If you can’t lift your foot upward at the ankle, you’re likely experiencing a condition called foot drop. It’s caused by weakness or paralysis of the muscles along the front of your lower leg, and it almost always traces back to a nerve problem somewhere between your lower back and your knee. Foot drop can come on suddenly or develop gradually, and the underlying cause determines whether it’s temporary or needs urgent treatment.
What’s Happening in Your Leg
Pulling your foot upward (the motion you’d use to walk on your heels) depends on muscles in the front of your shin. These muscles are controlled by a single nerve pathway that starts at the L4 and L5 nerve roots in your lower spine, travels through your hip and thigh as part of the sciatic nerve, then branches off near your knee as the common peroneal nerve (also called the fibular nerve). Damage or compression at any point along this chain cuts the signal to those muscles, and your foot drops.
Because the nerve pathway is long, the list of possible injury sites is too. But two locations account for the vast majority of cases: the lower spine and the outer side of the knee.
The Most Common Causes
Nerve Compression at the Knee
The single most frequent cause of foot drop is compression of the peroneal nerve where it wraps around the bony bump just below the outside of your knee (the fibular head). The nerve sits very close to the surface here, with almost no padding between it and the bone. Crossing your legs habitually, wearing a tight cast or brace, spending long periods in a squatting position, or even sleeping in a way that presses against this spot can be enough to damage the nerve. People who are very thin or who have recently lost significant weight are especially vulnerable because they’ve lost the small fat cushion that normally protects the nerve.
Peroneal nerve compression at the knee typically causes both weakness and numbness. You’ll notice you can’t lift your foot, and the skin on the top of your foot or the outer part of your lower leg may feel tingly or numb.
Lumbar Disc Herniation and Spinal Problems
The second major cause is a problem in the lower back, most often a herniated disc pressing on the L5 nerve root. This is the most common spinal cause of foot drop. In addition to weakness in the foot, L5 nerve compression usually comes with pain that starts in the lower back and radiates down the back of the thigh, along the outer shin, and into the foot, including the big toe. Bone spurs from spinal arthritis and narrowing of the spinal canal (spinal stenosis) can produce the same effect.
One important difference: with a spinal cause, you may also have trouble turning your foot inward, because the nerve root at that level controls more muscles than just the ones that lift the foot. With a peroneal nerve injury at the knee, inward turning strength is usually preserved.
Other Causes
Diabetes is a significant contributor. Between 50% and 66% of people with diabetes develop peripheral nerve damage during their lifetime, and while this most often causes numbness and tingling, it can also affect the motor nerves that control muscle strength, including those that lift the foot. The damage comes from prolonged high blood sugar triggering inflammation and oxidative stress inside nerve cells.
Less common causes include sciatic nerve compression in the hip (sometimes from the piriformis muscle), nerve tumors, autoimmune conditions like Guillain-Barré syndrome, and neurodegenerative diseases. In rare cases, a painless foot drop is the first sign of ALS (Lou Gehrig’s disease), though this is uncommon enough that it shouldn’t be your first assumption.
How It Affects Walking
When you can’t lift your foot, your body compensates automatically. You’ll lift your knee much higher than normal on the affected side to keep your toes from dragging on the ground. This exaggerated stepping motion is called a steppage gait. Even with this compensation, your toes may still catch on the ground, especially on uneven surfaces or stairs, which creates a real fall risk. You’ll also lose the normal heel-first landing when you step, and instead your whole foot slaps down flat, which can feel unstable and tiring over a full day of walking.
How Doctors Pinpoint the Problem
Finding the cause starts with a physical exam. Your doctor will test the strength of specific muscles in your foot and leg, check sensation in different areas, and look at your reflexes. These tests can often narrow down whether the problem is at the knee, the hip, or the spine.
If the exam doesn’t give a clear answer, nerve conduction studies and electromyography (EMG) are the next step. Nerve conduction studies send small electrical signals along the nerve to measure how well and how fast they travel, which can reveal exactly where the nerve is damaged. EMG uses a thin needle to record electrical activity in the muscles themselves, showing whether the muscle is getting any signal at all and how many nerve fibers are still functioning. Testing the muscles along the back near the spine can help distinguish a spinal problem from a peripheral nerve injury. MRI of the lower back or leg may also be ordered to look for disc herniations, tumors, or other structural causes.
Treatment Options
Bracing
The most immediate solution is an ankle-foot orthosis (AFO), a brace that holds your foot at a right angle so it doesn’t drag when you walk. The most common type is a custom-molded plastic brace made from polypropylene, shaped to fit your leg from a plaster cast. It’s lightweight, easy to clean, and fits inside most shoes. Other options include walking boots with inflatable bladders that reduce swelling and provide cushioning, and carbon fiber braces that are thinner and more responsive during walking. There are also designs that attach to the front of the foot with an open heel, which can be more comfortable in warmer weather. An AFO won’t fix the underlying nerve problem, but it restores a near-normal walking pattern and dramatically reduces the risk of tripping.
Treating the Underlying Cause
If a herniated disc is compressing the nerve root, treatment may start with physical therapy and anti-inflammatory approaches, but surgery to relieve the compression is sometimes necessary, especially if the weakness is severe or progressing. For peroneal nerve compression at the knee, removing the source of pressure (changing leg-crossing habits, adjusting a cast, or padding the area) is often enough to allow recovery. Physical therapy to strengthen the remaining muscle function and maintain ankle flexibility is important during recovery regardless of the cause.
Surgery for Persistent Cases
When nerve recovery stalls, there are surgical options. Nerve transfer surgery takes a working nerve branch from a nearby muscle and connects it to the damaged nerve closer to the target muscle, essentially rerouting the signal. This is typically considered when EMG shows very few functioning nerve fibers three or more months after injury. Another option is tendon transfer surgery, where the posterior tibial tendon (which normally pulls the foot inward and down) is rerouted to pull the foot up instead. This can eliminate the need for a brace, though the restored strength is often modest and the procedure carries risks including flat foot deformity and arthritis.
Recovery Timeline
How quickly you recover depends entirely on where and how badly the nerve was damaged. Peripheral nerves regenerate at roughly 1 to 3 millimeters per day. That sounds slow because it is. If the injury is at the knee, the nerve only needs to regrow a short distance to reach the muscles in the shin. But if the damage is higher up, at the hip or spine, the regenerating nerve fibers have a much longer path, and recovery can take many months to over a year.
Mild compression injuries where the nerve is bruised but not severed often recover well, sometimes within weeks. More severe injuries where nerve fibers are disrupted may recover partially or not at all. The key factor is time: muscle that goes without a nerve signal for too long undergoes irreversible changes (fibrosis) that make reinnervation impossible even if the nerve eventually regrows. This is why early diagnosis and treatment matter.
Signs That Need Emergency Attention
Foot drop on its own is not typically an emergency, but it can be part of a more serious spinal condition called cauda equina syndrome, where the bundle of nerves at the base of the spine is severely compressed. If your foot weakness comes with any combination of numbness in the groin or inner thighs (saddle area), loss of bladder or bowel control, difficulty sensing when your bladder is full, or severe pain in both legs, get to an emergency room immediately. Cauda equina syndrome requires urgent surgery to prevent permanent nerve damage.