ORIGINAL ARTICLE Anatomic considerations and the relationship between the piriformis muscle and the sciatic nerve Mustafa Gu ¨ venc ¸er Æ Pınar Akyer Æ Cihan _ Iyem Æ Su ¨leyman Tetik Æ Sait Naderi Received: 22 January 2008 / Accepted: 20 March 2008 / Published online: 6 May 2008 Ó Springer-Verlag 2008 Abstract Stating background The piriformis syndrome is one of the non-discogenics causes of sciatica. It results from the compression of the sciatic nerve (SN) by the piriformis muscle (PM) in the neutral and piriformis stretch test position. The evidence of the increase in pain in the test position requires a detailed anatomical study addressing the changes that occurred in the SN and PM anatomy during the test position. The aim of this study is to examine this relationship morphometrically. Materials and methods A total of 20 right and left lower limbs of ten adult cadavers were examined. The SN and the PM were made visible. The location of the SN was eval- uated with respect to the consistent bony landmarks, including the greater and the lesser trochanter of the femur, the ischial tuberosity, the ischial spine of the hip bone, the posterior inferior iliac spine of the hip bone and the pos- terior superior iliac spine of the hip bone. The study was done in both neutral and test positions (i.e., 30° adduction 60° flexion and approximately 10° medial rotation position of the hip joint). Results The width of the greater sciatic notch was 63.09 ± 13.59 mm. The length of the lower edge of the PM was 95.49 ± 6.21 mm, and whereas the diameter of the SN where it emerged from the infrapiriforme was 17.00 ± 3.70 mm, the diameter decreased to 11.03 ± 2.52 mm at the level of the lesser trochanter of the femur. The SN intersected the PM most commonly in its medial second quarter anatomically. The vertical distance between the medial edge of the SN–PM intersection point and the ischial tuberosity was 85.62 ± 17.23 and 72.28 ± 7.56 mm (P \ 0.05); the angle between the SN and the transverse plane was 66.36° ± 6.68° and 71.90 ± 8.48° (P \ 0.05); and the vertical distance between the medial edge of the SN and the apex of the ischial spine of the hip bone was 17.33 ± 4.89 and 15.84 ± 4.63 mm (P [ 0.05), before and after the test position, respectively. Conclusion This study provides helpful information regarding the course and the location of the SN. The pre- sented morphometric data also revealed that after stretch test position, the infrapiriforme foramen becomes nar- rower; the SN becomes closer to the ischial spine of the hip bone, and the angle between the SN and the transverse plane increases. This study confirmed that the SN is prone to be trapped in the test position, and diagnosis of this situation requires dynamic MR and MR neurography study. Keywords Piriformis muscle Á Sciatic nerve Á Sciatica Á Piriformis syndrome Á Gluteal region Introduction Sciatica commonly defines a painful state resulting from the compression of the nerves forming the sciatic nerve (SN) by intervertebral disc herniation. This state may also occur as a result of non-discogenic disorders. Piriformis syndrome (PS) is one of the major causes of non-disco- genic sciatica. The SN is the thickest nerve in the body and innervates the posterior compartment of the thigh and all compart- ments of the lower leg and foot. It is formed in the pelvis M. Gu ¨venc ¸er (&) Á P. Akyer Á C. _ Iyem Á S. Tetik Department of Anatomy, School of Medicine, Dokuz Eylu ¨l University, 35340 Balc ¸ova/ _ Izmir, Turkey e-mail: mustafa.guvencer@deu.edu.tr S. Naderi Department of Neurosurgery, School of Medicine, Yeditepe University, _ Istanbul, Turkey 123 Surg Radiol Anat (2008) 30:467–474 DOI 10.1007/s00276-008-0350-5