A nerve is a grouping of fibers that transmits information from one part of the body to another, using electrical or chemical signals. Motor nerves convey impulses from the central nervous system (CNS) — which is comprised of the brain and spinal cord — to muscles and organs, while sensory nerves transmit information from the outlying areas of the body to the CNS. The saphenous nerve is a sensory nerve that transmits information from the CNS to the skin on the inside of the leg. It is the biggest and longest branch of a larger nerve called the femoral nerve, which begins at the lumbar nerves and transmits information to the skin and muscle at the front of the thigh.
Nerve entrapment can occur when a nerve is repeatedly compressed over a long period of time, and the saphenous nerve is especially prone to entrapment in many different locations because of its length. Symptoms of entrapment of this nerve may include knee pain, an aching in the thigh or numbness in the leg and foot. A physician who suspects this condition may make the diagnosis simply by injecting a local anesthetic along the line of the nerve. To officially diagnose saphenous nerve entrapment neuropathy, the patient should have pain in the area served by the nerve, demonstrate normal motor function, and the site of entrapment must be tender to the touch.
Patients most at risk for this sort of neuropathy are likely to be over 40 years of age and have a moderate to high rate of obesity in the thigh area. Trauma sustained to the area during contact sports is also a common cause of the condition. Once a diagnosis of saphenous nerve entrapment neuropathy is confirmed, treatment with a local anesthetic, along with rest, may be sufficient. Corticosteroid injections or surgical decompression may be needed in more severe cases.
Since the saphenous nerve is a sensory nerve, a regional block placed on it — which usually involves the injection of a local anesthetic near the nerve — can quickly numb the lower extremity. This allows physicians in emergency departments to perform repairs on patients who have suffered trauma to their lower leg or foot. Many physicians prefer saphenous nerve block over other forms of anesthesia because it usually requires less anesthetic, fewer injections and is better tolerated by most patients. It can also be used to help manage pain after a surgical procedure.