Aneurysms occur in blood vessels in locations where, due to age, disease or genetic predisposition, insufficient blood vessel strength or resiliency may cause the blood vessel wall to weaken and/or lose its shape as blood flows through it, resulting in a ballooning or stretching of the blood vessel at the limited strength/resiliency location, thus forming an aneurysmal sac. Left untreated, the blood vessel wall may continue to expand to the point where the remaining strength of the blood vessel wall is insufficient and the blood vessel will fail at the aneurysm location, often with fatal result.
To prevent rupture, various implantable prostheses may be introduced into the blood vessel. Minimally invasive methods for implantation of these prostheses have been developed to deliver these prostheses within the lumen of a body vessel. These prostheses are advantageously inserted intravascularly, such as from an implantation catheter. For example, to prevent rupture of an aneurysm, a tubular stent graft may be introduced into the blood vessel and deployed and secured in a location within the blood vessel such that the stent graft spans the aneurysmal sac. The outer surface of the stent graft, at its opposed ends, abuts and seals against the interior wall of the blood vessel at a location where the blood vessel wall has not suffered a loss of strength or resiliency. U.S. Pat. Nos. 6,423,084 and 7,060,091 disclose stents having varying outward radial force along their length to provide greater force in vessel regions requiring greater force and less force in regions requiring less. The stent graft channels the blood flow through the hollow interior of the stent graft, thereby reducing, if not eliminating, any stress on the blood vessel wall at the aneurysmal sac location.
One particular example of an aneurysm is a thoracic aortic aneurysm. The tortuous and hardened anatomy of a thoracic aortic aneurysm presents several challenges when implanting a prosthesis. Many current prostheses may be limited in their ability to conform to the radial and tortuous curvature, possibly resulting in poor sealing at the proximal and/or distal portion of the prosthesis. Some prostheses designs incorporate features designed to improve the radial curvature and conformability of the prosthesis when used in a directionally constrained fashion. For example, U.S. Patent Application No. 2002/0052644 discloses a prosthesis having a support structure including sliding links to permit flexibility. While the directional constraint may provide improved conformance, the same directional constraint makes the prosthesis more difficult to properly deploy in the thoracic aorta with a possibly increased risk of nonconformance should the directional features not line up with the appropriate radius (inner and outer).