26 - 30 Physiology SBAs for the Primary FRCA

26 - 30 Physiology SBAs for the Primary FRCA
Photo by Unseen Studio / Unsplash

Question 26

You are anaesthetising a 74 year old woman for a total hip replacement, and elect to perform a lumbar plexus block.

Which nerve is not likely to be affected?

  • Genitofemoral nerve
  • Ilioinguinal nerve
  • Sciatic nerve
  • Femoral nerve
  • Obturator nerve


  • Sciatic nerve

A lumbar plexus block targets the nerve roots from L1-5, affecting the following nerves:

  • Subcostal
  • Iliohypogastric
  • Ilioinguinal
  • Lateral cutaneous nerve of the thing
  • Femoral
  • Genitofemoral
  • Obturator

The bigger the dose of local anaesthetic given during a lumbar plexus block, the more of these will be blocked.

The sciatic nerve originates from the lumbosacral plexus (L4-S3) and will not be affected by a lumbar plexus block.