Which description defines Kernig sign?

• A. Pain upon extending the knee when the thigh is flexed at 90 degrees
• B. Pain when bending the neck
• C. Nuchal rigidity without knee pain
• D. Positive Babinski sign

Answer: (A)

Kernig sign tests for meningeal irritation, often from meningitis. The test is done with the patient lying on the back and the hip flexed to 90 degrees; then the knee is extended. If extending the knee while the hip remains flexed produces pain or significant resistance, that describes a positive Kernig sign. The mechanism is stretching of inflamed meninges along the spinal canal when the leg is straightened with the hip flexed. By contrast, bending the neck causing pain points to nuchal rigidity, a different sign of meningeal irritation, while nuchal rigidity without knee pain does not indicate Kernig. A positive Babinski sign reflects an upper motor neuron lesion, not meningeal irritation. Therefore, the description that fits Kernig is pain upon extending the knee when the thigh is flexed at 90 degrees.