Background: Standard anatomy textbooks describe accessory obturator nerve (AON) as small arising from ventral branches of third and fourth lumbar ventral rami. It descends along medial border of psoas major, the accessory nerve emerges from the medial border of the psoas muscle and travels parallel but 2–3 cm ventrolateral to the main nerve. It reaches the thigh by crossing the superior pubic ramus behind the pectineus muscle and then divides into several branches. One branch directly innervates the pectineus, another joins the anterior division of the obturator nerve, and a third conveys sensory input from the hip joint. AON is still under recognized and its presence has great clinical consequences for lumbar plexus blockade. The presence of the AON leads to incomplete anesthesia during obturator nerve block, thus unable to achieve painless hip joint surgeries. The AON may also contribute to continued adductor spasm despite ON blockade. Misidentification of the nerve can also lead to injury. Objective: Looking to the applied anatomy of AON and its anatomical variability, we planned to study the detailed anatomy of AON in human cadavers. Methods: Permission from the Institutional Ethical Committee was obtained before starting the project. We have carried out thorough dissection of lumbar plexus in forty-six cadavers bilaterally. Only one male cadaver had a large retroperitoneal mass distorting the anatomy of concerned region on right side, was excluded from the study. The fibers of psoas major were then meticulously dissected at their origin from the lateral surface of the lumbar vertebra and the accessory obturator nerve was traced till its roots at the intervertebral foramen. The course and branches of AON was carefully recorded. Results: AON was observed in 29 of 91 cases (31%) of cases. Most commonly the AON was forming from the ventral rami of L3 and L4 but in cases AON was taking origin from the trunk of obturator nerve. The branching pattern of AON was variable: AON was connected to obturator nerve in 20 (21%), to anterior branch in 30 (31%) and to posterior branch in 4 (5%) of cases in present study. Pectineus muscle was solely supplied by AON in 13 (14%) specimens. Conclusion: The presence of AON is clinically important as it is also considered during ON blockade. The AON blockade can be indicated in superficial surgeries of thigh, treatment of pain due to thigh tourniquet, as a diagnostic aid for pain syndromes in the hip joint, inguinal areas or lumbar spine, and in relief of intractable hip pain due to osteoarthritis. These anatomical details of AON will help anesthetists, orthopedic surgeons, neurophysicians to perform safe and uncomplicated procedures.

Keywords: Accessory obturator nerve; Obturator nerve block; Branches; Anesthetic; Orthopedic surgeon.