The Obturator Nerve
The obturator nerve is a major peripheral nerve of the lower limb. In this article, we shall look at its anatomical course, motor and sensory functions, and its clinical significance.
Nerve roots: L2-L4
Motor: Innervates the medial (adductor) compartment of the thigh.
Sensory: Cutaneous branch innervates the skin of the medial thigh.
The obturator nerve is formed by the anterior divisions of the second, third and fourth lumbar nerves.
It descends through the fibres of the psoas major muscle and emerges from its medial border, running posteriorly to the common iliac arteries and laterally along the pelvic wall to the obturator foramen. It then enters the thigh through the obturator canal and splits into anterior and posterior divisions.
The anterior division descends between the adductor longus and adductor brevis muscles towards the femoral artery, giving off branches to the adductor longus, adductor brevis and gracilis muscles. In rare cases it also gives off a branch to the pectineus muscle. It then pierces the fascia lata to become the cutaneous branch of the obturator nerve.
The posterior division descends through the obturator externus muscle before passing anteriorly to adductor magnus and giving off branches to supply it.
The obturator nerve innervates all the muscles in the medial compartment of the thigh except the hamstring part of the adductor magnus, which is innervated by the tibial nerve.
- Adductor Longus – adducts thigh
- Adductor Brevis – adducts thigh
- Adductor Magnus – adductor part adducts and flexes thigh, hamstring part extends thigh
- Gracilis – adducts thigh
- Obturator Externus – laterally rotates thigh
The cutaneous branch of the obturator nerve supplies the skin of the middle part of the medial thigh.
Damage to the Obturator Nerve
The obturator nerve can be damaged during surgery involving the pelvis or abdomen. Symptoms include numbness and paraesthesia on the medial aspect of the thigh and weakness in adduction of the thigh. Alternatively, the patient could present with posture and gait problems due to the loss of adduction.
Obturator Nerve Block
Obturator nerve block is used in the management of pain after lower limb surgery or for chronic hip pain. The anaesthetic is injected inferior to the pubic tubercle and lateral to the tendon of the adductor longus muscle. The procedure can also be carried out under ultrasound guidance.