Background and indications: Lateral femoral cuTaneous nerve block is useful when sensory anesthesia of the lateral thigh is necessary. In most cases, this block is used in conjunction with femoral nerve block or when a “3-in-1” block does not provide adequate anesthesia of the lateral thigh. The block is also useful in the diagnosis and treatment of meralgia paresthetica.

Anatomy: The lateral femoral cuTaneous nerve is a branch of the brachial plexus. The nerve arises from the L2 and L3 nerve roots. After exiting the intervertebral foramina at these levels, the roots join the plexus and the branches combine to form the nerve, which travels in the space between the quadratus lumborum and psoas major muscles (Fig. 24.1). It then passes under the inguinal ligament and over the sartorius muscle into the thigh, where it divides into an anterior and posterior branch. The anterior branch becomes superficial about 10 cm below the inguinal ligament and supplies the skin of the anterior and lateral parts of the thigh as far as the knee. The posterior branch pierces the fascia lata and passes backward across the lateral and posterior surfaces of the thigh. After the nerve passes medial to the sartorius muscle and distal to the inguinal ligament, it can usually be imaged 2 cm medial and 5 cm inferior to the anterior-superior iliac spine. The nerve appears as a hyperechoic linear streak deep to the fascia iliaca (Fig. 24.2) at a depth of 1 to 3 cm. If the nerve is imaged lateral to the femoral artery and nerve, it can be found deep to the fascia iliaca or in the layer between the fascia iliaca and the fascia lata (Fig. 24.3).