What Causes Persistent Swelling And Bruising In Ankle?

I went to the fair about three years ago, and I was getting off one of the rides and the ride was probably about a foot and a half off the ground, and when I was getting down, I jumped and landed on my ankle. When I did, my ankle made this loud popping sound, and it hurt so bad. And by the time I got out of the gate, my whole foot was swollen. I continued to walk on it the rest of the night, for a good three to four hours. I went to the doctor about a week later, and he put me in a walking boot, and told me that if it wasn t better in a month then come back. So in a month, when I took it off, it was still bruised, and hurt. He then did a MRI, and called me a few days later and said that nothing was wrong. But my ankle twists very easily, and has a constant bruise on it. The bruise has never gone away, and is still sore often. But even when I don t twist or hurt it in a while, it stays bruised and sore. I don t know what is wrong with it. Do you think that since my doctor doesn t specialize in orthopedics, that he could have over looked something?