Lumbar plexus

Regarding the anatomy and regional anaesthesia of the lumbar plexus, the following

statements are true EXCEPT which one?

a) The lumbar plexus is described as being derived from spinal nerve roots T12–L4

b) The genitofemoral nerve is of L1–2 spinal root origin

c) The lumbar plexus is embedded in the psoas major muscle

d) A lumbar plexus block combined with a proximal sciatic nerve block can provide

complete anaesthesia for all leg and foot surgery

e) As the skin on the back is less sensitive, a lumbar plexus block is one which is better

tolerated by patients without the need for sedation/analgesia

Answer: e

Explanation

Sources vary on the spinal nerve roots that contribute to the lumbar plexus but

plenty, including Gray’s Anatomy, include a branch from T12 contributing to the

subcostal nerve. Other sources identify L1–L4 only. The spinal roots exit the

intervertebral foraminae and penetrate the psoas major muscle in which they

make some of their divisions and coalitions. When performed well by an experienced

practitioner, combined with a sciatic nerve block and allowing at least

20 minutes onset time, the block is adequate for sole anaesthesia for the leg and foot.

A lumbar plexus block provides excellent analgesia for hip surgery but due to the

many components of innervation of the hip, complete anaesthesia for hip surgery

cannot be guaranteed. The lumbar plexus block is emerging as a block amenable to

ultrasound-guided regional anaesthesia but currently is mostly performed with a

peripheral nerve stimulator. As the needle passes through the paravertebral muscles

and into psoas major, the stimulation of these large muscles is distinctly uncomfortable

and a small dose of alfentanil is recommended as well as some sedation as

necessary.