I don't think the damage actually happens from the anal sex itself. Its not relaxing the muscles of the rectum during the intercourse that causes the problems. When the muscles are not relaxed they get ripped and blood flow problems do to this also cause "grapes" after the fact. You can get it fixed by going to a surgeon but it is costly and painful to do, and if you do the same thing again the problem can get out of control after the surgery.

Correct me if I'm wrong... I don't have any links to back up this because I'm to lasy to find them. I read it a while back though.