Grantland posted an excellent piece on the history of the ACL injury a month or two ago. Arguably the best content they've ever put out. Here is the article:
http://www.grantland.com/story/_/id/10072331/derrick-rose-rob-gronkowski-rise-acl-tears
The ACL tears are becoming more common in all sports, not just football. The good thing is that new research is still coming out about how to correct and rehabilitate the injury.
I actually have a slight ACL tear in my right knee, no idea how I got it or how long I've had it, but it occasionally flares up. Inevitably, one day I'm going up getup from sitting down somewhere and it will completely tear. Hopefully the recovery process will be made even easier when it does.