Lateral femoral cutaneous nerve block

Anatomy

The lateral femoral cutaneous nerve of the thigh (LFCN) is a pure sensory nerve and a derivative of posterior branches of the lumbar plexus, namely L2 and L3 spinal nerves. It travels downwards along the lateral border of the psoas muscle and continues inferior-lateral towards the anterior superior iliac spine (ASIS), where it angulates acutely and exits in the lower pelvis, under the inguinal ligament, and over the sartorius muscle into the thigh. Near the inguinal ligament the nerve lies beneath the fascia lata. The nerve divides into anterior (main trunk) and posterior branches as it crosses the inguinal ligament. Importantly, it has several distinct patterns of division—the most common being caudal to the inguinal ligament. The anterior branch is roughly 7–10 cm below the ASIS and supplies the skin over the anterolateral aspect of the thigh, while the posterior branch passes through the fascia lata proximal to the division of the anterior branch, and supplies the lateral thigh, from greater trochanter to the midthigh.