European Journal of Cardiovascular Medicine

The sciatic nerve, the largest peripheral nerve in the human body, originates from the lumbosacral plexus (L4–S3) and typically exits the pelvis via the greater sciatic foramen, inferior to the piriformis muscle¹. This anatomical arrangement positions the nerve in close proximity to musculoskeletal structures, rendering it susceptible to compression or irritation, conditions often implicated in sciatica—a common clinical syndrome characterized by radiating pain, numbness, or weakness along the nerve’s distribution². While trauma, spinal pathology, and disc herniation are well-established etiologies of sciatica, emerging evidence suggests that anatomical variations in the sciatic nerve’s pelvic exit may also play a contributory role³.

Variations in the relationship between the sciatic nerve and the piriformis muscle have been documented since early anatomical studies, with reported patterns including the nerve piercing the piriformis or exiting superior to it. These deviations from the typical inferior exit are estimated to occur in 10–20% of individuals, though their prevalence and clinical implications remain debated⁴. Such anomalies may predispose the nerve to entrapment, particularly under conditions like piriformis hypertrophy, trauma, or prolonged sitting, potentially exacerbating or mimicking sciatic symptoms. Despite this, systematic investigations linking these variations to sciatica are limited, leaving a gap in understanding their biomechanical and clinical relevance⁵.

The present study addresses this gap by examining the sciatic nerve’s exit patterns in cadaveric lower limbs. By analyzing their frequency, morphometric characteristics, and spatial relationships, this study aims to elucidate the importance of these variations in the occurrence of sciatica, providing a foundation for future clinical and therapeutic insights.

This observational study was conducted at the Department of Anatomy, Siddardha Medical College, Vijayawada, India, between January 2016 and June 2017. The research involved the dissection of 60 lower limbs from 30 formalin-fixed adult cadavers (15 male and 15 female), obtained from the institution’s cadaveric collection. The cadavers were of Indian origin, with ages at death ranging from 40 to 70 years, and were selected based on availability and absence of visible pelvic or lower limb deformities. Ethical approval was obtained from the Institutional Ethics Committee of Siddardha Medical College prior to the study’s commencement.

Dissections were performed by standard anatomical techniques. The gluteal region of each lower limb was exposed by reflecting the skin, subcutaneous tissue, and gluteus maximus muscle to visualize the sciatic nerve’s exit from the pelvis relative to the piriformis muscle. The nerve’s exit pattern was classified into three types: Type A (exit below the piriformis), Type B (nerve or its divisions piercing the piriformis), and Type C (exit above the piriformis). Observations were recorded bilaterally, noting any accessory fibrous bands or structural anomalies.

Morphometric measurements were taken using a digital caliper (accuracy ±0.01 cm). The distance from the sciatic nerve’s exit point to the ischial spine was measured, and clearance space relative to surrounding structures was assessed. Data were compiled and analyzed using SPSS software (version 22.0). Descriptive statistics (means, standard deviations, percentages) were calculated, and differences across exit types, sexes, and sides were evaluated using one-way ANOVA and chi-square tests, with a significance threshold of p < 0.05.

The present study analyzed 60 lower limbs from 30 cadavers (15 male and 15 female) to explore variations in the sciatic nerve’s exit from the pelvis and their potential relevance to sciatica. Three distinct exit patterns were identified based on the nerve’s relationship with the piriformis muscle: Type A (normal exit below the piriformis), Type B (nerve piercing the piriformis), and Type C (nerve exiting above the piriformis).

The distribution of these variations is detailed in Table 1. Type A was the predominant configuration, observed in 48 limbs (80.0%), followed by Type B in 8 limbs (13.3%), and Type C in 4 limbs (6.7%). The distribution was consistent across sexes, with 24 Type A limbs in both males and females, 4 Type B limbs in each, and 2 Type C limbs in each (p = 0.72 for sex differences). Similarly, no significant asymmetry was noted between right and left limbs (p = 0.58).

In Type B cases, 6 of the 8 limbs (75%) exhibited a pattern where the tibial nerve pierced the piriformis muscle, while the common peroneal nerve passed below it, suggesting a potential predisposition to differential compression of nerve components.

Table 1: Distribution of Sciatic Nerve Exit Variations in 60 Lower Limbs

Morphometric analysis (Table 2) revealed significant differences in the sciatic nerve’s trajectory across the exit types. The mean distance from the nerve’s exit point to the ischial spine was 3.5 ± 0.8 cm in Type A, 2.9 ± 0.6 cm in Type B, and 2.7 ± 0.5 cm in Type C, with a statistically significant variation among groups (p = 0.03). Compared to Type A, both Type B and Type C exhibited a reduced clearance space of approximately 1.2 cm near surrounding structures (p < 0.05), particularly the superior gemellus muscle in Type C cases. Accessory fibrous bands were identified in 3 limbs (2 Type B, 1 Type C), further constricting the nerve’s path, whereas no such bands were observed in Type A limbs.

Table 2: Morphometric Analysis of Sciatic Nerve Exit Variations

In the 12 limbs with Type B or Type C variations, the sciatic nerve’s proximity to musculoskeletal structures appeared to increase the likelihood of compression, particularly in scenarios involving piriformis hypertrophy or fibrous bands.

Although direct evidence of sciatica could not be assessed in cadaveric specimens, these anatomical findings suggest that atypical exit patterns (Types B and C) may heighten susceptibility to nerve entrapment or irritation compared to the typical Type A configuration.

This study investigated variations in the sciatic nerve’s exit from the pelvis across 60 lower limbs, revealing a predominance of the typical Type A pattern (80%), where the nerve exits below the piriformis muscle, alongside less common Type B (13.3%) and Type C (6.7%) variants. These findings align with previous anatomical studies, such as Beaton and Anson (1938), who reported a similar prevalence of atypical exits (10–15%) in Caucasian populations, suggesting that such variations are a consistent feature across ethnic groups, including the Indian cohort examined here at Siddardha Medical College.

The morphometric differences observed—shorter distances to the ischial spine in Type B (2.9 ± 0.6 cm) and Type C (2.7 ± 0.5 cm) compared to Type A (3.5 ± 0.8 cm), with p = 0.03—indicate that atypical exits alter the nerve’s trajectory, reducing clearance by approximately 1.2 cm (p < 0.05). This spatial constraint, compounded by accessory fibrous bands in 3 limbs, supports the hypothesis that Types B and C may predispose individuals to sciatic nerve compression^6,7. Notably, in 75% of Type B cases, the tibial nerve pierced the piriformis while the common peroneal nerve passed below, this suggest that such splitting could lead to differential symptom presentation in sciatica^8,9.

The clinical relevance of these variations lies in their potential to exacerbate nerve irritation, particularly under dynamic conditions like piriformis hypertrophy or prolonged sitting—factors not assessable in cadaveric specimens¹⁰. While direct evidence of sciatica was beyond this study’s scope, the anatomical predisposition aligns with reports linking piriformis syndrome to atypical nerve paths (Jankovic et al., 2013). The absence of sex or side differences (p = 0.72, p = 0.58) further suggests that these variations are intrinsic rather than influenced by demographic factors.

Limitations include the study’s reliance on cadaveric material, precluding functional or symptomatic correlation, and the modest sample size, which may underrepresent rarer variants. Future research should integrate imaging or clinical data to confirm these anatomical findings’ impact on sciatica incidence. Nevertheless, this study underscores the importance of recognizing sciatic nerve exit variations in surgical planning, such as hip arthroplasty, and in diagnosing atypical sciatic pain.

The study highlights that variations in the sciatic nerve's exit from the pelvis, particularly Type B and Type C patterns, may increase the risk of sciatica due to reduced clearance and altered nerve trajectories. While Type A remains the most common variation, the anatomical differences observed in Types B and C suggest a higher predisposition to nerve compression, which could lead to sciatica. The presence of accessory fibrous bands further supports this association. These findings emphasize the need for clinical awareness and further research to explore the potential role of these variations in sciatica development and management strategies.

1. Berihu BA, Debeb YG. Anatomical variation in bifurcation and trifurcations of sciatic nerve and its clinical implications: in selected university in Ethiopia. BMC Res Notes. 2015 Nov 2;8:633. doi: 10.1186/s13104-015-1626-6. PMID: 26526618; PMCID: PMC4630888.
2. Issack PS, Helfet DL. Sciatic nerve injury associated with acetabular fractures. HSS J. 2009 Feb;5(1):12-8. doi: 10.1007/s11420-008-9099-y. Epub 2008 Dec 17. PMID: 19089496; PMCID: PMC2642541.
3. Ailianou A, Fitsiori A, Syrogiannopoulou A, Toso S, Viallon M, Merlini L, Beaulieu JY, Vargas MI. Review of the principal extra spinal pathologies causing sciatica and new MRI approaches. Br J Radiol. 2012 Jun;85(1014):672-81. doi: 10.1259/bjr/84443179. Epub 2012 Feb 28. PMID: 22374280; PMCID: PMC3474092.
4. Guvençer M, Iyem C, Akyer P, Tetik S, Naderi S. Variations in the high division of the sciatic nerve and relationship between the sciatic nerve and the piriformis. Turk Neurosurg. 2009 Apr;19(2):139-44. PMID: 19431123.
5. Agnollitto PM, Chu MWK, Simão MN, Nogueira-Barbosa MH. Sciatic neuropathy: findings on magnetic resonance neurography. Radiol Bras. 2017 May-Jun;50(3):190-196. doi: 10.1590/0100-3984.2015.0205. PMID: 28670031; PMCID: PMC5487234.
6. Son BC, Kim DR, Jeun SS, Lee SW. Decompression of the sciatic nerve entrapment caused by post-inflammatory scarring. J Korean Neurosurg Soc. 2015 Feb;57(2):123-6. doi: 10.3340/jkns.2015.57.2.123. Epub 2015 Feb 26. PMID: 25733994; PMCID: PMC4345190.
7. Saar TD, Pacquée S, Conrad DH, Sarofim M, Rosnay P, Rosen D, Cario G, Chou D. Endometriosis Involving the Sciatic Nerve: A Case Report of Isolated Endometriosis of the Sciatic Nerve and Review of the Literature. Gynecol Minim Invasive Ther. 2018 Apr-Jun;7(2):81-85. doi: 10.4103/GMIT.GMIT_24_18. Epub 2018 May 2. PMID: 30254944; PMCID: PMC6113996.
8. Feinberg J, Sethi S. Sciatic neuropathy: case report and discussion of the literature on postoperative sciatic neuropathy and sciatic nerve tumors. HSS J. 2006 Sep;2(2):181-7. doi: 10.1007/s11420-006-9018-z. PMID: 18751834; PMCID: PMC2488172.
9. Xu LW, Veeravagu A, Azad TD, Harraher C, Ratliff JK. Delayed Presentation of Sciatic Nerve Injury after Total Hip Arthroplasty: Neurosurgical Considerations, Diagnosis, and Management. J Neurol Surg Rep. 2016 Jul;77(3):e134-8. doi: 10.1055/s-0035-1568134. PMID: 27602309; PMCID: PMC5011454.
10. Martin HD, Khoury AN, Schroder R, Gomez-Hoyos J, Yeramaneni S, Reddy M, James Palmer I. The effects of hip abduction on sciatic nerve biomechanics during terminal hip flexion. J Hip Preserv Surg. 2017 Apr 11;4(2):178-186. doi: 10.1093/jhps/hnx008. PMID: 28630740; PMCID: PMC5467418.