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)
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.
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.
Cross-sectional anatomy of the lateral femoral cutaneous nerve (LFCN). Shown are the LFCN, sartorius muscle (SaM), and tensor fasciae latae muscle (TFLM). (Reproduced with permission from Hadzic A: Hadzic’s Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia, 2nd ed. New York: McGraw-Hill, 2011.)
Expected distribution of lateral femorocutaneous nerve sensory block.
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).
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
LANDMARKS AND PATIENT POSITIONING