Piriformis syndrome revealed: High rates of sciatic nerve variation in a donor population

There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Co-authors:

Jonathan Rozeboom - Midwestern University; Milena Douglas - Midwestern University; Colton Lane - Midwestern University; Thalia Olson - Midwestern University; Eshwar Karupakula - Midwestern University; Harsh Patel - Midwestern University; Kianna Ruble - Midwestern University; Timothy Campbell - Midwestern University; Terrence Ritzman - Midwestern University; Heather Smith - Midwestern University; Leigha Lynch - Midwestern University

Abstract Body : The piriformis muscle is an important lateral rotator of the thigh (especially when it is extended), as well as aiding in abduction of a flexed thigh, making it important in bipedal locomotion. The sciatic nerve, which innervates most of the posterior thigh and leg, typically exits the pelvis via the greater sciatic foramen, emerging inferior to piriformis. However, there are documented cases in which the association of the sciatic nerve and piriformis can be variable, with some or all of the sciatic nerve piercing through the belly of piriformis. This variation and hypertonicity of piriformis can cause compression or entrapment of the sciatic nerve (known as piriformis syndrome). Symptoms from compression or “sciatica” may result in low back pain or radiating pain, paresthesia, or weakness of the posterior thigh and leg. This variation may be a critical consideration in the treatment of patients such as pregnant people, athletes who externally rotate more frequently, and individuals who spend large amounts of time sitting, as these populations may be at higher risk for increasing tone of piriformis muscle and irritation of the sciatic nerve.

The objective of this study was to further document the anatomical relationship between the piriformis muscle and the sciatic nerve. Specifically, we quantified the relationship of the sciatic nerve and piriformis muscles on 90 cadaveric donors from Midwestern University’s Glendale and Downers Grove campuses. We observed that 22% of females (11/50) and 12.5% of males (5/40) possessed a sciatic nerve that pierced through the piriformis. Only one donor with bilateral presence of this variant was observed, whereas in the remaining donors, the variant was observed unilaterally. A chi-squared text revealed no significant difference in the presence of this variant between right and left sides (p=0.24). Although further data collection is needed, our results indicate a higher frequency of the variant in which the sciatic nerve pierces the piriformis muscle than previously reported. A better understanding of the frequency of sciatic nerve variants is clinically important in diagnosis and treatment of piriformis syndrome and sciatica. As we collect more data, we anticipate finding improved ways to identify individuals with this variant and evaluate their susceptibility to lower back pain and sciatica.