Lumbar and sacral plexuses

Abstract

The lumbar plexus (Figure 1) is formed by the anterior primary rami of L1-4 nerves. It lies within psoas major on the posterior abdominal wall. All nerves receive grey rami communicantes from the sympathetic trunk. From the plexus emerge: • the obturator nerve (L2-4), supplying the thigh adductors • the femoral nerve (L2-4), supplying iliacus and knee extensors • the lumbosacral trunk (L4-5), which descends over the sacrum to contribute to the sacral plexus • the ilioinguinal (L1) and the iliohypogastric nerves (L1), which obliquely traverse the abdominal wall muscles, supplying them and the inguinal and suprapubic skin • the lateral femoral cutaneous nerve (L2-3), entering the thigh just medial to the anterior superior iliac spine to supply the skin of the anterolateral surface of the thigh • the genitofemoral nerve (L1-2), supplying the skin of the genitalia and the femoral triangle.