Comparison of three obturator nerve block techniques for injectate spread into the obturator canal: a randomized controlled trial

Purpose The obturator nerve branches into the obturator canal; therefore, local anesthetic spread into the obturator canal predicts the success of the obturator nerve block (ONB). We compared three ONB techniques for the spread of local anesthetic mixed with contrast medium into the obturator canal. Methods We performed the ONB using the classical pubic approach (PA), inguinal approach (IA), or ultrasound-guided methodologic approach (UMA) in 143 patients undergoing transurethral resection of bladder tumors. The obturator nerve course and branching patterns of the UMA group were examined using ultrasound imaging. After injecting a local anesthetic mixed with a contrast medium, we evaluated its spread into the obturator canal using fluoroscopic imaging. P < 0.05 indicated statistical significance. Results Success rate of obturator canal enhancement was the greatest in the UMA group (84%; P < 0.001); the PA (42.6%; 20/47 patients) and IA (47.8%; 22/46 patients) groups did not differ significantly ( P = 1.000). Both branches of the obturator nerve passed above the superior margin of the external obturator muscle (EOM), and the obturator canal was enhanced in 13 of 50 (26%) patients in the UMA group. The posterior branch of the obturator nerve passed between the superior and main fasciculi of the EOM in 37 of 50 patients (74%) in the UMA group; the obturator canal was enhanced in 29 of these 37 patients (78%). Conclusion Local anesthetic spread into the obturator canal using the UMA was superior to that using the PA and IA. Both branches of the obturator nerve could be blocked using the UMA.