48
Complications of Lateral Femoral Cutaneous Nerve Procedures

Alan Berkman BSc (Hons), MBChB, FFA 1 (SA), FRCPC, FIPP, CIPS¹, María Luz Padilla del Rey MD, FIPP, CIPS, EDPM², and Agnes R. Stogicza MD, FIPP, CIPS, ASRA-PMUC³

¹ Changepain Clinic, University of British Columbia, Vancouver BC, Canada
2 University Hospital Complex of Cartagena, Cartagena, Region of Murcia, Spain
³ Saint Magdolna Private Hospital, Budapest, Hungary

Introduction

Entrapment or damage to the lateral femoral cutaneous nerve (LFCN) presents clinically as meralgia paresthetica (MP). The clinical presentation of anterolateral thigh pain was first described by the German neuropathologist, Martin Bernhardt in 1878, and in 1885, German surgeon Werner Hager postulated that LFCN injury was the cause of this pain. Approximately 20 years later, the Russian neurologist, Vladimir Roth, named the condition meralgia paresthetica (MP) derived from the Greek words “meros” for thigh, and “algos” for pain [1–3].

MP is a painful mononeuropathy presenting in the anterolateral thigh with an incidence of about 32–43 per 100 000 person years. The incidence is significantly increased in diabetes (7 times the incidence in the general population) and obesity [4, 5].

The clinical relevance of the LFCN is related to its course from its origin as spinal nerve roots through the retroperitoneum, then taking a sharp angle at the anterior superior iliac spine (ASIS) and passing under the inguinal ligament ending in the anterolateral thigh.

Entrapment, compression or iatrogenic damage can occur at various areas as the nerve courses from its spinal roots origin to the area innervated by the LFCN in the anterolateral thigh.

The most common area for entrapment occurs as the nerve takes a sharp angle of about 100^o at the inguinal ligament to enter the thigh.

Anatomy

Origin

The LFCN is a pure sensory nerve that originates from the dorsal spinal nerve roots of L2 and L3. The normal cross-sectional area (CSA) of the LFCN at the level of the ASIS is 1–3 mm² [6, 7]. It may be fused with the genitofemoral nerve [8] closer to its origin in some cases (2%) or even distally connected to the femoral nerve [2, 9].

Path

The LFCN courses through the superficial and deep portion of the psoas muscle to reach the lateral border of the muscle. It continues laterally and caudally in between the two layers of fascia over the surface of the iliacus muscle [8]. It then travels through an aponeurotic fascia tunnel, bounded fully by elements of fascia iliaca, fascia lata, the inguinal ligament and the iliopubic tract, and continues distally into the thigh where the peripheral branches pierce this canal [10]. Typically, the nerve passes laterally from the level of the ASIS over the proximal part of the sartorius muscle, and it branches into anterior and posterior branches in the fatty layer between the sartorius and tensor fascia lata (TFL) muscles. However, the course from the ASIS can be variable and the nerve can pass anywhere between 7 cm medial to the anterior superior iliac spine (ASIS) and over 2 cm lateral to it. A review of 205 nerves dissected showed that approximately 60% of the nerve passes medially to the ASIS, with about 30% passing over the ASIS and the remaining 10% passing lateral to the ASIS [11].

Near the ASIS, the LFCN passes under the lateral aspect of the inguinal ligament (IL) in most cases, superiorly over it (in 25–33% of cases) [12], or through it (in 14% of cases) [13]. It may pass superficially to or within the substance of the sartorius muscle as it passes into the thigh, or it may cross over the iliac crest lateral and posterior to the ASIS [14] (Figure 48.1).

**Figures 48.1 (a) and (b)** Identification of the LFCN (marked by arrows) just beneath the fascia lata in the wedge-shaped fatty tissue between sartorius and TFL muscles. “1” on upright image indicates US-probe placement. (*Source*: Courtesy of Agnes Stogicza.)

About 10 cm below the IL, it can divide into up to five terminal branches [6, 14], but normally into the anterior and posterior branches, ending in the skin of the anterolateral thigh.

Neurovascular Relations

As the LFCN approaches the ASIS, it courses under the deep circumflex iliac vessels. The superficial circumflex iliac artery passes over the LFCN below the inguinal ligament. The femoral vessels lie more medially but can be damaged by needle misadventure.

Innervation

The LFCN supplies sensory innervation to the anterior and lateral part of the thigh via, in 60% of cases [15], an anterior and posterior division. This branching is most commonly found around 5 cm below the ASIS [16]. The distal branches terminate in the subcutaneous tissue of the thigh.

Different patterns of branching have been identified. In a cadaver study looking at the course of the LFCN relative to different anterior skin incisions for total hip arthroplasty, Thaler et al. found 70.5% of nerves dissected were closely associated with the sartorius muscle, 13.6% were posterior branching and 15.9% were fan-type branching, which had three or more branches anteriorly [17].

Indications

The indications can be divided into:

Diagnostic:
- – Clinical presentation suggestive of LFCN entrapment with MP (postural changes, tight-fitting belt, pressure from backpack belt) [18, 19]
- – To exclude the LFCN as a cause of non-surgical anterolateral thigh pain
- – To confirm a cause of peri-surgical pain such as in the hip [20, 21], thigh (skin harvesting) [22] knee surgery [23], abdominoplasty, hernia repair or skin graft by using a diagnostic block of the LFCN to determine if this is a pain generator
- – For preoperative US mapping for LFCN surgical decompression [24].

Therapeutic:
- – After positive diagnostic block with addition of steroid
- – To treat iatrogenic and/or idiopathic MP of any cause
- – Perioperative pain management for anterolateral thigh/knee surgical procedures [25]
- – To manage pain and injury from other surgical interventions (abdominoplasty, hernia repair, skin graft or hip surgery) that involve LFCN innervation or course.

As an aid for mobilization after hip/thigh/knee surgery [20].

Indications for Nerve Ablation and Pulsed RF Treatment

MP unresponsive to physical therapy and conventional management.

Contraindications

These may be relative or absolute:

Active local or systemic infection
Coagulopathy
Allergy to anesthetic or injected drugs
Uncooperative patient or failure to obtain consent
Malignancy at injection site.

Techniques

If conservative measures fail after a few months, interventional therapies may be considered. This may include any of the percutaneous procedures, considered from least invasive to more invasive depending on response.

Percutaneous interventional procedures:

Nerve blocks (US guided) with or without steroids
Hydrodissection with dextrose 5%
Pulsed radiofrequency (PRF)
Cryoablation
Peripheral nerve stimulation, generally US guided.

Patient position is normally supine for any percutaneous procedures targeting LFCN.

Landmark-guided Technique

Skin entry is 2–3 cm medial and inferior to the ASIS. Using a fan type injection, about 5 ml volume is distributed.

The positive diagnostic block (confirmed by loss of sensation to pinprick testing of the LFCN normal distribution area 20 minutes after the block) using this approach can be as low as 40% [26, 27]. The use of a nerve stimulator may increase the success rate but may be uncomfortable for the patient and time consuming [14, 27].

Often, this technique is performed for regional anesthesia with more volume (30–40 ml) of local anesthetic which can produce a “3-in-1 block”

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