The Lumbar Plexus Quiz

See Obturator. Option D is correct. The obturator nerve comes from L2, L3 and L4, the anterior divisions of the lumbar plexus (the network of nerves formed from the front branches of the upper lumbar spinal nerves). It emerges from the inner border of psoas major, runs along the side wall of the pelvis and leaves the pelvis through the obturator canal, a small channel through the membrane that covers the obturator foramen (the large opening in the hip bone). In the thigh it divides into anterior and posterior branches that supply the muscles of the medial compartment (the inner thigh): adductor longus, adductor brevis, the adductor part of adductor magnus, gracilis and obturator externus. Together they adduct the thigh, which means they pull it towards the midline, the movement you make when you squeeze your knees together. The hamstring part of adductor magnus is the exception, because it is supplied by the tibial nerve and helps to extend the hip. The nerve also supplies a patch of skin on the middle of the inner thigh. If it is damaged, for example during pelvic or abdominal surgery, adduction of the thigh is weak, the inner thigh may be numb, and the gait can be affected.

• Roots: L2, L3 and L4
• Course: leaves the pelvis through the obturator canal
• Motor: supplies the muscles of the medial compartment of the thigh, which adduct the thigh
• Exception: the hamstring part of adductor magnus is supplied by the tibial nerve