Lumbar Plexus (T12 - L4)
Subcostal Nerve (T12)
Iliohypogastric Nerve (L1)
Ilioinguinal Nerve (L1)
Genitofemoral Nerve (L1, L2)
Lateral Femoral Cutaneous Nerve (L2, L3)
Femoral Nerve (L2, L3, L4)
Obturator Nerve (L2, L3, L4)
Accessory Obturator (L3, L4)
Lumbosacral Trunk (L4, L5)
Lumbar Plexus is formed from the anterior
primary rami of T12, L1, L2, L3, and half of L4. The lumbar plexus distributes
to the inguinal area, anterior abdominal wall, subinguinal area, anterolateral
and medial thigh. The Subcostal nerve innervates
the pyramidalis muscle, provides general sensation to the suprapubic area, and
occassionally contributes to the lumbar plexus. Its large lateral cutaneous
branch does not divide into anterior and posterior branches but passes downward
over the crest of the ilium several centimeters behind the anterior superior
spine of the ilium. This nerve distributes to the skin of the side of the hip.
The Iliohypogastric nerve innervates the internal abdominal oblique, and transversus abdominus muscles, and provides general sensation to the suprapubic area.
The Ilioinguinal nerve innervates the internal abdominal oblique and transversus abdominus muscles, and provides general sensation to the medial one third of the subinguinal area and the anterior aspect of the genitalia.
The Genitofemoral nerve innervates the cremaster muscle and provides general sensation to the intermediate one third of the subinguinal area. The genitofemoral nerve represents the efferent arm of the cremasteric reflex; the afferent arm is the ilioinguinal nerve. The iliohypogastric, ilioinguinal, and genitofemoral nerves may arise separately or in combination one with another. The iliohypogastric and ilioinguinal nerves emerge at the lateral margin of the psoas major muscle. These nerves lie on the quadratus lumborum and transversus abdominus muscles and course along the iliac crest. The genitofemoral nerve pierces the anterior aspect of the psoas major muscle and continues a course to the intermediate one third of the subinguinal area and the cremaster muscle.
The Lateral Femoral Cutaneous nerve innervates the lateral aspect of the thigh as far inferior as the knee. It emerges at the lateral margin of the psoas major and continues its pelvic course across the iliacus muscle. It passes beneath the lateral aspect of the inguinal ligament above or below the sartorius muscle to distribute to the lateral aspect of the thigh.
The Femoral nerve lies between the psoas major and iliacus muscles. It passes beneath the inguinal ligament and immediately divides into terminal muscular, articular, and cutaneous branches.
The Obturator nerve lies medial to the psoas major muscle. It passes through the lesser pelvis, lateral to the iliac vessels. In the obturator canal the nerve divides into anterior and posterior branches to supply the adductor group of muscles, the hip and knee joints, and a small cutaneous area of the medial thigh.
The Accessory Obturator nerve, when present, courses beneath the external iliac artery to supply the pectineus muscle.
The Lumbosacral Trunk arises from a communicating branch of L4 joining L5. It crosses the ala of the sacrum to contribute to the sacral plexus.