Surgical anatomy of the sciatic nerve and its relationship to the piriformis muscle with a description of a rare variant

Abstract

Aims: Variation of the sciatic nerve may increase the risk of iatrogenic injury during total hip arthroplasty or arthroscopy, result in failure of peripheral blocks, or be associated with piriformis syndrome. Studies from Africa are scarce, with none to date from South Africa. Thus, the aims were to document the relationship between the sciatic nerve and piriformis muscle, variation in the bifurcation level and in the length of the nerve. Any significant differences between sexes and sides were also investigated. Methods: The lower limbs of 42 cadavers (84 limbs) were dissected and the relationship between the sciatic nerve and piriformis classified according to the patterns described by Beaton and Anson. The region of sciatic nerve bifurcation was documented, and the length of the nerve was measured in individuals with bifurcation in the thigh. Results: The normal relationship between the sciatic nerve and piriformis muscle was present in 64 limbs (76.2%). The bifurcation level of the nerve was variable in more than half the sample. No significant differences occurred in any of the variant patterns or bifurcation regions between side or sex; however, variations were more common in females than in males. The mean length of the sciatic nerve was 133.30±19.33 mm, with no differences in length between sex or side. Conclusion: Variations in the anatomy of the sciatic nerve occurred in up to half of the sample, which may have implications for increased risk of iatrogenic injury in total hip arthroplasty and arthroscopy, piriformis syndrome or sciatic block failure. Level of evidence: Level 4