Need help figuring out what muscle cramp im getting because I dont think its a charley horse

So I (13, AMAB) have been getting what I belived to be charley horses in my knees, once every few months, but based on what i can find online about them, I think its something else. Mainly because i saw someone say to stand up, which i cant do, because my knee is locked, usually at a 90 ish degree angle, because it usually happens when I'm sitting down. And from what i can tell, charley horses usually go away on their own, (correct me if im wrong) and I have to kind of snap it back into place? Sorry if this is super vauge, If theres any other info i can provide, please ask.