We used to have a horse that suffered from sacroiliac strain. It's called "jumper's bump" among horse owners because it's often seen in horses who jump a lot.
Since our horses are competitive and they enter races, we had to give him away to a home that wouldn't require him to jump much. I think he is still racing, but only in flat races as a runner.
Sometimes I wonder if we could have kept him but I think that his sacroiliac injury would have given him too much pain to continue with us anyway. I'm glad he has a home where he isn't required to strain himself.