Lumbar plexus

Plexus lumbalis

NervousNervesWhole bodyLeft and right

View left in 3D View right in 3D

What it is

Formed inside the psoas major muscle by the ventral rami of L1-L4. Its branches emerge around psoas: the iliohypogastric, ilioinguinal and lateral femoral cutaneous nerves from its lateral border, the femoral nerve lower down, the genitofemoral nerve through its front and the obturator nerve from its medial border; part of L4 joins L5 as the lumbosacral trunk.

Function

Supplies the lower abdominal wall, hip flexors, knee extensors and thigh adductors, and the skin of the groin, the front and inner thigh and the inner leg.

Size

Spans ~12 cm inside psoas from L1 to the pelvic brim

Clinical note

A psoas haematoma or abscess can compress the whole plexus, causing groin and thigh pain with a weak knee; surgeons approaching the spine through psoas monitor it with electrodes.