Posterior branch of obturator nerve

At a glance

English

Posterior branch of obturator nerve

Latin (TA2)

Ramus posterior nervi obturatorii

System

Nerve

Region

Lower limb

Side

Paired, left and right

About the posterior branch of obturator nerve

The obturator nerve divides as it emerges from the obturator canal. Its posterior branch takes the deeper path: rather than passing over obturator externus, it goes straight through the front part of that muscle, supplying it on the way. It then descends behind adductor brevis and in front of adductor magnus, so that adductor brevis lies between it and the anterior branch.

On the front of adductor magnus the branch breaks into several muscular twigs. These supply the adductor part of adductor magnus, which it shares with the tibial part of the sciatic nerve that serves the hamstring part, and often adductor brevis too, when the anterior branch does not supply it alone.

The branch usually ends as a slender articular nerve to the knee, though this is sometimes missing. It reaches the popliteal fossa either by piercing the lower part of adductor magnus or by passing through the adductor hiatus with the femoral vessels. It then runs down on the popliteal artery, giving it fine filaments, and pierces the oblique popliteal ligament to reach the synovial membrane at the back of the joint.

This knee twig is one reason hip and pelvic problems that irritate the obturator nerve can show up as pain behind or inside the knee, and why a child with hip disease may complain only of the knee. Loss of the posterior branch weakens adduction, especially from the powerful adductor magnus, but leaves skin sensation largely untouched because the branch carries little cutaneous supply. In regional anaesthesia it lies in the plane between adductor brevis and adductor magnus, where it can be blocked on its own, and the articular twig can contribute to posterior knee pain after joint replacement. Surgeons have sometimes cut the obturator nerve branches on purpose to ease severe adductor spasm in cerebral palsy, though this is now done less often.

Course and supply

Arises from

The obturator nerve (L2-L4) at the obturator canal.

Ends in

Muscular twigs on adductor magnus and adductor brevis, and an articular branch ending in the synovial membrane at the back of the knee.

Supplies

Motor to obturator externus, the adductor part of adductor magnus and often adductor brevis; sensory to the posterior knee joint and twigs to the popliteal artery.