Numbness (anteriolateral aspect of the thigh)

The lateral cutaneous nerve of the thigh passes from the lateral border of psoas major across the iliac fossa to pierce the inguinal ligament. It travels in a fibrous tunnel medial to the anterior superior iliac spine and enters the thigh deep to the fascia lata before continuing distally into the subcutaneous tissues:

• lateral cutaneous nerve of the thigh can have one of three origins;
  • L1 and L2,
  • L2 and L3
  • or L3 alone
• divides into its anterior and posterior branches just distal to the inguinal ligament and supplies the anterolateral aspect of the thigh

Compression of the nerve as it passes through the inguinal ligament or as it pierces the fascia lata causes meralgia paraesthetica:

• entrapment of the lateral cutaneous nerve of the thigh is named meralgia paraesthetica or Roth's meralgia
  • it is known complication of several orthopaedic procedures. However, there are many non-surgical causes including seat belts, tight trousers, obesity, pregnancy, intraabdominal or intrapelvic pathology, diabetes mellitus, alcoholism, lead poisoning or it can occur spontaneously (1)

Characteristically, the patient complains of a burning or stinging sensation in the distribution of the nerve over the anterolateral aspect of the thigh. This is aggravated by walking or standing; it is relieved by lying down with the hip flexed:

• presenting complaints include pain, which may be worse on hip extension, paraesthesia and a reduced sensation to touch and temperature in the anterolateral aspect of the thigh
• examination findings include tenderness on palpation, reduced sensation; possibly a positive Tinel's sign (1)

Diagnosis is confirmed by the absence of motor signs and by excluding pelvic and intra-abdominal causes of irritation such as a tumour.

Conservative treatment is usually sufficient. Corsets and tight belts should be avoided. Local nerve blocks may be beneficial. Surgical interventions should be restricted to freeing the nerve; division may aggravate the original symptoms.

Reference:

• 1) Grossman MG, Ducey SA, Nadler SS, Levy AS. Meralgia paresthetica: diagnosis and treatment. J Am Acad Orthop Surg 2001; 9: 336-44.