Anatomical considerations of the neonatal ilio-inguinal/ iliohypogastric nerve block

Abstract

The ilioinguinal/ iliohypogastric nerve block is an effective technique that provides analgesia for a variety of inguinal surgical procedures in children. However, a relatively high failure rate of between 20-30% has been reported. The aim of this study was to determine the exact anatomical position of the ilio-inguinal and iliohypogastric nerves in relation to an easily identifiable bony landmark, the anterior superior iliac spine (ASIS), in neonates. Dissections were performed on a sample of 54 neonatal cadavers (51 left and 53 right sides; mean length: 0.43m ± 0.06m; mean weight: 1.64kg ± 0.72kg) and the distance from the ASIS to both these nerves, on a line connecting the ipsilateral ASIS to the umbilicus, was measured using a mechanical dial sliding calliper (accuracy: 0.01mm). No significant difference was found when comparing the left and right sides of the sample. The data for the left and right sides were therefore combined, i.e., a total of 104 ilio-inguinal and 103 iliohypogastric nerves were examined. The nerves were found to be much closer to the ASIS than was previously thought. The ilio-inguinal nerve was between 1.98mm-2.43mm from the ASIS, while the iliohypogastric nerve was approximately 3.56mm-4.07mm from the ASIS. The data obtained from this study suggest that the high failure rate of the ilio-inguinal/ iliohypogastric nerve block could be due to lack of spatial knowledge regarding the anatomy of these nerves in neonates. An improved needle insertion site was therefore developed, one that aims to block these nerves at a point closer to the ASIS.