Overview of Kernig Sign
The Kernig sign is a physical test that doctors use to detect meningitis, which is an infection of the coverings of the brain and spinal cord. The test is done when you’re lying down and involves trying to fully stretch your knees. If it’s difficult or painful to do this, it might mean inflammation linked to meningitis is affecting these areas. This sign has been used since the 1800s and is still commonly used today if meningitis is suspected.
It was first identified by a Russian doctor named Vladimir Kernig. He noticed that people who had bacterial meningitis or a similar type of the disease couldn’t fully stretch their legs while sitting. He spent many years studying this and first mentioned it at a medical conference in Russia in 1882.
According to Kernig, a positive sign – meaning meningitis might be present – was shown by an inability to stretch the knees more than 135 degrees. In serious cases, the patients couldn’t stretch their knees beyond 90 degrees. This was done with the person sitting straight up and their hips bent at a 90-degree angle. Kernig also found that some people couldn’t fully extend their elbows when they had meningitis. However, he believed that experiencing pain wasn’t a part of a positive test; instead, a positive test was determined by having a contraction or spasm at the knee. He also observed that the severity of the knee contraction didn’t always reflect the severity of the meningitis.
Anatomy and Physiology of Kernig Sign
The brain is protected by three layers known as meninges. These are named the dura mater, pia mater, and arachnoid mater. Meningitis is a disease which causes these layers to become inflamed or irritated. This is usually common in the pia and arachnoid layers.
In meningitis, patients can experience stiffness and increased sensitivity in their legs due to the inflammation. Some researchers believe that the Kernig sign, which is a medical method used to check for meningitis, triggers a protective response in the body to prevent painful spasms in the legs.
If the Kernig sign test is positive, it means the patient could have meningitis. To confirm this, doctors usually suggest the patient gets a CT scan which is a type of X-ray. This is typically followed by a lumbar puncture or a spinal tap, which is a procedure to collect and look at the fluid surrounding the brain and spinal cord, and antibiotic treatment.
Meningitis is often caused by infections from bacteria, viruses, and fungi. Doctors can tell the type of infection causing meningitis by analyzing the fluid collected during the lumbar puncture. In cases of bacterial and fungal infections, the sugar levels in this fluid are usually low. In cases of viral and fungal meningitis, there is an increase in white blood cells, specifically lymphocytes, in the fluid. Also, the pressure of the fluid is usually increased when the meningitis is caused by fungus or bacteria.
Why do People Need Kernig Sign
The Kernig sign is a popular test doctors use to check for meningitis, a serious infection that affects the protective membranes of your brain and spinal cord. However, it’s crucial to know that only around half of meningitis patients show typical symptoms that can be picked up during physical examinations such as the Kernig sign or the Brudzinski sign.
Because of this, doctors can’t rely on these signs alone to make a diagnosis. They often need to use other investigative methods like a lumbar puncture, which is a procedure where a needle is inserted into your lower back to collect a sample of your spinal fluid. This is done to help them diagnose meningitis more accurately.
When a Person Should Avoid Kernig Sign
Infants who have rigid or tight muscles might not be suitable for a certain test called the Kernig test. This test also might not give reliable results for patients who are extremely tired, paralyzed from the waist down, or in a coma, because these individuals might not show clear signs of meningeal disease (a condition affecting the membranes covering the brain and spinal cord). Moreover, the presence of Kernig’s sign doesn’t necessarily mean that the meningeal disease is severe. So, this test should be avoided for patients who have injuries to the leg, knee or hip because it may be uncomfortable and misleading.
Equipment used for Kernig Sign
No unique tools are necessary for this procedure. Nonetheless, a bed is required to make sure the patient can lay flat on their back. This position allows the doctor to properly perform the examination.
Who is needed to perform Kernig Sign?
Doctors can do this action by themselves and they don’t need any assistance.
Preparing for Kernig Sign
When doctors are performing medical tests, they need the baby to be calm and relaxed. So, if a baby is very fussy or tense, they are not the best fit for the test.
How is Kernig Sign performed
To understand the Kernig sign, imagine someone lying down flat on their back with their thighs pulled close to their stomach and knees bent. Now, a doctor tries to straighten the person’s legs. If that person has inflammation in the membranes covering their brain and spinal cord, known as meningitis, this movement will cause pain in the lower back or behind the thighs. This response is known as a positive Kernig sign.
The Kernig sign is generally checked along with other signs to confirm if a person has meningitis. One of these is the Brudzinski sign, named after a Polish pediatrician, Brudzinski, who described it in 1909. To check for this sign, the doctor gently bends the person’s neck. If it’s positive, the person’s hips and knees will automatically bend as well. Both signs help identify meningitis.
Possible Complications of Kernig Sign
If doctors think a baby might have meningitis, a serious infection, they shouldn’t only use the Kernig test. This test has the patient lying down and a doctor bends their leg to look for signs of stiffness or discomfort. Instead, the baby should get a procedure called a lumbar puncture. In this procedure, a small amount of fluid is taken from the spine with a needle to check for infection.
What Else Should I Know About Kernig Sign?
Meningitis is a potentially serious illness which happens when the protective membranes around the brain and spinal cord, known as the meninges, become inflamed. Certain signs can help doctors determine if a patient has meningitis, but these signs can also be found in other conditions such as spinal cord tumors, myelitis, slipped discs, sciatica, multiple sclerosis, trauma, bleeding under the membrane around the brain (subarachnoid hemorrhage), high pressure inside the skull, and stroke. Usually, if these signs are due to meningitis, they show up pretty quickly, typically within 24 hours of the symptoms starting. This occurs because when these protective membranes are inflamed, it hurts to stretch them, and these signs are thought to be the result of this mechanical reaction inside the body.
Bacterial meningitis is a very serious condition that contributes significantly to sickness and death around the world. In fact, it ranks among the top ten infectious causes of death, contributing to nearly 135,000 deaths annually. Certain physical exam findings, such as stiffness in the neck and specific signs known as Kernig and Brudzinski, can be helpful in diagnosing cases of suspected meningitis.
There have been a number of studies examining how useful these physical signs are in diagnosing meningitis. It turns out that while these signs might not be very good at ruling out meningitis when they’re not present (they have a low 5% sensitivity), they are very good at predicting meningitis when they are present, with a specificity of 95%. Another sign for detecting meningitis is the “jolt accentuation”, which involves worsening of headache when the head is moved side to side at a frequency of 2 or 3 times per second. This sign is one of the most sensitive for diagnosing meningitis, with a sensitivity of 97%.
While having the Kernig sign isn’t conclusive for diagnosing meningitis, if you have this sign along with a fever and recent onset of headaches, there’s a pretty high chance you could have bacterial meningitis.