Foot drop, medically termed “drop foot,” is a neuromuscular condition characterized by difficulty lifting the front part of the foot, causing it to drag along the ground during walking. This gait abnormality forces affected individuals to lift their knee higher than normal to prevent the toes from catching on surfaces—a compensatory movement known as steppage gait. While foot drop itself is not a disease, it serves as a symptom indicating underlying neurological, muscular, or anatomical problems. Understanding the diverse causes of this condition is essential for accurate diagnosis and appropriate treatment.

Neurological Causes

The most common causes of foot drop involve damage to the nervous system, particularly the peroneal nerve, which branches from the sciatic nerve and controls the muscles responsible for lifting the foot. Peroneal nerve injury can occur through various mechanisms, including direct trauma, compression, or stretching. One frequent scenario involves prolonged pressure on the nerve where it wraps around the fibular head just below the knee. This compression can happen during extended periods of leg crossing, prolonged squatting, wearing tight boots or casts, or even during surgical procedures when patients remain in certain positions for extended durations.

Beyond peripheral nerve damage, central nervous system disorders represent significant causes of foot drop. Stroke ranks among the leading neurological causes, as cerebrovascular accidents can damage the motor cortex or descending motor pathways that control foot and ankle movement. When brain tissue responsible for lower limb control is affected by ischemia or hemorrhage, weakness or paralysis of the dorsiflexor muscles results. Multiple sclerosis, a demyelinating disease affecting the central nervous system, can similarly impair nerve signal transmission to the muscles controlling foot elevation. The unpredictable nature of MS lesions means foot drop may develop gradually or appear suddenly, sometimes affecting one or both feet.

Spinal cord injuries and disorders also contribute to foot drop. Herniated lumbar discs, particularly at the L4-L5 or L5-S1 levels, can compress nerve roots that form part of the sciatic and peroneal nerves. Spinal stenosis, a narrowing of the spinal canal often associated with aging and degenerative changes, exerts similar pressure on these critical nerve structures. Additionally, tumors within or adjacent to the spinal cord, whether benign or malignant, can mechanically impinge upon nerves or disrupt their blood supply, leading to progressive foot drop.

Neurodegenerative diseases present another category of neurological causes. Amyotrophic lateral sclerosis (ALS), commonly known as Lou Gehrig’s disease, destroys motor neurons throughout the nervous system, eventually affecting virtually all voluntary muscle control including foot dorsiflexion. Charcot-Marie-Tooth disease, a group of inherited peripheral neuropathies, causes progressive muscle weakness and atrophy in the extremities, with foot drop often appearing as an early manifestation. Muscular dystrophies, particularly those affecting distal muscles, can similarly present with difficulty lifting the foot.

Muscular Causes

While less common than neurological causes, primary muscle disorders can directly cause foot drop. Muscular dystrophy variants that preferentially affect the anterior compartment muscles of the lower leg—primarily the tibialis anterior—result in weakness of foot dorsiflexion. Myositis, or muscle inflammation from autoimmune conditions, infections, or toxic exposures, can weaken the dorsiflexor muscles sufficiently to cause foot drop. These muscular causes typically involve bilateral symptoms, though asymmetry may occur.

Anatomical and Structural Causes

Anatomical abnormalities represent another important category. Compartment syndrome, whether acute or chronic, involves increased pressure within the muscle compartments of the leg. The anterior compartment contains the muscles responsible for lifting the foot, and when pressure rises sufficiently—from trauma, bleeding, or excessive exercise—muscle and nerve function becomes compromised. Chronic exertional compartment syndrome particularly affects athletes and can cause temporary foot drop during or after physical activity.

Bone fractures and dislocations around the knee or upper fibula can directly injure the peroneal nerve due to its superficial course around the fibular head. Surgical procedures in this region, including knee replacements, arthroscopic surgeries, or fibular fracture repairs, carry inherent risks of nerve damage. Even minimally invasive procedures may occasionally result in nerve injury through positioning, retraction, or direct trauma.

Metabolic and Systemic Causes

Diabetes mellitus represents a significant systemic cause of foot drop through diabetic neuropathy. Chronic hyperglycemia damages peripheral nerves through multiple mechanisms, including microvascular disease, oxidative stress, and metabolic dysfunction. Diabetic neuropathy typically affects longer nerves first, making the peroneal nerve particularly vulnerable. Other metabolic conditions, including chronic kidney disease, can produce similar neuropathic effects.

Toxic exposures also contribute to foot drop. Excessive alcohol consumption causes alcoholic neuropathy through direct toxic effects and nutritional deficiencies, particularly of B vitamins. Certain medications, including some chemotherapy agents, can produce peripheral neuropathy as a side effect. Lead poisoning and other heavy metal exposures historically caused foot drop, though these are now less common due to improved safety regulations.

Foot drop emerges from a remarkably diverse array of causes, spanning neurological, muscular, anatomical, metabolic, and toxic etiologies. The common denominator involves disruption of the neural pathway or muscular function necessary for foot dorsiflexion. Accurate identification of the underlying cause requires thorough clinical evaluation, including detailed history, physical examination, and often electrodiagnostic studies such as electromyography and nerve conduction studies. Imaging studies, including MRI of the brain, spine, or leg, may prove necessary depending on clinical suspicion. Understanding these varied causes enables clinicians to provide targeted treatment, whether through addressing the underlying condition, physical therapy, orthotic devices, or surgical intervention, ultimately improving patient mobility and quality of life.