What Causes Knee To Give Way?

While practicing simple jumps in a ballet class about five hous ago, I think I might have damaged ligaments in my knee.



Upon landing, I heard a loud pop sound and my knee gave out. I fell down (not landing on that knee) and it hurt quite a bit. I got an ice pack on it pretty quickly, and managed to walk for about ten meters before it hurt badly again.



At the moment, I can't straighten it or put much weight on it, and am walking with a sever limp. It hasn't been iced for a few hours, and there doesn't appear to be any swelling or redness, but it's pretty tender.