Common peroneal nerve dysfunction is a disorder caused by damage to the peroneal nerve, characterized by loss of movement or sensation in the foot and leg.

The peroneal nerve is a branching of the sciatic nerve, which supplies movement and sensation to the lower leg, foot and toes. Common peroneal nerve dysfunction is a type of peripheral neuropathy (damage to nerves outside the brain or spinal cord). This condition can affect people of any age.

Involvement of a single nerve, such as the common peroneal nerve, is classed as mononeuropathy. Mononeuropathy implies a local cause of the nerve damage, although systemic conditions may cause isolated nerve injuries (such as occurs with mononeuritis multiplex).

Damage to the nerve destroys the covering of the nerve cells (the myelin sheath) or causes degeneration of the entire nerve cell. There is a loss of muscle control, loss of muscle tone, and eventual loss of muscle mass because of lack of nervous stimulation to the muscles.

Common causes of damage to the peroneal nerve include the following:

• Trauma or injury to the knee
• Fracture of the fibula (a bone of the lower leg)
• Use of a tight plaster cast (or other long-term constriction) of the lower leg
• Habitual leg crossing
• Regularly wearing high boots
• Pressure to the knee from positions during deep sleep or coma
• Injury during knee surgery.

Another risk is being extremely thin or emaciated (for example, from anorexia nervosa). Systemic conditions such as diabetic neuropathy or polyarteritis nodosa can also cause damage to the common peroneal nerve. Charcot-Marie-Tooth disease (hereditary sensorimotor neuropathy) is an inherited disorder that affects all nerves, with peroneal nerve dysfunction apparent early in the disorder. Also, toxic exposure to chemicals such as polyvinyl chloride or styrene (made during the production of polystyrene) may lead to peroneal and other nerve damage.

• Decreased sensation, numbness or tingling at the top of the foot
• Weakness of the ankles or feet
• Walking abnormalities
• "Slapping" gait (walking pattern)
• Foot drop (unable to hold foot horizontal)
• Toes drag while walking

Examination of the legs may show a loss of muscle control over the legs and feet. The foot or leg muscles may atrophy (lose mass). There is difficulty with dorsiflexion (lifting up the foot and toes) and with eversion (toe-out movements).

Muscle biopsy or a nerve biopsy may confirm the disorder, but they are rarely necessary.

Tests of nerve activity include:

• EMG (a test of electrical activity in muscles)
• Nerve conduction tests
• MRI to look for compressive lesion along nerve

Treatment is aimed at maximizing mobility and independence. The cause should be corrected, if possible, to reduce further damage.

If there is no history of trauma to the area, the condition developed suddenly with minimal sensation changes and no difficulty in movement, and there is no test evidence of nerve axon degeneration, then a conservation treatment plan will probably be recommended.

Corticosteroids injected into the area may reduce swelling and pressure on the nerve in some cases.

Surgery may be required if the disorder is persistent or symptoms are worsening, if there is difficulty with movement, or if there is evidence on testing that the nerve axon is degenerating. Surgical decompression of the area may reduce symptoms if the disorder is caused by entrapment of the nerve. Surgical removal of tumors or other conditions that press on the nerve may be of benefit.

CONTROLLING SYMPTOMS

Over-the-counter or prescription analgesics may be needed to control pain (neuralgia). Other medications may be used to reduce the stabbing pains that some people experience, including gabapentin, carbamazepine, or tricyclic antidepressants such as amitriptyline. Whenever possible, medication use should be avoided or minimized to reduce the risk of side effects.

If pain is severe, a pain specialist should be consulted so that all options for pain treatment are explored.

Physical therapy exercises may be appropriate for some people to maintain muscle strength.

Orthopedic assistance may maximize the ability to walk and prevents contractures. This may include use of braces, splints, orthopedic shoes, or other equipment.

Vocational counseling, occupational therapy, or similar intervention may be recommended to help maximize mobility and independence.

The outcome depends on the underlying cause. Successful treatment of the underlying cause may resolve the dysfunction. Resolution may take several months until the nerve can grow back.

Alternately, if nerve damage is severe, disability may be permanent. The nerve pain may be quite uncomfortable. This disorder does not usually shorten the expected life span.

• Decreased ability to walk
• Permanent decrease in sensation in the legs or feet
• Permanent weakness or paralysis in the legs or feet
• Side effects of medication

Call your health care provider if you have symptoms that indicate common peroneal nerve dysfunction.

Avoid prolonged pressure to the back of the knee. Injuries to the leg or knee should be treated promptly.

If a cast, splint, dressing, or other possible constriction of the lower leg causes a tight feeling or numbness, notify your health care provider.