Obturator nerve

The obturator nerve, also referred to as nervus obturatorius, originates from the lumbar plexus and is formed by the anterior divisions of the anterior rami of the lumbar spinal nerves L2 to L4. The obturator nerve contributes motor fibers to most of the muscles in the medial thigh compartment, helping with hip adduction. It also supplies sensory branches to the skin of the medial thigh and provides articular branches to both the hip and knee joints.

Course

The obturator nerve begins within the psoas major muscle, arising from the union of the anterior rami of L2 to L4. It travels through the substance of the psoas major and emerges along its medial border near the pelvic brim. From there, it enters the pelvic cavity, where it descends posterior to the common iliac vessels and runs along the lateral wall of the pelvis. Ultimately, the nerve exits the pelvic cavity through the obturator canal, entering the medial compartment of the thigh. Within the canal, it divides into two primary branches: anterior and posterior. These branches are separated by the obturator externus and adductor brevis muscles, which lie between them.

Branches and Pathways

a) Anterior Branch

• The anterior branch travels anterior to the adductor brevis muscle, lying between the adductor longus and brevis muscles. It provides anterior muscular branches for motor innervation to:

  • Adductor longus (L2-L4)

  • Adductor brevis (L2-L3)

  • Gracilis (L2-L3)

  • Pectineus (L2-L3, although the femoral nerve may also contribute)

• It also gives off cutaneous branches that supply sensory innervation to the skin of the medial thigh.

• Additionally, this branch sends articular fibers to the hip joint.

b) Posterior Branch

• The posterior branch passes posteriorly to the adductor brevis muscle and lies on the anterior surface of the adductor magnus muscle. The posterior muscular branches of obturator nerve innervate the following muscles:

  • Obturator externus (L3-L4)

  • Adductor brevis (L2-L3)

  • The portion of adductor magnus that inserts at the linea aspera (L2-L4, with dual innervation from the tibial division of the sciatic nerve for other portions).

• It also provides articular branches to the knee joint.