Anatomical Relationships of the Sciatic Nerve and Pudendal Nerve to the Ischial Spine as They Exit the Greater Sciatic Foramen

Deep gluteal syndrome is a clinical condition in which discomfort may arise due to the pathoanatomy of the subgluteal space. In this study, we conducted an anatomical exploration to categorize the relationship of the piriformis muscle, sciatic nerve, and pudendal nerve to the ischial spine and sacrospinous ligament. Twenty-two cadavers were analyzed. The piriformis muscle, sciatic nerve, and pudendal nerve were exposed either through a transgluteal approach or a gluteal flap. The relationship of the neural structures to the ischial spine, sacrospinous ligament, and ischial bone as they exit the greater sciatic foramen was observed and the exit zones were classified as either: zone A medial to the ischial spine (entirely on sacrospinous ligament), zone B on the ischial spine, and zone C lateral to the ischial spine (entirely on ischial bone). The sciatic nerve was observed either in zone B or zone C in all specimens. The pudendal nerve was found to be either in zone A or B in 97.6% of specimens. The most common combinations were sciatic nerve in zone B and pudendal nerve in zone A (Type I), and sciatic nerve in zone C and pudendal nerve in zone B (Type II). The results from this study show clear anatomical differences in the sciatic nerve-pudendal nerve relationship, which may play a role in pain seen in deep gluteal syndrome. Moreover, classification of the sciatic nerve-ischial spine and pudendal nerve-ischial spine relationships described in this manuscript will help describe different pathologies affecting the deep gluteal area.