Lateral Femoral Cutaneous Nerve Block

The lateral femoral cutaneous nerve (L2 and L3) emerges at the lateral border of the psoas muscle immediately caudad to the ilioinguinal nerve. It descends under the iliac fascia to enter the thigh deep to the inguinal ligament 1 to 2 cm medial to the anterior superior iliac spine. The nerve emerges from the fascia lata 7 to 10 cm below the spine and divides into anterior and posterior branches. The skin of the lateral portion of the thigh from the hip to midthigh is supplied by the posterior branch; the anterior branch supplies the anterolateral thigh to the knee.

Clinical Applications

This block is useful for skin graft harvesting and can be used in concert with other peripheral nerve blocks for complete anesthesia of the lower extremity.

Technique

A point is marked 2 cm medial and 2 cm caudad to the anterior superior iliac spine. A 22-gauge, 4-cm needle is advanced perpendicular to the skin entry site until a sudden release indicates passage through the fascia lata. As the needle is moved in a fanlike pattern laterally and medially, 10 to 15 mL of solution is injected, depositing local anesthetic above and below the fascia (see Fig. 44-13A ; see Plate 12 in the color atlas of this volume).

The nerve can also be blocked just medial and posterior to the anterior superior iliac spine with 10 mL of anesthetic solution. Combining the two techniques (i.e., belt-and-suspenders method) increases the success rate, but the total volume of solution used may be limiting. Because this is a pure sensory nerve, a nerve stimulator is not helpful in performing this block.

Side Effects and Complications

The extent of anesthesia is quite limited with this block, but there is a low risk of associated complications. Neuritis of this nerve caused by needle trauma or drug toxicity is a potential but unlikely complication. There are no large blood vessels in the vicinity of this nerve, and the likelihood of rapid uptake or intravascular injection is very small.