Twitching of the Pectineus Muscle Under Ultrasound-Guided Complete Obturator Nerve Block at the Inguinal Crease: A Case Report

Introduction: This report showed that clinically significant adductor muscle contraction can be possible even when the anterior and posterior branches of the obturator nerve are completely blocked. Case Presentation: A 66-year-old male patient visited Gil Medical Center, Gachon University College of Medicine, Incheon, South Korea during the year 2016. He underwent transurethral resection of the bladder (TURB) of a bladder tumor under spinal anesthesia and obturator nerve block (ONB). ONB was performed at the right-side inguinal crease by an ultrasound-guided block of the anterior and posterior branches. At the beginning of surgery, he exhibited grade IV obturator reflex; therefore, general anesthesia was applied and the surgery completed. After the effect of neuromuscular blockade had been completely reversed, we confirmed twitching of the pectineus muscle by ultrasound using a nerve stimulator (stimulation current 0.3 mA). Main branches of the right obturator nerve were still completely blocked when we rechecked the previously blocked-site (stimulation current 2 mA). Conclusions: The described case cautions that investigators must be aware more than two branches may pass adjacent to interfascial layers at the inguinal crease level and that a missed obturator nerve branch might result in severe adductor muscle contraction. We report this observation and suggest the possibility of an anatomical variant that requires the need for nerve stimulation and ultrasound for obturator nerve block verification.