Johnny (P) was injured in an automobile accident. He was brought to Roseland Hospital, where surgery was performed on his left leg. In the hospital, he developed an infectious process in the fractured leg known as pseudomonas osteomyelitis. Ps claimed that Ds' negligence led to the amputation of P's left leg. Ps answered Supreme Court Rule 220 interrogatories by identifying Dr. Malcolm Deam as their expert witness against Ds. Dr. Deam is board certified in internal medicine and infectious diseases. Ds moved in limine to bar Dr. Deam's testimony as an expert at trial. A hearing was held on Dr. Deam's qualifications. The trial court granted the Ds' motion to bar Dr. Deam's testimony regarding the standard of care applicable to them. The court certified a question of law under this court's Rule 308.