Abstract:
A system for repairing body lumens including a modular graft and a method for deploying the graft within the body lumen. The modular graft includes a first component having first and second legs portions which mate with second and third graft components, respectively. The second leg portion has a bell bottom shape. The modular graft further includes expandable members which aid in implanting the modular graft as well as facilitates the mating of its components. In order to repair the body lumen, the first component is placed at the repair site and thereafter the first and second legs are advanced to the repair site and attached to the first component. A further aspect of the invention is a fixation device which is adapted to perform an attachment function. The graft and the fixation device are configured to be axially separated from one another so as to allow the graft to attach to the vascular wall proximal of the graft.

Description:
This application is a continuation of U.S. application Ser. No. 09/565,359, filed May 5, 2000, now U.S. Pat. No. 6,652,580, which is a continuation-in-part of application Ser. No. 09/469,341, filed Dec. 20, 1999, now U.S. Pat. No. 6,293,969, which is a continuation of application Ser. No. 09/014,945 filed Jan. 28, 1998, now U.S. Pat. No. 6,030,415, which is based on Provisional Application No. 60/036,518 filed Jan. 29, 1997. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to an intraarterial prosthesis, a modular stent-graft, for repair of abdominal aortic aneurysm (“AAA” herein). Moreover, the present invention relates to a graft which embodies a reduced profile in its compressed condition as well as to facilitating the insertion, in vivo, of one element of a modular graft into another. 
     BACKGROUND OF THE INVENTION 
     An intraarterial prosthesis for the repair of AAAs (grafts) is introduced into the AAA through the distal arterial tree in catheter-based delivery systems, and is attached to the non-dilated arteries proximal and distal to the AAA by an expandable framework (stents). An intraarterial prosthesis of this type has two components: a flexible conduit, the graft, and the expandable framework, the stent (or stents). Such intraarterial prosthesis used to repair AAAs is named stent-graft. AAAs typically extend to the aortic bifurcation of the common iliac arteries. There is rarely any non-dilated aorta below the aneurysm. If there is not then the distal end of the graft must be implanted in the lilac arteries, and for the graft to maintain prograde in-line flow to the legs and arteries of the pelvis, it must also bifurcate. Currently available stent-grafts fall into several categories. One category of grafts are those in which a preformed graft (either tube, aorto-mono-iliac or bifurcated) is inserted whole into the arterial system and manipulated into position about the AAA. This is a unibody graft. Another category of stent-grafts are those in which a graft is assembled in situ from two or more stent-graft components. This latter stent-graft is referred to as a modular stent-graft. 
     The use of modular stent-grafts may be attended by a number of problems. Generally, modular stent-grafts must be compressed for insertion and delivery into the vascular system in a delivery capsule. It will be appreciated that the larger the outer profile of the graft in its compressed condition, the more difficult it will be to insert the device into vasculature and to negotiate the twists and turns of the vasculature. Another significant problem is that, because of the restricted geometry of the vasculature, it can be difficult to insert one element of a modular stent-graft into another. Yet a further problem is that the aorta proximate the renal arteries can lack adequate healthy tissue for forming an attachment of the graft to the aortic wall. 
     Accordingly, there exists a need to provide a modular graft that can assume a profile better suited for navigating tortuous vasculature, and that is configured to facilitate assembly of its subcomponents. There is a further need to provide an apparatus which can be used where there is insufficient healthy aortic tissue near the renal arteries and which permits a fixation device thereof to be axially rotated with respect to the graft. The device of the present invention addresses these and other needs. 
     SUMMARY OF THE INVENTION 
     Briefly, and in general terms, the present invention is directed to a modular stent-graft comprising multi-components. The modular stent-graft of the present invention eliminates or avoids the main drawbacks common to the currently available modular stent-grafts for repair of AAAs. Stent-grafts are inserted into the AAA through the femoral arterial system. The graft must bridge the AAA and form a leak-proof conduit between the aorta and the iliac arteries. The surgeon can only view the operation by X-ray techniques and yet the surgery is performed in a three-dimensional environment. This is a demanding regime and requires a trained and skilled surgeon. 
     The main drawbacks common to the current modular stent-grafts are:
     1. The connection site between the stent-graft components is prone to leakage and a separation of the components which allows blood to leak directly into the AAA restoring the potential for rupture. If the AAA ruptures, the result is frequently the death of the patient.   2. The connection site on the first stent-graft component is often difficult to catheterize prior to introduction of the second stent-graft component. The necessary instrumentation required to insert catheters and carry out the repair of the abdominal aneurysm can dislodge mural thrombus in the AAA. The dislodged mural thrombus is carried in the blood flow through the femoral arteries to small distal arteries causing blockage and tissue necrosis.   3. Modular stent-grafts are conventionally prepared for delivery with one or more stents positioned within a lumen of the graft, thus substantially adding to the profile of the stent-graft assembly. Moreover, additional stents positioned in separate branches of a bifurcated graft are conventionally located at the same axial level, thus adding to the profile of the graft. Further, due to the nature of modular stent-grafts, it is sometimes difficult to assemble, in vivo, the various components of conventional stent-grafts. These factors add to the difficulty of inserting and delivering a graft within the vasculature of a patient.   

     The modular stent-graft of the present invention consists of at least three stent-graft components. The first stent-graft component resembles a pair of shorts with the trunk proximal and the two legs or docking sites distal. The second and third stent-graft components are tubes of almost uniform diameter that extend from the primary stent-graft component docking sites, through the AAA, to the iliac arteries. The completed modular stent graft bridges the AAA from the abdominal aorta to the iliac arteries. The proximal ends of the second and third stent-graft components, i.e., ends nearest the aorta, are inserted into the docking sites of the primary stent-graft. The second stent-graft component is inserted through the ipsilateral arteries to the ipsilateral docking site of the primary stent-graft component. The second stent-graft is also referred to as the ipsilateral extension. The third stent-graft component is inserted through the contralateral arteries to the contralateral docking site through the bell-bottom portion of the primary stent-graft component. The third stent-graft is also referred to as the contralateral extension. Further extensions can be added to any of the stent-graft components to lengthen the overall system. 
     The modular stent-graft of the present invention has a number of distinguishing elements. The stents that hold the two docking sites open are at different levels and are of different sizes. On the ipsilateral docking site, the stent is within the docking site. With regard to the contralateral docking site, the stent is within a wider distal segment, the bell-bottom segment below the contralateral docking site. 
     Because the distal stents of the primary stent-graft component are at different levels, one below the other, they occupy different segments of the delivery system. Since the stent-graft components are delivered to the AAA through a narrow catheter, they must be reduced to the smallest possible diameter to effect and ease delivery. By separating the stent-graft into three components, the necessary stents can be arranged at different levels permitting them to be as large as possible. Since the distal stents can be larger in a modular system than in a unitary system, the distal orifice of the ipsilateral and contralateral docking site can be large and thus easier to catheterize for the delivery. This is only important on the contralateral side, that is, the side with the contralateral docking site. On the ipsilateral side, that is, the side with the ipsilateral docking site, catheters can be introduced over the same guide wire that was used to introduce the first stent-graft component through the arterial system to the AAA. In practice, the distal orifice of the contralateral docking site can be at least as large as the trunk of the primary stent-graft component. The first stent-graft component and the second and third stent-graft components and can be made of the same different biologically inert graft and stent material, such as biologically inert knit or woven fabric, or membrane material, such as PTFE membrane material, and springy material, such as stainless steel or titanium. 
     In a further aspect of the present invention, an expandable framework configured to attach a primary stent-graft component to vasculature is axially separated from the graft, the same being connected to the graft by flexible longitudinally extending members, or ties. Where the graft and expandable framework are thus separated, additional expandable frameworks may be added to the graft after deployment of the graft to perform the function of sealing the graft to vascular wall and/or to maintain the patency of the graft. 
     An advantage of providing a fixation device axially separated from the graft, and providing support structures after deployment of the graft within vasculature, is that the unassembled components of the graft assembly can assume a smaller profile for insertion into vasculature than would a fully assembled stent-graft. This improvement is further enhanced by placing at different levels, stents adapted to maintain the patency of the graft. 
     In one aspect of the invention, the flexible longitudinally extending members may be of such a length that an end of the graft abuts the fixation device. Alternatively, the flexible longitudinally extending members may be of sufficient length to provide a gap between the fixation device and the graft. In both embodiments, the fixation device can assume a different diameter than the graft and an axis of the graft can be at an angle with respect to an axis of the fixation device. By permitting this axial angulation, the graft device can be placed in angulated necks and an effective seal with the vascular wall can be better achieved. 
     These and other advantages of the invention will become more apparent from the following detailed description of the preferred embodiments. When taken in conjunction with the accompanying exemplary drawings the person of skill in the art will appreciate that various embodiments incorporate the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of the modular stent-graft of the present invention implanted to repair an abdominal aortic aneurysm; 
         FIG. 2  is a front perspective view of the first stent-graft component of the modular stent-graft of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the first stent-graft component of  FIG. 2 ; 
         FIG. 4  is a top fragmentary cross-sectional view of the stent-graft of  FIG. 1 ; 
         FIG. 5  is an enlarged fragmentary cross-sectional view of the connection between the first stent-graft component and the third stent-graft component of the stent-graft of  FIG. 1 ; 
         FIG. 6  is a cross-sectional view of the second stent-graft component of the modular stent-graft of  FIG. 1 ; 
         FIG. 7  is a front perspective view of an alternative embodiment of the first stent-graft component of the modular stent-graft of the present invention; 
         FIG. 8  is a cross-sectional view of a second alternative embodiment of the first stent-graft component of the modular stent-graft of the present invention; 
         FIG. 9  is a front perspective view of a third alternative embodiment of the first stent-graft component of the modular stent-graft of the present invention; 
         FIG. 10  is a perspective view of a further embodiment of the first stent-graft component of the present invention; 
         FIG. 11  is a perspective view depicting a variation of the embodiment shown in  FIG. 10 . 
         FIG. 12  is a cross-sectional view of the stent-graft of  FIG. 10  implanted within vasculature in combination with extensions; 
         FIG. 13  is a perspective view of yet a further embodiment of the first stent-graft of the present invention; 
         FIG. 14  is a cross-sectional view of the stent-graft of  FIG. 12  with flexible longitudinally extending members and implanted within vasculature; 
         FIG. 15  is a perspective view of another further embodiment of the stent-graft of the present invention; and 
         FIG. 16  is a cross-sectional view of a variation of the stent-graft of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , the modular stent-graft  10  of the present invention is illustrated implanted to repair an abdominal aorta aneurysm  28 . The modular stent-graft  10  comprises a first stent-graft component  12  having a proximal end  13 A and a distal end  13 B, second stent-graft component  14 , often referred to as the ipsilateral extension, and a third stent-graft component  16 , often referred to as the contralateral extension. The three components comprise sheaths or grafts  41 ,  21  and  23  containing self-expanding stents (not shown in  FIG. 1 ). The proximal end  13 A of the trunk  40  of the first stent-graft component  12  is implanted in the proximal implantation site  30  in a non-dilated portion of the abdominal aorta  22 . To aid in affixing the proximal end  13 A to the abdominal aorta  12 , a fixation device may be employed. In one aspect of the invention, the fixation device  100  is attached to the first stent-graft component  14  so that it is positioned superior to the proximal end  13 A and as shown in  FIG. 1 , the fixation device  100  may be configured suprarenally. The proximal end  36  of the second stent-graft component, or ipsilateral extension, is connected to the first stent-graft component at the ipsilateral docking site  18 . The proximal end  37  of the third stent-graft component  16 , or contralateral extension, is connected to the contralateral docking site  20 . The distal end  38  of the second stent-graft component is implanted in the undilated portion of the ipsilateral iliac artery  24  at the ipsilateral distal implantation site  32 . The distal end of the third stent-graft component, or contralateral extension, is implanted in a non-dilated portion of the contralateral iliac artery  26  at contralateral distal implantation site  34 , as will be described herein. The contralateral leg  15 B of the first stent-graft component terminates in a bell-bottom  42 . Bell-bottom aids in the surgical implantation and manipulation of the modular stent-graft in the aorta and the aneurysm  28  as will be described below. 
     The ipsilateral catheter guide wire  80  is shown coming up from the ipsilateral arteries (the ipsilateral femoral artery and ipsilateral iliac artery) into the ipsilateral extension through the ipsilateral docking site and out through the proximal end  13 A of the trunk  40 . The contralateral catheter guide wire  82  is shown extending up from the contralateral femoral artery through the contralateral iliac artery and through the contralateral extension  16  through the contralateral docking site  20  and out through the proximal end  13 A of the trunk  40 . Normally, both guide wires are left in until the completion of the operation. After the modular stent-graft has been successfully implanted to repair the abdominal aortic aneurysm, the guide wires are removed. In the preferred embodiment, the ipsilateral catheter guide wire  80  is first inserted to permit the delivery of the first stent-graft component and the ipsilateral extension into the AAA. The contralateral catheter guide wire  82  is inserted from the contralateral iliac artery  26  into the contralateral docking site  20  of the first stent-graft component. As mentioned above, the surgeon is viewing the three-dimensional environment of the AAA with a two-dimensional x-ray screen. The large bell-bottom  42  of the first stent-graft component eases the surgeon&#39;s task in successfully snaking the guide wire  82  up into the bell-bottom  42  and into the contralateral docking site  20 . Obviously when the first guide wire  80  is inserted, the surgeon is concerned with having the guide wire come out of the ipsilateral iliac artery  24  through the AAA into the abdominal aorta  22 . Without the bell-bottom  42  below the contralateral docking site  20 , it would be very difficult, and in many instances impossible, to successfully snake the contralateral catheter guide wire  82  into the contralateral docking site  20  of the first stent-graft component. 
     Referring to  FIGS. 2 and 3 , the first stent-graft component  12  of the modular stent-graft  10  comprises a trunk  40  at the proximal end  13 A of the first stent-graft component and ipsilateral leg  15 A and contralateral leg  15 B at the distal end  13 B of the first stent-graft component. Optionally, the distal end of the ipsilateral leg  15 A has a constricted portion  62 . Optionally, the contralateral leg  15 B has a constricted portion  64  at approximately the same level as constricted portion  62 . A radioopaque marker  66  is placed on the first stent-graft component in the constricted portion  64 , if present, adjacent the constricted portion  62 , as shown in  FIG. 2 . This marker aids the surgeon in positioning the proximal stents of the ipsilateral and contralateral extensions. The first stent-graft component is delivered into the aorta aneurysm  28  via a conventional stent-graft catheter delivery system, such as disclosed in U.S. Pat. Nos. 4,580,568; 4,655,771; 4,830,003; 5,104,404; and 5,222,971. The modular stent-graft has three self-expanding stents; a proximal trunk stent  48 , situated above the first stent-graft component at the proximal end  13 A; an ipsilateral trunk stent  50 , positioned within the first stent-graft component near the distal end  13 B of the ipsilateral leg  15 A, and a bell-bottom stent, located within the bell-bottom  42  at the distal end  13 D of the contralateral leg  15 B. These are self-expanding stents of the conventional type, such as disclosed in U.S. Pat. Nos. 4,580,568; 4,655,771; 4,830,003; 5,104,404; and 5,222,971. A self-expanding stent embodying limbs having at least one flat surface for providing improved expansion characteristics such as that disclosed in U.S. Pat. No. 5,993,482 can also be used. 
     The stents employed in the present invention are self-expanding and thus are constricted in the catheter delivery system. Since the first stent-graft component delivered to the aortic aneurysm has three stents at different levels including one above the graft, the graft (the envelope of the first stent-graft component) and stents can be quite large since they can be contracted to a very small diameter for easy delivery of the stent-graft through the ipsilateral arteries by conventional means. If two or more stents were at the same level, it would not be possible to contract the first stent-graft component to the same degree without reducing the size of the distal stents. The first stent-graft component  12  is delivered through the AAA so that the fixation device  100  is positioned suprarenally and so that the proximal end  13 A of the first stent-graft component is positioned within the proximal implantation site  30  of the aorta  22 . The delivery system first facilitates the affixation of the fixation device  100  at the repair site and then slowly releases the remainder of the first stent-graft component allowing the proximal trunk stent  48  to self-expand to form a union between the inner wall of the undilated portion, i.e., healthy portion, of the aorta  22  and the outer wall of the proximal end of the first stent-graft component  12 . The surgeon observes this manipulation by fluoroscopic observation. As the delivery system is withdrawn, leaving the first stent-graft component in the aneurysm  28 , the ipsilateral trunk stent  50  expands and then the bell-bottom stent  52  expands to form the bell-bottom. The stents  50  and  52  keep the distal ends of the legs  15 A and  15 B open for insertion of the second and third stent-graft components  14  and  16 . The ipsilateral trunk stent  50  is optional. The ipsilateral catheter guide wire  80  utilized to guide the first stent-graft component through the ipsilateral iliac artery  24  and through the aorta aneurysm  28  to the undilated portion of the aorta  22  remains behind as a guide for the insertion, connection, and implantation of the second stent-graft component  14 . 
     The delivery system containing the contracted second stent-graft component is guided back to the AAA using the ipsilateral guide wire  80  in the same manner as the guide wire was used to implant the first stent-graft component. As shown in  FIG. 6 , the second stent-graft component or ipsilateral extension  14  is comprised of a tubular graft  21  with a plurality of self-expanding stents, the proximal ipsilateral extension stent  54 , the distal ipsilateral extension stent  55  and supporting stents  60 . Supporting stents  60  are optional. The stents are self-expanding and are contracted when inserted into the delivery system. Once the delivery system has correctly positioned the ipsilateral extension in the modular stent-graft and is withdrawn, the stents are sequentially expanded as the delivery system is withdrawn. 
     Referring to  FIGS. 1 and 4 , the proximal end  36  of the ipsilateral extension  14  is inserted into the ipsilateral docking site  18 . As the delivery system is withdrawn, the proximal ipsilateral extension stent  54  expands, compressing the tubular graft  21  between the ipsilateral trunk stent  50  and the proximal ipsilateral extension stent  54 . Preferentially, but not required, the internal diameter of the ipsilateral trunk stent  50  is greater than the internal diameter opening of the restriction  62 , causing a narrow waist  70  to form in the graft  21  as the proximal ipsilateral extension stent  54  expands. This physically locks or secures the ipsilateral extension  14  to the ipsilateral leg  15 A to prevent the ipsilateral extension from slipping out or being pulled out of the first stent-graft component. As the delivery system is fully withdrawn, the distal ipsilateral extension stent  55  expands compressing the graft  21  against the interior wall of the ipsilateral femoral artery  24  at the ipsilateral distal implantation site  32 . 
     After the surgeon confirms that the ipsilateral extension has been successfully implanted into the ipsilateral iliac artery  24 , a contralateral catheter guide wire  82  is then inserted into the AAA through the contralateral iliac artery  26 . As mentioned above, the bell-bottom  42  of the first stent-graft component aids the surgeon in snaking the guide wire into the contralateral docking site  20 . After the guide wire has been successfully positioned, the delivery system containing the compressed contralateral extension  16 , which for all intents and purposes is identical to the ipsilateral extension shown in  FIG. 6 , is guided along the guide wire  82  so that the proximal end  37  of the contralateral extension is positioned within the contralateral docking site  20 . The proximal end of the contralateral extension is positioned in the docking site so that the first proximal contralateral extension stent  56  is positioned above or proximal to the constriction  64  and the second proximal contralateral extension stent  58  is positioned below or distal to the constriction  64 . As the delivery system is withdrawn, stents  56  and  58 , which are self-expanding, expand forcing the graft  21  of the contralateral extension to expand out to compress the sheath against the inner walls of the contralateral docking site  20 . Since the outer diameter of the expanded stents  56  and  58  are larger than the inner diameter of the constriction  64 , a narrow waist  72  is created in the graft  21 . This physically locks or secures the proximal end  37  of the contralateral extension into the docking site  20  of the first stent-graft component. After the surgeon confirms that the proximal end of the contralateral extension has been successfully connected to the contralateral docking site, the surgeon manipulates the distal end  39  of the contralateral extension into the contralateral distal implantation site  34  of the contralateral iliac artery  26 . Once this positioning has been completed, the surgeon carefully withdraws the delivery system to permit the distal contralateral extension stent (not shown) to expand and compress the outer wall of the contralateral extension graft  21  against the inner wall of the contralateral femoral artery. When the surgeon confirms that the contralateral extension has been successfully implanted, the contralateral catheter guide wire is then withdrawn. At this point the modular stent-graft has been successfully implanted to repair the AAA, a repair that not only protects the life of the patient but also enhances the quality of the patient&#39;s life, since the aneurysm has been shunted out of the patient&#39;s circulatory system and no longer functions as a hydraulic accumulator. 
     The radioopaque marker  66  in the constriction  64  of the contralateral docking site  20  functions as a marker for the surgeon as he observes the manipulation of the various components during the operation. The marker permits the surgeon to easily locate the positioning of the proximal ipsilateral extension stent and the proximal contralateral extension stent  54 ,  56  respectively, with respect to the restrictions  62 ,  64  respectively. 
     Referring to  FIG. 7 , an alternative embodiment of the first stent-graft component  12 A of the present invention is illustrated wherein the bell-bottom  42  is angled towards the contralateral iliac orifice, making it easier to guide the contralateral catheter guide wire  82  into the contralateral docking site  20 , as described above. In all other respects, the first stent-graft component is identical to the stent-graft component  12  described above. The stents  48 ,  50  and  52  are shown in phantom. 
     Referring to  FIG. 8 , a second alternative embodiment of the first stent-graft component  12 B of the present invention is illustrated. The ipsilateral docking site  18 A is free of an ipsilateral trunk stent which is contained in the first stent-graft component  12  described above. However, the contralateral docking site  20 A has a contralateral trunk stent  51  with a series of longitudinal struts  53  extending distally or downwardly from the stents  51  biased to create a conical section with respect to cone  44  of the first stent-graft component. In all other respects, the first stent-graft component  12 B is identical to the first stent-graft component  12  described above. 
     When the alternative embodiment first stent-graft component  12 B is utilized to form a modular stent-graft, the proximal end  36  of the ipsilateral extension  14  is positioned slightly above the restriction  62  so that when the proximal ipsilateral extension stent  54  expands, it expands the outer wall of the graft  21  of the ipsilateral extension against the inner wall of the ipsilateral docking site  18 A to seal the ipsilateral extension to the first stent-graft component  12 B. 
     The outer diameter of the proximal ipsilateral extension stent is greater than the inner diameter of the constriction  62  causing the graft  21  of the ipsilateral extension to form a narrow waist (not shown), thus locking and securing the proximal end of the ipsilateral extension to the ipsilateral docking site  18 A to prevent the extension from slipping out or being pulled out of the first stent-graft component  12 B. The cone  44  acts in the same manner as the bell-bottom  42  to give the surgeon a greater target area to locate the contralateral catheter guide wire into the contralateral docking site  20 A. When the first stent-graft component  12 B is in the delivery system, it is compressed and struts  63  are aligned parallel to each other and adjacent to each other. When the delivery system is withdrawn after the first stent-graft component has been implanted into the proximal implantation site  30 , the struts  63  expand outwardly to expand the envelope  45  of the cone  44 . The struts bow out at the juncture of the constriction  64 A so as to help form the narrow waist  72 A at the proximal end  37  of the contralateral extension  16 . After the contralateral catheter guide wire has been positioned within the contralateral docking site  20 A, the proximal end  37  of the contralateral extension  16  is positioned within the docking site. The delivery system is slowly withdrawn, allowing the proximal contralateral extension stent  56  to expand, compressing the graft  21  of the extension between the inner side of the contralateral trunk stent  51  and the outer side of the first proximal contralateral extension stent  56 . The narrow waist  72 A formed in the graft  21  locks or secures the proximal end  37  of the contralateral extension to the contralateral docking site  20 A to prevent the extension from slipping out of being pulled out of the docking site. 
     Referring to  FIG. 9 , a third alternative stent-graft component  12 C is illustrated which is identical to the first stent-graft component  12  described above, with the exception that ipsilateral docking site  18 B of this first stent-graft component does not contain an ipsilateral front stent. In contrast, in this first stent-graft component  12 C, a flexible bracer  76  is located within the component to prevent longitudinal collapse of the ipsilateral leg  15 A during implantation into the proximal implantation site  30 . Alternatively, longitudinal collapse of the ipsilateral leg  15 A can be prevented in the first stent-graft component  12 C described above by attaching ipsilateral leg  15 A to contralateral leg  15 B by struts attached between the two legs, a membrane attached to the two legs, or by sewing the two legs together (not shown). 
     A further aspect of the present invention relates to the attachment between the trunk of the graft and the aortic wall. This aspect of the invention involves axially separating an expandable framework from the graft. 
       FIG. 10  exemplifies a further embodiment of the first stent-graft component  92  of the present invention, in its assembled condition before it is implanted in the patient&#39;s vasculature. As is seen in  FIG. 10 , the proximal trunk stent of the earlier embodiment is replaced by an expandable fixation device  100 , which is positioned to be axially separated from the trunk  40  of the first stent-graft component  92 , being connected to the trunk  40  by longitudinally extending members  110 . As the previously described embodiment, the stent-graft component  92  may include an ipsilateral leg  15 A and a contralateral leg  15 B, the contralateral leg having a bell-bottom or flared configuration  94 . Further, the flared end  94  is contemplated to be adapted with an external expandable stent  96  which operates to facilitate the flared configuration. It is to be recognized, however, that the stent  96  can alternatively be placed within an interior of the flared end  94 . 
     In a preferred embodiment, the fixation device  100  is self-expanding. In alternative embodiments, the fixation device  100  may be balloon expanded. The fixation device  100  may be formed from metal which follows a generally undulating path within a cylindrical profile, thereby defining a plurality of alternating proximal apices  102  and distal apices  104  which are joined by connecting members or legs  106 . Additionally, hooks  108  may be connected to the fixation device  100  to enhance its ability to attach to the aortic wall. It is contemplated that the hooks  108  are integrally formed at the proximal apices  102 , but can similarly be formed at the distal apices  104  as well. The connecting legs  106  have a generally rectangular profile defined by a circumferentially extending width and a radially extending depth. In one preferred embodiment, the depth is greater than the width. When the fixation device  100  is self-expanding, its legs  106  and apices  102 ,  104  are urged radially outward in a direction that is at a right angle to an axis of the fixation device  100 . 
     The fixation device  100  is contemplated to be manufactured from a continuous cylinder, into which a pattern may be cut by a laser or by chemical etching to produce slits in the wall of the cylinder. Manufacture of the preferred embodiment may additionally require stretching and annealing the fixation device  100  after it has been cut from the continuous cylinder, to give it a desired configuration. It is contemplated that the fixation device  100  be manufactured from a material having highly elastic properties such as nickel-titanium alloys since the same allows a great amount of expansion and compression of structures without permanent deformation. Implantable stainless steel is also known to be satisfactory for the purpose. An additional material from which such fixation device  100  may be manufactured is Elgiloy™ which is a chromium-cobalt-nickel alloy manufactured and sold by Elgiloy of Elgin, Ill. 
     The fixation device  100  is connected to the trunk  40  of the first stent-graft component  92  by a plurality of longitudinally extending members  110  which may be made from any flexible substance which is durable and biocompatible. For example, Dacron™ polyester suture material configured as ties may be suitable for forming the flexible longitudinally extending members  110 . The ties  110  may be configured to loop around the distal elements forming the fixation device  100 , and to penetrate the wall of the graft  112 , or may be routed in any other suitable manner to form a connection between fixation device  100  and trunk  40 . In one embodiment, the ties  100  may have a short length which causes the distal end of the fixation device  100  to abut the proximal end  13 A of the stent-graft  92 , but not to overlap it. Such an abutment may assist in preventing fluid flow around the outside of the stent-graft  92 . Furthermore, as shown in  FIG. 11 , in yet another aspect of the invention the trunk  40  can include a plurality of proximally directed, discreet material extensions  111  with holes configured therein for receiving portions of the fixation device  100  or the longitudinally extending members  110  (not shown). 
     By axially separating the fixation device  100  and the trunk  40 , the first stent-graft component  92  presents a more slender profile when packed in a delivery catheter than if there was an overlap, and thus may more easily be inserted into and negotiated through the patient&#39;s vasculature. This further reduces the profile obtained by separating the level of the ipsilateral trunk stent  50  (See  FIG. 4 ) and bell bottom stent  52 . 
     Using the methods of delivery described above, the modular stent-graft  90  of this embodiment is deployed within the vasculature, as exemplified in  FIG. 11 , so that the fixation device  100  is connected to healthy tissue of the aortic wall  22  above the renal arteries. Advantageously, the trunk  40  of the first stent-graft component  92  is positioned entirely distal of the fixation device  100 . 
     In order to provide a seal between the trunk at its proximal end  120  and the vascular wall  30 , one or more support structures  112  may be added to the lumen of the trunk at its proximal end portion  120  and throughout its length. Preferably, such a support structure  112  is delivered in a separate delivery catheter or loaded in a portion of the delivery catheter of the first component but at a different axial position in the delivery catheter and added after the first stent-graft component  92  has been deployed to thereby take advantage of the reduced profile achieved by separating the fixation device  100  from the trunk  40 . In a preferred embodiment, the support structures  112  used in the present invention may be self-expanding, manufactured according to the same principles as the self-expanding fixation device  100 . In another embodiment, the support structure  112  may be balloon-expanded. 
     To complete the configuration of the implanted modular stent-graft  90 , second and third stent-graft components  14 ,  16  are added to the distal ends of the legs  15 A,  15 B of the first stent-graft component  92 , according to the methods and principles described above.  FIG. 12  further exemplifies how the distal extension stents  55  may be positioned on the outside wall of the extensions  14 ,  16 , and how the bell-bottom stent  92  may be positioned on the outside wall of the bell-bottom  94 . 
     In a further aspect of the invention, instead of short ties  110 , relatively longer, substantially rigid, longitudinally extending members  110 A may be used to thereby permit the fixation device and the trunk to be separated by a gap. This aspect is exemplified in  FIG. 13 , where the longitudinally extending members  110 A provide a significant gap  113  between fixation device  100  and trunk  40 . The substantially rigid longitudinally extending members  110 A facilitate precise implantation by providing the device with additional stability. Alternatively, the longitudinally extending members may be of the same configuration and material as the ties described above, and therefore embody a relatively flexible material. 
     The advantage of increasing the extent of the separation between the graft  90  and the fixation device becomes apparent in  FIG. 14 , which depict how the fixation device  100  may be attached to the aortic wall  116  proximal of the renal arteries  118 , allowing the trunk  40  of the first stent-graft component  92  to be positioned distal of the renal arteries  118  in a severely angulated neck. The separation of the fixation device  100  and trunk  40  is facilitated by the longitudinal extending members  110 A. Positioning the fixation device  100  above the renal arteries  118  is particularly desirable when the aorta  22  below the renal arteries  118  is diseased and does not present sufficient resilience to withstand the forces which might be imposed by the fixation device  100  or otherwise required to successfully implant the stent-graft  90 . 
     Moreover, it is frequently found that the geometry of the aorta  22  above and below the renal arteries  118  is highly irregular. For example, the diameter of the aorta  22  above the renal arteries  118  may be substantially different than the diameter below the renal arteries  118 . Additionally, the aorta  22  above and below the renal arteries  118  may not share a common longitudinal axis. These irregularities may require the fixation device  100  to have a different diameter and a different axial alignment in the expanded state, than that of the stent-graft  90 . The same can be accommodated by employing flexible longitudinally extending members  110 A, which tend to buckle to thereby allow the stent-graft  90  to assume a position in contact with the aortic wall  116  at its proximal end-portion  120 , while permitting the fixation device  100  to assume a different alignment and diameter above the renal arteries  116 . Where such a misalignment is not accommodated, the wall of the trunk  40  of the first stent-graft component  92  might tend to kink at its proximal end-portion  120 , thus reducing the efficacy of the seal of the graft to the vascular wall. Although axial misalignment of the proximal end  120  of the stent-graft  90  may cause kinking to take place in the wall of the graft  90  as illustrated in  FIG. 14 , it will be appreciated that kinking at the center of the graft  90  will likely not adversely affect the quality of the seal between graft  90  and aorta  22 . It is to be recognized that although  FIG. 14  shows flexible longitudinally extending members  110 A, in certain circumstances, substantially rigid members may be desirable. 
     It has been found that, in the majority of cases, a separation  113  of up to 2 mm and as much as 10 mm or greater between the fixation device  110  and the proximal end  120  of the trunk  40  may be desirable. Such a gap  113  allows the fixation device to expand to a different diameter than the stent-graft  90  as well as to be rotated with respect to the stent-graft  90  sufficiently to accommodate expected axial misalignment which can exist in the region of the aorta  22 . 
     As further exemplified in  FIG. 14 , the first stent-graft component  92  is positioned in the aorta  22  so that, when fully expanded, its proximal end  120  is located as close to the renal arteries  118  as possible, without obstructing entry to the renal arteries  118 . It will be appreciated that it is imperative that renal arteries are not obstructed by the graft  90 , and, accordingly, the first stent-graft component  92  should be positioned so that this condition is met. It will be further appreciated that the elements forming the fixation device  100  and the longitudinally extending members  100 ,  110 A may be allowed to overlay the entry to the renal arteries  118  without ill effect, where they are not sufficiently large to cause any appreciable reduction in blood flow to the renal arteries  118 . 
     With reference to  FIG. 15 , an alternate embodiment of a fixation device  100 A is shown. The fixation device  100 A may be manufactured from a single piece of wire, which is formed by looping the wire around pins appropriately spaced and attached to a cylindrical mandrel. The two ends of the wire may be welded or glued together to form a continuous framework within a cylindrical profile. The configuration of the present variation similarly has proximal apices  102 A and distal apices  104 A connected by legs or members  106 A. Each of the apices  102 A,  104 A may further embody a helix  107 A. Further, hooks  108 A may be added to the fixation device  100 A to enhance attachment to the vascular wall. Suitable material from which the fixation device of this embodiment may be made include Nitinol and Elgiloy™. 
     In another aspect of the invention, the principle of separating the fixation device from the graft may be applied to grafts which are not bifurcated modular grafts, but which are bifurcated or cylindrical unitary grafts.  FIG. 16  exemplifies this variation, and shows a fixation device  100  of earlier described embodiment connected to a cylindrical graft  122  according to the same principles described above, in which ties  110  may be used to achieve the connection. This aspect of the invention contemplates that flexible longitudinally extending members, such as those ( 110 A) already described above, may also be used where required. This embodiment of the invention may be used where the quality of aortic tissue at the distal end  124  of the cylindrical graft  122  permits a seal to be formed with the aortal  16 . Such a seal may be formed using the same type of support structure  112  as earlier described to seal the proximal end  124  of the graft  122  to the aorta  22 . The fixation device can be implanted as shown or can be implanted above the renals such that the top edge of the graft is just below the renal artery openings 
     It will be apparent from the foregoing that, while particular forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. 
     Accordingly, it is not intended that the invention be limited, except as by the appended claims.