What are the etiologies of foot drop?

Etiology of Foot Drop

Foot drop results from injury to the neurological pathway enabling ankle dorsiflexion, spanning from the motor cortex through the lumbosacral spine to the peripheral nerves, with L5 radiculopathy and common peroneal nerve injury being the most common causes 1, 2.

Anatomical Pathway and Localization

The motor pathway for ankle dorsiflexion includes the motor cortex, lumbosacral plexus, and the sciatic, tibial, and peroneal nerves 1. Damage at any point along this pathway—central or peripheral—can produce foot drop 3, 4.

Primary Etiologies by Anatomical Location

Peripheral Nerve Causes (Most Common)

• Common peroneal nerve (CPN) palsy at the fibular neck: Comprises slightly more than half of all foot drop cases 5

  • Habitual leg crossing is the most frequent modifiable cause; most patients improve when they stop this habit 2
  • Direct trauma, compression, or entrapment at the fibular head

• L5 radiculopathy: One of the two most common causes alongside peroneal nerve injury 4

  • Lumbar spine complications and surgeries account for 13.9% and 12.8% of cases respectively 1
  • Failed back surgery syndrome is a leading cause, particularly in older patients (median age 60 years) 1

• Sciatic nerve injury: Partial sciatic neuropathy can present as foot drop 2

• Lumbar plexopathies 2

Central Causes

• Motor cortex lesions and cerebral pathology account for approximately 5% of cases 5
• Spinal cord lesions
• Motor neuron disease (5% of cases) 5

Iatrogenic Causes

• Hip replacement surgery: 7.8% of foot drop cases, with significant female predominance (85%) and older age (median 60 years) as risk factors 1
• Lumbosacral spine surgery: 13.9% of cases, affecting slightly more males (54%), median age 55 years 1

Traumatic Causes (Younger Males)

• Gunshot and stab wounds
• Motor vehicle accidents
• Sports and recreational injuries
• These predominantly affect younger male adults 1

Medical Conditions

• Diabetes: 10% of cases have diabetes as a contributing factor 5
• Compartment syndrome 6
• Malignancy: 12% of cases have associated cancer 5

Other Causes

• Injection drug use and medication overdoses (younger males) 1
• Anterior horn cell disease 2
• Extensor muscle injury 6

Important Clinical Patterns

Bilateral foot drop occurs in 8% of cases and should prompt investigation for central causes, motor neuron disease, or systemic conditions 5.

Asymmetrical presentation warrants careful evaluation for focal nerve injury, structural lesions, or malignancy rather than systemic neuropathy 7.

Critical Diagnostic Consideration

One-third of all foot drop cases reveal additional coexistent pathology in anatomic locations remote from the primary diagnosis 5. This underscores the importance of comprehensive neurophysiologic testing (NCS/EMG), which alters the initial working diagnosis in 27% of cases 5.

Age and Sex Patterns

• Older patients (median age 60-63 years): Lumbosacral spine complications, failed back surgery syndrome, hip replacement complications 1
• Younger male patients: Trauma, sports injuries, motor vehicle accidents, violence, drug-related causes 1
• Female predominance: Hip replacement-related foot drop (85% female) 1