On March 25, the Supreme Court of Pennsylvania issued an opinion in a case called Brady v. Urbas holding that evidence of consent to a surgery could be used in a prejudicial way to insinuate that consent to the procedure amounted to consent to risks of negligence.
As Max Kennerly explains in his comment about the case, defendant doctors often try "to make a big fuss about the “risks of the procedure” that were disclosed to the patient. The argument is irrelevant and prejudicial: obviously, the patient didn’t consent to the risk of negligent treatment; rather, the patient consented to the risks of the procedure if it was done properly. But the defendants always raise it anyway, mostly to confuse the jury into thinking that the patient accepted this “risk” when they went in."
In Brady, the court agreed and, for that reason, decided that the evidence related to the consent to the procedure is irrelevant in cases of medical malpractice, other that those cases in which the claim is based on lack of informed consent. Obviously, in those cases, the evidence of consent is not only relevant but critical.
The TortsProf has more on the story here. Professional Liability Matters has more here.