Background and Objectives: For knee surgery, obturator nerve block (ONB) has been shown to enhance postoperative analgesia provided by femoral block. Current techniques for obturator block use surface landmarks or ultrasound guidance (USG) with nerve stimulation. This preliminary observational study evaluated the success of an ultrasound-guided ONB without the additional use of nerve stimulation.

Methods: Thirty patients scheduled for knee surgery under general anesthesia with nerve block for postoperative analgesia had ONB performed using USG and injection of 10 mL 0.5% ropivacaine with epinephrine. Half of the ropivacaine was injected between the pectineus and adductor brevis muscles, and half between the adductor brevis and adductor magnus muscles. The strength of thigh adduction was measured at 5, 10, and 15 mins after injection, and 50% strength reduction at 15 mins indicated a successful block.

Results: All patients showed reduction of strength, and 28 of 30 or 93% met the criteria for successful block with mean strength reduction of 82.2% (SD, 21.6%) at 15 mins. Blocks were completed in 122 secs (SD, 33 secs).

Conclusions: Obturator nerve block using USG to achieve interfascial injection without nerve stimulation had success similar to that reported in studies using nerve stimulation.