Above is an animated model demonstrating the theoretical coupling motion between the cranial bones and sacrum.  Movement of the cranial bones is thought to occur between the sutures and is reported to be less than 1/100th of a centimeter (the width of a human hair).  A cranial lesion can lock the sacrum in either a nutated (anterior) or counternutated (posterior) position.

             

Glossary Of Osteopathic Terminology

Usage Guide, April 2004, Figs 57-8, pp 24