The network of nerve fibres in the lumbar region, supplying musculature and skin of lower limb is called lumbar plexus. It lies in the substance of psoas major muscle, anterior to the transverse processes of lumbar vertebrae.
It is formed by the anterior rami of the first four lumbar nerves (L1-L4) and from contributions of the last thoracic nerve also known as subcostal nerve (T12). Additionally, the ventral rami of the fourth lumbar nerve also pass communicating branches, the lumbosacral trunk, to the sacral plexus.
The roots of lumbar plexus divide into several cords and the cords combine together to form major nerves of lumbar plexus. These nerves travel through the posterior abdominal wall and reach the lower limb passing in front of the hip joint. With the exception of the obturator nerve which exits the pelvis through the obturator foramen, the larger branches of plexus leave the psoas major at various sites to run obliquely down through the pelvis to leave under the inguinal ligament
The major branches of lumbar plexus are Iliohypogastric Nerve, Ilioinguinal Nerve, Genitofemoral Nerve, Lateral Cutaneous Nerve of the Thigh, Obturator Nerve and Femoral Nerve.
|Nerve||Segment||Motor Function||Sensory Function|
|Iliohypogastric||T12-L1||• Transversus abdominis
• Abdominal internal oblique
|The posterolateral gluteal skin in the pubic region|
|Ilioinguinal||L1||The skin on the upper middle thigh. In males, also the skin over the root of the penis and anterior scrotum
In females, the skin over mons pubis and labia majora
|Genitofemoral||L1, L2||• Cremaster in males||The genital branch – the skin of the anterior scrotum (in males) or the skin over mons pubis and labia majora (in females).
The femoral branch – the skin on the upper anterior thigh.
|Lateral femoral cutaneous||L2, L3||The anterior and lateral thigh down to the level of the knee.|
|Obturator||L2-L4||• Obturator externus
• Adductor longus
• Adductor brevis
• Adductor magnus
|The skin over the medial thigh|
• Quadriceps femoris
|the skin on the anterior thigh and the medial leg
The saphenous nerve is the largest cutaneous branch of the femoral nerve.
|Short, direct muscular branches||T12-L4||• Psoas major
• Quadratus lumborum
• Lumbar intertransverse