Can anyone explain the mechanism behind Nuchal Rigidity, Brudziski, and Kernig?

[CuriousGeorge2]

I think I understand the mechanism for why one has nuchal rigidity with meningitis. If you flex the neck, the spinal canal elongates and the meninges stretch, which is painful if they are inflamed. As a result, you'll guard against neck flexion and this is what results in nuchal rigidity.


I think I understand Kernig's sign. If you try to extend the leg fully with the hips flexed, you strecth the peripheral nerves which pulls on the meninges and causes pain if you have meningitis.

However, I don't quite understand how Brudzinski's sign works...

If a patient is supine and I flex their neck, why do they flex their hips and knees if they have meningitis (+ Brudzkinski's sign)? Shouldn't flexion of the hips and knees further stretch the peripheral nerves/ nerve roots and pull on the meninges?

I guess I don't understand what happens to the spinal canal/ cord when the hips and knees are flexed compared to when they are extended. I am a visual person so I have tried to look for an image that shows what happens to the cord during these maneuvers, but haven't had any luck - if anyone has a good explanation or image that can explain it, that would be really helpful. Thanks in advance,

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[ArcGurren]

There's a lot of false positives and false negatives with Brudzinski's and Koenig's signs, but they work essentially on that principle - inflamed meninges will stretch, cause pain. These maneuvers all put some slight torsion or stretch on your spine.

Meningitis also doesn't always present with nuchal rigidity, but if there's mental status changes you should IMMEDIATELY suspect it