Kernig sign

Definition and Mechanism

Kernig sign is a meningeal sign indicating possible irritation of the meninges due to conditions like meningitis, subarachnoid hemorrhage, or other causes of meningeal inflammation or increased intracranial pressure.

Test Procedure

1. The patient lies flat on their back (supine position).
2. The examiner flexes the patient’s thigh at a 90-degree angle to the trunk.
3. The examiner then attempts to extend the leg at the knee joint.
4. If the leg cannot be fully extended due to pain and resistance, the Kernig sign is positive.

Clinical Significance

🔹 Positive Kernig sign suggests meningeal irritation, commonly due to:

• Bacterial or viral meningitis
• Subarachnoid hemorrhage
• Tuberculous meningitis
• Other conditions causing meningeal inflammation

🔹 Why does it happen?

• Inflammation of the meninges leads to muscle spasms and pain when stretching the spinal cord and nerve roots.
• The resistance to leg extension occurs due to reflexive muscle contraction in response to meningeal irritation.

Associated Signs

• Brudzinski’s sign – Involuntary hip and knee flexion when the neck is passively flexed.
• Nuchal rigidity – Stiffness and pain when trying to flex the neck.

Limitations

• Sensitivity: Kernig’s sign is not always present in all cases of meningitis.
• Specificity: A positive sign can also occur in other conditions affecting the spine or nervous system.