Anterior branch of obturator nerve

At a glance

English

Anterior branch of obturator nerve

Latin (TA2)

Ramus anterior nervi obturatorii

System

Nerve

Region

Lower limb

Side

Paired, left and right

About the anterior branch of obturator nerve

The obturator nerve splits into two as it leaves the obturator canal at the top of the obturator foramen. Its anterior branch passes forwards over the upper border of obturator externus and then descends through the medial compartment of the thigh. It lies on the front of adductor brevis and behind pectineus and adductor longus, so adductor brevis separates it from its partner, the posterior branch, which runs behind that muscle.

Near the foramen the branch sends an articular twig to the hip joint. As it descends behind pectineus it gives motor branches to adductor longus and gracilis, usually to adductor brevis as well, and occasionally to pectineus, which is normally supplied by the femoral nerve. When an accessory obturator nerve exists, the anterior branch receives a communication from it.

At the lower edge of adductor longus the branch becomes cutaneous. Here it links with the anterior cutaneous branches of the femoral nerve and with the saphenous nerve to form a small network, the subsartorial plexus, beneath sartorius. From this network a cutaneous branch reaches the skin of the middle and lower medial thigh, the area that obturator nerve damage leaves numb. A fine filament also runs to the femoral artery in the adductor canal.

Because this branch carries most of the motor supply to the superficial adductors, its injury weakens adduction of the thigh and can give a wide-based, swinging gait; pelvic surgery, tumours and pressure in the obturator canal are typical causes. Its sensory territory is variable and sometimes small. Anaesthetists can block the anterior and posterior branches separately in the space between pectineus and the adductors, guided by ultrasound, to stop the thigh jerking inwards during bladder surgery near the lateral wall, or to add pain relief after knee operations. The hip twig explains why hip disease can be felt as pain in the medial thigh or knee.

Course and supply

Arises from

The obturator nerve (L2-L4), dividing at or just beyond the obturator canal.

Ends in

Ends as a cutaneous branch to the medial thigh skin and a twig to the femoral artery, after joining the subsartorial plexus with femoral nerve branches.

Supplies

Motor to adductor longus, gracilis, usually adductor brevis and sometimes pectineus; sensory to the hip joint and to skin of the medial thigh.