Peroneal Neuropathy

Peroneal neuropathy refers to an impairment of the peroneal nerve.  It is the most common neuropathy of the lower extremities.  The common peroneal nerve is the most common nerve in the body to be injured as the result of trauma.  It can be injured by trauma to the knee or to the thigh.

Anatomy

The peroneal nerve branches off of the sciatic nerve in the thigh, where it is known as the common peroneal nerve.  This nerve then runs to the outside of the knee to wrap around the head of the fibula, the narrow cylindrical bone on the outside of the lower leg.  Here, the nerve lies against the bone close to the skin surface and is vulnerable to injury from pressure or direct trauma.

The common peroneal nerve divides into two branches, the superficial peroneal nerve and the deep peroneal nerve.  The superficial peroneal nerve supplies sensation to the outside of the calf and to the top of the foot.  It also powers muscles that lift, or evert, the outside edge of the foot.

The deep peroneal nerve supplies sensation to a small are between the first two toes.  It also powers the muscles that raise the feet and toes as you walk.

Causes

The common peroneal nerve can be injured at any point in the back of the thigh from a variety of trauma, but most injuries of the common peroneal nerve occur in the lower leg at the fibular head.  The most common form of nerve injury in this location occurs from unrelieved pressure during an extended period of leg crossing.  Injury can occur with immobility while under anesthesia, direct trauma to the area, or indirectly as the result of ankle sprains, knee dislocations or with manipulation during hip or knee replacement surgery.  An extended period of squatting can also place sufficient pressure on the nerve to cause the problem.

Symptoms

Numbness, tingling or weakness, including foot drop, can result from peroneal nerve injury.  The type of symptoms and the areas affected depend on the site of nerve injury.  This is based on whether the common peroneal nerve is affected, or if the problem is isolated to the superficial or deep peroneal branches.

Injury to the common peroneal nerve results in foot drop and inversion (turning inward) of the foot.  The patient may not be able to raise the foot or lift the toes while walking and may not be able to evert (turn outward) the foot.  There may be a foot slap when the person walks. Because of weakness in the foot and ankle, the leg often has to be lifted in exaggerated fashion to clear the floor, resulting in a so-called steppage gait.

Diagnosis

History and physical examination are the foundation of all medical diagnosis.  These steps help to identify weak muscles and the location of altered sensation.

Nerve conduction studies can show where the peroneal nerve is injured and whether other peripheral nerves are involved.  Electromyography (EMG) can also help to determine whether the injury is above or below the knee, which branches of the sciatic or peroneal nerves are involved and whether the problem may be coming from nerve root injury at the level of the spine.  EMG testing also helps to determine the prognosis of the injury.

Treatment

Treatment is often based on the type of problem that caused the nerve injury.  Most peroneal nerve injuries respond to rest and the avoidance of those factors, like local pressure or leg crossing, which caused the problem.  Bracing of the foot and ankle helps to improve the gait pattern and makes walking, despite the weakness, less effortful.  Use of the brace is tapered off as ankle strength is regained.

Surgery is reserved for those cases where severe trauma has occurred, nerve injury has resulted from the presence of a tumor or other mass, or if it is clear that the nerve is tethered at the fibular head and surrounding muscles and is not responding to non-surgical treatment.