Brudzinski’s sign is a physical test used to detect irritation of the membranes surrounding the brain and spinal cord, most commonly caused by meningitis. The test is positive when passively bending a patient’s neck forward causes their hips and knees to flex involuntarily. It’s one of the classic bedside signs taught to medical students worldwide, though its real-world accuracy is more limited than many people assume.
How the Test Is Performed
The patient lies flat on their back. A clinician places their hands behind the patient’s head and gently lifts it, flexing the neck so the chin moves toward the chest. The test is positive if this movement triggers an involuntary bending of the hips and knees. The patient isn’t choosing to pull their legs up; it’s a reflexive response.
This reflex happens because the inflamed membranes (called meninges) that line the brain and spinal cord are being stretched. When the neck bends forward, it pulls on these already-irritated tissues. The body responds by reflexively drawing the legs upward to reduce tension on the spinal cord and its coverings. Think of it as the body’s attempt to shorten itself and relieve the painful stretch.
How It Compares to Kernig’s Sign
Brudzinski’s sign is often mentioned alongside Kernig’s sign, another bedside test for meningeal irritation. While Brudzinski’s sign starts at the neck and watches for a response in the legs, Kernig’s sign works in the opposite direction. For Kernig’s test, the clinician bends the patient’s hip and knee to 90 degrees, then tries to straighten the knee. If the patient resists or feels pain when the leg is extended, the test is positive. Both tests probe the same underlying problem (inflamed meninges being stretched), just from different ends of the spine.
Along with neck stiffness, these two signs make up the trio of classic meningeal signs that clinicians check during a physical exam.
Diagnostic Accuracy
Brudzinski’s sign is far better at ruling meningitis in than ruling it out. A pooled analysis of nine studies found the sign has a sensitivity of only about 27.5%, meaning it misses roughly three out of four confirmed meningitis cases. Its specificity, however, is much higher at about 88.8%, meaning a positive result is fairly reliable as a red flag.
In practical terms: if the test is positive, there’s a meaningful chance meningitis is present and further testing is warranted. But a negative result offers little reassurance. Many people with meningitis will have a completely normal Brudzinski’s test. This is why clinicians never rely on physical signs alone to diagnose or exclude meningitis. Spinal fluid analysis remains the definitive test.
Populations Where It’s Less Reliable
The sign becomes even less dependable at the extremes of age. In infants younger than 6 months, Brudzinski’s sign and neck stiffness are not accurate for diagnosing meningitis. Babies’ neurological systems are still developing, and their meningeal response to infection can look very different from an older child’s or adult’s. In this age group, clinicians look for other clues: a bulging soft spot on the skull, irritability, poor feeding, or a high-pitched cry.
Elderly patients also frequently lack classic meningeal signs, even with severe infection. The same is true for people who are immunocompromised or in a coma. In all of these groups, the absence of Brudzinski’s sign carries essentially no diagnostic weight.
The Four Original Brudzinski Maneuvers
Most people know only the neck sign, but Józef Brudzinski, the Polish pediatrician who developed the test in the 1890s, actually described four separate maneuvers for detecting meningitis. The neck sign became the most widely used, but the others target the same underlying problem through different movements:
- Cheek sign: Pressing on both cheeks just below the cheekbone triggers involuntary bending of the forearms and arms.
- Symphyseal sign: Pressing on the pubic bone at the front of the pelvis causes reflexive bending and outward movement of the hips and knees.
- Contralateral reflex sign: Passively bending one leg causes the opposite leg to flex in response.
These lesser-known variations are rarely used in modern practice, but they all exploit the same principle: when inflamed meninges are stretched or compressed, the body reflexively contracts to minimize that stretch.
What a Positive Sign Means for the Patient
A positive Brudzinski’s sign is not a diagnosis. It’s an early physical clue that the protective membranes around the brain and spinal cord may be inflamed. Meningitis is the most common cause, but other conditions can irritate the meninges too, including bleeding around the brain (subarachnoid hemorrhage) and certain cancers that spread to the central nervous system.
When the sign is positive, the next step is typically a lumbar puncture (spinal tap) to collect and analyze spinal fluid. That fluid sample reveals whether infection is present, what type of organism is responsible, and how severe the inflammation is. Blood tests and imaging may also be part of the workup. The physical exam gets the process started, but the fluid analysis is what drives treatment decisions.