Novel anatomical findings with implications on the etiology of the piriformis syndrome

Abstract

Purpose The cause of the piriformis-related pelvic and extra-pelvic pain syndromes is still not well understood. Usually, the piriformis syndrome is seen as extra-pelvic sciatica caused by the entrapment of the sciatic nerve by the piriformis in its crossing through the greater sciatic foramen. However, the piriformis muscle may compress additional nerve structures in other regions and cause idiotypic pelvic pain, pelvic visceral pain, pudendal neuralgia, and pelvic organ dysfunction. There is still a lack of detailed description of the muscle origin, topography, and its possible relationships with the anterior branches of the sacral spinal nerves and with the sacral plexus. In this research, we aimed to characterize the topographic relationship of the piriformis with its surrounding anatomical structures, especially the anterior branches of the sacral spinal nerves and the sacral plexus in the pelvic cavity, as well as to estimate the possible role of anatomical piriformis variants in pelvic pain and extra-pelvic sciatica. Methods Human cadaveric material was used accordingly to the Swiss Academy of Medical Science Guidelines adapted in 2021 and the Federal Act on Research involving Human Beings (Human Research ACT, HRA, status as 26, May 2021). All body donors gave written consent for using their bodies for teaching and research. 14 males and 26 females were included in this study. The age range varied from 64 to 97 years (mean 84 ± 10.7 years, median 88). Results three variants of the sacral origin of the piriformis were found when referring to the relationship between the muscle and the anterior sacral foramen. Firstly, the medial muscle origin pattern and its complete covering of the anterior sacral foramen by the piriformis muscle is the most frequent anatomical variation (43% in males, 70% in females), probably with the most relevant clinical impact. This pattern may result in the compression of the anterior branches of the sacral spinal nerves when crossing the muscle. Conclusions These new anatomical findings may provide a better understanding of the complex piriformis and pelvic pain syndromes due to compression of the sacral spinal nerves with their somatic or autonomous (parasympathetic) qualities when crossing the piriformis.

The piriformis muscle syndrome – anatomy, diagnosis and the role of physiotherapy. A Review

“…In the pelvic cavity, the piriformis muscle is adjacent to the sacral plexus, pelvic organs and vessels. However, the detailed relationships between the PM, the sacrum, the sacroiliac joint and the ventral branches of the sacral spinal nerves are still poorly understood [13]. The PM is the only muscle that moves laterally through the greater sciatic foramen, and it is a key landmark for all the important nerves and vessels that pass from the pelvis to the gluteal region [14].…”

Sciatic Nerve and Its Anatomical Variations: In-Depth Understanding Acquired During Dissection Classes

“…Due to its course and close relationship and interaction with the PM, the variations of this muscle, if present, should also be known [ 18 ]. The PM is an external muscle of the hip, located in the gluteal region, and together with other muscles allows different movements of the hip, such as lateral rotation, abduction, and extension.…”