Chapter 33C: Ultrasound-Guided Lateral Femoral Cutaneous Nerve Block

LATERAL FEMORAL CUTANEOUS NERVE BLOCK AT A GLANCE

• Indications: postoperative analgesia for hip surgery, meralgia paresthetica, and muscle biopsy of the proximal lateral thigh

• Transducer position: transverse, inferior to the anterior superior iliac spine; the lateral edge of the sartorius muscle should be visualized with ultrasound

• Goal: local anesthetic spread around LFCN between the tensor fasciae latae and sartorius muscles

• Local anesthetic: 5 mL (adults)

GENERAL CONSIDERATIONS

The lateral femoral cutaneous nerve (LFCN) divides into several branches innervating the lateral and anterior aspects of the thigh. Of note, in 45% of patients, innervation of the LFCN extends even to the anterior thigh.¹ The variable anatomy of the lateral femoral cutaneous nerve makes it challenging to perform an effective landmark-based block. US guidance, however, allows for more accurate needle insertion into the appropriate fascial plane through which the LFCN passes.

ULTRASOUND ANATOMY

The LFCN typically is visualized between the tensor fasciae latae muscle (TFLM) and the sartorius muscle (SaM), 1–2 cm medial and inferior to the anterior superior iliac spine (ASIS) and 0.5–1.0 cm deep to the skin surface (Figure 33C–1).² Ultrasound (US) imaging of the LFCN yields an oval hypoechoic small structure with a hyperechoic rim that can be easily seen in the hypoechoic background. The LFCN can be traced proximally, as it runs from the lateral to the medial edge of the superficial fascia of the SaM. The lateral edge of the SaM is a useful landmark, and as such, it can be relied on throughout the procedure. The posterior branch of the LFCN may sometimes be seen across the anterior margin of the TFLM.

DITRIBUTION OF ANESTHESIA

Block of the LFCN provides anesthesia or analgesia in the anterolateral thigh. There is a large variation in the area of sensory coverage among individuals because of the highly variable course of the LFCN and its branches (Figure 33C-2).

EQUIPMENT

The equipment recommended for an LFCN block is as follows:

• Ultrasound machine with linear transducer (18-6 MHz), sterile sleeve, and gel

• Standard nerve block tray

• Syringe(s) with 10 mL of local anesthetic

• 3–5 cm, 22- to 24-gauge needle

• Sterile gloves

LANDMARKS AND PATIENT POSITIONING

Block of the LFCN is performed with ...