I work in the medical field in surgical functions. Most of the MD's I work with have 1 day a month they advise as expert witnesses...
I can say with a high level of accuracy that medical malpractice is VERY hard to prove....not to mention the 2nd and 3rd opinions given will be from other MD's and most of them don't want to bite the hand that feeds, especially if they are located in a close proximity to the facility in question.
In addition, you have to prove beyond a shadow of a doubt that the doctor, facility, employee etc was negligent and caused the harm.