my adult son wants to sue related to post-surgery bone-bleeding and associated pain that he was told could not be that bad. Went on for hours. Now has

Medical malpractice cases are very difficult to pursue and win in Wisconsin. I wrote a blog about how hard it is at our firm's web site. You mention this occurred in 2012, which would take your son out of the statute of limitations. In Wisconsin, you must file a lawsuit for medical malpractice within three years from the date of the occurrence or the claim is forever barred. There is an exception under the "discovery rule," but I don't see anything in your post that your allegation or suspicion of medical malpractice was only recently discovered.