Lateral Cutaneous Nerve Injection

Meralgia paraesthetica

Causes and findings:
• Entrapment neuropathy due to compression of the lateral cutaneous nerve of the thigh
• Obesity, pregnancy or prolonged static flexed positions
• Sharply defined oval area of numbness over anterolateral thigh
• Occasionally painful paraesthesia
• Tenderness over nerve at inguinal ligament or where the nerve emerges through the fascia

Equipment:
Syringe - 1ml
Needle - 21G 2 inches (50mm) green
Kenalog 40 - 20 mg
Lidocaine - Nil
Total volume - 0.5 ml

Anatomy:
The lateral cutaneous nerve of the thigh arises from the outer border of the psoas and crosses over the iliacus. It passes under or through the inguinal ligament, through the femoral fascia and emerges superficially about 10 cm distal and in line with the anterior superior iliac spine.

Technique:
• Patient lies supine
• Identify tender area at inguinal ligament or at distal point in thigh
• Inject as bolus around compressed nerve, avoiding nerve itself

Aftercare:
Removing the cause is of prime importance, i.e. losing weight, avoiding tight clothing, correcting sitting posture. If the patient is pregnant the compression might be from the growing fetus, and symptoms will normally abate after delivery.

Comments:
Differential diagnoses include referred symptoms from lumbar spine or sacroiliac joint lesions, or local lesions such as hip joint pathology, arterial claudication, herpes zoster. As with other nerve compression injections, the nerve itself must not be injected. If the patient reports increased tingling or burning pain, the needle
point should be moved before the steroid is injected.

Alternative approach:
This lesion often spontaneously resolves. Advice on avoidance of compression and reassurance as to the nature and normal outcome of the condition might be all that is required.