Lumbar Plexus

Question 1

What are the roots of the lumbar plexus and where is it located

Answer 1

Roots: Spinal nerves T12-L4
Location: within posterior part of psoas major (from here it supplies the abdominal wall + lower extremities)

Question 2

What are the branches of the lumbar plexus

Answer 2

> Iliohypogastric
> Ilio-inguinal
> Genitofemoral
> Lateral Cutaneous nerve of thigh
> Femoral nerve 
> Obturator nerve

Question 3

Describe the iliohypogastric nerve branch

Answer 3

• L1 origin
  Sensory: skin of lower abdomen, lower back + hip
  Motor: Internal + external obliques
  : Transversus Abdominis

Question 4

Describe the ilio-inguinal nerve branch

Answer 4

- L1 origin
Sensory: skin of external genitalia 
              : proximal medial thigh
Motor: Transversus Abdominis
          : Internal + External Obliques

Question 5

Describe the genitofemoral Nerve branch

Answer 5

L1-2 origin:

Sensory: anterior thigh (inferior to inguinal region)

Question 6

Describe the Lateral cutaneous Nerve branch

Answer 6

L2-3 origin: Passes under inguinal ligament (medial to ASIS)
Sensory: lateral skin of thigh
*If nerve = compressed (usually in pregnancy/obesity) causes pins + needles/stabbing pain on lateral thigh = meralgia parasthetica

Question 7

Describe the Femoral Nerve branch:

Answer 7

Ventral rami of L2-4
- Runs through Psoas major (deep to inguinal ligament)
- 4cm inferior to inguinal ligament it splits into anterior and posterior divisions
Innervates
- In pelvis:
> Iliacus
> part of pectineus (with obturator nerve)
- Anterior division:
> Sartorius
> Anterior cutaneous branches: intermediate cutaneous nerve of thigh = skin over mid thigh + Medial cutaneous nerve of thigh = skin of medial lower thigh
- Posterior division
> Saphenous nerve (skin of medial leg + foot)
> Quadriceps

Question 8

Describe the Obturator Nerve branch

Answer 8

Ventral Rami of L2-4
- runs deep to psoas major
- exits pelvis via obturator foramen
- travels between adductors + along adductor magnus
> Innervates:
Motor:
- adductor magnus (with sciatic nerve)
- adductor longus
- adductor brevis
- gracilis 
- pectineus (with femoral nerve)
Sensory;
- skin of medial upper thigh
- knee & hip joints - brain can confuse where pain is