How has the material contribution test been interpreted in medical malpractice cases?

The Hanke court at paras. 24-25 expanded on this notion when it said: [T]he cases in which the "material contribution" test is properly applied involve two requirements. First, it must be impossible for the plaintiff to prove that the defendant's negligence caused the plaintiff's injury using the "but for" test. The impossibility must be due to factors that are outside of the plaintiff's control; for example, current limits of scientific knowledge. Second, it must be clear that the defendant breached a duty of care owed to the plaintiff, thereby exposing the plaintiff to an unreasonable risk of injury, and the plaintiff must have suffered that form of injury. In other words, the plaintiff's injury must fall within the ambit of the risk created by the defendant's breach. See also Nattrass v. Weber, 2010 ABCA 64 at paras. 43-47.