Anterior Approach to the Sciatic Nerve Block: Adaptation to the Patient's Height

To improve the incidence of block of the posterior femoral cutaneous nerve (PFCN) when using an anterior approach as described recently, we hypothesized that the distance between the inguinal line and the puncture site depends on the patient's height. A preliminary radiological study performed in 13 patients established a formula describing the relationships between the patient's height and the puncture site “S.” A line was drawn between the anterior iliac spine and the superior angle of the pubic tubercle (inguinal line) and another line from the midpoint of the inguinal line to the puncture site “S.” “S” was calculated from the midpoint of the inguinal line as “S” = (height in cm −100)/10. A prospective study was conducted in 53 patients. Results are presented as median (range, 0.25–0.75). Two minutes were required to locate the sciatic nerve at a depth of 12 cm (10.5–13.0 cm). Complete sciatic and PFCN blocks were observed in 92% of the patients. We conclude that consideration should be given to the patient's height when the sciatic nerve is blocked using an anterior approach. This technique seems to improve the success of block of the PFCN, essential to tolerate a thigh tourniquet.