Peroneal nerve palsy: causes, foot drop, tests and recovery

The common peroneal nerve (also called the fibular nerve) is a branch of the sciatic nerve that runs down the outside of the leg and passes close to the surface just below the knee, near the top of the fibula. It supplies the muscles that lift the foot and toes and carries sensation from the outer shin and the top of the foot. Palsy means weakness or paralysis. Peroneal nerve palsy is therefore weakness of these muscles because the nerve is not working properly.

The NHS page on foot drop describes the practical result: it is difficult to lift or move the foot and toes, it usually affects one foot, and it can affect the way you walk. People often describe the foot slapping down, tripping on kerbs or rugs, or lifting the knee higher than usual to clear the toes.

The NHS says the most common cause of foot drop is an injury to a nerve that runs down the leg and controls the muscles that lift the foot. Because the nerve is superficial near the knee, pressure or stretch there is a recognised route to injury.

• Sports injuries.

• A slipped disc in the spine.

• Crossing the legs, kneeling or squatting for long periods of time.

• Peripheral neuropathy caused by diabetes.

• Hip or knee replacement surgery.

• Not moving for a long time, for example when staying in hospital.

Foot drop is not always a nerve problem at the knee. The NHS lists less common causes including inherited conditions such as Charcot-Marie-Tooth disease, muscle weakness caused by muscular dystrophy, spinal muscular atrophy or motor neurone disease, and damage to the brain or spinal cord from stroke, cerebral palsy, Parkinson's disease or multiple sclerosis.

This is why a clinician examines the whole leg, the back and the way you walk rather than assuming the knee nerve is at fault. A slipped disc in the lower spine can produce a similar picture to a peroneal nerve problem, and the treatment and urgency differ.

The NHS foot drop page gives non-urgent advice to see a GP if you find it difficult to lift the front part of your foot and toes. Peripheral neuropathy more broadly, according to the NHS, can cause numbness and tingling, burning or shooting pain, loss of balance and muscle weakness, especially in the feet. It advises seeing a GP early for pain, tingling or loss of sensation in the feet, loss of balance or weakness, or a cut or ulcer on the foot that is not getting better.

Sudden weakness that comes with other symptoms such as facial drooping, slurred speech, new confusion or loss of bladder or bowel control is a different situation and needs emergency care through 999 or A&E; these are not features of an isolated knee nerve problem. If you are unsure, NHS 111 can advise.

The NHS says a GP will examine your leg and foot and look at the way you walk. You may be referred to a specialist for more tests, such as an X-ray, ultrasound scan or CT scan, to find out what is causing the dropped foot.

In practice a clinician will also ask about recent surgery, injuries, long periods in one position, diabetes and weight loss, and will test the strength of the foot lifting and turning muscles and the feeling over the shin and foot. Nerve conduction studies and electromyography are commonly used by neurologists to show where the nerve is affected and how badly, although the NHS foot drop page does not list them by name.

The NHS says that how foot drop is treated depends on what is causing it and how long you have had it, and that sometimes it gets better on its own. Common treatments include physiotherapy to strengthen or stretch the muscles in the leg and foot, a brace, splint or shoe insert to hold the foot in position, and a small device that gives electrical signals to help the nerves work (electrical stimulation), especially after stroke or in multiple sclerosis.

If there is permanent loss of movement the NHS says surgery may be considered, either to fuse the ankle and foot joints or to repair or graft the nerve. Peripheral neuropathy guidance from the NHS adds that treatment depends on the underlying cause, that some cases may improve with time if the cause is treated and that in others the damage may be permanent.

Recovery is therefore variable. Nerve injury from pressure often improves once the pressure is removed, while injuries from surgery, trauma or a disc problem depend on severity and on treating the cause.

The NHS says there is a higher risk of tripping and falling with foot drop and suggests simple changes to reduce it.

• Wear shoes that fit well and support your feet.

• Use a walking aid, such as a stick, if you need one.

• Keep floors in your home clear and remove trip hazards such as loose rugs and electrical cables.

• Keep the house well lit.

• Fit handrails on stairs and put glow-in-the-dark tape on the top and bottom steps.

On the NHS the starting point is the GP, who can arrange imaging or refer to physiotherapy, orthotics or a neurologist. Waiting times for specialist nerve tests vary. Some people self-refer privately for physiotherapy or a brace; it is still worth telling your GP, because the cause of foot drop needs to be identified rather than only managed.