I was walking the other day and all of a sudden my left knee almost gave out, felt like a nail was hammered through it. With every few steps there is excruciating pain. I limp when I walk. I have an ace bandage wrapped around my knee, the tighter the better it seems. Almost like it is holding something in place. It feels like it needs to pop, but it hurts. There is a grinding sensation as it pops. It is not swollen though. What is wrong with my knee?