Study on Variant Anatomy of Sciatic Nerve

Abstract

Knowledge regarding such variation and differences in the course of SN is important for the surgeons to plan for various surgical interventions pertaining to the gluteal region. The variant anatomy of SN may cause piriformis syndrome and failure of SN block. Hence present study is undertaken to know the level of division, exit, course, relationship to piriformis and variations in the branching pattern of SN.

Surgical anatomy of the sciatic nerve: A meta‐analysis

“…A total of 45 studies ( n = 7068 lower limbs) were included in the meta‐analysis on the variations with respect to the piriformis muscle and are summarized in Table S4 and Figure S1A–H . The normal Type A variation where the SN exits the pelvis as a single entity below the PM was the most common with a pooled prevalence of 85.2% (95%CI: 78.4–87.0), followed by Type B with a pooled prevalence of 9.8% (95%CI: 6.5–13.2), where the SN bifurcated in the pelvis with the CPN exiting piercing the PM and the TN coursing below the PM.…”

“…The sciatic nerve (SN), the largest nerve in the human body, is formed in the pelvis from the union of L4‐S3 ventral nerve roots . The SN normally courses as a single trunk following its union and exits as the most lateral structure from the greater sciatic foramen below the piriformis muscle (PM) . The source of pelvic exit variation most likely stems from the existence of the branches of the SN, the common peroneal nerve (CPN) and tibial nerve (TN), as separate entities during the embryological period .…”

“…The SN normally courses as a single trunk following its union and exits as the most lateral structure from the greater sciatic foramen below the piriformis muscle (PM) . The source of pelvic exit variation most likely stems from the existence of the branches of the SN, the common peroneal nerve (CPN) and tibial nerve (TN), as separate entities during the embryological period . The SN, despite its normal appearance as a single trunk, is composed of either fibers from the anterior divisions of the anterior rami which compose the TN, or fibers from the posterior divisions of the anterior rami which compose the CPN, bound together by a singular connective tissue sheath .…”

“…Understanding the variant anatomy of SN course is vital to performing complication free total hip arthroplasty (THA), SN blocks, as well as avoiding iatrogenic injury during any gluteal or pelvic surgery. The widely variable relationship of the SN to the PM can predispose a patient to piriformis syndrome (PS), which results from SN entrapment as it exits through the greater sciatic foramen . Piriformis syndrome is the most common etiology of sciatica of non‐discogenic cause .…”

“…The CPN is also anatomically more susceptible to injury in many cases of variation due to its decreased depth from the skin surface . In instances of pelvic division of the nerve, anesthetization attempts in popliteal SN block can lead to a successful block of only a single branch of the SN and inadequate analgesia . Manipulations during orthopedic procedures often require stretching of muscles and traction of structures to accommodate implantation of hardware.…”