Foot Drop

Relevant physical signs

• Inspection
  • Wasting of tibialis anterior (lower motor neurone)
  • Wasting of peroneal muscles
  • Fasciculations (if chronic denervation occurs)
  • Unilateral / bilateral foot drop
  • Scars: previous spinal / leg surgery
  • Presence of ankle orthosis at bedside
• Tone: flaccid / spastic
• Reflexes (knee jerk – L3/4, ankle S1/2) should be preserved in both common peroneal and L5 lesions
  • If ankle jerk depressed: consider motor neuropathies or plexopathy involving S1
• Power:
  • Hip abduction (L5, superior gluteal nerve)
  • Knee flexion (L5/S1, sciatic nerve)
  • Ankle dorsiflexion (L5/S1, deep peroneal nerve)
  • Ankle plantarflexion (S1/S2, tibial nerve)
  • Foot eversion (L5, superficial peroneal nerve)
  • Foot inversion (L5, tibial nerve)
• Sensation
  • Tinnel’s of common peroneal nerve (over fibula head)
  • Lateral aspect of calf (L5)
  • Dorsum of foot (superficial peroneal)
  • First dorsal web space (deep peroneal nerve)
  • Proprioceptive loss (diabetic neuropathy)
• If sensation is spared and foot drop is bilateral, consider:
  • Percussion myotonia
  • Grip myotonia
• Gait: high steppage

Differential diagnosis of flaccid foot drop

• Anterior horn cell disease
• L5 radiculopathy (degenerative disc disease at L4-5)
• Lumbar plexopathy
• Sciatic nerve injury
  • Hip surgery
  • Trauma
  • Tumours: neurofibromas, sarcomas
  • Sciatic nerve injury following IM injections
• Common peroneal nerve injury
  • External compression
    • Plaster casts / braces
    • Habitual leg crossing
    • Prolonged squatting / kneeling
  • Trauma
    • Blunt injuries / laceration
    • Complication of knee surgery
    • Knee dislocation / traction injuries
    • Fracture of fibula head
  • Entrapment neuropathy
    • Fibular tunnel
    • Anterior tibial compartment syndrome
  • Mononeuritis multiplex
    • Leprosy
    • Lyme disease
    • Polyarteritis nodosa
    • Wegner’s granulomatosis
    • Churg-Strauss syndrome
    • Systemic lupus erythematosus
    • Rheumatoid arthritis
    • Sarcoidosis
  • Diabetes mellitus
  • Drugs
    • Isoniazid
    • Chemotherapy
    • Alcohol
  • Tumours
    • Schwannomas
    • Neurofibromas
    • Sarcomas
• Distal myopathy
  • Inclusion body myositis
  • Myotonic dystrophy
• Trauma, e.g. rupture of tibialis anterior tendon

Differential diagnosis of spastic foot drop

• Meningioma of the para-sagittal cortex
• Internal capsule stroke
• Anterior cerebral artery infarction

Investigations

• Confirm diagnosis
  • Common peroneal nerve palsy: nerve conduction studies
  • L5 radiculopathy: magnetic resonance imaging of lumbar spine (disc herniation)
• Look for underlying cause
  • Take thorough history for trauma, compression neuropathy
  • Fasting plasma glucose for diabetes mellitus
  • Autoimmune screen if MSK examination suspicious
    • Antinuclear antibody
    • Anti-neutrophil cytoplasmic antibody

Management

• Multidisciplinary approach
• Directed at underlying cause, if any
• Patient education
  • Walking aids
  • Falls precautions
• Physiotherapy
• Ankle orthoses to correct foot drop

Summary

Sir, this patient has a right-sided flaccid foot drop which is associated with weakness of foot eversion, but preservation of foot inversion and hip abduction. There is wasting of the tibialis anterior, as well as sensory loss over the lateral aspect of the distal leg and the dorsum of the foot. Tinnel’s test over the common peroneal nerve is positive. Knee and ankle jerk reflexes are normal, and there is no evidence of cerebellar dysfunction. In light of the preservation of foot inversion and hip abduction, the most likely cause of the foot drop is a common peroneal nerve palsy.

Or

Sir, this patient presents with a flaccid foot drop which is associated with wasting of the tibialis anterior and peroneal muscles. There is weakness of ankle dorsiflexion, foot eversion and inversion as well as hip abduction. There is sensory loss over the lateral aspect of the proximal leg. Reflexes are intact and plantars are downgoing. There is no evidence of cerebellar dysfunction. Given the muscle groups involved, the most likely cause of the foot drop is an L5 radiculopathy, which may be caused by degenerative disc disease of the L4-5 nerve root.