Nerves - Lumbar Plexus

Question 1

What makes up the lumbar plexus?

Answer 1

The lumbar plexus is made up of the anterior rami of L1, L2, L3, L4 and some contribution from the T12 spinal nerve.

Question 2

How many nerves are derived from the lumbar plexus (L1, L2, L3, L4)?

Answer 2

There are six major peripheral nerves of the lumbar plexus.

They descend down against the posterior abdominal wall when they will go onto innervate the structures of the leg.

Question 3

What are the branches of the lumbar plexus?

Answer 3

1) Iliohypogastric nerve
2) Ilioinguinal nerve
3) Genitofemoral nerve
4) Lateral cutaneous nerve of the thigh
5) Obturator nerve
6) Femoral nerve

Question 4

Iliohypogastric

Answer 4

Roots: L1 (with contributions from T12)

Motor functions - internal oblique and transversus abdominis

Sensory function - innervates the posterolateral gluteal skin in the pubic region.

Tip: Iliohypogastric, comes before ilioinguinal. ‘H’ comes before ‘I’.

Question 5

Ilioinguinal

Answer 5

Roots - L1

Motor functions - internal oblique and tranversus abdominis.

Sensory functions - skin of the superior anteromedial thigh. It also supplies the skin over the root of the penis and the anterior scrotum.

In females, it supplies the mons pubis and labia majora.

Question 6

Genitofemoral

Answer 6

Roots - L1, L2

Motor function - genital branch innervates the cremasteric muscle.

Sensory function (genital branch) -

innervates the skin of the anterior scrotum.

Innervates the mons pubis and labia majora in females.

Sensory function (femoral branch) - upper anterior thigh.

Question 7

Lateral cutaneous nerve of the thigh

Answer 7

Roots - L2, L3

Sensory function - innervates the anterior and lateral thigh down to the level of the knee.

No motor function.

Question 8

Obturator

Answer 8

Roots: L2, L3, L4

Motor functions - muscles of the medial thigh - obturator externus, adductor longus, adductor brevis, adductor magnus, gracilis.

Sensory function - skin over medial thigh

Question 9

Femoral

Answer 9

Roots - L2, L3, L4

Motor functions - muscles of the anterior thigh - iliacus, pectineus, sartorius, quadriceps femoris.

Sensory functions - skin of the anterior thigh and medial leg.

Tip: mnemonic for the branch of the lumbar plexus

I, I Get Left Overs on Friday

Question 10

Clinical relevance: lumbosacral plexopathy

Answer 10

This is a disorder affecting either the lumbar or sacral plexi of nerves.

They are rare syndromes, caused by damage to the nerve bundles.

Plexopathy is suspected if symptoms cannot be localised to a single nerve. Patients complain of neuropathic pain, numbness, weakness, or wasting of muscles.

One of the main causes of lumbosacral plexopathy is diabetic amyotrophy or lumbosacral radioplexus neurophagy. In this condition high blood sugar levels damage the nerves.

Idiopathic plexopathy is another cause, which is the lumbosacral equivalent of Parsonage-Turner syndrome (which affectes the brachial plexus).

Tumour and other invasions can compress the plexus.

Treatment: tumours should be removed. For diabetic and idiopathic causes, corticosteroids may be helpful.