Lateral Femoral Cutaneous Nerve Block

The LFCN is a pure sensory nerve arising from the second and third lumbar nerve roots. Emerging from the lateral border of psoas major muscle, the LFCN runs across the iliacus muscle traveling toward the ASIS. The nerve travels under the inguinal ligament medial and close to the ASIS. On entering the anterior compartment of the thigh region, this nerve runs in a lateral and caudad direction and divides into anterior and posterior branches. The diameter of LFCN at the level of inguinal ligament is approximately 3mm.

Lateral femoral cutaneous nerve block is useful in the evaluation and management of lateral thigh pain thought to be mediated by the lateral femoral cutaneous nerve, including meralgia paresthetica.

The technique can also be useful in providing surgical anesthesia for harvesting of skin grafts from the lateral thigh and in relieving tourniquet pain.

Lateral femoral cutaneous nerve block with local anesthetic can be used as a diagnostic tool when differential neural blockade is performed on an anatomic basis in the evaluation of lateral pain to differentiate peripheral nerve entrapment from lumbar radiculopathy.

Injections are generally avoided in patients with systemic infection or skin infection over puncture site, bleeding disorders or coagulopathy, allergy to local anaesthetics or any of the medications to be administered.

The procedure is done on an outpatient basis. The procedure is performed under ultrasound guidance to ensure accuracy of needle placement. Patients need to be aware that the outcome of the procedure is variable and they may not receive the desired benefits. Similarly, they must be aware of the transient nature of the therapeutic benefits and that there may need repeated injections.

Generally a mixture of local anaesthetic and steroid is injected. The local anaesthetic is probably responsible for immediate pain relief, whereas steroids are believed to be responsible for pain relief 2–6 days after their administration. For a diagnostic block, a short-acting anaesthetic alone is sufficient.

Though landmark technique is well described in literature, the whole course of the LFCN as well as its formation is highly variable among individuals. Thus the LFCN may not be found immediately medial to the ASIS. Ultrasound guided technique can reliably identify the nerve and be very useful in ensuring a successful block.

The lateral femoral cutaneous nerve is usually visualized as a relatively hyperechoic nerve structure in the proximal thigh (several cm inferior to the anterior superior iliac spine) within a fat filled hypoechoic space. This space is found between the sartorius muscle medially and the tensor fascia lata muscle laterally. The nerve is covered by the fascia lata, thus the nerve is subfascial.

Patients who get temporary relief from lateral femoral cutaneous nerve block may be suitable for lateral femoral cutaneous nerve ablation (pulsed radiofrequency treatment). This is likely to provide long-term pain relief.

Complications are rare, particularly if the injections are performed using a precise needle-positioning technique. Possible complications include bruising, infection, hematoma, nerve injury and reaction to the injectates. Infection can be avoided with appropriate aseptic precautions. Severe allergic reactions to local anaesthetics are uncommon. Steroid injections may produce local reactions, occurring most often immediately after injection. These local reactions last for 24 to 48 hours, and are relieved by application of ice packs. Post-procedural pain flare-up may occasionally occur, and may be treated with painkillers. Neurological complications including paraesthesias and numbness have been described but are rare.