Ultrasonographic Evaluation of Sciatic Nerve Bifurcation in Relation to Patient Height: A Prospective Observational Study

Abstract

Background: The Sciatic nerve demonstrates considerable anatomical variability in its level of bifurcation into the Tibial nerve and Common peroneal nerve. Such variability has significant implications for popliteal sciatic nerve block and regional anaesthesia outcomes. Anthropometric parameters, particularly height, may influence the anatomical level of nerve division; however, evidence remains limited.

Objectives: To compare the proportion of patients with sciatic nerve division within 10 cm from the popliteal crease between two height groups (<170 cm and >171 cm) using ultrasonography. Secondary objectives included evaluation of anatomical variations in division level, nerve thickness, depth from skin, and determination of the sciatic nerve–thigh coefficient in relation to anthropometric parameters.

Methods: This prospective observational study was conducted in the Department of Anaesthesiology at Chettinad Hospital and Research Institute in 2023. A total of 100 patients undergoing elective and emergency lower limb surgeries were divided into two groups based on height (<170 cm and >171 cm; n=50 each). Ultrasound was used to identify the sciatic nerve bifurcation. Distances measured included: (1) sciatic nerve division to popliteal crease, (2) greater trochanter to sciatic nerve division, and (3) greater trochanter to popliteal crease. Nerve thickness and depth from skin were also recorded. The sciatic nerve–thigh coefficient and its coefficient of variation were calculated. Statistical analysis was performed using SPSS version 21 and Microsoft Excel.

Results: The mean sciatic nerve division–popliteal crease distance was 40.87 ± 7.54 mm in the <170 cm group and 45.42 ± 8.63 mm in the >171 cm group (p = 0.405). The mean greater trochanter–sciatic nerve division distance was 305.55 ± 12.91 mm and 309.57 ± 12.23 mm in the respective groups (p = 0.738). The greater trochanter–popliteal crease distance was significantly higher in the >171 cm group (354.35 ± 14.69 mm vs. 346.87 ± 15.10 mm; p = 0.027). No statistically significant differences were observed in nerve thickness or depth between groups. A considerable anatomical variability in bifurcation level was identified in both height categories.

Conclusion: The level of sciatic nerve bifurcation exhibits substantial inter-individual variability and does not demonstrate a statistically significant association with height when assessed within 10 cm of the popliteal crease. These findings underscore the importance of ultrasound guidance during popliteal sciatic nerve block to enhance precision and reduce the risk of incomplete blockade. Recognition of demographic and anatomical variability may further optimize clinical outcomes in regional anaesthesia.