Getting your medical info on Wiki is not the best place to be looking. Don't forget that when any muscle in the body is worked it rips, tears, stretches and when it heals it becomes stronger and can be more flexible too. I've been playing with my ass for a long time now and I've never had any problems relating to it. I've never had an anal injury except for the minor pokes from fingernails on occasion. People think my ass is always being penetrated but it's not.. I do a lot of anal on film and in my personal life but it is spaced out. The great thing about what I do to my ass? It always tightens back up immediately after I'm done playing with it. Some seem to think it stays open forever after I fuck it with big stuff and flaps in the wind but sorry, it doesn't, if that was the case, I wouldn't even do anal..
Thanks for your medical concern though, I think? lol..