Ultrasound-guided midthigh sciatic nerve block-a clinical and anatomical study.

BACKGROUND AND OBJECTIVES: Ultrasound-guided sciatic nerve block is a relatively new regional anesthesia technique with few descriptions in the literature. The objective of this study was to assess the ease with which the sciatic nerve could be imaged in the midthigh region using ultrasound and to describe the anatomy surrounding the sciatic nerve at this location.

METHODS: In this prospective observational study, 40 patients scheduled for surgery where sciatic nerve block was indicated were scanned between the gluteal and the popliteal regions using an ultrasound machine (Vivid-i, GE Healthcare, Chalfont St. Giles, Bucks, UK). Patients then received real time ultrasound-guided sciatic nerve block. Validation of the ultrasound image of the sciatic nerve was achieved using nerve stimulation. Description and confirmation of the anatomy surrounding the sciatic nerve was based on a review of anatomical texts and an anatomical study on 5 unembalmed cadavers.

RESULTS: The sciatic nerve was identified with ultrasound and its image validated using nerve stimulation in 38 of 40 patients (95%). In 15 patients (37.5%) nerve stimulation was required to confirm identification of the sciatic nerve. Surrounding muscles (biceps femoris, vastus lateralis, and adductor magnus) and fascial planes (lateral intermuscular septum) were identified as sonographic landmarks and were confirmed in the anatomical study.

CONCLUSIONS: Ultrasonic identification of the sciatic nerve at the midthigh level can be achieved; however, in this study, 37.5% of patients required nerve stimulation to confirm its sonographic appearance. Target nerve localization and the subsequent performance of the sciatic nerve block may be enhanced by recognition of surrounding muscular and fascial structures which were also identified using ultrasound.