Lumbar Plexus Block
Coauthored with Susie Eklund
Indications: Hip and proximal femur procedures
Hip preservation surgeries: surgical dislocation, derotational osteotomy; periacetabular osteotomy.
Corrective surgeries (common in cerebral palsy patients): various hip or femoral osteotomies.
Proximal femur fractures: especially when it is cephalad enough that it may not be completely covered by femoral or adductor canal blocks.
Slipped capital femoral epiphysis.
Oncological procedures: radical femur resection, rotationplasty, hemipelvectomy; amputation.
Hip labrum repairs and arthroscopic procedures: alternative to suprainguinal fascia iliaca.
Coverage: Lumbar plexus nerve roots (L2-L4)
Considerations:
Some variability where the plexus can extend from L1 or L5, however, this isn’t consistent.
Peripheral nerves blocked the femoral, lateral femoral cutaneous, and obturator nerves.
Patient Positioning
Lateral with procedural side up (non-dependent).
Flank bump: under dependent flank to extend the contralateral / procedural side and allow more space between the iliac crest and 12th rib.
Positioning is critical for the smallest and largest patients.
Prep the midline into field to allow for identification of lumbar level with midline spine scanning, if needed.
Technique: < 20 Kg: High frequency Linear probe; >20 Kg: Low frequency Curvilinear probe
While there are numerous approaches to conducting this block, we describe the most modern widely-accepted technique. Often combined with stimulation to improve safety and efficacy
Needling
Needle entry in-plane and parallel to the ground, approximately two finger breadths lateral (skyward) from midline (spinous processes).
Do not insert adjacent to probe, but deep and parallel to the ultrasound beam. This creates better needle visualization given the insonation angle of the ultrasound waves.
Once through the ESM, there will be an acoustic shadow that blocks the view of the needle as it passes beyond the TP.
Positioning and potential needle paths (close to probe; parallel to probe)
Anatomy
“Shamrock” view
Start scanning from true lateral (skyward-most aspect in lateral decubitus patient) to identify psoas muscle, quadratus lumborum, anterior vertebral body, transverse process, and erector spinae muscle.
Boney landmarks
Anterior vertebral body and transverse process appear like a “thumbs up” sign, with transverse process vertical if positioning and scanning angles are squared to floor.
Psoas muscle is located in the space between the vertebral body and the transverse process.
Once the needle tip reemerges in the psoas muscle, start stimulation.
Endpoint
Target the posterio-medial quadrant of psoas muscle, where lumbar nerve roots travels.
Sometimes the nerves appear as hyperechoic (bright) band near anterior vertebral body.
Using nerve stimulation in conjunction, begin stimulation when the needle tip advances just beyond transverse process. Aim is to observe patellar snap at 0.6-1.2 mAmps
Stimulation posterior to the transverse process will result in erector spinae complex firing.
QL: Quadratus Lumborum; TP: Transverse Process; LP: Lumbar Plexus
Dosing
Ropivacaine 0.2% with a volume of 0.25-0.5 mL/kg to a maximum of 25mL can be injected in small aliquots with intermittent aspirations to make sure that the needle tip did not migrate intravascularly
Ropivacaine 0.35% can also be used when a denser block is needed (a max dose of 2.5mg/kg)
Additives like dexmedetomidine, clonidine, or dexamethasone can also be added if a longer duration block is desired
Considerations
Continuous catheter-based techniques are well matched for this type of block and the relevant procedures.
The IVC and aorta are deeper to the psoas muscle, so careful visualization of the needle tip and using the anterior portion of the VB is critical to avoid overshooting and advancing the needle too deep.
Careful visualization of vasculature in the psoas compartment is important to reduce the risk of inadvertent vascular puncture. Colour Doppler can help identify the vessels in this space.
This block covers primarily the anterior nerve roots of the hip / lower extremity. It is important to note that additional blocks might be needed depending on the surgical procedure or desired coverage needed.
For example: A QL block can be additive for ilioinguinal/iliohypogastric coverage of iliac crest because iliac screws are often placed during periacetabular osteotomy surgery
Potential Complications
Bleeding: this is a deep plexus block in a very vascular area. Important to evaluate when considering anticoagulation guidelines.
Infection: same risk profile as any other peripheral nerve catheter.
Epidural spread: risk of spread of local anesthetic to the epidural space or contralateral side necessitates assessment of strength of contralateral leg prior to mobilization.
Bowel perforation: due to proximity of peritoneum to the psoas muscle.
Local anesthetic toxicity.
Innervation of the Lower Extremity (via Lumbar Plexus)
Ultrasound Images
The lumbar plexus block, often also called the psoas compartment block, was first described in the 1970s using a landmark-based technique.1 The primary objective is to inhibit the neurotransmission of signals using local anesthetics along the lumbar spinal roots from 2 to 4 (L2-4) with variable inconsistent coverage of L1 and L5. This involves the anterior and medial portions of the hip and thigh. The primary peripheral nerves blocked include the femoral, lateral femoral cutaneous, and obturator nerves. This is critical to note as many of the procedures that this would be considered for often require other additive blocks. Examples include blocking the sciatic nerve, for posterior coverage, or the quadratus lumborum / truncal block for iliohypogastric coverage for more cephalad blockade (T10-12).
This is considered an expert-level block given the proximity to higher risk anatomy. As such, this block should be attempted after extensive training and competency in the field of regional anesthesiology. Complications have been reported such as hematomas and local anesthetic toxicity, so being adept at conducting these blocks and any adverse events is critical.
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Sauter AR, Ullensvang K, Niemi G, et al. The Shamrock lumbar plexus block: A dose-finding study. Eur J Anaesthesiol. 2015;32(11):764-770. doi:10.1097/EJA.0000000000000265
Yörükoğlu UH, Gürkan Y. Combined quadratus lumborum block and lumbar plexus block for a pediatric patient undergoing Ilizarov procedure. J Clin Anesth. 2018;49:40-41. doi:10.1016/j.jclinane.2018.06.002
