Foot drop: causes, evaluation and treatment

What is foot drop?

Foot drop is weakness in the muscles that lift the front of the foot and the toes. Normally these muscles raise your toes as you swing your leg forward, so your foot clears the ground. When they are weak, the toes drag. Many people lift the knee higher than usual to compensate, or the foot slaps down after the heel strikes the floor. Trips and falls are common.^[2,1]

The signal that lifts your foot travels a long way. It starts in the brain, runs down the spinal cord, leaves the lower spine as the L4 and L5 nerve roots, joins the sciatic nerve, and then continues as the peroneal nerve (also called the fibular nerve). A problem at any point along that pathway can cause foot drop, which is why finding the location of the problem is the most important step.^[1,4]

Symptoms

• toes that catch or drag on the floor, or a foot that slaps down when you walk
• lifting the knee higher than usual (a “steppage” walk) to clear the foot
• numbness or tingling on the top of the foot or the outer part of the lower leg, in some people^[3]
• tripping, stumbling or new difficulty on stairs and uneven ground
• weakness that came on suddenly, or gradually over weeks or months

What causes foot drop?

The cause depends on where along the pathway the problem sits.

• The lower back. A pinched L5 nerve root, most often from a disc problem or narrowing of the spinal canal, is one of the two most common causes.^[1] This often comes with back or buttock pain that runs down the leg. See back or foot? finding the source of nerve pain.
• The peroneal nerve near the knee. The nerve wraps around the outside of the knee just under the skin, where it can be squeezed or stretched. This is the most common site of nerve compression in the leg.^[3,5] Causes include injury, long periods of kneeling or squatting, a habit of crossing the legs, and a tight cast or brace.^[4] In one review, habitual leg crossing was the most frequent cause of a compressed peroneal nerve, and most people improved once they stopped.^[2]
• The sciatic nerve, or the nerve plexus in the pelvis. Injury or pressure higher up can weaken the same muscles.^[2]
• The spinal cord or brain. Conditions such as a stroke can cause foot drop, and the treatment is different.^[1]
• Body-wide nerve disease, such as diabetic neuropathy, can make nerves more vulnerable, and it can exist alongside a pinched nerve in the back or knee.^[6]

More than one problem can be present at once. In a small case series, a pinched L5 nerve root and a compressed peroneal nerve at the knee occurred together more often than expected.^[7]

How foot drop is evaluated

Because so many problems can cause it, evaluation is systematic:

• History: how quickly it started, whether you have back pain, whether you had a knee or hip injury, surgery, a cast or weight loss, and what other health conditions you have.
• Examination: the strength of the muscles that lift the foot and toes, the muscles that turn the foot in and out, and the hip. Testing muscles that share the L5 root but are supplied by different nerves helps show whether the problem is in the back or at the peroneal nerve. We also map numbness, tap along the nerve at the knee, and check the back, hip and circulation.
• Nerve studies and EMG: these tests help locate the problem, measure how much nerve damage there is and estimate how well the nerve may recover.^[3,2,8] They are performed by another specialist, such as a neurologist, and we coordinate them and review the results with you. Read more in nerve testing for foot pain.
• Imaging: an MRI of the lower back, or an ultrasound or MRI of the nerve, can show what is pressing on it.^[2]

Treatment options

Treatment follows the cause.

Non-surgical care

• An ankle-foot orthosis (AFO), a light brace that holds the foot up, helps many people walk more safely.^[2]
• Physical therapy to strengthen the muscles that still work, keep the calf and ankle flexible, and improve balance and gait.
• Removing the cause, for example stopping leg crossing, changing a tight brace, or treating the back problem.
• Activity changes and medicine for nerve pain, coordinated with your other clinicians.^[3]

Surgery

Surgery is considered when there is a realistic chance the nerve will recover, or when a cause can be removed. One review suggests that people with foot drop from a compressed peroneal nerve should hear about the option of releasing the nerve at the outside of the knee.^[1] Surgery is usually considered for cases that haven’t improved with non-surgical care, for a mass pressing on the nerve, for a cut nerve, or when nerve studies show severe damage. Results of decompression are typically favorable.^[3]

In a pooled analysis of 368 people who had the peroneal nerve released, ankle-lifting strength improved and serious complications were uncommon. About half (54%) reached full strength. The studies varied in design and quality, so the results are encouraging but not definitive.^[9]

If the nerve is unlikely to recover, or a release didn’t work, options include nerve transfers and tendon transfers, which use other working nerves or tendons to restore the lifting movement.^[3,10] For foot drop that comes from the spine, treatment is directed by a spine specialist. Learn more about nerve decompression and nerve repair and reconstruction.

Recovery and outlook

The outlook depends on the cause, how weak the muscles are, and how long the weakness has been present. Nerves regrow slowly, about a millimetre a day, so recovery is measured in months.^[11] Muscles that go a long time without a nerve signal lose their ability to recover, which is one reason early evaluation matters.^[12] Many people improve, some improve partly, and a brace can keep them walking safely in the meantime.

When to seek care

Have foot drop checked promptly, even if it seems mild. Get an evaluation soon if your toes catch when you walk, you have started to trip, or your foot feels weak or numb after a knee injury, surgery or a long stretch in a cast.