What are the causes of foot drop?

Causes of Foot Drop

Foot drop is most commonly caused by peripheral neuropathy, particularly diabetic peripheral neuropathy, followed by peroneal nerve compression or injury at the fibular neck, and various central and peripheral nervous system disorders. 1

Peripheral Nerve Causes

• Common peroneal nerve injury (most frequent cause)

  • Compression at fibular neck from:
    • Habitual leg crossing (most common reversible cause) 2
    • External compression (casts, tight boots)
    • Trauma/fractures around knee or fibular head
    • Mass lesions (ganglion cysts, tumors)
    • Ankle inversion sprains (rare but documented) 3
  • Susceptibility due to superficial anatomical location

• Peripheral neuropathies

  • Diabetic peripheral neuropathy (leading systemic cause) 4, 1
  • Toxic neuropathies (medication-induced)
  • Nutritional deficiencies (vitamin B12)
  • Heavy metal poisoning
  • Uremia in end-stage renal disease 1

Radicular and Spinal Causes

• L5 radiculopathy (compression of L5 nerve root)
• Lumbar spinal stenosis
• Tethered cord syndrome (especially in children) 4
  • Presents with progressive foot weakness, muscle atrophy, and "saber shins"
  • Often associated with cutaneous markers
• Lumbar disc herniation affecting L4-L5 nerve roots

Central Nervous System Causes

• Stroke affecting motor cortex or corticospinal tracts
• Multiple sclerosis
• Motor neuron disease (ALS)
• Brain tumors/metastases (rare presentation) 5
• Cerebral palsy 6
• Significant head trauma 1

Muscular Causes

• Direct trauma to anterior compartment muscles
• Compartment syndrome
• Muscular dystrophies
• Myositis

Systemic Disease Associations

• Diabetes mellitus (most common systemic association) 4, 1
• Connective tissue diseases
• Vasculitis
• End-stage renal disease (especially patients on dialysis) 4

Diagnostic Approach

1. Physical examination:

   • Assess foot dorsiflexion strength bilaterally
   • Test sensation (pinprick, vibration, light touch)
   • Check deep tendon reflexes (ankle reflexes)
   • Evaluate for foot deformities
   • Assess pedal pulses for vascular status 4, 1

2. Neurophysiological studies:

   • Nerve conduction studies and electromyography to localize lesion site
   • Helps establish degree of damage and predict recovery 2

3. Imaging:

   • MRI of lumbosacral spine (for radiculopathy)
   • Ultrasound of peroneal nerve at fibular head
   • CT or MRI of knee/leg for mass lesions
   • Brain imaging if central cause suspected 2

4. Laboratory testing (based on suspected etiology):

   • Diabetes screening
   • B12/folate levels
   • Vasculitic/autoimmune markers
   • Thyroid function 1

Early identification and management of foot drop is crucial to prevent falls, maintain mobility, and preserve quality of life. For persistent foot drop, ankle-foot orthoses are the first-line treatment to improve mobility and prevent complications 1, 7.