Foot drop is most commonly caused by compression of the peroneal nerve, which wraps around the top of the shinbone just below the knee. This nerve controls the muscles that lift the front of your foot, so when it’s damaged or squeezed, the foot hangs downward and can’t be raised properly. While peroneal nerve compression accounts for the majority of cases, foot drop can also result from spinal problems, brain and nerve diseases, diabetes, and direct muscle damage.
Peroneal Nerve Compression
The peroneal nerve sits remarkably close to the surface near the head of the fibula, the thin bone on the outside of your lower leg just below the knee. That shallow position makes it vulnerable to pressure from the outside. Habitual leg crossing is one of the most recognized triggers. Prolonged kneeling or squatting, common among athletes, flooring installers, and gardeners, can do the same thing. Even extended bed rest, such as during a long hospitalization or coma, can compress the nerve enough to cause foot drop.
In mild cases, the nerve is temporarily stunned but not structurally damaged. One published case report documented a patient who developed foot drop after prolonged cross-legged sitting and recovered full strength within a month using conservative treatment alone. More severe compression can damage the nerve fibers themselves, leading to a longer and less predictable recovery.
Herniated Discs and Spinal Nerve Roots
A herniated disc in the lower back can press on the L5 nerve root, one of the nerves that eventually feeds into the muscles controlling your foot. When the L5 root is compressed, you typically feel pain that starts in the lower back and radiates down the back of the thigh, along the outer leg, and into the foot and big toe. Numbness often appears on the inner part of the foot, particularly the web space between the first and second toes.
The key difference between an L5 nerve root problem and a peroneal nerve injury at the knee is which muscles are affected. With peroneal nerve compression, you lose the ability to lift the foot and turn it outward, but the muscles that turn the foot inward still work. With an L5 radiculopathy, the inward-turning muscles can weaken too. This distinction helps clinicians figure out exactly where the problem is, which matters because the treatments are very different.
Stroke, MS, and Other Brain Disorders
Foot drop doesn’t always start in the leg. Conditions that damage the brain or spinal cord can interrupt the signals traveling down to the foot muscles. Stroke is a common example: if the area of the brain controlling leg movement is affected, the foot may drag. Multiple sclerosis can cause foot drop when it damages the nerve pathways in the spinal cord. Cerebral palsy, ALS, and certain forms of spinal muscular atrophy can also produce it.
In these cases, foot drop is usually one piece of a larger picture. A stroke patient, for example, often has weakness throughout one side of the body, not just in the foot. This makes the cause relatively straightforward to identify, though the foot drop itself still needs to be managed to prevent falls and maintain mobility.
Diabetes and Nerve Vulnerability
Diabetes makes peripheral nerves more susceptible to damage from external pressure. High blood sugar causes sugar molecules to attach to proteins in connective tissue, making that tissue stiffer and bulkier. In tight anatomical spaces like the channel where the peroneal nerve passes near the knee, this swollen tissue can squeeze a nerve that may already be weakened by diabetic nerve damage. The result can be pain and numbness on the top of the foot, progressing in advanced cases to full foot drop. This combination of internal nerve damage and external compression is why people with diabetes develop foot drop at higher rates than the general population, and why a seemingly minor habit like crossing the legs can cause disproportionate harm.
Muscle and Other Causes
Less commonly, foot drop results from direct damage to the muscles themselves rather than the nerves controlling them. Muscular dystrophies and other conditions that progressively weaken muscle tissue can eventually affect the muscles in the front of the lower leg. Trauma to the leg, including fractures near the knee or surgical complications, can injure the peroneal nerve directly. Growths such as ganglion cysts near the nerve’s path can compress it from within.
How Foot Drop Is Diagnosed
A physical exam is the starting point. Your doctor will ask you to lift your foot against resistance and grade your strength on a 0 to 5 scale, where 0 means no muscle activation at all and 5 means full strength against resistance. Testing specific muscles helps pinpoint the location of the problem. If muscles that turn the foot inward are also weak, the issue is more likely in the spine than at the knee.
Nerve conduction studies and electromyography (EMG) are the primary tools for confirming the diagnosis. In a nerve conduction study, small electrical impulses are sent along the nerve, and the speed and strength of the signal are measured at different points. A significant drop in signal strength across the knee area points to compression at the fibular head. EMG involves inserting thin needles into muscles to measure electrical activity, which reveals whether the nerve damage is causing the muscle fibers to deteriorate or whether the nerve is simply being squeezed without permanent fiber loss. Importantly, these tests also check muscles supplied by other nerves to rule out broader problems like L5 radiculopathy or sciatic nerve injury.
Treatment and Recovery
Treatment depends entirely on the cause. When foot drop results from mild nerve compression, removing the source of pressure is often enough. That might mean stopping the habit of crossing your legs, using padding around the knee during sleep or work, or adjusting your position during prolonged bed rest. Physical therapy to maintain flexibility and gradually rebuild strength plays a central role during recovery.
An ankle-foot orthosis (AFO) is the most common tool for managing foot drop while healing occurs or when the condition is permanent. Traditional plastic braces hold the foot at a neutral angle to prevent it from dragging. Carbon fiber models are lighter, more durable, and store energy during walking to make each step more efficient. Some newer designs attach to the outside of a shoe and use elastic energy to restore the foot-lifting motion automatically. In a study of patients with severe lower-leg injuries, passive dynamic braces led to a 21% increase in patients able to walk independently and a 53% increase in those able to run.
When conservative treatment fails and the nerve compression is chronic, surgical decompression is an option. In a study of 34 patients who underwent this procedure, 85% improved by at least one strength grade. Pain improved in 84% of cases. Sensation recovery was less reliable, with 45% regaining normal feeling. Two factors predicted worse sensory outcomes: a BMI above roughly 29, and waiting longer than about 17 months between injury and surgery. For foot drop caused by a herniated disc, spinal surgery to relieve the L5 nerve root may be necessary. When stroke or MS is the underlying cause, treatment focuses on managing the neurological condition while using bracing and therapy to maintain walking ability.