Anatomic variations of the obturator nerve in the inguinal region: implications in conventional and ultrasound regional anesthesia techniques.

BACKGROUND AND OBJECTIVES This study was conducted to provide a thorough description of the variability in the obturator nerve branching pattern in the inguinal region. METHODS The anatomic variability of obturator nerve branching among 84 dissected embalmed cadavers was investigated. Ultrasound examination of the inguinal region was undertaken in 20 cases and the location of the obturator nerve was identified. RESULTS The point of division for the obturator nerve into the anterior and posterior branches was intrapelvic (23.22%), within the obturator canal (51.78%), or in the thigh (25%). Most commonly, the anterior branch was divided among 3 major muscular branches (66.66%) that innervated the adductor longus, adductor brevis, and gracilis muscles. Four, and 2 subdivisions of the anterior branches were observed, in 4.76% and 28.57% of cases, respectively. The posterior branch predominantly separated into 2 divisions (60.11%), which provided innervation to the adductor brevis and adductor magnus muscles. In addition, either 1 (13.69%), 3 (19.04%), or 4 (7.14%) muscular divisions of the posterior branch were observed. The articular branch of the obturator nerve showed 9 different branching patterns, which most frequently arose from the common obturator nerve. The fascias medial to the femoral vessels and deep to the pectineus muscle were clearly visualized (100%) by ultrasound imaging. This region was used as an "imaging" landmark for localization (success rate of 80%) of the common obturator nerve. CONCLUSIONS High anatomic variability in the obturator nerve's divisions and subdivisions does exist, and explains the difficulty frequently encountered in the application of regional anesthetic techniques.