Lateral femoral cutaneous nerve block
Introduction: The lateral femoral cutaneous nerve (LFCN) is a branch of the lumbar plexus. Isolated LFCN block is not commonly performed for two reasons. First, the LFCN innervates a relatively small area of skin on the anterolateral thigh and knee, and therefore indications for surgical anesthesia are limited. Secondly, being a cutaneous nerve it is not a significant nerve for mediating postoperative pain (with the possible exception of skin graft harvasting). LFCN block has been described using common neurolocalizing techniques: a 'fascial click' surface land mark technique medial to the anterior superior iliac spine (ASIS); a nerve stimulation technique and an ultrasound guided technique. 2-5 However, because the LFCN has a highly variable course 1,2 and is a pure sensory nerve, both the surface landmark and neurostimulation techniques have been associated with low success rates.3
Fig. 1. Left inguinal region showing the LFCN crossing superficial then lateral to the sartorius muscle.
Anatomy: The LFCN enters the thigh deep to the inguinal ligament between the anterior superior iliac spine and the (ilio)psoas muscle (Fig. 1). Near the ASIS, the LFCN crosses the sartorius muscle (Fig. 1). At the level of inguinal crease, the LFCN usually lies within a facial pocket (a double sheet reflection of fascia lata) just lateral to the lateral border of the sartorius muscle (Fig 1 and 2).4 In its proximal course in the thigh, it lies deep to the fascia iliaca.1,2 Therefore, local anesthetic injected deep to the fascia iliaca (during fascia iliaca and femoral nerve blocks), may, but not always, spread laterally and block the nerve. 2
The LFCN supplies the skin on the anterolateral aspect of the thigh from the level of the greater trochanter down to the knee. In 1/3 of patients, it also supplies the anterior aspect (Fig 3).1
Fig. 2. LFCN lies within a facial pocket adherent to the lateral border of the sartorius muscle.
1. Isolated LFCN block e.g. for meralgia paresthetica and skin harvesting. 6,7
2. Combined with other lower limb nerve blocks for surgery with an incision over the lateral or anterior thigh (e.g. TKJR, ACLR, above knee amputation).
Skill level: Simple.
Procedure time: Approx. 1-2 min.
Sedation: Minimal required.
Surface landmarks: Probe placement is on the inguinal crease.
Needle: 22G short bevel.
1. High frequency linear probe.
2. 22G short bevel needle.
1. Position: patient supine
2. Place the probe on the inguinal crease and identify the sartorius muscle, which lies superficial and lateral to femoral artery - superficial to the iliopoas and rectus femoris muscles. (Fig. 1 and Fig. 4). It has a characteristic tapering medial end.
Fig. 3. LFCN innervstion (red). In 1/3 of patients, the LFCN also innervates the anterior aspect of the thigh (green).
Fig. 4. The sartorius muscle has a tapering medial end. It lies superficial to the iliopoas muscle.
3. Fellow the sartorius muscle laterally until its curved lateral border is identified (Fig 2).
4. A facial pocket will be visualized adherent to the lateral border of the sartorius muscle; within this facial pocket the LFCN may be seen (Fig. 2, 5).
5. Advance the needle (in- or out-of-plane) and inject 1-5 ml LA.
a) The LFCN lies superficial and runs from medial to lateral (Fig. 1). Therefore, to improve identification, use the highest probe frequency and rotate the lateral end of the probe slightly cephalad.
b) Occassionally, the LFCN divides into 2 or 3 branches at the level of the inguinal crease, and may lie within one or separate pockets.
Fig. 5a,b. LFCN dividing at the level of the inguinal crease into 2 or 3 branches.
c) On rare occasions, the facial pocket containing the LFCN may lie superficial to the sartorius muscle (Fig 6).
d) Injection pain is relatively common during a perineural LFCN injection, possibly due to LA irritation (without intra-neural injection).
Fig. 6. Rarely, the LFCN lies within a facial pocket superficial to the sartorius muscle. In this figure, the LFCN divides into 3 branches.
Video 1. LFCN block description.
1. Corujo A, Franco CD, Williams JM. The sensory territory of the lateral cutaneous nerve of the thigh as determined by anatomic dissections and ultrasound-guided blocks. Reg Anesth Pain Med.2012;37:561-4.
4. Fondi MA, Nava S, Posteraro CM, Vigorita I, Alessandri F, Dauri P. Peripheral nerve block: lateral femoral cutaneous nerve (LFCN): in vivo anatomical study and ultrasound (US) imaging. Reg Anesth Pain Med 2008;33:101.
7. Shteynberg A, Riina LH, Glickman LT, Meringolo JN, Simpson RL. Ultrasound guided lateral femoral cutaneous nerve (LFCN) block: safe and simple anesthesia for harvesting skin grafts. Burns. 2013 ;39:146-9.