Lateral Femoral Cutaneous Nerve Block
The lateral femoral cutaneous nerve (LFCN) arises from the dorsal divisions of L2-3. After emerging from the lateral border of the psoas major muscle, it courses inferiorly and laterally towards the anterior superior iliac spine (ASIS). It then passes under the inguinal ligament and over the sartorius muscle into the thigh, where it divides into two branches (anterior and posterior). The LFCN, a small subcutaneous nerve located between the fascia lata and iliaca, provides sensory innervation to the lateral thigh.
- Position the patient supine with the leg extended in the neutral position.
- Expose the groin and mark the anterior superior iliac spine (ASIS).
- After skin and transducer preparation, place a linear transducer with the appropriate frequency range (10-12 MHz) immediately medial to the ASIS along the inguinal ligament. The lateral end of the transducer is placed on the ASIS. Scan medially and inferiorly from the ASIS.
- Optimize machine imaging capability; select appropriate depth of field (usually within 1-2 cm), focus range and gain.
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Transducer medial and inferior to the right anterior superior iliac spine (ASIS) and inferior to the inguinal ligament (IL). |
- Perform a systematic anatomical survey medial and inferior to the ASIS. The LFCN is expected to lie in the subcutaneous plane deep to the fascia lata and superficial to the fascia iliaca below the ASIS.
- Identify the ASIS which casts a bony shadow. Then move the transducer medially and inferiorly to locate the fascia lata, the fascia iliaca and the sartorius muscle. The LFCN, a small hypoechoic structure is often found in the interfascial plane above the sartorius muscle.
- Percutaneous nerve stimulation further confirms nerve identity.
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Sonogram of the right lateral femoral cutaneous nerve (arrowhead) below the inguinal crease.
FI = facia iliaca
FL = fascia lata
SAR = sartorius muscle |
IN PLANE NEEDLE INSERTION APPROACH
- Ultrasound guided LFCN block is considered an INTERMEDIATE skill level block because the nerve is small and may not be clearly visualized in the subcutaneous plane.
- Insert a 5 cm 22 G needle inline with the transducer and the ultrasound beam.
- Insert the needle at a shallow angle to enter the skin surface to reach the plane between the fascia lata and iliaca immediately medial and inferior to the ASIS.
- If the nerve cannot be visualized, place the needle immediately medial and inferior to the ASIS close to where the sartorius muscle attaches to the ASIS.
- Hydro dissection with saline in the plane between the fascia lata and iliaca may enhance the visibility of LFCN after introduction of a hypoechoic fluid collection.
Lateral Femoral Cutaneous Nerve Block (In Plane Approach)
Scanning the Lateral Femoral Cutaneous Nerve
- Hurdle MF, Weingarten TN, Crisostomo RA, Psimos C, Smith J: Ultrasound-guided blockade of the lateral femoral cutaneous nerve: technical description and review of 10 cases. Arch Phys Med Rehabil 2007; 88: 1362-4.