My knee does'nt hurt when I run, sprint, make cuts, jump, walk up/down stairs or anything. But when I step up on something decently high where almost all my body is completely on my knee joint I get a pain that feels like someone is stabbing me in my knee its very intense and also when I do leg extensions with a decent amount of weight and when I step up on something while walking backwards. It is my right knee and hurts below my knee cap on the left and sometimes on the bottom left of the knee cap. Also the knee that hurts looks smaller than my left knee and mishapen. I am in Army ROTC and would really appreciate the help. I dont understand how I can do so many different movements but those three little simple movements kill me. Please help!