I had it before. I had to keep this brace contraption on my knee, ice it and stay off it (I could walk around, just nothing strenuous) until it healed.
I did go to physical therapy for my knee, yup. I had to do all those stretches and exercises. And yeah, I have a lot of knee issues still, but I was in a car accident that made it worse, I have cartilage floating around in my knee that I need to have taken out.