Patent Publication Number: US-2019192320-A1

Title: Prosthesis having an everting pivoting fenestration

Description:
RELATED APPLICATIONS 
     The present application is a divisional application that claims priority to U.S. Utility application Ser. No. 13/826,289 filed Mar. 14, 2013, entitled Prosthesis Having An Everting Pivoting Fenestration, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The functional vessels of human and animal bodies, such as blood vessels and ducts, occasionally weaken or even rupture. For example, the aortic wall can weaken, resulting in an aneurysm, or it may develop a tear in one of the layers of the aortic wall resulting in an aortic dissection. 
     One common surgical intervention for weakened, aneurysmal or ruptured passageways or ducts involves the use of an endoluminal prosthesis to provide some or all of the functionality of the original, healthy passageway or duct and/or preserve any remaining vascular integrity by replacing a length of the existing passageway or duct wall that spans the site of failure or defect. Endoluminal prostheses may be of a unitary construction or may be comprised of multiple prosthetic modules. They also may be a single tubular device or a bifurcated branching device depending on the desired application. 
     In many cases, however, the damaged or defective portion of the vasculature may include a branch vessel branching from the main vessel. For example, in the case of the abdominal aorta, there are at least three major branch vessels, including the celiac, mesenteric, and renal arteries, as well as others, leading to various other body organs. Thus, when the damaged portion of the vessel includes one or more of these branch vessels, some accommodation must be made to ensure that the prosthesis does not block or hinder blood flow through the branch vessel. In many instances, there may be insufficient healthy tissue in the aorta near the branching vessels to adequately seal a prosthesis without partially or completely blocking one or more of the branching vessels. 
     SUMMARY 
     The present disclosure relates to an endoluminal prosthesis, such as a stent graft, that includes one or more fenestrations to accommodate endovascular disease, such as an aneurysm, in cases where one or more side branches are involved. In one aspect, the prosthesis includes fenestrations that are pivotable to accommodate the dynamic geometry of the aortic branches. The use of pivotable fenestrations also allows the design of a family of standard stent grafts for “off-the-shelf” use to accommodate a majority of aneurysm cases involving side branches and reducing the need for customization in many cases. 
     In one aspect, a prosthesis includes one or more pivotable fenestrations that accommodate the variability associated with patient anatomy, both statically and dynamically. For example, one or more pivotable fenestrations provided on a prosthesis may lie outside the surface plane of the body of the prosthesis and will allow a branch vessel stent, graft or stent-graft that has been placed in the fenestration to pivot into any orientation required to meet and seal the branch vessel device in the branch vessel. 
     The pivotable fenestrations may include an inner perimeter surrounding the fenestration (the hole) in the graft, a band of material surrounding the inner perimeter and extending radially outwardly from the surface plane of the prosthesis, and an outer perimeter surrounding the band of material where the band joins the surface of the prosthesis. The band of material extending from the surface of the prosthesis is sufficiently flexible to permit the fenestration to move such that a branch stent disposed in the fenestration may be oriented upwardly, downwardly, laterally, diagonally and the like. Hence, a device of a single geometry may accommodate a variety of patient anatomies. 
     In a further aspect, the inner perimeter, the band of material, and the outer perimeter may have a geometric shape and include a support frame disposed about a surface of the band of material. In one embodiment, the support frame includes a plurality of support units having curved segments interconnected by a plurality of apices; a circular reinforcement member disposed on an end of the support frame; and at least one flange positioned on an end of the support frame opposite of the reinforcement member. The curved segments may curve radially outward and away from a longitudinal axis of the prosthesis. The curved segments may have a generally concave configuration with respect to the exterior surface of the prosthesis. The support frame may also include a flange. In some embodiments, the flange may be comprised of a portion of a curved segment and at least one apex. In some embodiments, the support frame is monostable. The band of material may have a depth relative to the surface plane of the prosthesis. The prosthesis may include one stent that is positioned in an out-of-phase configuration with the remaining stents. The inner perimeter, the band, and the outer perimeter of the pivotable fenestration may be at least partially demarcated by the struts of a stent positioned on the body of the stent graft. The support frame may, in some embodiments, comprise helical support units. 
     The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows an embodiment of a fenestrated prosthesis having everting pivotable fenestrations. 
         FIG. 2  shows an enlarged view of a pivotable fenestration shown in  FIG. 1 . 
         FIG. 3  shows a perspective view of a support frame for a fenestrated prosthesis having everting pivotable fenestrations shown in  FIG. 1 . 
         FIG. 4  is a partial and internal view of the prosthesis as shown in  FIG. 1 . 
         FIG. 5 a    shows a view from within the lumen of an embodiment of a fenestrated prosthesis having an embodiment of a retention assembly for restraining everting pivotable fenestrations of a fenestrated device. 
         FIG. 5 b    shows a view from the exterior of an embodiment of a fenestrated prosthesis having an embodiment of a retention assembly for restraining everting pivotable fenestrations of a fenestrated device. 
         FIG. 5 c    shows a side cross-sectional view of an embodiment of a fenestrated prosthesis having an embodiment of a retention assembly for restraining everting pivotable fenestrations of a fenestrated device. 
         FIG. 6 a    shows a view from within the lumen of an embodiment of a fenestrated prosthesis having an alternative embodiment of a retention assembly for restraining everting pivotable fenestrations of a fenestrated device. 
         FIG. 6 b    shows a view from the exterior of an embodiment of a fenestrated prosthesis having an alternative embodiment of a retention assembly for restraining everting pivotable fenestrations of a fenestrated device. 
         FIG. 6 c    shows a side cross-sectional view of an embodiment of a fenestrated prosthesis having an alternative embodiment of a retention assembly for restraining everting pivotable fenestrations of a fenestrated device. 
         FIG. 7  shows an embodiment of a delivery device used with a retention system for deployment of a fenestrated prosthesis having everting pivotable fenestrations. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to an endoluminal prosthesis, such as a stent graft that includes one or more fenestrations to accommodate endovascular disease, such as an aneurysm in cases where one or more side branches are involved, and a side branch prosthesis is deployed within the fenestration to permit fluid flow from the endoluminal prosthesis into the branch vessel. The prosthesis includes fenestrations that pivot as needed to accommodate the dynamic geometry of the aortic branches. In various aspects shown and described in more detail below, for example, one or more pivotable fenestrations provided on a prosthesis lie outside the surface plane of the body of the prosthesis and will allow a branch vessel stent, graft or stent-graft that has been placed in the fenestration to pivot into a variety of orientations required to meet and seal the branch vessel device in the branch vessel. The orientation of the fenestrations may dynamically change over time as needed by changing anatomy. 
     Definitions 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. 
     The term “distal” means a location or direction that is, or a portion of a device that when implanted is further downstream in the direction of or with respect to blood flow. 
     The term “proximal” means a location or direction that is, or a portion of a device that when implanted is further upstream in the direction of or with respect to blood flow. 
     The term “fenestration” means an opening provided through a surface of a prosthesis from the interior of the prosthesis to the exterior of the prosthesis and may have a variety of geometries, including circular, semi-circular, oval, oblong, as well as other geometries. 
     The term “biocompatible” refers to a material that is substantially non-toxic in the in vivo environment of its intended use, and that is not substantially rejected by the patient&#39;s physiological system (i.e., is non-antigenic). Examples of biocompatible materials from which textile graft material can be formed include, without limitation, polyesters, such as polyethylene terephthalate, fluorinated polymers, such as polytetrafluoroethylene (PTFE) and fibers of expanded PTFE, and polyurethanes. In addition, materials that are not inherently biocompatible may be subjected to surface modifications in order to render the materials biocompatible. Examples of surface modifications include graft polymerization of biocompatible polymers on the materials surface, coating of the surface with a cross-linked biocompatible polymer, chemical modification with biocompatible functional groups, and immobilization of a compatibilizing agent such as heparin or other biocompatible substances. Thus, any fibrous material having sufficient strength to survive in the in vivo environment may be used to form a textile graft, provided the final textile is biocompatible. Fibers suitable for making textile grafts include polyethylene, polypropylene, polyaramids, polyacrylonitrile, nylon, and cellulose, in addition to the polyesters, fluorinated polymers, and polyurethanes as listed above. Furthermore, bioremodelable materials may also be used singly or in combination with the aforementioned polymer materials. The textile may be made of one or more polymers that do not require treatment or modification to be biocompatible. The graft may be constructed from woven multifilament polyester, for example and without limitation, Dacron™, produced by DuPONT. Dacron™ is known to be sufficiently biologically inert, non-biodegradable, and durable to permit safe insertion inside the human body. 
     The term “prosthesis” means any device for insertion or implantation into or replacement for a body part or function of that body part. It may also mean a device that enhances or adds functionality to a physiological system. The term prosthesis may include, for example and without limitation, a stent, stent-graft, filter, valve, balloon, embolization coil, and the like. 
     The term “tubular” refers to the general shape of an endoluminal device which allows the module to carry fluid along a distance or fit within a tubular structure such as an artery. Tubular prosthetic devices include single, branched, and bifurcated devices. Tubular may refer to any shape including, but not limited to, tapered, cylindrical, curvilinear, or any combination thereof. A tubular device may have a cross-sectional shape that is, circular, substantially circular or the like. However, it should be understood that the cross-sectional shape is not limited thereto, and other shapes, such as, for example, hexagonal, pentagonal, octagonal, or the like are contemplated. The term “endoluminal” refers to or describes objects that can be placed inside a lumen or a body passageway in a human or animal body. A lumen or a body passageway can be an existing lumen or a lumen created by surgical intervention. As used in this specification, the terms “lumen” or “body passageway” are intended to have a broad meaning and encompass any duct (e.g., natural or iatrogenic) within the human body and can include a member selected from the group comprising: blood vessels, respiratory ducts, gastrointestinal ducts, and the like. “Endoluminal device” or “endoluminal prosthesis” thus describes devices that can be placed inside one of these lumens. 
     The term “graft” or “graft material” describes an object, device, or structure that is joined to or that is capable of being joined to or implanted in or against a body part to enhance, repair, or replace a portion or a function of that body part. A graft by itself or with the addition of other elements, such as structural components, may comprise an endoluminal prosthesis. The graft may be comprised of a single material, a blend of materials, a weave, a laminate, or a composite of two or more materials. The graft may be constructed from natural or organic materials, for example and without limitation, a biological scaffold or bioremodelable material, such as small intestine submucosa (“SIS”), which is commercially available by Cook Biotech, West Lafayette, Ind. The graft may also be constructed from a synthetic material, for example and without limitation, a polymer. The graft may be formed from a single layer or multiple layers of material. In embodiments employing a plurality of layers of material, the layers may remain separate, or may be attached to each other through a secondary process such as sintering, curing, adhesives, and sutures or the like. 
     The term “stent” means any device or structure that adds rigidity, expansion force or support to a prosthesis. A stent is used to obtain and maintain the patency of the body passageway while maintaining the integrity of the passageway. Also, the stent may be used to form a seal. The stent may be located on the exterior of the device, the interior of the device, or both. A stent may be self-expanding, balloon-expandable or may have characteristics of both. A variety of other stent configurations are also contemplated by the use of the term “stent.” The stents may be comprised of a metallic material selected from stainless steel, silver, platinum, palladium, gold, titanium, tantalum, iridium, tungsten, cobalt, chromium, cobalt-chromium alloy 1058, cobalt-based 35N alloy, nickel-based alloy 625, a molybdenum alloy, a molybdenum alloy including about 0.4% to about 0.8% of lanthanum oxide (Li 2 O 3 ), and a nickel-titanium alloy, such as Nitinol, or other suitable materials as known in the art. The stents may be made of a wire, or may be laser or cannula cut, or manufactured by other known methods. 
     The term “branch vessel” refers to a vessel that branches off from a main vessel. Examples are the celiac and renal arteries which are branch vessels to the aorta (i.e., the main vessel in this context). As another example, the hypogastric artery is a branch vessel to the common iliac, which is a main vessel in this context. Thus, it should be seen that “branch vessel” and “main vessel” are relative terms. 
     “Longitudinally” refers to a direction, position or length substantially parallel with a longitudinal axis of a reference. 
     “Circumferentially” refers to a direction, position, or length that encircles a longitudinal axis of reference. The term “circumferential” is not restricted to a full 360° circumferential turn or to a constant radius. 
     The terms “patient,” “subject,” and “recipient” as used in this application refer to any animal, especially humans. 
     The figures show a fenestrated prosthesis  10 , here a stent graft, having a tubular body and comprising a biocompatible material, having one or more fenestrations  12  pivotable in a direction away from an axis perpendicular to a longitudinal axis of the prosthesis. For example, the fenestrations  12  may be pivotable in any direction away from an axis perpendicular to a longitudinal axis of the prosthesis  10 . The pivotable fenestrations  12  include a first, inner perimeter  26  surrounding the fenestration  12  having a diameter, a band  28  of flexible material attached to and surrounding the first perimeter  26 , and a second, outer perimeter  30  attached to and surrounding the band  28  of flexible material. The band  28  of material has a first diameter that is substantially the same as the diameter of the first perimeter  26 , and a second diameter substantially the same as the second perimeter  30 . The diameter of the band of material decreases in a direction away from the surface  20  of the graft  14  from the second perimeter to the first perimeter. The band  28  of flexible material includes a support frame  48  having a plurality of support units disposed about a surface of the band  28 . In a deployed position, the pivotable fenestrations  12  have an everted configuration with respect to a surface of the prosthesis  10  and have a diameter extending from a side wall of the graft forming a geometric shape. The fenestration  12  may be disposed at the apex of the geometric shape. 
     In some aspects, the prosthesis  10  is intended for placement in the abdominal aorta and to accommodate vessels that branch from the aorta, for example, the renal arteries, and into which a branch vessel prosthesis may be placed. However, the prosthesis  10  is not limited for use in the abdominal aorta but may be used in other vessels of the body from which other vessels branch, such as the ascending thoracic aorta, the descending thoracic aorta, as well as other body vessels. 
       FIG. 1  shows an embodiment of a prosthesis  10  that is a stent graft. The prosthesis  10  includes graft material  14  associated with one or more stents  16 . The prosthesis  10  has a proximal end  22 , a distal end  24 , and a lumen  18  extending through the prosthesis  10  to permit passage of blood flow from the proximal end  22  to the distal end  24 . The stents  16  may be placed on the external surface  20  and/or internal surface  21  of the graft material  14 . In one particular embodiment, the prosthesis  10 , such as that shown in  FIG. 1 , has external body stents  16   a ,  16   b ,  16   c ,  16   d  and  16   e , and at least one internal stent  16   f . Additionally, or alternatively, depending on the location of the place of the prosthesis  10  or a particular need, a sealing stent  45  may be placed at either or both the proximal and distal ends  22 ,  24  of the prosthesis  10 . The prosthesis  10  also may include an attachment mechanism, for example, an attachment stent  42 , at either or both ends of the prosthesis  10 , to further secure the prosthesis  10  within the body vessel and prevent migration of the prosthesis  10 . The attachment stent  42  includes barbs  43  that may assist with securing the prosthesis  10  within the target vessel. 
     The prosthesis  10  has several openings or fenestrations that extend from the internal surface  21  to the external surface  20  of the graft material  14 . The prosthesis  10  of  FIG. 1  has two pivotable fenestrations  12 , at least one non-pivotable fenestration  38 , and a scallop  40 . Here, the scallop  40  is placed at the proximal end of the prosthesis  10 . As shown in greater detail in  FIG. 2 , the pivotable fenestration  12  has an inner perimeter  26  surrounding the fenestration  12 , a band  28  surrounding the inner perimeter  26 , and an outer perimeter  30  surrounding the band  28 . The outer perimeter  30  diameter is greater than the band  28  diameter and the inner perimeter diameter  26 . The inner perimeter  26 , the band  28  and the outer perimeter  30  would be substantially concentric with one another if they were in the same plane, for example the surface plane of the graft. The inner perimeter  26 , the band  28  and the outer perimeter  30  may form a geometric shape, resembling, for instance, a frustoconical cone extending from the surface of the graft material  14 . The fenestration  12  is provided at the peak or top of the geometric shape. In other embodiments, the band  28  may comprise a tapered, flexible tube extending from the outer perimeter  30  and the inner diameter  26 . In this embodiment, the pivotable fenestrations  12  have a generally circular configuration. In alternative embodiments, the pivotable fenestrations  12  may have other suitable configurations, including, but not limited to, oblong, oval, rectangular, or triangular. A support frame  48  having a plurality of support units  50  surrounds the fenestration  12  and is positioned on a surface of the band  28 . In the embodiment shown in  FIGS. 1 and 2 , the frame is positioned on the outer surface of the band  28 . In other embodiments, the frame may be positioned on an inner surface of the band  28 . 
     As shown by  FIGS. 1 and 2 , the pivotable fenestration  12  has an everting configuration with respect to the surface of the prosthesis  10 . As used throughout this specification, the term “everting” means extending or protruding radially outward from a surface of the graft material  14 . The term “inverting” means extending or protruding radially inward from a surface of the graft material. The outer perimeter  30  lies substantially flush (in the same plane) of the graft material  14 , and the band  28  and the outer perimeter  30  form a geometric shape, such as a dome, or frustoconical cone extending outward from the surface of the prosthesis  10 . As will be discussed below, the support units  50  of the support frame  48  help to maintain the pivotable fenestration  12  in the everting configuration when the prosthesis  10  is deployed in a patient and prevent the pivotable fenestration  12  from inverting. The pivotable fenestrations  12  are positioned to align with, for example, the renal arteries of a patient. In other aspects, the one or more pivotable fenestrations  12  may be positioned to align with other branch arteries throughout a diseased vasculature. Additional fenestrations and scallops as disclosed here may also be included. As shown in these Figures and throughout the Figures, imageable markers  35 , which may be viewed during and after placement of the prosthesis  10  may be placed at various locations on the prosthesis  10  to identify certain aspects of the prosthesis and their location during the implantation procedure and facilitate correct placement of the fenestrations  12 ,  38 , scallop  40 , the ends of the prosthesis and the like. 
     In some embodiments, the outer perimeter  30  surrounding the band  28  may be attached to the graft material  14  by a suitable attachment method including suturing circumferentially about an aperture disposed through graft material  14 . In alternative embodiments, inner perimeter  26 , band  28 , and the outer perimeter  30  may be integral with and formed from the graft material  14  of the prosthesis  10  by creating a protrusion, as described in co-pending U.S. patent application Ser. No. 12/548,120, herein incorporated by reference. The band  28  may be comprised of the same or different biocompatible material as the graft material  14 . For example, the biocompatible material of the band  28  may have greater pliability than the first biocompatible graft material used for the tubular graft body. The band  28  is sufficiently flexible to permit the fenestration  12  to move such that a branch stent disposed in the fenestration  12  may be oriented upwardly, downwardly, laterally, diagonally and the like. In some embodiments, the band has up to about 180 degrees of freedom of movement relative to the surface plane of the prosthesis  10 . In other embodiments, the band may have greater than 180 degrees of freedom of movement or less than 180 degrees of freedom of movement. Accordingly, the pivotable fenestration  12  allows the prosthesis  10  to be used with a variety of patients, due to its ability to adapt to the variance in the positioning of the diseased branch vessels. For example, if a body branch vessel is or becomes offset longitudinally or axially from a pivoting fenestration  12 , the pivoting fenestration  12  may pivot the branch vessel prosthesis in the necessary direction and to the necessary degree to maintain the branch vessel prosthesis in place in the branch vessel. 
     The band  28  may be tapered such that the diameter decreases throughout its depth. The depth of the band  28  may range from 3 to 10 mm, and preferably is about 6 mm. The inner perimeter  26  has a diameter that is smaller than the diameter of the outer perimeter  30 . The diameter of the inner perimeter  26  may be determined based on the average size of the targeted branch vessel. In this aspect, the prosthesis  10  may be used to repair a diseased renal artery. Accordingly, the average diameter of the inner perimeter  26  may be based on the average of the diameter of the openings to the renal arteries, or about 6 mm. The diameter of the outer perimeter  30  may be determined based on the desired amount of movement and the desired patency of the prosthesis  10 . The diameters of the inner perimeter  26  and the outer perimeter  30 , combined with depth of the band  28 , provide the requisite amount of surface area for the pivotable fenestration  12  to pivot during deployment of a secondary branch prosthesis into the fenestration  12  based on dynamic changes to the anatomy. Reinforcement members may be attached to the graft  14  surrounding the outer perimeter of the pivotable fenestrations  12 . In addition, reinforcement members may be provided about the perimeter of the non-pivoting fenestration  38 , and the perimeter of the scallop  40 , respectively. In one preferred aspect, the reinforcement members comprise a wire that is sutured about the fenestration  12 ,  38 , or scallop  40 , to reinforce the fenestration or scallop. The reinforcement members may be made of any suitable material. One preferred material is a superelastic or shape memory material, such as Nitinol. In another preferred embodiment, the reinforcement members may be made of radiopaque or other imageable material. In another embodiment the reinforcement members may be a wire that is looped about itself into a ring with unattached ends such that the ring may be expanded or contracted in diameter, such as described in co-pending U.S. patent application Ser. No. 10/962,632, herein incorporated by reference. 
       FIG. 3  shows an embodiment of the support frame  48 . In a preferred aspect, the support frame  48  is a continuous wire formed into a plurality of support units  50  comprising curved segments  54  having a generally concave configuration with respect to the exterior surface  20  of the prosthesis  10  joined by apices  56   a  and  56   b  and a circular, reinforcement member  44 . The reinforcement member  44  is configured to be positioned about the inner perimeter  26  of the pivotable fenestrations  12 . As shown in this embodiment, the support frame  48  has three support units  50 . Apices  56   a  are positioned adjacent to the reinforcement member  44 . The ends of the concave, curved segments  54  and apices  56   b  form a flange  58  positioned on an end of the support frame  48  opposite of the reinforcement member  44 . The flange  58  may abut or connect to the reinforcing member  44  positioned about the outer perimeter  30  of the pivotable fenestration  12 . The flange  58  is configured to lie generally against a surface of the band  28  and help facilitate attachment of the frame  48  to the band  28 . The concave, curved segments  54  of the support members  50  generally curve radially outward and away from a surface of the prosthesis  10 . As such, the support units  50  are configured to extend radially outward from the surface of the prosthesis  10  when positioned on the band  28  of the pivotable fenestration  12 . The support frame  48  is generally monostable, which means that the frame will always return to its expanded, resting configuration upon removal of any compression or restraint, which prevents the support frame  48  from inverting. While not being held to any theory, it is believed that the concave, curved segments  54  of the support units  50  of the support frame  48  help prevent any inversion of the frame. As such, the support frame  48  helps bias the pivotable fenestration  12  into an everting configuration with respect to a surface of the prosthesis  10  and prevents the pivotable fenestration  12  from protruding into the lumen of the prosthesis  10 . In addition, the pivotable fenestration  12  having an everting configuration provides flexibility to ensure compatibility with an array of patient vessel locations. While the support frame  48  of this embodiment is comprised of a single, continuous wire, alternative embodiments of the support frame  48  may comprise a plurality of wire segments joined together to form the support units  50  and desired configuration of the support frame  48 . In addition, alternative embodiments of the support frame  48  may comprise a continuous wire formed into one or more support units having a generally coiled helical configuration. 
     Referring back to  FIG. 1 , stents  16  may be configured in the form of one or more “Z-stents”, each of which may comprise a series of substantially straight segments  32  interconnected by a series of bent segments  36 . The bent segments may comprise acute bends or apices. The stents are arranged in a zigzag configuration in which the straight segments  32 ,  34  are set at angles relative to each other and are connected by the bent segments. However, the stents  16  may comprise any suitable configuration and one or more stents  16  may be provided. When Z-stents are used, a portion of the outer perimeter  30  of one or more of the fenestrations  12  may lie between adjacent struts  32 ,  34  of one of the stents  16 . The stents  16  may be either self-expanding or balloon expandable. Preferably, they are self-expanding. However, a combination of self-expanding and balloon expandable stents  16  also may be contemplated. 
     Stent amplitude, spacing and stagger are preferably optimized for each prosthesis design. In some aspects, the apices or bends  36  of the struts  32 ,  34  may be staggered for minimal contact with each other. As shown in  FIG. 1 , the stents  16   a ,  16   b , and  16   c  are positioned adjacent each other and the apices  36  of each row are in circumferential alignment or “in phase”, with the apices of longitudinally adjacent rows. In addition, stent  16   e  is also positioned in phase with stents  16   a ,  16   b , and  16   c . Stent  16   d  is positioned “out of phase” by about 180 degrees with longitudinally adjacent row  16   c , such that circumferentially about the surface of the graft, every other apex of the stent  16   c  matches with every other apex of stent row  16   d . In other embodiments, the stent  16   d  may be positioned in phase with longitudinally adjacent row  16   c , or the stent  16   d  may be out of phase with stent  16   c  by an amount less than 180 degrees. Furthermore, internal stent  16   f  is positioned out of phase by about 180 degrees with longitudinally adjacent row  16   a , such that circumferentially about the surface of the graft, every other apex of the stent  16   a  matches with every other apex of stent row  16   e . In other embodiments, the stent  16   f  may be positioned in phase with longitudinally adjacent row  16   a , or the internal stent  16   f  may be out of phase with stent  16   a  by an amount less than 180 degrees. In an exemplary embodiment, the inner perimeter  26 , the band  28 , and the outer perimeter  30  of the pivoting fenestration  12  are demarcated by a pair of longitudinally adjacent struts of internal stent  16   f  and stent  16   a , respectively. In this embodiment, the area of the prosthesis  10  located between the internal stent  16   f , which is out of phase, and the stent  16   a  provides additional space for the movement of the band  28  of the pivoting fenestration  12 , which allows for increased flexibility for the pivoting fenestration  12 . 
       FIG. 4 , which is a partial internal view of the prosthesis  10  of  FIG. 1 , shows a view of the prosthesis  10  looking into the lumen  18  of the prosthesis  10  from the proximal end  22 . As shown, pivotable fenestrations  12  are in fluid communication with the lumen  18 . The outer perimeter  30  lies substantially flush (in the same plane) of the graft material  14 , and the band  28  and the outer perimeter  30  form a geometric, frustoconical cone shape extending outward from the lumen  18  of the prosthesis  10 . In this embodiment, the pivotable fenestrations  12  are not disposed within the lumen  18  of the prosthesis  10  and fail to protrude within the lumen of the prosthesis. The prosthesis  10  has a clear lumen  18  once the prosthesis  10  is deployed, and minimizes the possibility of blood flow through the lumen  18  being interrupted by the pivotable fenestration  12 . The pivotable fenestration  12  having an everting configuration also allows for additional room for the placement of medical devices through the fenestration to minimize the disruption to blood flow. For example, when a covered stent is placed within the pivotable fenestration  12 , the lumen extension of the covered stent has additional room to minimize disruption to blood flow. 
       FIGS. 5 a -5 c    show an embodiment of a retention assembly  70  for the pivotable fenestration  12  of the prosthesis  10 . The retention system  70  includes trigger wires  72  and  74 .  FIG. 5 a    and  FIG. 5 b    show views from the interior and the exterior of the prosthesis  10 , respectively. As shown trigger wires  72  and  74  extend from within the lumen of the prosthesis  10 . The trigger wires  72  and  74  are configured to extend through the length of the prosthesis  10 . The trigger wires  72  and  74  engage with the band  28  of pivoting fenestration  12 . In order to facilitate engagement of the trigger wires  72  and  74  through the band  28  a plurality of apertures  76   a - 76   h  are disposed through the surface of the band  28 . In particular, trigger wire  72  exits the lumen of the prosthesis  10  through aperture  76   a  and re-enters into the lumen through aperture  76   b . Trigger wire  72  also exits the lumen of the prosthesis  10  through aperture  76   c  and re-enters into the lumen through aperture  76   d . Similarly, trigger wire  74  exits the lumen of the prosthesis  10  through aperture  76   e  and re-enters into the lumen through aperture  76   f . Trigger wire  74  also exits the lumen of the prosthesis  10  through aperture  76   g  and re-enters into the lumen through aperture  76   h . The trigger wires  72  and  74  form a plurality of segments  78  on an interior surface and an exterior surface of the band  28 . As shown in  FIG. 5 a   , the trigger wires  72  and  74  form one segment  78  on the interior surface of the band  28 . As shown in  FIG. 5 b   , the trigger wires  72  and  74  form two segments  78  on the exterior surface of the band  28 . In addition, the segments  78  on the exterior surface of the band  28  are positioned such that they avoid coming into contact with the support frame  48  of the pivotable fenestration  12 . As shown, the trigger wires  72  and  74  do not engage the graft material  14  surrounding the band  28 . When the pivotable fenestrations  12  are restrained by the trigger wires  72  and  74 , the pivotable fenestrations  12  lie on the same plane as a sidewall of the prosthesis  10 , as shown in  FIG. 5 c   . The trigger wires  72  and  74  may be placed in the configuration shown in the figures upon placement within a delivery device for the prosthesis  10 . Upon removal of the trigger wires  72  and  74 , the pivoting fenestration  12  is deployed within the targeted vessel and the support frame  48  expands and the pivotable fenestration  12  is positioned in the everting configuration. 
       FIGS. 6 a -6 c    show an alternative embodiment of a retention assembly  80  for the pivotable fenestration  12  of the prosthesis  10 .  FIG. 6 a    and  FIG. 6 b    show views from the interior and the exterior of the prosthesis  10 , respectively. The retention system  80  includes trigger wires  82  and  84 . As shown, trigger wires  82  and  84  are from within the lumen of the prosthesis  10 . The trigger wires  82  and  84  are configured to extend through the length of the prosthesis  10 . The trigger wires  82  and  84  engage with the band  28  of pivoting fenestration  12 . In order to facilitate engagement of the trigger wires  82  and  84  through the band  28  a plurality of apertures  86   a - 86   p  are disposed through the surface of the band  28  and the graft material  14  surrounding the band  28 . In particular, trigger wire  82  exits the lumen of the prosthesis  10  through aperture  86   a  and re-enters into the lumen through aperture  86   b . Trigger wire  82  also exits the lumen of the prosthesis  10  through aperture  86   c  and re-enters into the lumen through aperture  86   d . Trigger wire  82  also exits the lumen of the prosthesis  10  through aperture  86   c  and re-enters into the lumen through aperture  86   d ; exits the lumen of the prosthesis  10  through aperture  86   e  and re-enters into the lumen through aperture  86   f ; and exits the lumen of the prosthesis  10  through aperture  86   g  and re-enters into the lumen through aperture  86   h . Similarly, trigger wire  84  exits the lumen of the prosthesis  10  through aperture  86   i  and re-enters into the lumen through aperture  86   j . Trigger wire  84  also exits the lumen of the prosthesis  10  through aperture  86   k  and re-enters into the lumen through aperture  86   l ; exits the lumen of the prosthesis  10  through aperture  86   m  and re-enters into the lumen through aperture  86   n ; and exits the lumen of the prosthesis  10  through aperture  86   o  and re-enters into the lumen through aperture  86   p . The trigger wires  82  and  84  form a plurality of segments  88  on an interior surface and an exterior surface of the band  28 . As shown in  FIG. 6 a   , the trigger wires  82  and  84  form one segment  88  on the interior surface of the band  28 . As shown in  FIG. 6 b   , the trigger wires  82  and  84  form two segments  78  on the exterior surface of the band  28 . In addition, the segments  88  on the exterior surface of the band  28  are positioned such that they avoid coming into contact with the support frame  48  of the pivotable fenestration  12 . When the pivotable fenestrations  12  are restrained by the trigger wires  82  and  84 , the pivotable fenestrations  12  lie on the same plane as a sidewall of the prosthesis  10 , as shown in  FIG. 6 c   . The trigger wires  82  and  84  may be placed in the configuration shown in the figures upon placement within a delivery device for the prosthesis  10 . Upon removal of the trigger wires  82  and  84 , the pivoting fenestration  12  is deployed within the targeted vessel and the support frame  48  expands and the pivotable fenestration  12  is positioned in the everting configuration. 
     The restrained configuration of the pivotable fenestration  12  allows abluminal clearance between the device and a patient&#39;s branch vessel to ease cannulation. While this embodiment shows two trigger wires, other embodiments may comprise fewer trigger wires or more trigger wires to constrain the pivotable fenestrations  12 . For example, one embodiment may use one trigger wire to constrain the pivotable fenestrations  12 , which may reduce the width of the prosthesis  10  and provide additional space to cannulate the branch vessels. In addition, in other embodiments, the trigger wires may restrain the pivotable fenestrations  12  such that they lie in a plane that is within the lumen of the prosthesis  10  prior to deployment of the vessel. In these embodiments, the trigger wires may be slightly biased inward toward a longitudinal axis of the prosthesis  10 , in order to allow for support and space for cannulation of a branch vessel. 
     The retention systems  70  and  80  may be used with various delivery systems for endoluminal devices, such as that described in U.S. Pat. No. 7,651,519, entitled “Prosthesis Deployment System”, and U.S. Pat. No. 7,666,219, entitled “Prosthesis Deployment System Retention Device”, which are incorporated herein by reference in their entirety. In the aspect shown in  FIG. 7 , the delivery system  100  for deploying an endoluminal prosthesis  10  in a vessel of a patient includes an external manipulation section  101 , a distal positioning mechanism or attachment region  103 , and a proximal positioning mechanism or attachment region  105 . The external manipulation section  101 , which is acted upon by a user to manipulate the introducer  100 , remains outside of the patient throughout the procedure. The proximal attachment region includes a retention device  102 . The retention device  102  has at its proximal end a long tapered flexible extension  104 , or dilator. A thin walled tube  112  generally made of metal is fastened to the extension  104 . The thin walled tube  112  is flexible so that the introducer can advance within a relatively tortuous vessel, such as the femoral artery. The thin walled tube  112  also allows manipulation longitudinally and rotationally of the proximal attachment region  105 . The thin walled tube  112  extends throughout the introducer  100  to the manipulation section  101 , terminating at a connection means  111 . The connection means  111  is adapted to accept a syringe to facilitate the introduction of reagents into the metal tube  112 . A tube  114  is coaxial with and radially outside the thin walled tube  112 . The tube  114  is “thick walled”, which is to say the thickness of the wall of tube  114  is several times that of the thin walled tube  112 . A sheath  110  is coaxial with and radially outside the thick walled tube  112 . 
     The external manipulation section  101  has a body  120  that is mounted onto the thick walled plastic tube  114 , which passes through the body  120 . The pin vice  118  has a screw cap  116 . When screwed in, vice jaws (not shown) clamp against and engage the thin walled tube  112 , and the thin walled tube  112  can only move with the body  120 , and hence can only move with the thick walled tube  114 . A proximal wire release mechanism  122  and a distal wire release mechanism  124  are mounted for slideable movement on the body  120 . A pin vice  118  is mounted onto the distal end of the body  120 . The positioning of the proximal and distal wire release mechanisms  122  and  124  is such that the proximal wire release mechanism  122  must be moved before the distal wire release mechanism  124  can be moved. The retention systems  70  and  80  may be associated with either the proximal wire release mechanism or the distal wire release mechanism. 
     In use, the operator deploys the delivery device  100  over a guide wire and into the patient through an artery, such as the femoral artery, via an incision and the introducer is extended up into the aortic bifurcation and positioned such that the dilator  104  is proximal of the renal arteries. The sheath  110  is withdrawn such that the prosthesis  10  is exposed. The operator may then position the prosthesis  10  within the vessel such that the pivotable fenestrations  12  are positioned in the vicinity of the branch vessel. Once the prosthesis  10  and the pivotable fenestrations  12  are in the proper position, the operator may cannulate the branch vessels. The pivotable fenestrations remain in the restrained position by the retention mechanism, which allows for adequate space for cannulation. The operator may introduce additional endoluminal prostheses, such as an indwelling catheter for deploying a branch stent into an internal artery, as described, for example, in U.S. Pat. No. 6,524,335, herein incorporated by reference. Following cannulation, the operator may release and remove the trigger wires of the retention system  70  and  80 , which allows the support frame  48  of the pivotable fenestration  12  to expand, where the pivotable fenestration  12  has an everted configuration. In this position, the operator may introduce a branch stent into the branch vessel through the pivotable fenestration  12 . 
     Throughout this specification various indications have been given as to preferred and alternative examples and aspects of the invention. However, the foregoing detailed description is to be regarded as illustrative rather than limiting and the invention is not limited to any one of the provided aspects. It should be understood that it is the appended claims, including all equivalents, that are intended to define the spirit and scope of this invention.