Anatomical relation between sciatic nerve and piriformis muscle and its bifurcation level during fetal period in human

The aim of this study is to determine the morphometric development, location and variant formations of the sciatic nerve using anatomic dissection method during the fetal period. Sciatic nerves of 200 human fetuses (103 males and 97 females) aged between 9 and 40 weeks of gestation were studied bilaterally. The bifurcation level of the sciatic nerve to its terminal branches was evaluated with respect to popliteal fossa. Then the length of the sciatic nerve, starting from where it leaves the piriformis muscle till the bifurcation point of the nerve, and its width at the point where it leaves infrapiriforme foramen and its width at the bifurcation level were measured. We also measured the distance of the sciatic nerve to the ischial tuberosity, the greater trochanter and the intergluteal sulcus. Mean values and standard deviations of all parameters according to trimesters were calculated. We found that all parameters increase with age during the fetal period (P < 0.05). Parameters do not show any significant differences between sexes (P > 0.05). In our analysis, we observed that in 98 % of the cases (on the right and the left side) the sciatic nerve leaves the pelvis below the piriformis muscle. The remaining cases (2 %) are variant formations. We believe that our study will be useful for better understanding of sciatic nerve development and it may contribute to future studies in obstetrics, orthopedics and fetal pathology. Knowledge of variant formations of the sciatic nerve, its bifurcation level and its relation with neighboring structures may be important for blockade of the nerve in newborn surgeries.