How to Perform Kernig's and Brudzinski's Signs
While Kernig's and Brudzinski's signs are classically taught for detecting meningeal irritation, they have extremely poor sensitivity (5-11%) and should not be relied upon to rule in or rule out meningitis. 1, 2
Technique for Kernig's Sign
Original Kernig's Sign (as described by Kernig):
- With the patient supine, flex the hip to 90 degrees while keeping the knee bent 3
- Then attempt to extend the knee while maintaining hip flexion 3
- A positive sign occurs when the patient experiences pain or resistance to knee extension, typically preventing full extension beyond 135 degrees 3
Note: The test as currently performed in most clinical settings differs from Kernig's original description, which has contributed to variability in its diagnostic utility 3
Technique for Brudzinski's Signs
Brudzinski's "Nape of the Neck" Sign (most commonly known):
- With the patient supine, place your hands behind the patient's head 3
- Passively flex the neck, bringing the chin toward the chest 3
- A positive sign occurs when this maneuver causes involuntary flexion of the hips and knees 3
Brudzinski's Contralateral Leg Signs (less familiar but historically described):
- Brudzinski described several additional signs involving contralateral leg movements during examination 3
- These are unfamiliar to most modern clinicians but were considered useful by Brudzinski because some signs may be present while others are absent 3
Clinical Performance and Limitations
Diagnostic Accuracy:
- Kernig's sign has a sensitivity of only 5% and a positive likelihood ratio of 0.97, meaning it does not discriminate between patients with and without meningitis 4
- Brudzinski's sign similarly has a sensitivity of only 5% and a positive likelihood ratio of 0.97 4
- Even in patients with moderate meningeal inflammation (≥100 WBCs/mL of CSF), these signs show no significant diagnostic value 4
- Only in patients with severe meningeal inflammation (≥1000 WBCs/mL of CSF) does nuchal rigidity show any diagnostic value 4
Critical Pitfall:
- The absence of these signs does NOT rule out meningitis—patients suspected of having meningitis should undergo lumbar puncture regardless of whether these physical signs are present or absent 5, 4
Alternative Examination Approach
Modified technique with potentially better sensitivity:
- Have the patient sit up with knees fully extended 6
- Then ask the patient to flex the neck forward 6
- This maneuver stretches the neural elements along the entire length of the spinal canal simultaneously and may be more sensitive than traditional methods 6
Clinical Context
When to suspect meningitis despite negative signs:
- The classic triad of fever, neck stiffness, and altered mental status is present in less than 50% of bacterial meningitis cases 1, 2
- Neck stiffness itself has a sensitivity of only 31% in adults 1
- Positive meningitic signs increase the likelihood of meningitis, but their absence reduces probability only minimally 7
- These signs have greatest utility when combined with other clinical features rather than used in isolation 7