Piriformis Syndrome By Paul L Liebert, MD, Tomah Memorial Hospital, Tomah, WI Reviewed / Revised Oct 2021 | Modified Sep 2022 View Patient Education Symptoms and Signs Diagnosis Treatment Topic Resources Side-Lying Hip External Rotation... Bridging Piriformis syndrome is compression of the sciatic nerve by the piriformis muscle in the posterior pelvis, causing pain in the buttocks and occasionally sciatica.