It was hyperextended, had nothing to do with being out of shape........although the meniscus tear (which is common) was probably done earlier!
Have you had a knee done before? I ask, because when you recover, you have to be very stubborn about getting back all range of motion before any scar tissue sets up. People who don't stretch it and regain ROM can end up worse that before. It's painfull. Light leg exts, while helping or lightly pressing down even helped me get the last bit of ROM back. I had chunks floating around in there that felt like I'd kneel on a nail. Nasty. That knee is now stronger than the other which is the dominant one. Good luck w/ it.