How to Test for Kernig Sign
To perform Kernig sign, place the patient supine, flex the hip to 90 degrees, then attempt to passively extend the knee; a positive sign occurs when this maneuver causes resistance or pain at less than 135 degrees of knee extension, or when the patient cannot fully extend the knee due to hamstring spasm. 1
Technique
The original Kernig sign technique involves:
- Position the patient supine (lying flat on their back) 2
- Flex the patient's hip to 90 degrees 1
- While maintaining hip flexion, passively attempt to extend the knee 1
- A positive sign is present when knee extension is limited by pain or resistance, typically occurring before reaching 135 degrees of extension 1
Clinical Context and Limitations
Kernig sign has extremely poor sensitivity and should never be used alone to exclude meningitis. The diagnostic performance is severely limited:
- Sensitivity is only 11% in adults, meaning it misses 89% of meningitis cases 3
- Sensitivity ranges from 20-30% across studies 4
- Specificity is relatively high at 85-95%, but this does not compensate for the poor sensitivity 4
- The sign has low diagnostic accuracy for predicting cerebrospinal fluid pleocytosis 2
The absence of Kernig sign cannot be used to exclude bacterial meningitis. 2 No single clinical sign of bacterial meningitis is present in all patients, and the classic triad of fever, neck stiffness, and altered mental status appears in only 41-51% of cases. 5, 3
Clinical Management Implications
All patients with suspected meningitis require hospital referral and cerebrospinal fluid examination, regardless of whether Kernig sign is present or absent. 5, 2 CSF analysis remains the cornerstone of diagnosis with the highest diagnostic accuracy, not physical examination signs. 5, 3
Combining multiple meningeal signs (Kernig, Brudzinski, nuchal rigidity, jolt accentuation) may decrease the risk of misdiagnosis, as approximately half of patients with meningitis may not present typical meningeal signs upon physical examination. 4