Northwestern Memorial HealthCare and Cadence Health have finalized their plan to combine, creating a health system with four acute-care hospitals, 1,600 inpatient beds and a medical staff of more than 4,000 physicians. The merger, approved unanimously by the Illinois Health Facilities and Services Review Board in July, takes effect Sept. 1, Northwestern said Wednesday. Northwestern Chief Executive Dean Harrison will retain that role in the combined system. Cadence Health's CEO, Mike Vivoda, will become a Northwestern regional president. John Orsini, Cadence's CFO, will take over that role at Northwestern. Another Cadence executive, Liz Rosenberg, was named a senior vice president of strategy for the combined system.