The influence of age on the anatomical variability of sciatic nerve divisions in the thigh: an ultrasound study

Abstract

Purpose: The Sciatic Nerve Division (SND) into the Common Peroneal Nerve and Tibial Nerve presents a great anatomical variability in its location in the thigh, but the influence of age on it has not been fully addressed.

Methods: Anatomical distances from greater trochanter to SND and from SND to popliteal crease were obtained by ultrasound examination in 60 children (age 1-12 years) and 60 adult patients (age 13-80 years) who were scheduled for programmed surgery. A sciatic nerve/thigh coefficient [Greater Trochanter-SND/(Greater Trochanter-popliteal crease)*100] and its coefficient of variation (standard deviation/mean*100) were calculated. Greater Trochanter-SND and SND-Popliteal crease were also correlated with patients´ age, weight and height.

Results: There were statistically significant differences between children and adult in Greater Trochanter-SND (20.5 ± 5,5 vs 33.9 ± 2.7; p < 0.0001) and in SND-Popliteal (4.9 ± 2.1 vs 6.7 ± 1.6; p < 0.0001) distances measured in cm. There were also statistically significant differences between children and adults in Sciatic nerve/thigh coefficient (80% vs 83%; p < 0.0001) and its index of variation (8.1% vs 4.8%; p < 0.0001). In children, both Greater Trochanter-SND and SND-Popliteal distances were strongly correlated with age (r2 = 0.868 and r2 = 0.261, respectively; p < 0.0001), weight (r2 = 0.778 and r2 = 0.278, respectively; p < 0.0001) and height (r2 = 0.898 and r2 = 0.225, respectively; p < 0.0001). However, in older patients, only Greater Trochanter-SND distance was statistically correlated with height (r2 = 0.372; p = 0.0001) and not with age or weight; SND-Popliteal distance did not show statistically relevant correlation, either.

Conclusion: Children presented even more anatomical variability than adults in sciatic nerve division due to the growth of both the proximal and distal nervous structures of the thigh before 12 years of age.

Keywords: Age changes; Anatomical variability; Pediatric anesthesia; Sciatic nerve block; Ultrasound anatomy.