Surgical Treatment of Meralgia Paresthetica

In 1895 Bernhardt and Roth first described lesions of the lateral femoral cutaneous nerve (LFCN) leading to burning and tingling of the anterolateral thigh. Originally termed Bernhardt’s disease, meralgia paresthetica had previously been used to describe any painful dysesthesia of the anterior thigh. Presently, the term meralgia paresthetica refers specifically to a sensory mononeuropathy with coldness, tingling, and burning in the distribution of the LFCN.

69.2 Relevant Anatomy

The anatomical variations of the LFCN are particularly relevant both to understanding the pathological mechanisms that produce the classical picture of meralgia paresthetica and to determining appropriate surgical treatment for cases refractory to conservative therapy. Extensive anatomical studies of the LFCN have revealed several variations in the course of the nerve as it exits the pelvis. The LFCN originates from the posterior divisions of the L2 and L3 ventral rami and emerges from the lateral border of the psoas major muscle below the iliolumbar ligament. The nerve then crosses over the anterior aspect of the iliacus muscle inferiorly toward the inguinal ligament, where it is covered by the iliac fascia. The nerve then usually exits the pelvis just medial and inferior to the anterior–superior iliac spine (ASIS) in a narrow tunnel between the attachments of the inguinal ligament ( ▶ Fig. 69.1). The deep circumflex artery and vein cross the LFCN at this level and can be used as anatomical landmarks to help identify the nerve during surgery. Marked angulation of the nerve occurs as it exits the pelvis. This angulation is increased by extension of the thigh secondary to pull on the inguinal ligament from sartorius muscle contraction during hip extension. This striking angulation of the LFCN as it departs the pelvis often plays a major role in the mechanical compression of the nerve leading to the development of meralgia paresthetica.

Fig. 69.1 The lateral femoral cutaneous nerve can be identified distally along the medial border of the sartorius muscle. The nerve can then be traced proximally to the inguinal ligament and the anterior superior iliac spine. (Reproduced with permission from Kline DG, Hudson AR, Kim DH. Ilioinguinal, iliohypogastric, and genitofemoral nerves. In: Kline DG, Hudson AR, Kim DH, eds. Atlas of Peripheral Nerve Surgery. Philadelphia: WB Saunders; 2001:157–161.)

The exit site of the LFCN from the retroperitoneal portion of the pelvis into the thigh shows considerable variation and has been divided into five classic pathways, types A through E, each of which can lead to compression of the nerve producing meralgia paresthetica. Meralgia paresthetica occurs most commonly in patients with either type B or C variant. In the type B variation, the LFCN exits just medial to the ASIS above the sartorius muscle, whereas in the type C variation, the LFCN exits medial to the ASIS but does not pierce the inguinal ligament as it does in type B, rather the nerve courses beneath the ligament and is enclosed by the sartorius tendon.

After exiting the retroperitoneal portion of the pelvis, the LFCN pierces the fascia lata ~ 4 to 5 cm below the inguinal ligament ( ▶ Fig. 69.2). The nerve then divides into a posterior and anterior branch as it enters the subcutaneous tissues of the thigh. The small posterior branch supplies sensation to the skin from the greater trochanter to the middle of the thigh. The anterior branch supplies the skin of the lateral thigh down to the knee.

Fig. 69.2 Typically the lateral femoral cutaneous nerve (LFCN) runs medial to the anterior superior iliac spine (ASIS). However, the nerve can have an anomalous course exiting the pelvis posterior to the ASIS over the crest of the iliac bone. In this position, the LFCN is vulnerable to injury during anterior iliac crest bone graft harvesting. Therefore, graft harvest should be performed 3 to 4 cm posterior to the ASIS. (Reproduced with permission from Zileli M, Benzel EC, and Bell GR. Bone graft harvesting. In: Benzel EC, ed. Spine Surgery: Techniques, Complication Avoidance, and Management. 2nd ed. Vol 2. Philadelphia: Elsevier Churchill Livingstone; 2005:1253–1261.)

69.3 Patient Selection

Patients with meralgia paresthetica typically complain of numbness, burning, pain, paresthesia, or hypersensitivity over the anterolateral thigh in the distribution of the LFCN. Although the sensory distribution of the LFCN overlaps the L2 and L3 dermatomes, it is distinctly different ( ▶ Fig. 69.3). Symptoms of meralgia paresthetica are usually unilateral, but up to 20% of patients complain of bilateral symptoms.

Fig. 69.3 The sensory distribution of the lateral femoral cutaneous nerve (LFCN, shaded) overlaps the L2 and L3 sensory dermatomes. (Reproduced with permission from Placide RJ, Mazenac DJ. Spinal masqueraders: nonspinal conditions mimicking spine pathology. In: Benzel EC, ed. Spine Surgery: Techniques, Complication Avoidance, and Management. 2nd ed. Vol 1. Philadelphia: Elsevier Churchill Livingstone; 2005:144–159.)

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