The accessory obturator nerve is a normal anatomical variant of the lumbar plexus that is often underrepresented and therefore unknown to many specialists, including surgeons, which can lead to serious injuries during surgery. In fact, it is frequently mistaken for other regional nerves, such as the obturator nerve (Read more!). It is present in up to 30% individuals.

The accessory obturator nerve is a mixed nerve that typically arises from the ventral rami of the third and fourth lumbar nerves (L3 - L4). However, it may also receive a contribution from the second lumbar nerve (L2), or it may arise from the second and third lumbar nerves (L2 - L3), or exclusively from the third lumbar nerve (L3). Additionally, it may also originate from the obturator nerve or femoral nerve (this happens rarely).

After arising, the accessory obturator nerve descends within the psoas major muscle (Read more!). It emerges from its medial margin and goes along the posterior abdominal wall toward the ilium. Typically, it then runs alongside the obturator nerve toward the obturator foramen, passing on its lateral side at a distance of 0.79 - 1.18 inches (2 - 3 centimeters). The accessory obturator nerve is usually located medial to the psoas major and femoral nerve. Instead of passing through the obturator canal, it passes over it, crossing the superior pubic ramus beneath the femoral vein.

Once it has passed over the superior pubic ramus, the accessory obturator nerve descends and passes under the pectineus muscle, where it usually divides into several branches. One of the branches is distributed to the hip joint, while another innervates the pectineus muscle, penetrating its deep surface. And finally, the third branch typically forms an anastomosis with the anterior branch of the obturator nerve at its exit from the obturator canal.

Overall, the accessory obturator nerve exhibits multiple variations in its terminal branches. Occasionally, it is very small and supplies only the pectineus muscle. Additionally, this nerve may also give branches to the psoas major muscle along its course.

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Accessory obturator nerve