Obturator nerve

At a glance

English

Obturator nerve

Latin (TA2)

Nervus obturatorius

System

Nerve

Region

Lower limb

Side

Paired, left and right

About the obturator nerve

The obturator nerve is formed in the substance of psoas major from the front divisions of the ventral rami of L2, L3 and L4; the L3 contribution is the largest and the L2 one often slight. It is the main nerve of the medial, adductor compartment of the thigh, in the way that the femoral nerve serves the front and the sciatic nerve the back.

The nerve leaves psoas at its medial border close to the pelvic brim, unlike most of its plexus neighbours, which emerge laterally. It passes behind the common iliac vessels and lateral to the internal iliac vessels, then runs forwards along the lateral pelvic wall on obturator internus, above and anterior to the obturator artery and vein. At the top of the obturator foramen it passes through the obturator canal into the thigh, where it divides into anterior and posterior branches. These are kept apart first by some fibres of obturator externus and then by adductor brevis.

Its motor supply covers obturator externus, adductor longus, adductor brevis, the adductor part of adductor magnus and gracilis, and sometimes pectineus. It does not supply obturator internus, despite the name; that muscle has its own nerve from the sacral plexus. Sensory fibres reach a variable patch of skin on the medial thigh and twigs go to both the hip and the knee joints.

Its position on the pelvic side wall puts it at risk in pelvic operations, from tumours and pelvic fractures, and in an obturator hernia, which can press on it and cause pain down the inside of the thigh to the knee. Injury weakens adduction and may leave a small area of numbness. Because its fibres run near the lateral bladder wall, an obturator nerve block is added during some bladder resections to stop sudden adductor jerks, and it is also used with other blocks for knee surgery. Shared supply of hip and knee explains why hip disease may be felt as knee pain.

Course and supply

Arises from

Ventral rami L2-L4 (their anterior divisions), uniting within psoas major; emerges from the muscle's medial border at the pelvic brim.

Ends in

Divides at the obturator canal into anterior and posterior branches that end in the adductor muscles, medial thigh skin and the hip and knee joints.

Supplies

Motor to obturator externus, the adductors, gracilis and sometimes pectineus; sensory to the medial thigh skin and the hip and knee joints.