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Must be some subtrope of Body Horror
Maybe To the Pain?
Health sure is versatile. It's possible to be both light-headed and dim-witted. At the same time, no less.
Just plain "someone breaks someone's limbs by bending them the wrong way" is People Sit on Chairs. (It's simply a fact of anatomy and physics.)
As far as situations with meaning where this can happen, though, check out Cold-Blooded Torture, Jack Bauer Interrogation Technique, and for more specific situations, Fold-Spindle Mutilation and Knee-capping. It's also a good way to immediately mark someone as a Sadist and/or Combat Sadomasochist
Sickening "Crunch!" is related.
Edited by Scorpion451
Breaking the joints of your enemies by bending them backward until it snap.