Correlation between Sciatic Nerve Variants
and Diagnosis of Sciatica
Typically, the sciatic nerve exits the pelvis below the piriformis muscle through a larger opening known as the greater sciatic foramen. To classify the sciatic nerve, the Beaton and Anson system identifies six distinct variations.
In the first variant, both the common peroneal nerve (CPN) and the tibial nerve (TN) components travel together in front of the piriformis muscle, which is the most prevalent pattern seen in the majority of individuals.
Variant two involves the CPN passing through the piriformis muscle, while the TN component remains anterior to it. In the third variant, the CPN component is situated posteriorly to the piriformis muscle, while the TN component stays anteriorly positioned.
Variants four, five, and six, which collectively have a prevalence of less than 1% in the general population, are classified as rare occurrences.
It is essential to comprehend these variations since they can potentially contribute to sciatica, a clinical condition caused by the compression of the sciatic nerve. Symptoms consist of sharp or burning pain in the lower back that extends down the leg following the nerve’s pathway.
Taking into account anatomical variations in patients with sciatica is important, as nerve compression can result in similar symptoms resembling sciatica.
Because there is a scarcity of existing research on this subject, a new study was initiated to explore the possible connection between variations in the sciatic nerve and the occurrence of sciatica. This study aims to investigate and shed light on the correlation between sciatic nerve variations and the development of sciatica, considering the limited information currently available.
In a study reported by literature, the limb scans of 93 individuals were analyzed, and it was found that 55.9% exhibited type 1 variation, 41.9% showed type 2 variation, and only 2.2% had type 3 variation.
No instances of type 4, 5, or 6 variations were observed. The application of the Fisher exact test indicated a statistically significant difference (P < 0.0001) between the expected and observed groups concerning the frequency of specific sciatic nerve variant types.
A Z-statistic test was used to compare each individual subtype, and the P values were adjusted using the Bonferroni method (Table 2). The corrected P value for the type 1 variant (P < 0.001) indicated a significant difference in proportions.
Similarly, the corrected P value for the type 2 variant (P < 0.001) also showed a significant difference. However, there were no significant differences observed for the type 3, 4, 5, and 6 variants (P = 1.000).
Out of the total of 93 reads, there was consensus between the two radiologists in 85 cases, leading to a simple agreement rate of 91.4%. The interrater reliability, as determined by the κ statistic, yielded a value of 0.831, signifying a high level of agreement.
In our patient cohort, the occurrence of type 1 variant sciatic nerve anatomy was notably lower than anticipated, whereas the prevalence of type 2 variation was significantly higher than what had been previously reported.
There is evidence from case reports indicating a possible link between sciatic nerve variation and the clinical diagnosis of sciatica or piriformis syndrome. Our study seeks to investigate this association in more detail and presents compelling statistical findings that support the connection between sciatic nerve variation and the clinical diagnosis of sciatica.
In the study reported by literature, a higher proportion than anticipated was found in patients with type 2 sciatic nerve variation who had a clinical diagnosis of sciatica. Conversely, the proportion of patients with type 1 sciatic nerve variation diagnosed with sciatica was lower than expected.
The study reported by literature’s results have important implications, suggesting the potential benefit of preoperative MRI scans in patients with sciatica undergoing pelvic surgeries. This practice can help identify the sciatic nerve’s course and minimize the risk of iatrogenic nerve injury during the surgical procedure.
The study reported by literature raises the possibility of whether patients with variant anatomy may not receive optimal analgesia from a sciatic nerve block, questioning its effectiveness in such individuals.
Furthermore, it emphasizes the utility of MRIs in diagnosing sciatica, offering a more accurate assessment, especially for patients experiencing unexplained hip or back pain. Previous studies have shown promising outcomes in relieving symptoms through surgical interventions to release the sciatic nerve.
The study, conducted at a center in Philadelphia, Pennsylvania, utilized independent evaluations by two musculoskeletal radiologists, enhancing diagnostic accuracy.
The disparities in findings may be due to variations in patient populations, particularly the inclusion of predominantly African American individuals in this study.
The study’s focus was specifically on the clinical diagnosis of sciatica, but limitations arose due to the small number of recorded cases of piriformis syndrome in the electronic medical record (less than 20).
Consultations with clinicians revealed a tendency to label the diagnosis as sciatica rather than piriformis syndrome, underscoring the broad usage of the term sciatica.
This term encompasses various conditions, such as lumbar disc herniation, foraminal stenosis, tumors, cysts, and other extraspinal causes, resulting in a wide range of reported prevalence (1.2% to 43%) in previous reviews.
The findings of the study indicate a greater prevalence of type 2 sciatic nerve anatomical variant in patients diagnosed with sciatica.
These results have important implications, suggesting the potential utility of preoperative MRI scans to minimize iatrogenic injury during pelvic surgery, as well as the consideration of imaging and endoscopic decompression surgeries for individuals experiencing unexplained hip pain.
Further large-scale studies are necessary to delve deeper into the examination of sciatic nerve variations in patients with a sciatica diagnosis.