I have a pain that radiates down from my knee on the outside of my leg. It feels like it is at a diagonal from my knee for 4 - 6 inches. With the pain, it feels like my knee wants to give way. It happens if I'm hiking downhill or jar my knee. I want to go backpacking, but I don't think I could go downhill with a heavy pack. I have not sustained any kind of injury or impact. It just started doing this all of a sudden. What could possibly be the problem and treatment?