Meralgia paraesthetica

Entrapment of the lateral femoral cutaneous nerve will cause lateral knee pain, initially related to sports participation. Later on patients will report numbness of the lateral thigh from the greater trochanter to the lateral knee.
Body or trunk shifts can stress the nerve, also adduction of the leg. A traumatic hematoma of the iliacus or stretching in gymnastics can cause paralysis of both the femoral nerve and the lateral femoral cutaneous nerve.
Adiposity, pregnancy, lumbar orthosis and narrow clothing also may cause the problem.

Anatomy

The nerve emerges from the lateral border of the psoas major muscle to run down and laterally around the pelvis lying on the iliacus muscle. An entrapment point is where it goes through an opening or tunnel in the lateral attachment of the inguinal ligament to the anterior superior spine. A second entrapment point is where it pierces the fascia lata.

Diagnosis
Decreased sensation can be found in the lateral thigh. Tests of the lumbar spine are negative. Increase in symptoms can be found with pressure on the iliacus muscle in the area of the inguinal ligament attachment or with pressure on the place where the nerve pierces the fascia lata.
Leg length discrepancy must be evaluated.
Electromyographic investigation could show decreased latency after stimulation.

Treatment
Perineural infiltration of a anesthetic, eventually mixed with a corticosteroid, at the entrapment point may solve the problem. Otherwise surgical treatment, i.e. neurolysis, is suggested.
Leg length discrepancy must be corrected by a heel lift in the shoe or a block on the bicycle cleat.

References
Beazell, JR. Entrapment neuropathy of the lateral femoral cutaneous nerve. JOSPT 10 (3) 1988, 85-86.