Sciatic Nerve Bifurcation Level and its Anatomical Relationship to the Piriformis Muscle: A Magnetic Resonance Imaging–Based Assessment in the Iraqi Population

Background: The sciatic nerve is the major nerve supply to the lower extremity and a critical structure in orthopedic surgery, radiologic evaluation, and regional anesthesia. Precise characterization of its relationship to the piriformis muscle is essential for safe procedural planning and for understanding anatomical variation. Objectives: This study aimed to determine the relationship between the piriformis muscle and the sciatic nerve with reference to sex and anatomical variations. Methods: This prospective cross-sectional observational study included 35 adults undergoing pelvic Magnetic Resonance Imaging (MRI) at Imam Al-Hussein Medical City, Karbala, Iraq, providing data from 70 lower limbs. MRI parameters such as the diameter and thickness of the sciatic nerve, its level of bifurcation, and its relationship to piriformis muscle according to the classical Beaton and Anson classification were recorded and statistically analyzed. Results: The study population included 18 men and 17 women (age mean 31.8 ± 6.2 years; mean BMI 24.6 ± 3.1 kg/m²). The mean sciatic nerve diameter and thickness were 11.62 ± 1.56 mm and 6.4 ± 1.2 mm, respectively and both measurements were significantly greater in males than females as p value less than 0.05. The typical piriformis morphology predominated (82.9%). Sciatic nerve bifurcation occurred most frequently at the popliteal fossa (78.6%), followed by pelvic (17.1%) and thigh (4.3%) levels, without significant association with sex or laterality (p > 0.05). Beaton and Anson Type I was observed in 78.6% of cases followed by Type II (10%) , type III (5.7%) , type IV (2.9%) and type V and VI each with 1.4%, without significant association with sex or laterality (p > 0.05). Conclusion: The present study demonstrated that the sciatic nerve diameter and thickness were significantly higher in males than females while no significant side-related differences were indicated. Furthermore, Piriformis muscle variation, level of sciatic nerve bifurcation and sciatic nerve-piriformis relationships showed no significant association with either gender or laterality. These findings highlight that sexual dimorphism may influence the size of sciatic nerve. In contrast, the anatomical patterns and relationships of the sciatic nerve remain comparable across sexes and sides. KEYWORDS: Sciatic nerve, Piriformis muscle, Anatomical variation, Magnetic Resonance Imaging (MRI).