Chapter 82A: Lumbar Plexus Block

INTRODUCTION

Lumbar plexus is an advanced regional anesthesia technique, practiced by relatively few, experienced regional anesthesiologists. This is because these techniques have been challenging to master and resulted in frequent failure.^1,2,3 Dogliotti⁴ pointed out, “the nerve trunks of the lumbar plexus which run into the inferior extremity are at a great distance from each other, so much so that in order to produce anesthesia, multiple procedures are necessary with separate injections, for each nerve trunk.” Hence, anesthesiologists preferred the more time-efficient, simpler and reliable techniques of spinal or epidural anesthesia. Several variations of the original technique have been proposed, the main differences in these various approaches being in the level of blockade and the distance from the midline for the needle insertion.^4,5,6 However, given the deep location of the lumbar plexus, various approaches often represent miniscule technical variations rather than clinically relevant modifications. For instance, Chayen’s approach is thought to result in too high incidence of epidural blockade,⁷ but another proposed technique also resulted in a 15% incidence of epidural blockade.⁸ Although ultrasound guidance may allow visualization of the lumbar plexus, the ultrasound guided technique still requires expertise and is technically challenging; refer Chapter 38.^9,10,11 Regardless of which technique is followed, certain safety precautions must be used for successful and safe use of this technique.

Indications

Lumbar plexus block has been used for a number of lower extremity procedures. It has been shown to be particularly useful for femoral shaft and neck fractures, knee procedures, and procedures involving the anterior thigh.^1,12,13,14 However, lumbar plexus block alone cannot provide adequate anesthesia for major surgery of the lower extremity because of the contributing innervation by the sciatic nerve. In one report, even when combined lumbar plexus–sciatic blocks are used for anesthesia in patients undergoing total knee arthroplasty, 22% of patients still required general anesthesia.¹⁵

Regional Anesthesia Anatomy and Management

The lumbar plexus consists of five nerves on each side, the first of which emerges between the first and second lumbar vertebrae and the last between the last lumbar vertebra and the base of the sacrum. As the L2, L3, and L4 roots of the lumbar plexus split off their spinal nerves and emerge from the intervertebral foramina, they enter the psoas major muscle¹⁶ (Figure 82A–1). Within the muscle, these roots then split into anterior and posterior divisions, which reunite to form the individual branches (nerves) of the plexus.¹⁷ The major branches of the lumbar plexus are the genitofemoral nerve, lateral femoral cutaneous nerve, femoral nerve, and obturator nerve (Figure 82A–2). Within the psoas major muscle, the lateral femoral cutaneous and femoral nerves are separated from the obturator nerve by a muscular fold in more than ...