Foot Drop

Aka: Foot Drop, Ankle Dorsiflexion Weakness, Foot Dorsiflexion Weakness

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II. Anatomy

  1. Common Fibular Nerve
    1. Deep Fibular Nerve (ankle and toe extension)
    2. Superficial Fibular Nerve (foot eversion)
    3. Injury
      1. May be compressed at lateral gastrocnemius or lateral fibular head
      2. Compression occurs with crossing legs, prolonged kneeling or immobilization
  2. Proximal Compression Sites
    1. Central lumbar canal
      1. Compressed in Central Spinal Stenosis and Cauda Equina Syndrome
    2. Lumbar Nerve Root
      1. Foot Drop may be due to injury to the L5 nerve root (exiting in the L5-S1 interspace)
    3. Sciatic Nerve
      1. Foot Drop may be due to injury to sciatic nerve, arising from L4 to S4 within Lumbosacral Plexus
      2. Gives rise to the common fibular nerve when it divides within the popliteal space

III. Differential Diagnosis

  1. Compression Neuropathy
  2. See Gait Abnormality
  3. See Hemiplegia
  4. Compression Neuropathy
    1. Central spinal stenosis
    2. Cauda Equina Syndrome
    3. Lumbar Radiculopathy (L5)
    4. Prolonged ICU Admission (>4 weeks)
      1. Isolated Fibular Nerve Injury (10% of patients)
      2. Critical Illness Polyneuropathy
      3. García-Martínez (2020) Clin Nutr 39(5):1331-44 [PubMed]
  5. Trauma
    1. Sciatic Neuropathy
    2. Lumbosacral Plexopathy
  6. Other neurologic disorders
    1. Cerebrovascular Accident with Hemiplegia
    2. Amyotrophic Laterel Sclerosis (ALS)
    3. Guillain Barre Syndrome (Acute Inflammatory Demyelinating Polyneuropathy, AIDP)
    4. Charcot Marie Tooth
    5. Mononeuritis multiplex
      1. Neuropathy due to Small Vessel Vasculitis, in this case, involving sciatic nerve

IV. Exam

  1. See Neurologic Exam
  2. See Motor Exam
  3. See Sensory Exam

V. Imaging

  1. MRI Lumbar Spine
    1. Indicated in suspected central spinal stenosis, Cauda Equina Syndrome, or Lumbar Radiculopathy

VI. Diagnostics

  1. Nerve Conduction Study (NCS)
  2. Electromyography (EMG)

VII. Labs

  1. Consider Collagen vascular causes (RF, ANA, CBC, ESR, CBC, Basic Chemistry)

VIII. Evaluation

  1. Walk the nerve tree from Lumbosacral Spine, sciatic nerve and common fibular nerve
  2. Consider MRI Lumbar Spine
  3. Consider other diagnostic testing as above (labs, ENG, EMG)

IX. Management

  1. Surgical Indications
    1. Trauma with nerve transection (emergency surgery recommended within 72 hours)
    2. Severe, complete Compression Neuropathy
  2. Medical Management
    1. Improve mobility and prevent falls and contractures
      1. Physical Therapy
        1. Work on strengthening, Stretching, possible electrical stimulation
      2. Splinting in Ankle Foot Orthosis (AFO)
        1. Prevent pressure points and skin breakdown

X. References

  1. Bowley (2019) Med Clin North Am 103(2):371-82 [PubMed]
  2. Subhadra (2021) Foot Drop, StatPearls, accessed online 2/8/2022
    1. https://www.ncbi.nlm.nih.gov/books/NBK554393/

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