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