Chapter 61: Lateral Femoral Cutaneous Nerve Block

INTRODUCTION

The lateral femoral cutaneous nerve (LFCN) is a purely sensory nerve from the lumbar plexus and is derived from the L2-L3 nerve roots. LFCN pain is believed to be associated with obesity, pregnancy, or a constricting belt. Symptoms are thought to be due to entrapment of the LFCN as it passes through or under the inguinal ligament. The LFCN is also at risk of irritation from bone graft due to the nerves close proximity to the iliac crest. Because it is a sensory nerve, symptoms after injury, irritation, or laceration to the LFCN include dysaesthetic pain, numbness and paresthesias localized or radiating to the buttocks or anterolateral thigh. The lateral femoral cutaneous nerve innervates the skin on the lateral part of the thigh and because it is 1 of the 6 nerves that comprise the lumbar plexus, the LFC can be blocked as part of the lumbar plexus block or on occasion with a femoral nerve block.

INDICATIONS

• Diagnosing and treating nerve entrapment (meralgia paresthetica)

• Regional aesthesia

  • Skin grafting from the upper thigh

  • Muscle biopsy

• Postoperative analgesia after hip surgery

• Repeated blocks can function as a treatment for meralgia paresthetica

• Predicting outcome of neuromodulation techniques or surgical neurolysis

RELEVANT ANATOMY

• The lateral femoral cutaneous nerve of the thigh is 1 of the 6 nerves of the lumbar plexus. It arises from the posterior division of the second and third lumbar nerves.

• The nerve traverses the psoas muscle and emerges alone from the lateral aspect of the muscle.

• After crossing the psoas muscle, the lateral femoral cutaneous nerve follows an oblique and lateral course between the iliac muscle and the fascia iliaca in the direction of the anterosuperior iliac spine (ASIS).

• At this point, it provides branches for the peritoneum. It then enters the thigh by passing through or under the inguinal ligament and over the sartorius muscle, where it bifurcates into an anterior and posterior branch (Figure 61-1).

• The anterior branch supplies the anterolateral part of the thigh as far as the knee. It emerges approximately 10 cm below the inguinal ligament.

The distal most fibers communicate with the anterior cutaneous branches of the femoral nerve and the infrapatellar branches of the saphenous nerve creating the peripatellar plexus. The posterior branch pierces the tensor fascia lata and supplies the skin of the superior and lateral aspects of the thigh from the greater trochanter to the middle of the thigh (Figure 61-2).

Anatomical variations that may explain failure of anesthesia after a femoral nerve block:

• Described ...