What could be causing numbness above the knee on the outside front left thigh in an adult patient?

Meralgia Paresthetica (Lateral Femoral Cutaneous Nerve Entrapment)

The numbness you describe on the outside front of your left thigh above the knee is most likely meralgia paresthetica, a benign sensory nerve entrapment that causes numbness, tingling, or burning on the anterolateral thigh without motor weakness. 1, 2

Clinical Presentation

The lateral femoral cutaneous nerve (LFCN) provides pure sensory innervation to the anterolateral thigh. When entrapped, patients experience:

• Numbness, tingling, or burning sensation on the outer front thigh, typically above the knee 1, 2
• No motor weakness (quadriceps strength remains normal) 3
• Symptoms may worsen with prolonged standing, tight clothing, or hip extension 2
• Pain quality varies from mild numbness to sharp, burning discomfort 1, 2

Anatomic Entrapment Sites

The LFCN is most commonly entrapped at two locations:

• Inguinal ligament level (most common): as the nerve passes around the anterior superior iliac spine or through the inguinal ligament 2
• Fascia lata of the thigh (less common but important): more distal entrapment at the thigh level, which can be missed if only the inguinal region is examined 1

Diagnostic Approach

A careful neurologic examination is usually all that is necessary for diagnosis and can prevent unnecessarily expensive tests and consultations. 2

Key Physical Examination Findings:

• Sensory loss limited to the anterolateral thigh distribution 1, 2
• Normal quadriceps strength (distinguishes from femoral neuropathy) 3
• Normal patellar reflex 3
• Tinel's sign may be positive over the inguinal ligament or lateral thigh 1
• No hip or knee joint pathology on examination 2

When to Consider Alternative Diagnoses:

• Motor weakness present: consider femoral neuropathy or lumbar radiculopathy 3
• Medial thigh numbness: consider saphenous nerve neuropathy 4
• Bilateral symptoms with bowel/bladder dysfunction: urgent evaluation for spinal cord pathology 5

Risk Factors and Precipitating Causes

Common triggers include:

• Tight clothing or belts compressing the nerve 2
• Pregnancy (hormonal changes and weight gain) 2
• Recent weight gain or obesity 2
• Prolonged standing or walking 2
• Recent pelvic or spinal surgery (iatrogenic injury) 1
• Direct trauma to the hip or thigh 1

Management Algorithm

Step 1: Conservative Treatment (First-Line)

Conservative therapy should be attempted for at least 3-6 months before considering surgical intervention. 2

• Eliminate tight clothing around the waist and hips 2
• Minimize prolonged standing periods 2
• Weight loss if applicable 2
• Oral analgesics (NSAIDs or gabapentin for neuropathic pain) 2
• Reassurance that symptoms are usually self-limited 2

Step 2: Surgical Decompression (If Conservative Treatment Fails)

Surgical therapy has been shown to be effective when conservative measures are inadequate. 1, 2

• Intraoperative exploration should assess both the inguinal ligament and fascia lata levels, as entrapment can occur at either site 1
• Neurolysis or neurectomy of the LFCN provides symptom relief 1, 2

Critical Pitfalls to Avoid

• Do not assume inguinal ligament entrapment only: the LFCN can be entrapped at the fascia lata level more distally, and this must be considered if symptoms persist after inguinal decompression 1
• Do not order expensive imaging routinely: MRI or EMG is rarely needed unless atypical features suggest alternative diagnoses 2
• Do not confuse with lumbar radiculopathy: meralgia paresthetica has pure sensory symptoms without motor weakness or reflex changes 3
• Do not rush to surgery: most cases resolve with conservative management within months 2

When to Refer or Escalate

Refer to neurology or neurosurgery if:

• Progressive motor weakness develops (suggests femoral neuropathy or radiculopathy) 3
• Bilateral symptoms with bowel/bladder changes (urgent spinal cord evaluation needed) 5
• Symptoms persist beyond 6 months despite conservative treatment 1, 2
• Severe pain interfering with daily activities despite analgesics 1