Lumbar Plexus

The lumbar plexus is a nervous plexus in the lumbar region of the body which forms part of the lumbosacral plexus. It is formed by the ventral divisions of the first four lumbar nerves (L1-L4) and from contributions of the subcostal nerve (T12), which is the last thoracic nerve. Additionally, the ventral rami of the fourth lumbar nerve pass communicating branches, the lumbosacral trunk, to the sacral plexus. The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior part of the thigh.

The plexus is formed lateral to the intervertebral foramina and pass through psoas major. Its smaller motor branches are distributed directly to psoas major, while the larger branches leave the muscle at various sites to run obliquely downward through the pelvic area to leave the pelvis under the inguinal ligament, with the exception of the obturator nerve which exits the pelvis through the obturator foramen.