Ultrasound-guided obturator nerve block technique at the distal end of the obturator canal: case series and cadaver evaluation

The obturator nerve variably gives off the anterior, posterior, and hip articular branches along its course; however, all branches invariably pass through the obturator canal. Herein, we describe our obturator nerve block technique, which promises to deliver local anesthetic directly into the obturator canal. We performed the obturator nerve block in six patients undergoing transurethral resection of bladder tumor under spinal anesthesia. We also evaluated the spread of dye in a cadaver. With patient placed in the lithotomy position, a linear ultrasound transducer was placed on the anterior part of the genitofemoral sulcus, oriented cephalad, to observe the external orifice of the obturator canal, which is present immediately posterior to the posterior end of the inferior margin of the superior pubic ramus and just medial to the body of the ischium. The needle tip was guided to this location, and 10 ml of 1.5% lidocaine was injected into the obturator canal. The procedure was repeated using 10-ml dye in a cadaver. No obturator jerks were observed during the transurethral resection of bladder tumors in all six cases. Cadaver examination confirmed the dye stained the obturator nerve, with retrograde spread into the pelvic cavity via the obturator canal.