3.17 Sciatic Nerve

Question 1

Outline the Course of the Sciatic Nerve

Answer 1

1. Largest peripheral N. body
   Anterior Primary rami L4-S3
   Main branch Sacral plexus
2. Roots converge anterior surface piriformis
   Exiting inferior portion greater sciatic foramen
   as Sciatic N.

3. Leaves pelvis + enters thigh
passing midway between 
ischial tuberosity 
\+
Greater trochanter

Question 2

Outline the Course of the Sciatic Nerve

Answer 2

4. Descends posterior compartment thigh
   towards pop fossa
5. Divides
   forms 2 main terminal branches
   Tibial and CPN

~6-10cm above fossa
Possible for branches divide more proximally

6. Nerve trunk
   2 nerves bound 1 epineurium
   CPN lateral to Tibial

Question 3

Sciatic Nerve block Using Beck approach - Anterior

Answer 3

Standard preop assess + SLIMRAG

Anterior approach

1. Supine
2. Line 1 ASIS to Tubercle

Line 2 Parallel
Begins @ GT extends to medial border thigh

3. @ junction medial + middle third
   Connect two lines perpendicularly

• Puncture site where perpendicular crosses line 2

Question 4

Sciatic Nerve block Using Beck approach - Anterior

Answer 4

4. 150 mm 
advanced touch femur
withdraw pass under medial border
2-3cm further
average 10-13cm

5. Femoral N stim
   Not uncommon
   (consider fem nerve block first in awake patient)

Question 5

Complications of Sciatic Nerve Block

Answer 5

Needle

1. Mechanical trauma to nerve
intraneuronal injection (Intrafasicular)

2. Inadvertent placement and injury - haematoma
3. Vessel injury

Question 6

Complications of sciatic N Block

Answer 6

Due to LA/

1. Systemic Toxicity d/t IV injection
2. Neuronal ischaemia
   d/t pressure induced by LA
3. Neurotox of LA
   large volumes
4. Drug error
   wrong type/volume/concentration
5. Infection
6. Failure of block
7. Avoiding adrenaline d/t nerve blood supply easily compromised