Four symptoms define the piriformis syndrome: an updated systematic review of its clinical features.

Purpose: To update the evidence on the clinical features of the piriformis syndrome since the first systematic review published in 2010.

Method: A systematic review of all case, cross-sectional and prevalence studies.

Results: The commonest features reported were: buttock pain, pain aggravated on sitting, external tenderness near the greater sciatic notch and pain on any maneuver that increases piriformis muscle tension, and limitation of straight leg raising. The quality of case reports since the previous review has not improved with considerable under-reporting of presumed negative tests. Three recent cross-sectional and prevalence studies have been reported, but the two larger studies are at high risk of bias.

Conclusions: Piriformis syndrome can be defined by a quartet of symptoms and signs. Many physical tests have been described, but the accuracy of these tests and the symptoms cannot be concluded from studies to date. Straight leg raising does not rule out the diagnosis. Piriformis syndrome is at a stage previously encountered with herniated intervertebral disc: that piriformis muscle pathology can cause sciatica has been demonstrated, but its prevalence among low back pain and sciatica sufferers and the diagnostic accuracy of clinical features requires cross-sectional studies free of incorporation and verification biases. One small cross-sectional study provides an encouraging example of how such studies could be conducted but would need replication in a broader population and better reporting.