Foot Drop Is Caused by Which Nerve? A Physiotherapist’s Guide

Medically Reviewed by Dr. Venkatesh Mishra, BPT, MPT, Certified Dry Needling Practitioner, VS Physiotherapy Clinic. Last updated October 2026.

Foot drop is most often caused by damage to the common peroneal nerve (also called the common fibular nerve). This nerve wraps around the bony bump on the outside of your leg just below the knee, called the fibular head. It sits so close to the skin there that pressure, injury or surgery can easily affect it. The second most common cause is a pinched L5 nerve root in the lower back, usually from a slipped disc. Less often, the problem lies in the sciatic nerve, the peripheral nerves as a whole, or the brain and spinal cord.

Knowing which nerve is involved matters more than most people realise. A peroneal nerve problem at the knee and an L5 problem in the spine can look almost identical when you watch someone walk, yet they are treated very differently. This guide explains each possibility, how clinicians tell them apart, and what recovery usually looks like.

How your foot lifts: the nerve pathway from spine to shin

Every time you take a step, your brain sends a signal down a chain of nerves to the muscles at the front of your shin. Those muscles pull the foot and toes upward (dorsiflexion) so your toes clear the ground. A break anywhere along that chain can cause foot drop.

The pathway runs like this:

1. Brain and spinal cord. The motor signal starts in the brain and travels down the spinal cord.
2. L4 and L5 nerve roots. The signal leaves the spine through nerve roots in the lower back. L5 carries most of the signal for lifting the big toe and foot.
3. Sciatic nerve. The roots join to form the sciatic nerve, which runs through the buttock and down the back of the thigh.
4. Common peroneal nerve. Just above the knee, the sciatic nerve splits. Its peroneal branch curves around the fibular head on the outer side of the knee.
5. Deep and superficial peroneal nerves. Below the knee it divides again. The deep branch powers tibialis anterior, the main foot-lifting muscle, along with the toe extensors. The superficial branch turns the foot outward and carries sensation from the top of the foot.

When a patient tells us their foot slaps the floor or their toes catch on steps, our job is to work out which link in this chain has failed.

1. Common peroneal nerve: the most common cause

Peroneal neuropathy at the fibular head is the most frequent nerve injury in the lower limb and the usual answer to “which nerve causes foot drop?” At this spot the nerve lies over bone with very little padding, so it is easy to compress.

Common triggers include:

• Habitual leg crossing, especially for long hours at a desk.
• Prolonged squatting or kneeling. This is a frequent cause we see in India, in people who sit on their haunches for work, prayer or farm labour.
• Rapid weight loss, which thins the fat pad that normally cushions the nerve. Doctors sometimes call this “slimmer’s palsy”, and it can follow bariatric surgery or a long illness.
• Tight plaster casts, braces or bandages around the upper calf.
• Long bed rest or surgery where the outer knee presses against a mattress or table edge.
• Knee injuries, including fractures of the fibula, ligament tears and dislocations.
• Knee replacement surgery, particularly when correcting a severe knock-knee deformity.

Typical signs: weakness lifting the foot and turning it outward, with numbness over the outer shin and top of the foot. Back pain is usually absent. Tapping over the fibular head may send tingling down the leg.

2. Deep peroneal nerve

Sometimes only the deep branch is affected. The foot still drops, but turning the foot outward stays normal and numbness is limited to a small patch of skin between the big toe and second toe. Causes include direct trauma to the front of the shin and compartment syndrome, where swelling inside the front muscle compartment squeezes the nerve. Compartment syndrome after an injury is an emergency and needs surgical review the same day.

3. L5 nerve root (lumbar radiculopathy)

A disc bulge or herniation at the L4-L5 level is the classic spinal cause, because it presses on the L5 root as it leaves the spine. Lumbar spinal stenosis (narrowing of the canal), bony spurs and spinal tumours can do the same. If you already have a diagnosed disc problem, our guide to the L4-L5 disc bulge explains how it affects the leg.

What sets L5 radiculopathy apart from a peroneal nerve problem:

• Back or buttock pain, often with pain shooting down the outer leg (sciatica).
• Weak inversion. Turning the sole inward uses tibialis posterior, which is supplied by L5 through a different nerve (the tibial nerve). A peroneal palsy leaves inversion normal; L5 weakens it.
• Weak hip abduction. Gluteus medius, the muscle that lifts the leg out to the side, is also an L5 muscle. A noticeable hip dip when walking points to the spine rather than the knee.
• Numbness over the outer shin, top of the foot and big toe, following the L5 dermatome.

4. Sciatic nerve

The sciatic nerve can be injured higher up, in the hip or buttock. Known causes include hip replacement surgery, posterior hip dislocation, pelvic fractures, and intramuscular injections given too low or too far inward in the buttock. Injection-related sciatic nerve injury is still reported in India and other countries where buttock injections are common.

The peroneal fibres inside the sciatic nerve are more fragile than the tibial fibres, so a partial sciatic injury often looks exactly like a peroneal palsy at the knee. An EMG that tests the short head of the biceps femoris (a hamstring muscle supplied above the knee) helps separate the two.

5. Peripheral neuropathy

Conditions that damage many nerves at once can cause foot drop on one or both sides. The most common is long-standing diabetes. Others include vitamin B12 deficiency, alcohol-related neuropathy, kidney failure, some chemotherapy drugs and inherited conditions such as Charcot-Marie-Tooth disease.

Leprosy deserves a specific mention. The common peroneal nerve is one of the nerves leprosy most often affects, and India still reports a large share of the world’s new cases. Any foot drop with thickened nerves or patches of numb, pale skin needs testing for it, because early treatment protects the nerve.

6. Brain and spinal cord causes

Foot drop is not always a leg nerve problem. Stroke, multiple sclerosis, cerebral palsy, spinal cord injury and motor neuron disease (ALS) can all disrupt the signal before it reaches the nerve roots. Clues include stiffness rather than floppiness, brisk reflexes, weakness in the arm or face on the same side, and slurred speech.

Sudden foot drop with face drooping, arm weakness or speech difficulty is a stroke warning. Call emergency services immediately.

Which nerve is it? A quick comparison

Feature	Common peroneal nerve (knee)	L5 nerve root (spine)	Sciatic nerve (hip/buttock)	Brain or spinal cord
Back pain	Usually none	Common	Sometimes buttock pain	Variable
Foot turning outward (eversion)	Weak	Weak	Weak	Weak
Foot turning inward (inversion)	Normal	Weak	Often weak	Weak
Hip lifting sideways	Normal	Often weak	Normal	Weak
Numbness	Outer shin, top of foot	Outer shin, top of foot, big toe	Outer shin and sole possible	Variable
Reflexes	Normal	Normal or reduced	Ankle reflex may drop	Often brisk
Typical trigger	Leg crossing, squatting, weight loss, knee injury	Disc bulge, stenosis	Hip surgery, injection, trauma	Stroke, MS, ALS

This table is a guide for understanding, not a self-diagnosis tool. A full examination by a physiotherapist, neurologist or orthopaedic specialist is what confirms the source.

How doctors confirm the nerve involved

• Clinical examination. Muscle-by-muscle strength testing, sensation mapping, reflexes and a gait assessment narrow it down quickly.
• Nerve conduction study and EMG. These measure how well the nerve carries signals and whether muscles have lost their nerve supply. They give the clearest picture about three weeks after the onset of weakness, once changes have had time to show.
• MRI of the lumbar spine if L5 radiculopathy is suspected.
• Ultrasound or MRI of the knee to look for a cyst, tumour or scar pressing on the peroneal nerve.
• Blood tests for blood sugar (HbA1c), vitamin B12, thyroid and kidney function when neuropathy is possible.
• Brain or spinal cord MRI when there are signs of a central cause.

A simple self-check at home

These checks can tell you whether you should get assessed. They cannot tell you which nerve is involved.

1. Heel walk. Stand near a wall for support and try walking 10 steps on your heels with your toes off the floor. If one forefoot keeps dropping, that side is weak.
2. Toe tap. Sit with your heel on the floor and tap your toes up and down quickly. Compare both sides.
3. Listen while walking. A slapping sound as your foot lands, or lifting your knee higher than usual on one side (steppage gait), are both signs of foot drop.

Can foot drop go back to normal?

Often, yes, but it depends on the cause and how badly the nerve is damaged.

• Compression without nerve fibre damage (neurapraxia) is the most common situation with leg crossing or squatting. Once the pressure is removed, recovery usually takes a few weeks to about three months.
• Axonal injury, where nerve fibres are damaged, takes longer. Nerves regrow at roughly 1 mm a day, so recovery is measured in months. Because the fibular head is fairly close to the shin muscles, many peroneal injuries still recover well.
• Disc-related foot drop tends to recover better when the pressure on the root is relieved early. Weakness that is severe or getting worse needs a spine specialist’s opinion promptly.
• Progressive conditions such as ALS or some neuropathies may cause permanent foot drop. Here the aim is safe, efficient walking with the right brace and training.

If there is no improvement after three to four months, surgeons may consider nerve decompression, nerve grafting, nerve transfer or a tendon transfer.

Seek urgent care if foot drop comes with loss of bladder or bowel control, numbness in the groin or inner thighs, or weakness in both legs. These can signal cauda equina syndrome, which needs emergency surgery.

How physiotherapy helps foot drop

Physiotherapy does not replace treating the cause, but it protects the ankle, keeps muscles ready for the nerve’s return, and gets you walking safely in the meantime. A typical plan includes:

• Protection first. Stop the habit that compressed the nerve, whether that is leg crossing, squatting or a tight cast. An ankle-foot orthosis (AFO) holds the foot up and prevents trips and falls.
• Calf stretching to stop the ankle stiffening in a pointed-down position, which can make recovery harder even after the nerve heals.
• Electrical muscle stimulation to keep tibialis anterior active while nerve signals are weak. Functional electrical stimulation devices can also lift the foot during walking for some patients.
• Graded strengthening of the shin, toe extensor and outer ankle muscles as they start to switch back on, from assisted movements to resistance band work.
• Gait and balance training so you stop compensating with hip hitching or a high-stepping walk.
• Core and hip work when the cause is in the spine, alongside management of the disc problem itself. Our spinal decompression therapy page explains one option we use for disc-related nerve compression.

Is walking good for foot drop? Yes, walking is good for overall recovery, as long as you are safe. Wear an AFO or supportive shoes if your toes catch, remove loose rugs at home, and use a stick on uneven ground until your strength returns.

Frequently asked questions

Can L5-S1 cause foot drop? The S1 root mostly powers the calf muscles that push you onto your toes, so an L5-S1 disc more often causes weakness in push-off rather than true foot drop. A large or far-lateral L5-S1 disc can still press on the L5 root and cause it.

Can L3 and L4 cause foot drop? L4 contributes to tibialis anterior, so an L4 root problem can cause partial weakness lifting the foot, often with knee weakness and thigh numbness. L3 alone rarely causes foot drop.

Is foot drop an early symptom of ALS? It can be one of the early signs, but ALS is a rare cause. Foot drop that slowly worsens without pain, with muscle twitching or weakness spreading to other limbs, needs a neurologist’s review.

Does foot drop hurt? Peroneal compression is often painless. Pain in the back or down the leg points more toward a nerve root problem.

How long does it take for a foot drop nerve to heal? From a few weeks for mild compression to 12 months or more for significant nerve damage. Steady improvement in the first three months is a good sign.

Get your foot drop assessed

If your foot has started to drag or slap, an early assessment makes a real difference to recovery. At VS Physiotherapy Clinic, Dr. Venkatesh Mishra and our team examine each patient muscle by muscle to find where the nerve signal is breaking down, then build a rehabilitation plan around that cause. Book a visit or call us to discuss your symptoms.

References

• Nori SL, Das JM. Foot Drop. StatPearls, NCBI Bookshelf.
• Foot drop: Symptoms and causes. Mayo Clinic.
• Foot Drop. Cleveland Clinic.
• Foot drop. NHS.

This article is for general information and does not replace a medical diagnosis. If you have new or worsening weakness, please see a qualified healthcare professional.