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BLOCK AT A GLANCE

Block of the lumbar plexus (femoral, lateral femoral cutaneous, and obturator nerves) at the level of the lumbar paravertebral space in the psoas muscle compartment.

  • Indications: Anesthesia and analgesia for the hip, knee, and lower extremity surgery. Combined with a proximal sciatic nerve block produces complete anesthesia of the ipsilateral lower extremity

  • Goal: Spread of local anesthetic around the lumbar plexus in the psoas muscle compartment

  • Local anesthetic volume: 20 to 30 mL

GENERAL CONSIDERATIONS

The lumbar plexus block is an advanced regional anesthesia technique for hip and knee procedures. Its use has decreased over time due to the technique’s complexity and potential for complications. The main disadvantages of the lumbar plexus block are the deep location of the neural elements and their close proximity to the epidural space, lumbar arteries, and the kidneys. Although ultrasound (US) can be used to help guide needle advancement and local anesthetic (LA) spread, this still requires a high degree of skill. An assessment of the risk-benefit ratio should be made for each patient. The indications for lumbar plexus blocks are declining in favor of more specific, distal nerve blocks, particularly blocks targeting only the sensory branches to the lower extremity joints. These considerations explain the paucity of data on ultrasound-guided lumbar plexus block.

Limitations and Complications

Obtaining adequate US images of the psoas compartment and tracking the needle can be challenging due to its deep location and the complexity of the sonoanatomy. Consequently, the lumbar plexus block is associated with a relatively high-risk failure rate and epidural spread. Given the vascularity of the lumbar paravertebral region, LA toxicity and hematomas have all been reported.

ANATOMY

The lumbar plexus is formed by the union of the anterior primary rami of L1, L2, L3, and a part of L4. It also receives a variable contribution from T12 (subcostal nerve) and L5 (Figure 21-1). After exiting the intervertebral foramen, the nerve roots of the lumbar plexus enter the lumbar paravertebral space, a wedge-shaped compartment between the anterior and posterior insertions of the psoas muscle. The lumbar paravertebral space also contains branches of the lumbar artery and vein. The roots follow a steep caudal course through the psoas compartment within the posterior third of the psoas muscle, close to the lumbar transverse processes. The terminal nerves originating from the lumbar plexus course caudally and laterally along the pelvis in a fan-shape distribution (Figure 21-2).

FIGURE 21-1.

Organization of the lumbar plexus.

FIGURE 21-2.

Anatomy of the lumbar plexus and the posterior abdominal wall.

CROSS-SECTIONAL ANATOMY AND ULTRASOUND VIEW

A cross-section at the level of L4-L5 shows the transverse ...

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