Atypical anatomy of sciatic nerve and piriformis muscle is common
PainSci summary of Natsis 2014?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focussed on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided at the bottom of the page, as often as possible. ★★★★☆?4-star ratings are for larger and better studies and reviews published in more prestigious journals, with only quibbles. Ratings are a highly subjective opinion, and subject to revision at any time. If you think this paper has been incorrectly rated, please let me know.
This dissection study of 275 dead buttocks found that 6.4% of them had variations of sciatic nerve and piriformis muscle anatomy, with considerable variety in the variation. They found several different arrangements, and concluded: “Some rare, unclassified variations of the sciatic nerve should be expected during surgical intervention of the region.” Prepare to be surprised, surgeons!
All of these differences are potentially clinically significant, probably especially in the cases where the nerve (or part of it) passes right through the muscle. For a couple case studies, see Arooj 2014 and Kraus 2015.
PURPOSE: To detect the variable relationship between sciatic nerve and piriformis muscle and make surgeons aware of certain anatomical features of each variation that may be useful for the surgical treatment of the piriformis syndrome.
METHODS: The gluteal region of 147 Caucasian cadavers (294 limbs) was dissected. The anatomical relationship between the sciatic nerve and the piriformis muscle was recorded and classified according to the Beaton and Anson classification. The literature was reviewed to summarize the incidence of each variation.
RESULTS: The sciatic nerve and piriformis muscle relationship followed the typical anatomical pattern in 275 limbs (93.6 %). In 12 limbs (4.1 %) the common peroneal nerve passed through and the tibial nerve below a double piriformis. In one limb (0.3 %) the common peroneal nerve coursed superior and the tibial nerve below the piriformis. In one limb (0.3 %) both nerves penetrated the piriformis. In one limb (0.3 %) both nerves passed above the piriformis. Four limbs (1.4 %) presented non-classified anatomical variations. When a double piriformis muscle was present, two different arrangements of the two heads were observed.
CONCLUSIONS: Anatomical variations of the sciatic nerve around the piriformis muscle were present in 6.4 % of the limbs examined. When dissection of the entire piriformis is necessary for adequate sciatic nerve decompression, the surgeon should explore for the possible existence of a second tendon, which may be found either inferior or deep to the first one. Some rare, unclassified variations of the sciatic nerve should be expected during surgical intervention of the region.
- “Piriformis Syndrome with Variant Sciatic Nerve Anatomy: A Case Report,” an article in PM & R: The Journal of Injury, Function, and Rehabilitation, 2015.
- “Piriformis syndrome--a rare cause of extraspinal sciatica,” an article in J Pak Med Assoc, 2014.
- “Piriformis syndrome: a real pain in the buttock?,” an article in Neurosurgery, 2009.
These three articles on PainScience.com cite Natsis 2014 as a source:
- PS How Many Muscles? — A (slightly tongue-in-cheek) tally of the body’s many muscles
- PS Sciatica Science & Solutions — A guide to buttock and leg pain (which may or may not involve the sciatic nerve)
- PS You Might Just Be Weird — The clinical significance of normal — and not so normal — anatomical variations