How can you diagnose a peroneal nerve injury?

Diagnosis of Peroneal Nerve Injury

The most effective diagnostic approach for peroneal nerve injury includes clinical examination for foot drop, sensory deficits in the lateral leg and dorsum of foot, and confirmatory electrodiagnostic studies. 1

Clinical Examination

Motor Assessment

• Test for weakness in:
  • Ankle dorsiflexion (tibialis anterior)
  • Foot eversion (peroneus longus and brevis)
  • Toe extension (extensor digitorum longus and extensor hallucis longus)
• Grade muscle strength on a scale of 0-5:
  • 0: No contraction
  • 1: Visible contraction without movement
  • 2: Movement with gravity eliminated
  • 3: Movement against gravity
  • 4: Movement against resistance
  • 5: Normal strength

Sensory Assessment

• Check for sensory deficits in:
  • Lateral aspect of the leg
  • Dorsum of the foot
  • First web space (deep peroneal nerve)
• Assess for:
  • Numbness
  • Paresthesia
  • Dysesthesia

Special Tests

• Tinel's sign: Percussion over the fibular head or along the nerve course eliciting tingling or electric sensations
• Assess for foot drop during gait
• Look for compensatory steppage gait (high stepping to clear the foot)

Advanced Diagnostic Testing

Electrodiagnostic Studies

• Nerve conduction studies (NCS) and electromyography (EMG) are essential for:
  • Confirming diagnosis
  • Determining severity (partial vs. complete)
  • Localizing the site of injury
  • Establishing prognosis 1, 2

Imaging

• MRI of the knee/leg:

  • Highly sensitive for identifying nerve compression at the fibular head
  • Can detect associated soft tissue injuries, masses, or anatomical variants 1, 3
  • Particularly useful in traumatic cases or when associated with multiligament knee injuries 4

• Ultrasound:

  • Allows dynamic assessment of the nerve
  • Can guide interventional procedures
  • Useful for detecting nerve subluxation or dislocation 1

Common Mechanisms of Injury to Check For

• Direct trauma to fibular head
• Knee dislocation (95.3% associated with ACL tears) 4
• Prolonged external compression (e.g., improper positioning during surgery) 5, 1
• Stretch injuries from leg positioning (especially lithotomy position) 1
• Habitual leg crossing
• Tight casts or braces

Differential Diagnosis

• L5 radiculopathy
• Sciatic neuropathy
• Lumbosacral plexopathy
• Motor neuron disease
• Anterior compartment syndrome

Pitfalls to Avoid

• Failing to assess for associated vascular injuries, especially with knee dislocations 1
• Overlooking partial nerve injuries that may have better recovery potential 6
• Delaying diagnosis beyond 3-4 months, which can reduce surgical success rates 7
• Not considering nerve compression at multiple sites (double crush syndrome)
• Neglecting to protect the common peroneal nerve during surgical procedures, particularly when patients are in lithotomy position 1, 5

Early and accurate diagnosis is crucial as timely intervention significantly improves outcomes. Patients with partial nerve injuries have much better recovery potential (83% regain antigravity ankle dorsiflexion) compared to complete injuries (38%) 6.