I actually have a problem similar to that. I have been diagnosed with tendinitis in my left knee, but I have frequent pain in my right knee also. My right wrist often hurts, as do both ankles. I have sprained my right ankle once, but I've never sprained or broken any other body part. (except my nose)
I really wonder if there may be some disease or condition that causes my tendons to become weak.
When I was diagnosed with tendinitis, the doctor said that my knee cap had a black spot on it that he said might have been a bruised bone. Maybe that's a syptom for something that I've just never heard of?
Also, I'm only 18, so I seriously doubt that I have any type of arthritis, but I guess it is possible.