This block can be used to provide postoperative analgesia following hip surgery, upper lateral thigh skin grafting, and neurolysis for refractory meralgia paresthetica.
Combined with other lower extremity blocks, it reduces the discomfort from the tourniquet during procedures on the lower leg.
This is a very superficial block, hence a high-frequency transducer is preferred for this block.
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.
With the patient in a supine position, the ASIS is marked and the block needle is inserted at a point 2 cm medial and 2 cm caudal to the ASIS as shown in Fig. 17.1 . The needle is advanced until a “pop” is felt as the needle passes through the fascia lata. Local anesthetic is then injected in a fanlike manner from medial to lateral as illustrated in Fig. 17.2 .