In any action arising from negligence in the rendering of medical care, a presumption of negligence shall arise if the following foundation facts are first established:
1. The plaintiff sustained any injury;
2. Said injury was proximately caused by an instrumentality solely within the control of the defendant or defendants; and 3. Such injury does not ordinarily occur under the circumstances absent negligence on the part of the defendant. If any such fact, in the discretion of the court, requires a degree of knowledge or skill not possessed by the average person, then in that event such fact must be established by expert testimony.