How do you check for Kernig's sign?

How to Check for Kernig's Sign

To check for Kernig's sign, position the patient supine, flex their hip 90 degrees, and then attempt to extend the knee - resistance or pain with knee extension indicates a positive sign. 1

Proper Technique for Eliciting Kernig's Sign

1. Patient Position:

   • Have the patient lie flat on their back (supine position)
   • Ensure the patient is relaxed and comfortable

2. Examination Steps:

   • Flex the patient's hip to 90 degrees (thigh perpendicular to the examination table)
   • While maintaining hip flexion, attempt to extend the patient's knee
   • Observe for resistance or pain during knee extension

3. Interpretation:

   • Positive sign: Pain or resistance when attempting to extend the knee
   • Clinical significance: Suggests meningeal irritation, potentially indicating meningitis

Clinical Value and Limitations

Kernig's sign has significant limitations as a diagnostic tool for meningitis:

• Low sensitivity: Only detects approximately 11-30% of meningitis cases 1, 2
• Moderate specificity: Approximately 85-95% 2
• Limited diagnostic accuracy: Cannot reliably rule in or rule out meningitis 3

Multiple guidelines strongly recommend against relying solely on Kernig's sign for diagnosis:

• The UK Joint Specialist Societies explicitly state that "Kernig's sign and Brudzinski's sign should not be relied upon for diagnosis" 1
• The European Society of Clinical Microbiology and Infectious Diseases notes that "the sensitivity and negative predictive value of Kernig and Brudzinski sign is low in the diagnosis of meningitis" 1

Alternative and Complementary Assessments

When evaluating for meningitis, consider more reliable clinical indicators:

• Classic triad: Fever, neck stiffness, and altered mental status (present in <50% of cases) 1
• More sensitive indicators: Headache, fever, photophobia, and vomiting 1
• Nuchal rigidity: More sensitive than Kernig's sign but still limited 2
• Jolt accentuation test: Worsening headache when horizontally nodding the head 2-3 times 1, 4

Important Clinical Caveat

Despite proper technique, a negative Kernig's sign does not exclude meningitis. The ESCMID guidelines emphasize that "bacterial meningitis should not be ruled out solely on the absence of classic symptoms" 1. When meningitis is clinically suspected, lumbar puncture remains the definitive diagnostic procedure regardless of physical examination findings 3.