Lumbar Plexus (Psoas) Block

Indications

• The lumbar plexus is formed by contributions from L1-L4 with variable involvement from T12. The nerves travel within the psoas muscle and supply motor and sensory innervation to the lower abdomen and proximal lower extremity. Psoas blocks are commonly used for post-operative analgesia for surgeries involving the hip.

Set-Up

• Insulated 22G, 4 inch stimulating needle
• 30 ml of local anesthetic of choice

Essential Anatomy

• Iliac crests
• Spinous processes of L2, L3, and L4

Technique

• Place the patient in a lateral position with operative side up.
• Draw a line connecting the iliac crests and identify the spinous processes of L2-L4; place a skin mark 5 cm lateral and 4 cm caudad to the spinous process of L3. This will mark the location of the L4 transverse process.
• Prepare the skin with Betadine lotion.
• Infiltrate skin mark with local anesthetic using 25 gauge 1.5 inch long needle.
• Initially set the nerve stimulator current at 2 mA (preferably 2 Hz).
• Insert the stimulating needle perpendicular to the skin angled slightly medially; advance until the needle contacts the transverse process, noting the depth of the needle. If the transverse process is not contacted in approximately 5-6 cm, then reassess insertion point.
• Pull the needle back to the skin and re-direct the needle caudally approximately 15 degrees and advance the needle until the appropriate motor response (quadriceps contraction) is obtained to less than 0.6 mA.
• If no motor response, pull the needle to the skin and redirect the needle slightly more caudal and medial.
• Once stimulation of the lumbar plexus is obtained to less than 0.6 mA, gently aspirate the syringe to rule-out intravascular placement of the needle and inject 30 cc of local anesthetic of choice.

Limitations

• Patients with coagulation abnormalities.
• Patients with lumbar vertebral trauma or inability to be properly positioned.
• Complications
• Inadvertent needle puncture of epidural space, dural puncture, peritoneal puncture, and kidney or ureter puncture.
• As in all peripheral nerve blocks, nerve injury from needle puncture, intraneural injection of local anesthetics, or local anesthetic toxicity.
• Intravascular injection

Identified landmarks

Successful needle placement

Pearls

• Paresthesia from contact of the somatic nerves is more likely elicited when the needle is directed caudad to the transverse process
• Needle contact to the vertebral body should be avoided or the sympathetic chain may be blocked
• A distal sciatic nerve stimulation (posterior tibial n. or common peroneal n.) should be avoided, to reduce the risk of retrograde spread of the local anesthetic into the epidural space (4).

References

1. Bogoch ER, Henke M, Mackenzie T, Olschewski E, Mahomed NN, “Lumbar paravertebral nerve block in the management of pain after total hip and knee arthroplasty: a randomized controlled clinical trial,” J. Arthroplasty 17(4):398-401 (2002)
2. Stevens RD, Van Gessel E, Flory N, Fournier R, Gamulin Z, “Lumbar plexus block reduces pain and blood loss associated with total hip arthroplasty,” Anesthesiology 93(1):398-401 (2000)
3. Serpell MG, Millar FA, Thomson MF, “Comparison of lumbar plexus block versus conventional opioid analgesia after total knee replacement,” Anaesthesia 46(4):275-7 (1991).
4. Turker G. et al, “Comparision of catheter technique psoas compartment block and the epidural block for analgesia in partial hip replacement surgery,” Acta Anesthesiologica Scandinavica 47(1):30-6 (2003).

These technique descriptions are presented for educational purposes and are not intended to substitute for actual hands-on training.