What is the Kernig sign?
The Kernig sign is a medical examination finding that can point to irritation of the meninges, which are the membranes surrounding the brain and spinal cord. It is used mainly during neurological examinations to look for signs of a possible inflammation of the meninges, known as meningitis.
How does the Kernig sign present?
During the examination, the person being tested usually lies on their back. The doctor then bends the leg at a right angle at both the hip and the knee. If the doctor then tries to straighten the knee further, this can cause pain or resistance when the meninges are irritated. The leg cannot be fully extended. This is what is called the Kernig sign.
The reason for this is that when the meninges are inflamed, the nerve pathways along the spine also become irritated. When the leg is straightened, the sciatic nerve is stretched, and with it the meninges. This can be painful during inflammation or can even trigger a protective muscle tension.
When is the Kernig sign tested for?
The Kernig sign is most relevant when meningitis is suspected. Typical symptoms of meningitis include severe headache, a stiff neck, fever, and sensitivity to light. In such cases, the doctor may specifically look for signs of meningeal irritation. Alongside the Kernig sign, the Brudzinski sign is also used for this purpose.
The Kernig sign is not always clearly positive or negative. In young children, older people, or those with muscle or joint problems, the reliability of the test can be reduced. The result is therefore always assessed alongside other symptoms and findings.
What does a positive Kernig sign mean?
A positive Kernig sign means that the leg cannot be fully straightened during the examination without causing pain or a clear resistance response. This suggests irritation of the meninges, as seen for example in meningitis.
However, a positive Kernig sign alone is not proof of meningitis. It can also occur in other conditions, and sometimes even without any underlying illness. Equally, the absence of the Kernig sign does not rule out meningitis with certainty. It is therefore always just one piece of the puzzle within the overall diagnostic process.
What happens when meningitis is suspected?
When meningitis is suspected, every minute counts. Alongside the Kernig sign, further neurological examinations are carried out and the doctor will ask about typical symptoms. A blood test is often done, and sometimes a lumbar puncture is performed. During a lumbar puncture, cerebrospinal fluid is taken from the spinal canal and examined for signs of inflammation.
Treatment depends on the cause of the inflammation. In bacterial meningitis, antibiotics are usually started straight away to stop the infection as quickly as possible. In viral meningitis, specific medicines or supportive measures are used. The earlier treatment begins, the better the chances of recovery.
Summary of the key points
The Kernig sign is a clinical examination finding that can suggest irritation of the meninges, as occurs in meningitis. It is tested by straightening the bent leg and is most meaningful when considered alongside other symptoms and examinations. A positive Kernig sign alone is not enough to diagnose or rule out meningitis with certainty. If meningitis is suspected, prompt medical assessment is essential.
