Open aortic surgery ("OAS", also known as Open aortic repair, "OAR") describes a technique whereby an abdominal or retroperitoneal surgical incision is used to visualize and control the aorta for purposes of repair. OAS is used to treat aneurysms of the abdominal and thoracic aorta, aortic dissection, acute aortic syndrome, and aortic ruptures. In 2003, OAS was surpassed by endovascular aneurysm repair (EVAR) as the most common technique for repairing abdominal aortic aneurysms in the United States. In OAS for abdominal aortic aneurysm, the aneurysmal portion of the aorta is replaced with a graft, usually made of dacron or PTFE.