PNS: Lateral Femoral Cutaneous Nerve

• The lateral femoral cutaneous nerve originates from the lumbar plexus, specifically from nerve roots L2-L3.
• This nerve is sensory, it does not contain any motor fibers.
• The lateral femoral cutaneous nerve is located between the ASIS (anterior superior iliac spine) and the femoral nerve.
• The lateral femoral cutaneous (LFC) nerve is more lateral and quite close to the ASIS.
• The femoral nerve is typically in the middle of the ASIS and the pubis, positioned just lateral to the femoral artery.

Function

• The LFC nerve lacks motor function.
• It provides sensory function to the skin over the lateral thigh.

Palpation

• The LFC nerve emerges from underneath the inguinal ligament, very close to the ASIS.
• It runs superficially between the muscle and skin.
• It is typically first palpable just medial to the sartorius tendon.
• The nerve crosses the thin band of the sartorius muscle.
• It remains superficial as it sends small branches fanning out over the tensor fasciae latae (TFL) and vastus lateralis muscles.
• The area of innervation of the nerve continues down the lateral thigh to the lateral aspect of the distal thigh and, in some cases, the lateral patellar retinaculum.
• Muscle tone remains unchanged with injury to the LFC nerve.
• Palpation is primarily for sensation over the lateral thigh.

Meralgia Paresthetica

• This is the name for the condition caused by compression of the lateral femoral cutaneous nerve.
• Meros means thigh, algos means pain
• It is a compressive mononeuropathy which often presents as burning pain in the anterolateral thigh.
• The goal of treatment is to alleviate compression.
• Compression commonly occurs below the inguinal ligament, as the nerve travels through a fibrous tunnel to emerge from the pelvis.
• Compression can also result from tight clothes, belts, or equipment worn over the top of the nerve.
• Treatment options include surgical decompression, injections (steroid or nerve block), or conservative management like weight loss, physiotherapy, or massage therapy.
• Meralgia paresthetica can involve any grade of nerve injury.
• Neuropraxia results from internal compression from soft tissue or external compression from clothes, belts, or equipment.
• Axonotmesis or neurotmesis results from iatrogenic causes, such as post-surgery, post-injections, or the presence of pathology like diabetes or other metabolic pathologies.

Etiology

• The most common cause is entrapment at the inguinal ligament.
• Other causes include trauma (seat belt in MVA), pregnancy/delivery (hips in flexion), tight clothing, and surgery (hernia).
• The incidence is higher in people with diabetes compared to those without diabetes.

Signs & Symptoms

• Symptoms occur in the upper lateral thigh, including numbness, paresthesia, and burning pain.
• Walking and standing aggravate symptoms, while sitting relieves them.
• It is usually unilateral.

Differential Diagnosis

• Consider and rule out trigger points in the vastus lateralis, vastus intermedius, gluteus minimus, and TFL muscles.
• Radiculopathy - L2 dermatome
• Lumbar cutaneous nerves (iliohypogastric, subcostal) will have associated low back pain wrapping around obliques and be more proximal than the LFC distribution

Precautions

• Working in the area may exacerbate symptoms if the nerve is badly irritated.
• Ensure symptoms do not increase when applying pressure in the area of the nerve.
• Stop trying to directly decompress or mobilize the nerve if recreating or producing symptoms persist beyond when pressure is removed.
• Always ask how quickly symptoms dissipate after pressure removal.

Treatment

• Skin rolling the entire lateral thigh
• Cross-hands around ilium / inguinal ligament and abdomen
• Address any active TrP which refer into area
• Bow inguinal ligament
• Thigh 3D wringing either supine or supine with hip flexion
• Side-lying lift skin and mobilize nerve (hip flex-ext)
• Supine lift skin and mobilise nerve (knee flex-ext)
• Techniques should be modified to suit the healing stage and severity of the condition, less direct for acute or severe cases.

Other info

• Neuropraxia typically results from internal or external compression.
• Axonotmesis or neurotmesis typically results from iatrogenic causes or underlying pathologies.

Home Care

• Modify ADLs around external compression sources like clothes and belts.
• Encourage posterior pelvic tilt to slacken the inguinal ligament.
• Lift skin and flex hip while standing.

Assessment

Prone Knee Bending Test

• The cervical spine is rotated to the same side
• The hip is extended and adducted
• The knee is flexed as much as possible
• A positive test recreates the patient's symptoms

Pelvic Compression Test

• The patient lies on their side with the affected side up
• Downward pressure is applied to the pelvis for 45 seconds
• The patient is asked if their symptoms have dissipated after 30 seconds
• If symptoms dissipate, the test is positive

Tinel's Sign

• Tapping over the LFC nerve below the inguinal ligament may recreate symptoms