A novel approach for anterior sciatic nerve block: cadaveric feasibility study

Abstract

Sciatic nerve block is a commonly used technique for providing anesthesia and analgesia to the lower extremity. It is classically performed through posterior or lateral approaches. However, an anterior approach should be considered in certain conditions where patient positioning would be complicated. The success rate of the sciatic nerve block with previously defined approaches has been reported to be low, however, the complication rate with such approaches has been found to be high. Therefore, we aimed to conduct an anatomical study defining a new anterior approach to block the sciatic nerve and also to examine if the femoral nerve can be blocked via the same approach. Initially, various landmarks and practical measurements were examined on 11 lower extremities. Eight of the lower extremities were used for defining the best approach to the sciatic nerve anteriorly. Once defined, Indian ink was injected into two cadaveric extremities with an anesthetic needle through such an approach. The route of the needle was evaluated via dissection and we observed whether the ink stained the sciatic nerve or injured regional neurovascular structures. The remaining extremity was cut axially to observe the route of the needle after injection. The ideal site of needle insertion was found to be 4-5 cm distal to the inguinal crease and 1-2 cm lateral to the femoral artery. On average, this point corresponded to a point located 8.0 ± 0.7 cm distal to a perpendicular line drawn midway through the straight line connecting the anterior superior iliac spine (ASIS) and the pubic tubercle (PT). The distance of this point to the straight line drawn between the ASIS and PT was approximately equal to half the distance of this line. The technique described herein appears anatomically safe with a lower risk of damage to major neurovascular structures. Additionally, the femoral nerve can be blocked simultaneously to obtain a larger area of anesthesia of the lower limb.