Lumbar Plexus

Question 1

What is it?

Answer 1

Network of nerve fibres that supplies the skin and musculature of the lower limb

Question 2

Location

Answer 2

Lumbar region within psoas major muscle, anterior to the transverse process of the lumbar vertebrae

Question 3

What forms it?

Answer 3

Anterior rami of the lumbar spinal nerves L1-L4

Also receives contributions from the thoracic spinal nerve T12

Question 4

Branches

Answer 4

Iliohypogastric nerve 
Ilioinguinal nerve
Genitofemoral nerve
Lateral cutaneous nerve of the thigh 
Obturator nerve 
Femoral nerve 
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Question 5

Iliohypogastric nerve

Answer 5

• Roots - L1 (with contributions from T12)
• Motor functions - innervates internal oblique and transverse abdominis
• Sensory functions - innervates posterolateral gluteal skin in the pubic region

Question 6

Ilioinguinal nerve

Answer 6

• Roots - L1
• Motor functions - innervates the internal oblique and transverse abdominis
• Sensory functions - innervates the skin on the upper middle thigh, also supplies skin over root of the penis and anterior scrotum (in males), supplies skin over the mons pubis and labium majus (in females)

Question 7

Genitofemoral nerve

Answer 7

• Roots - L1, L2
• Motor functions - innervates the cremasteric muscle (genital branch)
• Sensory functions - genital branch - innervates the skin of the anterior scrotum (in males), innervates the skin over the mons pubis and labium majus (in females) / femoral branch - skin on the upper anterior thigh

Question 8

Lateral cutaneous nerve of the thigh

Answer 8

• Roots - L2, L3
• Motor functions - none
• Sensory functions - anterior and lateral thigh down to the knee

Question 9

Obturator nerve

Answer 9

• Roots - L2, L3, L4
• Motor functions - innervates obturator externus, pectineus, adductor longus, adductor brevis, adductor magnus and gracilis
• Sensory functions - skin over medial thigh

Question 10

Femoral nerve

Answer 10

• Roots - L2, L3, L4
• Motor function - innervates iliacus, pectineus, sartorius and quadriceps femoris
• Sensory functions - skin over anterior thigh and medial leg

Question 11

Lumbrosacral plexopathy

Answer 11

Rare syndromes caused by damage to nerve bundles in lumbar or sacral plexus
Patients may complain of neuropathic pains, numbness or weakness or wasting of muscles
- Diabetic amyotrophy - blood sugar levels damage the nerves
- Idiopathic plexopathy - lumbrosacral equivalent of Parsonage - Turner syndrome of the brachial plexus
- Tumours - cause damage due to compression
Treatment - tumours and space occupying lesions removed, high dose corticosteroids can be useful