Nutation (anterior rotation) of the sacrum, places the Piriformis Muscle on a Stretch.  This can entrap the Sciatic Nerve between the muscle belly of the Piriformis and the Greater Sciatic Notch (See Arrow), resulting in a Mechanically Induced Sciatica.

This research in delineating the link between the position of the sacrum and the development of sciatica was instrumental in the development of a therapy that, in many cases, permanently eliminates chronic musculoskeletal pain without the use of drugs or surgery.  This therapy is called Rothbart Proprioceptive Therapy, in which I use a series of proprietary tests to analyze the patient’s condition, custom designed Rothbart Proprioceptive Insoles and ongoing monitoring to address all of the changes in the patients condition and necessary changes in prescriptions until the chronic muscle and/or joint pain is eliminated.

Here is an excerpt from the article, "Piriformis Syndrome" published in my research website, written by myself, that ultimately led to the development of Rothbart Proprioceptive Therapy:

“In approximately 15% of the population, the peroneal portion of the sciatic nerve passes through the muscle belly of the piriformis muscle, or the undivided sciatic nerve penetrates the belly of the piriformis muscle (ChaitowL, Walker J, 2000. Clinical Application of Neuro Muscular Techniques. Volume I, The Upper Body. Churchill Livingstone).  These people are more prone to develop a mechanically induced piriformis syndrome.”

When the sacrum is in nutation, the sciatic nerve
is more prone to be mechanically trapped between
the stretched piriformis muscle (see black arrow)
and the greater sciatic notch.

To access the article in its entirety and view the animations, go to Piriformis Syndrome on my research website.