The meaning of these waivers is to reduce the things you can sue for to negligence. Thus, if I've told you amputation is a possibility even if I do everything right, you can't complain afterward that you didn't know amputation was a possibility. Note that you are still allowed to claim that my actions caused the need for the amputation. You can even claim (with associated evidence) that my rate of amputations is inexplicably higher than the background rate. This evidence is not really there to give you information about whether or not you should have the operation....