oblique axis. In a posterior torsion, the sacrum undergoes rotation about a diagonal line that links the sacrum with the ilia, so one side of the sacral base moves posteriorly while the opposite sulcus moves relatively anterior. This diagonal, oblique axis explains the torsion pattern you see clinically. If the axis were horizontal, you’d expect a different, mainly flexion/extension motion in a single plane, which isn’t how torsions behave. And bilateral flexion or no sacral motion wouldn’t fit the rotating, diagonal axis nature of a torsion.