What is the test for negligence in a medical malpractice case involving a sore in the foot?

Although Cottrelle v. Gerrard is a medical malpractice case involving delayed diagnosis and treatment, it is very different from this case. In Cottrelle, the plaintiff who had suffered from diabetes for more than 30 years, developed a sore in her left foot between her toes. It became infected and eventually became gangrenous requiring her leg to be amputated below the knee. The trial judge found the defendant, the plaintiff’s family doctor, negligent in the treatment of the sore and that the negligence was a “material cause” of the loss.