Thigh nerve entrapment is a neuropathy caused by the compression of the lateral femoral cutaneous nerve, which provides sensation to the outer thigh. The condition is also termed meralgia paraesthetica (from ancient Greek: meros = thigh; algos = pain) or Bernhardt-Roth Syndrome as firstly described by Bernhardt in 1878.
The lateral femoral cutaneous nerve arises at the lumbar spine from the innervations of the lumbar nerve roots (L2, L3). It runs from these vertebrae to the pelvis under the inguinal ligament to innervate the upper thigh. The lateral femoral cutaneous nerve has sensorial and no motor function. This nerve is mostly compressed by the inguinal ligament extending diagonally from the iliac crest to the pubis. The pathology results into partial damage to the nerve with loss of the protective myelin sheath. Its compression leads to typical sensory symptoms on the skin of the upper, lateral thigh like a burning sensation, tingling and numbness. A neuropathy of the lateral femoral nerve can also arise following trauma or as an injury during surgery at the groin area (e.g. inguinal hernia).
The compression of the lateral femoral nerve can be caused by a number of factors:
Intensive sport activity involving the abdominal musculature (gymnastics, baseball, soccer, weight-lifting)
Trauma (seat belt compression of lower abdomen in car accidents)
Standing, walking or cycling for prolonged periods of time
Tumor growths of the pelvic area compressing the nerve
Neuroma or benign tumors of the nerves
Diabetes neuropathy (affecting several nerves)
Leading risk factors for the development of compression lateral femoral cutaneous nerve are:
Age between 30 and 60 years
Intensive physical training
Obesity: pressure on the nerve of excessive weight
Medical conditions: diabetes, thyroid disorders
Pregnancy increased weight in the groin area
Iatrogenic injury during surgery in the lower abdomen (hip replacement, iliac crest bone grafting)
Wearing tight clothes
Use of heavy tool belt
The symptoms of lateral femoral cutaneous nerve compression mostly involve the upper and outer side of the thigh causing altered sensation with stimuli such as heat and touch. Symptoms may increase with movement (e.g. hip extension: legs moved backwards) and subside by lying down with the knees flexed. Most common symptoms are:
Pain in the groin area and buttocks (seldom)
Clinical examination is usually sufficient for the diagnosis of lateral femoral cutaneous nerve entrapment. Medical history is critical to pinpoint physical activities, chronic diseases or changes in body weight that may have leaded to the neuropathy.
Clinical examination is performed to acquire information on the type, location and intensity of sensory symptoms that have arisen.
X-ray is only performed to exclude other pathologies of the pelvis and hip (avulsion fracture of anterior superior iliac spine)
Electromyography is a test to assess muscle and nerve function through electric stimulation with an electrode implanted in the thigh muscle and recording neural activity. The function is usually unchanged in thigh nerve entrapment.
Nerve conduction study is similar to the previous although the electrodes are located onto the skin and the stimulation only triggers the nerve and not the muscle.
Nerve blockade via injection of anaesthetic into the lateral femoral cutaneous nerve confirms the diagnosis of entrapment when the symptoms subside with the injection.
Other investigations include:
Blood tests for diabetes and thyroid dysfunction
Identifying tumours or metastases to the iliac crest, uterine fibroids, chronic appendicitis
Conservative treatment is usually successful to relieve the symptoms of a femoral cutaneous nerve entrapment. The prognosis lasts between few weeks to months. In pregnancy this condition is usually transitory.
Anti-inflammatory therapy with NSADs
Local injection of steroids (severe symptoms)
Pain killers (analgesics)
Anti-seizure medications (gabapentin, pregabalin, phenytoin)
Life style changes
Reducing intense sport training
Avoid prolonged standing and walking
Wearing loose clothes and belts
Surgery is only performed in case of severe and ongoing symptoms. It consists of nerve release or decompression with or without transposition of the nerve or nerve repair in case of injury. It usually results in poorer prognosis. A 2-3-cm incision along the inguinal ligament is achieved followed by dissection of the soft tissues (fascial planes) to identify the nerve. At the crossing point of the ligament and nerve, the ligament is incised followed by nerve decompression.
In parallel to conservative treatment to control inflammation and neuropathic pain, the patient undergoes physiotherapy to improve the symptoms as follows:
Strengthening exercise of the hip
Activity modifying regime
Return to sport plan
Weight loss program
The approach for preventing lateral femoral cutaneous entrapment can only be partially achieved by modifying some life style activities. These include:
Maintenance of muscular strength and flexibility in the abdomen, hip, pelvis and buttocks
Avoid premature return to sport
Reduce sport intensity
Include stretches and warm-ups before sport
Reduce periods of standing, walking and intense physical activities
Prevent weight gain
Avoid wearing tight clothes and belts
Monitor onset and progress of neuropathies in chronic diseases (diabetes)