Patent Document

FIELD OF THE DISCLOSURE 
     The present disclosure relates to an implant and a system for delivering the implant to a site in a body lumen. More particularly, this disclosure pertains to a vascular implant such as a stent. 
     BACKGROUND OF THE DISCLOSURE 
     Stents are widely used for supporting a lumen structure in a patient&#39;s body. For example, stents may be used to maintain patency of a coronary artery, carotid artery, cerebral artery, other blood vessels including veins, or other body lumens such as the ureter, urethra, bronchus, esophagus, or other passage. 
     Stents are commonly metallic tubular structures made from stainless steel, Nitinol, Elgiloy, cobalt chrome alloys, tantalum, and other metals, although polymer stents are known. Stents can be permanent enduring implants, or can be bioabsorbable at least in part. Bioabsorbable stents can be polymeric, bio-polymeric, ceramic, bio-ceramic, or metallic, and may elute over time substances such as drugs. Non-bioabsorbable stents may also release drugs over time. Stents are passed through a body lumen in a collapsed state. At the point of an obstruction or other deployment site in the body lumen, the stent is expanded to an expanded diameter to support the lumen at the deployment site. 
     In certain designs, stents are open-celled tubes that are expanded by inflatable balloons at the deployment site. This type of stent is often referred to as a “balloon expandable” stent. Stent delivery systems for balloon expandable stents are typically comprised of an inflatable balloon mounted on a two lumen tube. The stent delivery system with stent compressed thereon can be advanced to a treatment site over a guidewire, and the balloon inflated to expand and deploy the stent. 
     Other stents are so-called “self expanding” stents and do not use balloons to cause the expansion of the stent. An example of a self-expanding stent is a tube (e.g., a coil tube or an open-celled tube) made of an elastically deformable material (e.g., a superelastic material such a nitinol). This type of stent is secured to a stent delivery device under tension in a collapsed state. At the deployment site, the stent is released so that internal tension within the stent causes the stent to self-expand to its enlarged diameter. 
     Other self-expanding stents are made of so-called shape-memory metals. Such shape-memory stents experience a phase change at the elevated temperature of the human body. The phase change results in expansion from a collapsed state to an enlarged state. 
     A very popular type of self expanding stent is an open-celled tube made from self-expanding nitinol, for example, the Protege GPS stent from ev3, Inc. of Plymouth, Minn. Open cell tube stents are commonly made by laser cutting of tubes, or cutting patterns into sheets followed by or preceded by welding the sheet into a tube shape, and other methods. Another delivery technique for a self expanding stent is to mount the collapsed stent on a distal end of a stent delivery system. Such a system can be comprised of an outer tubular member and an inner tubular member. The inner and outer tubular members are axially slideable relative to one another. The stent (in the collapsed state) is mounted surrounding the inner tubular member at its distal end. The outer tubular member (also called the outer sheath) surrounds the stent at the distal end. 
     Prior to advancing the stent delivery system through the body lumen, a guide wire is first passed through the body lumen to the deployment site. The inner tube of the delivery system is hollow throughout at least a portion of its length such that it can be advanced over the guide wire to the deployment site. The combined structure (i.e., stent mounted on stent delivery system) is passed through the patient&#39;s lumen until the distal end of the delivery system arrives at the deployment site within the body lumen. The delivery system and/or the stent may include radiopaque markers to permit a physician to visualize stent positioning under fluoroscopy prior to deployment. At the deployment site, the outer sheath is retracted to expose the stent. The exposed stent is free to self-expand within the body lumen. Following expansion of the stent, the inner tube is free to pass through the stent such that the delivery system can be removed through the body lumen leaving the stent in place at the deployment site. 
     It can be difficult to estimate the length of the diseased portion of a vessel and therefore the stent length needed for treatment of the disease. This is particularly true for long diseased segments, segments that are tortuous, and segments that are oriented at angles to the plane of the imaging modality used (due to image foreshortening). If the stent chosen for treatment is too long then un-diseased vessel will be treated, and if the stent chosen is too short then diseased vessel will be untreated. Both of these scenarios are undesirable. In some cases physicians will treat a portion of the length of the diseased vessel with a first stent and will implant a second stent to treat the remainder of the length of the diseased vessel, overlapping the two stents to assure that no portion of the diseased vessel is left untreated. This approach is also undesirable because problems such as corrosion between dissimilar metals, excessive vessel stiffening, stent fracture, and reduced stent fatigue life can arise at the site of overlap. Problems secondary to stent fracture can include pain, bleeding, vessel occlusion, vessel perforation, high restenosis rate, non-uniform drug delivery profile, non-even vessel coverage and other problems. Re-intervention may be required to resolve these problems. Further, use of multiple stents to cover a treatment site increases procedural time and cost. 
     Some have attempted to improve the precision with which to estimate the needed implant length. For example, a guidewire having visualizable markers separated by a known distance can be inserted into the treatment region. However, these techniques have not become widespread in part because marker wires do not perform as well as the specialty guidewires preferred by physicians. 
     What is needed is an implant and associated delivery system that permits delivery and deployment of stents that are well matched to the length of diseased segments. 
     SUMMARY OF THE DISCLOSURE 
     An implant delivery catheter enables permanent modification of the implant length in the vicinity of the treatment site prior to radial expansion thereof. The implant is releasable carried between inner and outer tubular members of the delivery catheter which, upon repositioning relative to one another using an actuator mechanism, impart any of tensile, compressile or torquing forces to the implant causing permanent modification of the implant length. In one embodiment, the circumference of the implant is substantially similar both before and after modification of the implant length. In another embodiment, the implant includes a plurality of strut sections interconnected by bridges which are capable of the deformation along the longitudinal axis of the implant. 
     According to one aspect of the disclosure, an implant for insertion into a body lumen comprises a plurality of cells at least partially defined by a plurality of struts and a plurality of bridges, selected of the cells disposed at proximal and distal ends of the implant and having terminal ends attached thereto The implant has an initial length L 1  extending along a longitudinal axis and an initial circumference C 1  extending circumferencially about the longitudinal axis, wherein the implant assumes a deformation circumference C 2  having a value within 0% to 10% of a value of the initial circumference C 1  following application of a deformation force to the terminal ends thereof. 
     According to a second aspect of the disclosure, a medical device comprises a tubular implant having first and second ends and extending for an initial length L 1  along a longitudinal axis and an implant delivery system. The implant delivery system comprises a catheter having an outer tubular member disposed about an inner tubular member, the first end of the implant operatively secured to the outer tubular member and the second end of the implant operatively secured to the inner tubular member; and an actuator mechanism movably coupled to one of the outer tubular member and the inner tubular member for changing relative positions of the outer tubular member and the inner tubular member along a second axis substantially parallel with the longitudinal axis; wherein changes in the relative positions of the outer tubular member and the inner tubular member change the initial length L 1  of the implant to a modified length L 2 . 
     According to a third aspect of the disclosure, a method for placement of an implant within a body lumen comprises: A) providing an implant having a generally tubular shaped body defining a number of cells and extending for an initial continuous length L 1  along an axis; B) advancing the implant with a delivery catheter to a site within the body lumen; C) modifying the length L 1  to a second continuous length L 2  along the axis with the delivery catheter prior to deployment at the site within the body lumen, the number of cells defined by the tubular shaped body being the same for both length L 1  and length L 2 ; and D) initiating radial expansion of the implant about the axis at the site within the body lumen. 
     According to a fourth aspect of the invention, implant for insertion into a body lumen comprises a tubular body extending for an initial length L 1  along a longitudinal axis and having and initial circumference C 1  about the longitudinal axis. The tubular body further comprises plurality of strut structures and a plurality bridge structures collectively defining a plurality of cells, selected of the plurality of cells being disposed at proximal and distal ends of the tubular body and having terminal ends attached thereto. One of the plurality of strut structures and bridge structures are capable of deformation in a direction tending toward the longitudinal axis of the tubular body when a force, parallel to the longitudinal axis, is applied to the end terminals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and further advantages of the inventive concept may be better understood by referring to the following description in conjunction with the accompanying drawings in which: 
         FIGS. 1A and 1B  illustrate plan views of an exemplary stretchable implant embodiment having structure that interlocks with structure of a stretchable implant delivery catheter. The implant is shown contracted and un-stretched in FIG.  1 A and contracted and stretched in  FIG. 1B . The implant and interlock structures are shown cut longitudinally and laid flat; 
         FIGS. 2A ,  2 B,  2 C,  2 D,  2 E and  2 F illustrate plan views of portions of exemplary stretchable implants; 
         FIG. 2G  is a graph illustrating certain characteristics of exemplary stretchable implant portion illustrated in  FIG. 2F ; 
         FIGS. 3A ,  3 B,  4 A, and  4 B illustrate characteristics of exemplary stretchable implants; 
         FIGS. 5A and 5B  illustrate side elevation views of one embodiment of a stretchable implant system having features that are examples of inventive aspects in accordance with the principles of the present disclosure; 
         FIG. 5C  illustrates a cross sectional view of the system of  FIGS. 5A and 5B ; 
         FIGS. 5D ,  5 E and  5 F illustrate side elevation partial cross sectional views of a portion of the stretchable implant system illustrated in  FIGS. 5A to 5C ; 
         FIGS. 5G and 5H  illustrate enlarged views of the distal and proximal portions, respectively, of an alternate embodiment of a stretchable implant system having features that are examples of inventive aspects in accordance with the principles of the present disclosure; 
         FIG. 6  illustrates an enlarged view of the proximal portion of the system of  FIG. 5A ; 
         FIGS. 7A ,  7 B and  7 C illustrate enlarged views of the distal portion of the system of  FIG. 5A  in various states of implant deployment; 
         FIGS. 8A and 8B  illustrate enlarged views of the distal and proximal portions, respectively, of an alternate embodiment of a stretchable implant system having features that are examples of inventive aspects in accordance with the principles of the present disclosure; 
         FIGS. 9A and 9B  illustrate enlarged views of the distal and proximal portions, respectively, of an alternate embodiment of a stretchable implant system having features that are examples of inventive aspects in accordance with the principles of the present disclosure; 
         FIG. 9C  illustrates a cross sectional view of a portion of the system of  FIGS. 9A and 9B ; 
         FIGS. 10A and 10B  illustrate enlarged views of the distal and proximal portions, respectively, of an alternate embodiment of a stretchable implant system having features that are examples of inventive aspects in accordance with the principles of the present disclosure; 
         FIG. 11  illustrates an enlarged view of the distal portion of an alternate embodiment of a stretchable implant system having features that are examples of inventive aspects in accordance with the principles of the present disclosure; 
         FIGS. 12A-C  illustrate schematic views of the distal portion of the system of  FIG. 11  in various states of implant deployment. 
     
    
    
     DETAILED DESCRIPTION 
     With reference now to the various drawing figures a description is provided of embodiments that are examples of how inventive aspects in accordance with the principles of the present disclosure may be practiced. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive aspects disclosed herein. It will also be appreciated that while the inventive concepts disclosed herein are often described using stents as exemplary implants these inventive concepts are not limited to stents or to the particular stent configurations disclosed herein, but are instead applicable to any number of different implant configurations. 
     In this specification various drawing figures and descriptions are provided of embodiments that are examples of stretchable implants, that is, implants that can be lengthened from a shorter length to a longer length, generally by applying a tensile force to the ends of the implant. It is contemplated that the implants described in the examples can also be used as shortenable implants, that is, implants that can be compressed from a longer length to a shorter length by applying a compressile force to the ends of the implant. It is further contemplated that the implant delivery catheters, systems, and methods described for use with stretchable implants are equally useful when applied to shortenable implants. 
       FIGS. 1A and 1B  illustrate stretchable implant  10  comprised of struts  12 , bridges  14 , and one or more tab  16  at each end  10   b ,  10   a  of implant  10 . The implant is shown cut longitudinally and laid flat. While eight rows of struts are illustrated in  FIGS. 1A and 1B  it is understood that any number greater than two rows of struts are suitable for the disclosure. Similarly, while fifteen struts per row are illustrated in  FIGS. 1A and 1B  it is understood that any number greater than three struts per row are suitable for the disclosure. The perimeters enclosed by struts and bridges define cells  18 . Struts are joined at bend regions  13 . In some embodiments tabs  16  are comprised of holes therethrough having markers  17  attached to tabs. Tabs  16  interlock with retainers of stretchable implant delivery catheter (discussed below). Implant  10  can be stretched along axis A by stretchable implant delivery catheter (also discussed below). 
     Implant  10  has length L and circumference C, and includes a plurality of struts  12 . At least some of the struts  12  have bend regions  13  without tabs  16 , or free terminal ends  15  that define proximal and distal ends  10   a  and  10   b  of implant  10 . Implant  10  includes interlock geometry in the form of tabs  16  attached to or integral to one or more free terminal ends  15  of struts  12 . The tabs  16  project outwardly from the struts  12  in a circumferential direction (i.e. in a direction coinciding with the circumference C of the implant  10 ). Markers  17  are located adjacent the proximal or distal ends  10   a ,  10   b  or both of implant  10  and may be located at any position along the length of the stent between the proximal and distal stent ends  10   a ,  10   b . Markers  17  can be attached to implant  10  by techniques such as adhesives, heat fusion, interference fit, fasteners, intermediate members, as coatings, or by other techniques. In one embodiment, markers  17  are comprised of radiopaque materials press fit into a through-hole provided in tab  16 . In one embodiment, shown in  FIGS. 1A and 1B , the tabs are circular enlargements. It will be appreciated that other shapes and other interlock configurations could also be used. Suitable designs of tabs  16  and markers  17  include but are not limited to those described in  FIGS. 6A ,  6 B,  7  to  13 ,  14 A,  14 B,  15 A and  15 B and related discussions thereof in U.S. Pat. No. 6,623,518 entitled “Implant Delivery System with Interlock”, and include but are not limited to those described in  FIGS. 4 to 15  and related discussions thereof in U.S. Pat. No. 6,814,746 entitled “Implant Delivery System with Marker Interlock”, the contents of which being incorporated in their entirety herein by reference for all purposes. 
     In other embodiments markers  17  are comprised of ultrasonic markers, MRI safe markers, or other markers. In one embodiment ultrasonic markers  17  permit a physician to accurately determine the position of implant  10  within a patient under ultrasonic visualization. Ultrasonic visualization is especially useful for visualizing implant  10  during non-invasive follow-up and monitoring. Materials for ultrasonic marker  17  have an acoustical density sufficiently different from implant  10  to provide suitable visualization via ultrasonic techniques. Exemplary materials comprise polymers (for metallic stents), metals such as tantalum, platinum, gold, tungsten and alloys of such metals (for polymeric or ceramic stents), hollow glass spheres or microspheres, and other materials. 
     In another embodiment MRI safe markers permit a physician to accurately determine the position of implant  10  within a patient under magnetic resonance imaging. MRI visualization is especially useful for visualizing implant  10  during non-invasive follow-up and monitoring. Exemplary materials for making MRI safe marker  17  have a magnetic signature sufficiently different from implant  10  to provide suitable visualization via MRI techniques. Exemplary materials comprise polymers (for metallic stents), metals such as tantalum, platinum, gold, tungsten and alloys of such metals (for polymeric or ceramic stents), non-ferrous materials, and other materials. 
     Implant  10  may be comprised of metal, polymer, ceramic, permanent enduring materials, and may comprise either of or both of non-bioabsorbable and bioabsorbable materials. Exemplary materials include but are not limited to Nitinol, stainless steel, cobalt chromium alloys, Elgiloy, magnesium alloys, polylactic acid, poly glycolic acid, poly ester amide (PEA), poly ester urethane (PEU), amino acid based bioanalogous polymers, tungsten, tantalum, platinum, polymers, bio-polymers, ceramics, bio-ceramics, or metallic glasses. Part or all of implant  10  may elute over time substances such as drugs, biologics, gene therapies, antithrombotics, coagulants, anti-inflammatory drugs, immunomodulator drugs, anti-proliferatives, migration inhibitors, extracellular matrix modulators, healing promoters, re-endothelialization promoters, or other materials. In one embodiment, implant  10  is comprised of shape memory urethane polymer. Implant  10  can be manufactured by forming cells  18  through the wall of the tube, by means such as laser cutting, electrochemical etching, grinding, piercing, or other means. In some embodiments implant  10  is formed by electroforming. In one embodiment, implant  10  can be manufactured by cutting (e.g., laser cutting) the various features from a solid tube of superelastic Nitinol metal. In some embodiments implant  10  is finished by processes to remove slag (such as microgrit blasting), to remove implant material having a heat affected zone or other imperfections (e.g. by electropolishing), and to render surface of implant  10  more resistant to corrosion (e.g. by surface passivation). 
     In other embodiments implant  10  may be comprised of intertwined, joined, or non-woven filaments. In some embodiments filaments are braided, woven, knitted, circular knitted, compressed, or otherwise fabricated into a porous mesh structure having cells  18 . Filaments may be joined at one or more filament crossings by sintering, bonding, soldering, fusing, welding, or other means. 
     Implant  10  may have one or more of the following characteristics: self expanding, self contracting, balloon expandable, and shape memory. In one embodiment implant  10  is comprised of balloon expandable stainless steel alloy. In another embodiment implant  10  is comprised of superelastic nitinol struts  12  and non-superelastic malleable bridges  14 . In various embodiments implant  10  is a stent, a stent graft, a mesh covered stent, or other implants. 
     Implant  10  has un-stretched length L 1  as illustrated in  FIG. 1A  and stretched length L 2  as illustrated in  FIG. 1B . In the examples of  FIGS. 1A and 1B  bridges  14  can be lengthened along axis A in response to tensile force applied to ends  10   a ,  10   b  of implant  10 . Lengthening of implant  10  causes bridges  14  to align in a direction more parallel with stent axis A, thereby increasing distance D 3  between free terminal ends and causing a small offset  11  between adjacent rows of struts  12 . Lengthening of contracted implant  10  causes little or no change in stretched circumference C 2  as compared to un-stretched circumference C 1 . In some embodiments lengthened implants remain lengthened after removal of the tensile forces which caused the implant to lengthen. Implants are envisioned which can be lengthened any incremental amount up to the maximum stretched length of the implant. Implants having a maximum stretched length L 2  from 3% to 50% greater than the implant un-stretched length L 1  are contemplated. In one embodiment, implant  10  has a maximum stretched length 5% greater than the implant un-stretched length. In other embodiments, implant  10  has a maximum stretched length 10%, 15%, 20%, 25%, 30%, 35%, 40%, or 45% greater than the implant un-stretched length. Implants having a stretched circumference C 2  within 0% to 10% of un-stretched circumference C 1  are contemplated. In one embodiment, implant  10  has a maximum stretched circumference within 9% of the implant un-stretched circumference. In other embodiments, implant  10  has a maximum stretched circumference within 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8% of the implant un-stretched circumference. 
     In some embodiments of stretchable implants, for example a metallic arterial stent, it is desirable to have the percentage of vessel inner wall area that is covered by the expanded metal stent (“percent metal coverage”) to fall within a pre-programmed range. In one example a 6 mm diameter by 100 mm long (6×100) stent is designed to be lengthened only by a maximum of 29%, to have a pre-programmed average percent metal coverage of 14% at the nominal size of 6×100 and to have a percent metal coverage of 14-18% over its indicated usable range. As illustrated in  FIG. 3A , the exemplary stent, deployed at 100 mm long in a 6 mm vessel, has 14% metal coverage. The exemplary stent, deployed at 100 mm long in a 4.7 mm vessel, has 18% metal coverage ((14%/18%)*6 mm=4.7 mm). The exemplary stent, deployed at 129 mm long in a 4.7 mm vessel, has 14% metal coverage ((18%/14%)*100 mm=129 mm) and deployed at 129 mm long in a 3.7 mm vessel, has 18% metal coverage ((14%/18%)*4.7 mm=3.7 mm). The shaded region S 1  in  FIG. 3A  describes the indicated usable range of this exemplary stent when stretched. Stents deployed in vessels having a length and diameter combination within shaded region S 1  will have percent metal coverage of 14-18%. 
     In another example a 6 mm diameter by 100 mm long (6×100) stent is designed to be deployed in vessels having a limited diameter range (6 mm to 5.3 mm), be mainly stretchable but to a limited extent contractable, to have a pre-programmed average percent metal coverage of 14% at the nominal size of 6×100, and to have a percent metal coverage of 14-18% over it&#39;s indicated usable range. As illustrated in  FIG. 3B , the exemplary stent, deployed at 100 mm long in a 6 mm vessel, has 16% metal coverage. The exemplary stent, deployed at 114 mm long in a 6 mm vessel, has 18% metal coverage, and deployed at 88 mm long in a 6 mm vessel, has 14% metal coverage. The exemplary stent, deployed at 100 mm long in a 5.3 mm vessel, has 18% metal coverage and deployed at 129 mm long in a 5.3 mm vessel, has 14% metal coverage. The shaded region S 2  in  FIG. 3B  describes the indicated usable range of this exemplary stent when stretched and the shaded region C 2  in  FIG. 3B  describes the indicated usable range of this exemplary stent when contracted. Stents deployed in vessels having a length and diameter combination within shaded regions S 2  and C 2  will have percent metal coverage of 14-18%. 
     In other embodiments of stretchable implants it is desirable for a plurality of repeating units, such as a cell  18 , to have similar or the same axial and radial expansion or contraction characteristics, or both. In one embodiment the implant has similar axial and radial cellular expansion characteristics so that the implant will uniformly stretch and will uniformly expand. In  FIGS. 4A and 4B , cell  18  of implant  10  is represented by cell  48 . Cell  48  is shown unexpanded, cut longitudinally and laid flat. In one embodiment of implant  10 , when the implant is expanded, representative cell  48  will expand from length  41  to length  42  with little or no change to axial dimension  46  ( FIG. 4A ). In another embodiment ( FIG. 4B ), when implant  10  is first stretched and then expanded, representative cell  48  will first stretch from axial dimension  46  to axial dimension  47  with little or no change to length  41 , and will then expand from length  41  to length  42  with little or no change to axial dimension  47 . Ratio&#39;s of expanded cell length  42  to unexpanded cell length  41  of from 200% to 800% are contemplated. In one embodiment, implant  10  has a ratio of expanded cell length to unexpanded cell length of 300%. In other embodiments, implant  10  has a ratio of expanded cell length to unexpanded cell length of 350%, 400%, 450%, 500%, 550%, 600%, 675%, or 750%. Ratio&#39;s of stretched cell axial dimension  47  to unstretched cell axial dimension  46  of from 3% to 50% are contemplated. In one embodiment, implant  10  has a ratio of stretched cell axial dimension to unstretched cell axial dimension of 5%. In other embodiments, implant has a ratio of stretched cell axial dimension to unstretched cell axial dimension of 10%, 15%, 20%, 25%, 30%, 35%, 40%, or 45%. 
       FIGS. 2A to 2E  illustrate alternate embodiments of stretchable implants.  FIG. 2A  illustrates stretchable implant  20 A comprised of struts  12   a , bridges  14   a , and one or more tabs  16  having markers  17 . The implant is shown partially expanded, cut longitudinally and laid flat. The perimeter of struts and bridges define cells  18   a . Struts are joined at bend regions  13   a . Implant  20 A has substantially the same construction, dimensions, and function as implant  10  described above in conjunction with  FIGS. 1A ,  1 B,  3 A,  3 B,  4 A, and  4 B. Implant  20 A can be stretched along axis A by stretchable implant delivery catheter (discussed below). In one embodiment cross sectional area of bridges  14   a  normal to axis A is less than cross sectional area of struts  12   a  normal to axis A and less than cross sectional area of tabs  16  normal to axis A. In one embodiment bridges are locally thinned using processes such as electroetching with or without use of masks, grinding, polishing, laser ablation, or other processes. In another embodiment strut thickness is selectively increased by stiffening a particular region by means of an additive process such as plating, electrodeposition, sputtering, coating, or other processes. In another embodiment yield force of bridges  14   a  normal to axis A is less than yield force of struts  12   a  normal to axis A and less than yield force of tabs  16  normal to axis A. In a further embodiment cross sectional area of bridges  14   a  normal to axis A is less than cross sectional area of struts  12   a  normal to axis A and less than cross sectional area of tabs  16  normal to axis A and yield force of bridges  14   a  normal to axis A is less than yield force of struts  12   a  normal to axis A and less than yield force of tabs  16  normal to axis A. In some embodiments one or more bridge  14   a  is comprised of malleable material such as annealed metal, engineering polymer, or other materials. Annealed metal may be produced by selectively heating bridges  14   a  using processes such as laser heating, electrical resistive heating, inductive heating, or other processes. 
     In use, when tension is applied to implant  20 A bridges  14   a  lengthen in the direction of axis A (i.e. dimension  21  increases) but struts  12   a  and tabs  16  do not lengthen in the direction of axis A. In some embodiments bridges  14   a  are permanently deformed by the applied tensile forces. After implant lengthening the implant is radially expanded. In one embodiment implant  20 A is a self expanding stent and the stent is allowed to self-expand by means of sheath removal. In another embodiment implant  20 A is a balloon expandable stent and the stent is expanded by means of balloon inflation. During implant  20 A stretching and expansion implant dimensional changes fall within the ranges disclosed for implant  10  (above). 
       FIGS. 2B and 2C  illustrate stretchable implants  20 B,  20 C comprised of struts  12   b ,  12   c , bridges  14   b ,  14   c , and one or more tabs  16  having markers  17 . The implants are shown partially expanded, cut longitudinally and laid flat. The perimeter of struts and bridges define cells  18   b ,  18   c . Struts are joined at bend regions  13   b ,  13   c . Implant  20 A has substantially the same construction, dimensions, and function as implant  10  described above in conjunction with  FIGS. 1A ,  1 B,  3 A,  3 B,  4 A, and  4 B. Implants  20 B and  20 C can be stretched along axis A by stretchable implant delivery catheter (discussed below). Bridges  14   b ,  14   c  are comprised of a serpentine shape and one or more gap  23 . The perimeter of struts and bridges define cells  18   b ,  18   c . Struts are joined at bend regions  13   b ,  13   c .  FIG. 2B  illustrates stretchable implant  20 B comprised of bridges  14   b  having one gap  23  and  FIG. 2C  illustrates stretchable implant  20 C comprised of bridges  14   c  having three gaps  23 . In other embodiments bridges can have serpentine shapes with any number of bends and lengths along circular perimeter of stent. Bridges can also join one or more bend regions radially adjacent to each other or can join one or more bend regions radially offset from each other. In some embodiments one or more bridge  14   b ,  14   c  is comprised of malleable material such as annealed metal, engineering polymer, or other material. In one embodiment yield force of bridges  14   b ,  14   c  normal to axis A is less than yield force of struts  12   b ,  12   c  normal to axis A and less than yield force of tabs  16  normal to axis A. In some embodiments one or more bridge  14   b ,  14   c  is comprised of malleable material such as annealed metal, produced by selectively heating bridges  14   a  using processes such as laser heating, electrical resistive heating, inductive heating, or other processes. In another embodiment bridges are locally thinned using processes such as electroetching with or without use of masks, chemical milling, EDM, grinding, polishing, laser ablation, or other processes. 
     In use, when tension is applied to implant  20 B,  20 C gap(s)  23  in bridges  14   b ,  14   c  widen in the direction of axis A but struts  12   b ,  12   c  and tabs  16  do not elongate in direction of axis A. In some embodiments bridges  14   b ,  14   c  are permanently deformed by the applied tensile forces. After implant lengthening the implant is radially expanded. In one embodiment implant  20 B,  20 C is a self expanding stent and the stent is allowed to self-expand by means of sheath removal. In another embodiment implant  20 B,  20 C is a balloon expandable stent and the stent is expanded by means of balloon inflation. During implant  20 B,  20 C stretching and expansion implant dimensional changes fall within the ranges disclosed for implant  10  (above). 
       FIGS. 2D and 2E  illustrate stretchable implant  20 D comprised of struts  12   d , bridges  14   d , and one or more tabs  16  having markers  17 . The implant is shown cut longitudinally and laid flat, also the implant is shown partially expanded in  FIG. 2D  and contracted to a delivery configuration in  FIG. 2E . The perimeter of struts and bridges define cells  18   d . Struts are joined at bend regions  13   d  and follow a serpentine path along their length with one or more bend regions  24  along the length of each strut. Implant  20 D has substantially the same construction, dimensions, and function as implant  10  described above in conjunction with  FIGS. 1A ,  1 B,  3 A,  3 B,  4 A, and  4 B. Implant  20 D can be stretched along axis A by stretchable implant delivery catheter (discussed below). In some embodiments one or more bend region  24  is comprised of malleable material such as annealed metal. In one embodiment yield force of bend region  24  normal to axis A is less than yield force of struts  12   d  normal to axis A and less than yield force of tabs  16  normal to axis A. In some embodiments one or more bend region  24  is comprised of malleable material such as annealed metal, produced by selectively heating bend region  24  using processes such as laser heating, electrical resistive heating, inductive heating, or other processes. In another embodiment bend points are locally thinned using processes such as electroetching with or without use of masks, grinding, polishing, laser ablation, or other processes. 
     In use, when tension is applied to implant  20 D struts  12   d  straighten and lengthen in the direction of axis A due to deformation in bend regions  24 . Tabs  16  do not lengthen when tension is applied. In some embodiments bend regions  24  are permanently deformed by the applied tensile forces. After implant lengthening the implant is radially expanded. In one embodiment implant  20 D is a self expanding stent and the stent is allowed to self-expand by means of sheath removal. In another embodiment implant  20 D is a balloon expandable stent and the stent is expanded by means of balloon inflation. During implant  20 D stretching and expansion implant dimensional changes fall within the ranges disclosed for implant  10  (above). 
       FIG. 2F  illustrates a portion of stretchable implant  20 F comprised of struts  12   f , bridges  14   f , proximal end  25   a  (not shown), distal end  25   b , and one or more tabs  16  having markers  17 . The implant is shown contracted to a delivery configuration, cut longitudinally and laid flat. The perimeter of struts and bridges define cells  18   f . Struts are joined at bend regions  13   f , are malleable at least in part, and are oriented at twist angle α relative to axis A. Implant  20 F has substantially the same construction, dimensions, and function as implant  10  described above in conjunction with  FIGS. 1A ,  1 B,  3 A,  3 B,  4 A, and  4 B. In one embodiment torsional yield force of struts  12   f  and bridges  14   f  is less than torsional yield force of tabs  16 . In some embodiments one or more strut  12   f  and bridge  14   f  is comprised of malleable material such as annealed metal, produced by selectively heating strut  12   f  and/or bridge  14   f  using processes such as laser heating, electrical resistive heating, inductive heating, or other processes. In another embodiment struts  12   f  and/or bridges  14   f  are locally thinned using processes such as electroetching with or without use of masks, grinding, polishing, laser ablation, or other processes. Implant  20 F can be lengthened along axis A by stretchable implant delivery catheter (discussed below) by twisting proximal end  25   a  (not shown) relative to distal end  25   b  in a direction that reduces twist angle α. In one embodiment, a stent having a length of 71 mm when α=45° can be lengthened by any incremental amount by twisting proximal end  25   a  (not shown) relative to distal end  25   b  in a direction that reduces twist angle α, to a maximum length when α=0°. For one embodiment where implant  20 F is a 100 mm long stent when fully stretched,  FIG. 2G  illustrates stent length vs. stent twist angle. 
     In use, when proximal end  25   a  (not shown) of implant  20 F is twisted relative to distal end  25   b  of implant in a direction that reduces twist angle α, struts  12   f  become oriented in a direction more parallel to axis A, thereby lengthening the implant the direction of axis A. In some embodiments malleable struts  12   f  and bend regions  13   f  are permanently deformed by the applied torsional forces. After implant lengthening the implant is radially expanded. In one embodiment implant  20 F is a self expanding stent and the stent is allowed to self-expand by means of sheath removal. In another embodiment implant  20 F is a balloon expandable stent and the stent is expanded by means of balloon inflation. During implant  20 F stretching and expansion implant dimensional changes fall within the ranges disclosed for implant  10  (above). 
     In some embodiments the implant when stretched will lengthen preferentially in certain regions along the length of the implant. For example, implants  10 ,  20 A,  20 B and  20 C tend to lengthen in the region adjacent to bridges  14 ,  14   a ,  14   b  and  14   c  respectively. When expanded, implants  10 ,  20 A,  20 B and  20 C will have a structure that may be characterized as a series of linearly separated serpentine rings interconnected by axial bridges. In one example deployed implants  10 ,  20 A,  20 B and  20 C are stretched more in the distal superficial femoral artery where challenging fatigue conditions are prevalent and stretched less in the mid and proximal superficial femoral artery where fatigue conditions are less challenging. In another example deployed implants  10 ,  20 A,  20 B and  20 C are stretched more in the region of a previously deployed stent so as to minimize vessel stiffening in the already stiffened portion of the vessel and stretched less in the regions proximal to and distal to the previously deployed stent so as to provide adequate vessel scaffolding in the previously unstented region of the vessel. In other embodiments the implant when stretched will lengthen the majority of cells along the length of the implant. For example, each cell  18   d ,  18   f  of implants  20 D and  20 F tend to lengthen in similar amounts when the implant is stretched. In the case of stent implants, structures similar to implants  20 D and  20 F may be advantageous by maintaining a uniform percent metal coverage over the length of the stent. 
     In some embodiment&#39;s stretchable implant  10 ,  20 A,  20 B,  20 C,  20 D, or  20 F offers advantages when comprised of biologically active drugs in the form of coatings, bound moieties, elutable molecules, or other forms over some or all of the implant. In one embodiment a uniformly coated implant is deployed with more implant structure (such as unstretched stent) in one region of the treatment site and less implant structure (such as stretched stent) in a second region of the treatment site, thereby allowing more drug to be delivered in the first region as compared to that delivered in the second region. In another embodiment a uniformly coated implant is deployed with more implant structure in one region of the treatment site and less implant structure in a second region of the treatment site, thereby allowing the structure in the second region to be driven more deeply into the treatment site as compared to the structure in the first region, allowing different kinetics of drug delivery in the two regions. In yet another embodiment, a stretchable implant can be comprised of drugs confined in a brittle coating that is cracked on stretching of the implant. Said coating can isolate reactive drugs from each other, can provide barrier functions for improved drug shelf life, can confine liquids, or have other functions. In one example a stretchable implant comprised of brittle coating is stretched prior to deployment over at least a portion of it&#39;s length to alter drug release kinetics from the coating. In another example a stretchable implant comprised of brittle coating is stretched over at least a portion of it&#39;s length prior to deployment to fracture reservoirs of two or more drugs that will react with one another so as to form a more desirable bioreactive species. In another example a stretchable implant comprised of brittle coating is stretched over at least a portion of its length prior to deployment to fracture reservoirs of two or more drugs that desirable are delivered simultaneously to a treatment site. 
       FIGS. 5A ,  5 B and  5 C illustrate stretchable implant system  50  comprised of catheter  51  having stretchable stent  54  mounted on distal region  50   d  of catheter. Catheter  51  is comprised of catheter shaft  52 , manifold  56 , and retainers  55   p  and  55   d . System  50  is configured to be advanced through the patient&#39;s body lumen. In use, system  50  is sufficiently long for distal region  50   d  to be placed at the deployment site in the patient&#39;s body lumen with proximal region  50   p  remaining external to the patient&#39;s body for manipulation by an operator. Working length of catheter  51 , defined as the catheter length distal to manifold  56 , is contemplated to be from 60 to 200 cm. Stretchable stent  54  has proximal end  54   p , distal end  54   d , is balloon expandable, and is secured to catheter  51  by crimping the stent to a delivery diameter onto balloon  59  with interlock of stent tabs  16  into pockets of retainers  55   p  and  55   d . Stretchable stent  54  may be but is not limited to any of the stretchable stents  10 ,  20 A,  20 B,  20 C,  20 D, or  20 F discussed previously and unstretched stent  54  lengths of from 20 mm to 400 mm are contemplated. Catheter shaft  52  is fixedly attached to proximal retainer  55   p . Manifold  56  is attached to proximal region  50   p  of catheter shaft  52  and provides means for attachment of a stent expansion device and means for stretching stent  54 . A guidewire channel (not shown in  FIGS. 5A and 5B ), extending from distal region  50   d  to proximal region  50   p , is optionally provided in catheter shaft  52 .  FIG. 5C  illustrates further that catheter  51  is comprised of bilumen inner member  57  having balloon inflation lumen  62 , guidewire lumen  61 , tip  58 , distal retainer  55   d , and having balloon  59  sealingly attached thereto at bonds  59   p ,  59   d . Tip  58  and distal retainer  55   d  are fixedly attached to distal portion of bilumen inner member  57 . Lumen  62  is in fluid communication with interior of balloon  59 . Bilumen inner member  57  is slideable within catheter shaft  52  and attached retainer  55   p    
     Catheter shaft  52  of system  50  may have a variety of different constructions. Shaft  52  may have a tubular construction adapted to resist kinking, traverse through tortuous passageways, and to transmit axial and in some embodiments torsional forces along the length of the shaft. Shaft  52  may be constructed so as to have varying degrees of flexibility along its length, and may be comprised of nylon, PEBAX, polyester, Polyurethane, PVC, PEEK, liquid crystal polymer, polyimide, braid reinforcement, metal reinforcement, or other materials. In one embodiment, shaft  52  has a tubular construction of braid-reinforced polyester. Inner member  57  of system  50  is relatively flexible in bending, resists kinking, has high column stiffness and in some embodiments has high torsional stiffness. Inner member  57  may be comprised of nylon, PEBAX, polyester, PEEK, liquid crystal polymer, polyimide, braid reinforcement, metal reinforcement, or other materials. In one embodiment, inner member  57  has a bilumen tubular configuration, defining one lumen  61  that extends through an entire length of inner member  57  and one lumen  62  that extends through most of a length of inner member  57 . This type of configuration allows the system to be passed over a guidewire for guiding the system to a desired implant deployment location and allows inflation of balloon  59 . However, in other embodiments, inner member  57  can have a single lumen configuration that provides for balloon inflation only. Distal region  50   d  of system  50  includes a tapered and flexible distal tip  58  that is sufficiently flexible to permit advancement of stretchable implant system  50  through a patient&#39;s lumen while minimizing trauma to the walls of the patient&#39;s lumen. Tip  58  may be comprised of PEBAX, PVC silicone rubber, C-Flex, polyurethane, thermoplastic elastomer, polyfluoroethylene, hydrogenated (styrene-butadiene) copolymer, or other materials and may be connected to inner member  57  by bonding, overmolding, adhesives, or other means. Proximal facing edges of tip may be chamfered so as to reduce the possibility of snagging on an implant during proximal withdrawal of the tip through the implant. Balloon  59  is capable of expanding a balloon expandable stent at inflation pressures as high as 10, 14, 18, or 20 atmospheres and may be comprised of biaxially oriented polymers such as nylon, PEBAX, polyester, or other materials. Balloon  59  is sealingly attached to inner member  57  at bonds  59   p  and  59   d  using processes such as laser welding, heat bonding, adhesive bonding, or other processes as are known to those skilled in the art. Distal and proximal retainers  55   d ,  55   p  are attached to inner member  57  and shaft  52  respectively and have sufficient strength to stretch stent  54  without mechanical failure. Distal and proximal retainers  55   d ,  55   p  in the form of separate pieces can be secured to inner member  57 , and proximal facing edges of distal retainer may be chamfered so as to reduce the possibility of snagging on an implant during proximal withdrawal of the retainer through the implant. Retainers  55   d ,  55   p  can be machined, etched, stamped, formed, injection molded from thermoplastics or metals, or otherwise fabricated into the surface of a ring of metal, engineering polymer, ceramic, or other material and the ring applied to inner member  57  and shaft  52  by adhesive bonding, welding, solvent welding, fusing, or other techniques known in the art. In some embodiments one or both of distal and proximal retainers  55   d ,  55   p  are formed as an integral/unitary structure with inner member  57  and shaft  52  respectively. In one embodiment one or both of retainers  55   p ,  55   d  are provided with inclined surface  55   x  that prevents tab  16  from exiting out of retainer when stent is tensioned along axis A ( FIG. 5D ). In another embodiment one or both of retainers  55   p ,  55   d  are provided with inclined surface  55   y  that prevents tab  16  from exiting out of retainer when stent is compressed along axis A ( FIG. 5E ). In yet another embodiment one or both of retainers  55   p ,  55   d  are provided with inclined surfaces  55   x  and  55   y  that prevent tab  16  from exiting out of retainer when stent is tensioned or compressed along axis A ( FIG. 5F ). Further, in some embodiments the minimum opening distance between inclined surfaces  55   x  and  55   y  is less than the corresponding dimension of tab  16  to prevent tab  16  from exiting out of retainer when stent is neither in tension nor in compression. In said embodiments stent is forced out of retainers  55   d ,  55   p  by the expanding force of balloon  59  against stent  54 . Alternatively, pockets of retainers  55   p ,  55   d  can be filled with an adhesive or a space filling substance (not shown) to prevent exit of tab  16  from retainer  55   d ,  55   p  when stent is in tension, in compression, or in neither. Said substance may be comprised of polymers such as polyethylene, polyurethane, polybutylene, PEBAX, bioabsorbable polymers such as polyethylene oxide, Carbowax, malleable metals, or other materials. 
     Lumen  61  slideably receives a guidewire (not shown) and is dimensioned to allow low friction passage of a guidewire therewithin. Guidewires suitable for use with system  50  have a nominal outer diameter of 0.010″, 0.012″, 0.014″, 0.018″, 0.025″, 0.035″, 0.038″, or other diameters. Catheter shaft  52  maximum outside diameter can range from about 3 Fr to about 10 Fr. A catheter shaft  52  outside diameter of about 5 Fr is desirable for compatibility with currently popular guide catheter (not shown) dimensions. In one embodiment catheter working length is about 145 cm. 
       FIG. 6  illustrates manifold  56  at proximal region  50   p  of stretchable implant system  50 . Manifold  56  is comprised of Y-fitting  63 , advancer  64 , and flange  65 . Outer surface of proximal most portion of inner member  57  is sealingly attached to inner wall  63   g  of Y-fitting  63  proximal to lumen  62   a , and outer surface of inner member  57  is sealingly attached to inner wall  63   b  of Y-fitting  63  distal to lumen  62   a . Lumen  62  of inner member  57  is in fluid communication with lumen  62   a  of Y-fitting  63  and lumen  61  of inner member  57  is in fluid communication with lumen  61   a  of Y-fitting  63 . Y-fitting  63  is comprised of standard luer fittings  66   b ,  66   g  at proximal end of lumens  62   a ,  61   a  respectively. Shaft  52  is fixedly attached to flange  65 , flange is held captive within groove  64   a  of advancer  64 , flange is slideable within groove  64   a  and flange is slideable over inner member  57  by means of through hole  65   a . In an alternate embodiment where length of stretchable stent is changed by applying torque to the stent, flange  65  is fixedly bonded to advancer  64 . Advancer is slideably attached to Y-fitting  63  by means of threads  64   t  and  63   t  integral with advancer  64  and Y-fitting  63  respectively. Rotation of advancer  64  displaces catheter  52  relative to inner member  57 , causing tensile or compressile forces to be transmitted through retainers  55   p ,  55   d  and tabs  16  to implant  54 . In one embodiment manifold  56  is comprised of one or more indicators which display one or more of implant stretched, nominal, or compressed length. 
     Y-fitting  63 , advancer  64 , and flange  65  may be comprised of polycarbonate, polystyrene, or other materials. Alternate materials for these components are generally well known in the art can be substituted for any of the non-limiting examples listed above provided the functional requirements of the component are met. Inner member  57  may be sealingly attached to Y-fitting  63  using adhesives, welding, or other means as are known in the art. Catheter shaft  52  may be attached to flange  65  using adhesives, welding, or other means as are known in the art. Advancer/Y-fitting threaded connection is provided with sufficient axial travel to stretch and/or contract stent  54  over the entire design range of the stent. Optionally, a strain relief (not shown) may be attached to catheter shaft  52 , flange  65 , or both to prevent kinking of system  50  in the region proximate flange  65 . Optionally, an access port and sealing means (not shown) may be provided on flange  65  so that fluid can be injected into the system to displace air from the annular space between inner member  57  and catheter shaft  52 . 
     Exemplary methods of using stretchable implant system  50  in a body of a patient are now described with the assistance of  FIGS. 7A ,  7 B and  7 C. While a stent is chosen as the exemplary implant in the methods it is understood that the disclosure is not limited to stent implants. 
     Using techniques well known in the art, a guidewire GW is percutaneously inserted into a patient&#39;s blood vessel V and advanced to a region of interest in the patient&#39;s body. Using imaging techniques such as fluoroscopy the diseased portion D of the vessel is identified and a stretchable stent system comprised of a stretchable stent  54  having the correct length range and diameter range for treating the diseased portion D is chosen. Stretchable implant system  50  is advanced over the guidewire to the treatment site and by using imaging techniques such as fluoroscopy, markers  17  at distal end  54   d  of stent  54  are positioned at a correct location relative to the diseased portion D ( FIG. 7A ). Markers  17  at proximal end  54   p  of stent  54  are then imaged and by rotating advancer  64  stent  54  is stretched or contracted to the desired length as evidenced by positions of proximal and distal markers relative to disease length D ( FIG. 7B ). 
     Stretchable implant system  50  is held stationary, an inflation device (not shown) is attached to luer fitting  66   b  and used to inflate balloon  59 . Inflated balloon expands stent  54  into contact with lumenal wall of vessel V, and balloon is then deflated using inflation device. Catheter  51  is repositioned such that balloon is within any unexpanded or underexpanded portion of stent  54 , balloon is reinflated and subsequently deflated as many times as are needed to effect satisfactory stent contact with lumenal wall of vessel V. System  50  is then withdrawn from vessel V ( FIG. 7C ). 
     An alternative exemplary method of using a stretchable implant system  50  in a body of a patient is now described. Using techniques well known in the art, percutaneous access to a patient&#39;s blood vessel V is established. Using imaging techniques such as fluoroscopy the diseased portion of the vessel is identified and a stretchable stent system comprised of a stretchable stent  54  having the correct length range and diameter range for treating the diseased portion D is chosen. A guidewire is either back-loaded or front-loaded into lumen  61  of stretchable implant system  50  and the position of the guidewire is adjusted such that a short length (typically 10-20 cm) of the guidewire extends distally of tip  58 . The system/guidewire combination is advanced through the patient&#39;s vessel to a region of interest in the patient&#39;s body. The combination is advanced to the treatment site and by using imaging techniques such as fluoroscopy markers  17  at distal end  54   d  of stent  54  are positioned at a correct location relative to the diseased portion D. Alternatively, the treatment site is initially crossed by further advancement of the guidewire alone, stretchable implant system  50  is subsequently advanced over the guidewire to the treatment site and by using imaging techniques such as fluoroscopy, markers  17  at distal end  54   d  of stent  54  are positioned at a correct location relative to the diseased portion D. Markers  17  at proximal end  54   p  of stent  54  are then imaged and by rotating advancer  64  stent  54  is stretched or contracted to the correct length as evidenced by positions of proximal and distal markers relative to disease length D. 
     Fitting/advancer of stretchable implant system  50  is held stationary, an inflation device is attached to luer fitting  66   b  and used to inflate balloon  59 . Inflated balloon expands stent  54  into contact with lumenal wall of vessel V, and balloon is then deflated using inflation device. Catheter  51  is repositioned such that balloon is within any unexpanded or underexpanded portion of stent  54 , balloon is reinflated, and subsequently deflated as many times as are needed to effect satisfactory stent contact with lumenal wall of vessel V. System  50  is then withdrawn from vessel V. 
       FIGS. 5G and 5H  illustrate stretchable implant system  50 ′, similar in many respects to stretchable implant system  50 , and comprised of catheter  51 ′ having stretchable stent  54  mounted on distal region  50   d ′ of catheter. Catheter  51 ′ is comprised of catheter shaft  52 , manifold  56 ′, and retainers  55   p ′ and  55   d . System  50 ′ is configured to be advanced through the patient&#39;s body lumen. In use, system  50 ′ is sufficiently long for distal region  50   d ′ to be placed at the deployment site in the patient&#39;s body lumen with proximal region  50   p ′ remaining external to the patient&#39;s body for manipulation by an operator. Working length of catheter  51 ′, defined as the catheter length distal to manifold  56 ′, is contemplated to be from 60 to 200 cm. Stretchable stent  54  has proximal end  54   p , distal end  54   d , is balloon expandable, and is secured to catheter  51 ′ by crimping the stent to a delivery diameter onto balloon  59 ′ with interlock of stent tabs  16  into pockets of retainers  55   p ′ and  55   d . Stretchable stent  54  may be but is not limited to any of the stretchable stents  10 ,  20 A,  20 B,  20 C,  20 D, or  20 F discussed previously and unstretched stent  54  lengths of from 20 mm to 400 mm are contemplated. Catheter shaft  52  is fixedly attached to proximal retainer  55   p ′ and corrugated balloon  59 ′ is attached to proximal retainer  55   p ′ at bond  59   p ′. Manifold  56 ′ is attached to proximal region  50   p ′ of catheter shaft  52  and provides means for attachment of a stent expansion device and means for stretching stent  54 . A guidewire channel extending from distal region  50   d ′ to proximal region  50   p ′ is optionally provided in catheter shaft  52 . Catheter  51 ′ is comprised of single lumen inner member  57 ′ having guidewire lumen  61 , tip  58 , distal retainer  55   d , and having balloon  59 ′ sealingly attached thereto at bond  59   d . Balloon lumen  62  is formed by the annular space between the outer diameter of inner member  57 ′ and the inner diameter of catheter shaft  52 . Tip  58  and distal retainer  55   d  are fixedly attached to distal portion of inner member  57 ′. Lumen  62  is in fluid communication with interior of balloon  59 ′. Inner member  57 ′ is slideable within catheter shaft  52  and attached retainer  55   p′.    
     Retainer  55   p ′, inner member  57 ′, and bond  59   p ′ have substantially the same construction, dimensions, and function as retainer  55   p , inner member  57 , and bond  59   p  respectively described above in conjunction with  FIGS. 5A to 5C , as do all components having the same numbers in  FIGS. 5A to 5C  and  5 G to  5 H. Balloon  59 ′ is capable of expanding a balloon expandable stent at inflation pressures as high as 10, 14, 18, or 20 atmospheres and has corrugations formed into the balloon during the balloon blowing process such that balloon is capable of stretching axially as stent is stretched prior to stent radial expansion. Balloon  59 ′ may be comprised of biaxially oriented polymers such as nylon, PEBAX, polyester, polyurethane or other materials in monolithic or layered structures. Balloon  59  is sealingly attached to inner member  57  at bond  59   d  and to proximal retainer  55   p  at bond  59   p  using processes such as laser welding, heat bonding, adhesive bonding, or other processes as are known to those skilled in the art. 
       FIG. 5H  illustrates manifold  56 ′ at proximal region  50   p ′ of stretchable implant system  50 ′. Manifold  56 ′ is comprised of Y-fitting  63 ′, advancer  64 , and flange  65 ′. Outer surface of proximal most portion of inner member  57 ′ is sealingly attached to inner wall  63   g  of Y-fitting  63  proximal to lumen  62   a . Lumen  62  of catheter  51 ′ is in fluid communication with lumen  62   a  of Y-fitting  63  and lumen  61  of inner member  57 ′ is in fluid communication with lumen  61   a  of Y-fitting  63 . Y-fitting  63  is comprised of standard luer fittings  66   b ,  66   g  at proximal end of lumens  62   a ,  61   a  respectively. Shaft  52  is fixedly attached to flange  65 ′, flange is held captive within groove  64   a  of advancer  64 , flange is slideable within groove  64   a  and flange is slideable over inner member  57  by means of through hole  65   a . Flange  65 ′ has proximal extension  65   b  with seal  67  housed in a groove in proximal extension  65   b . Seal  67  creates a fluid tight axially slideable seal between exterior diameter of proximal extension  65   b  and inner diameter of counterbore  63   c  in Y-fitting  63 . Advancer is slideably attached to Y-fitting  63  by means of threads  64   t  and  63   t  integral with advancer  64  and Y-fitting  63  respectively. Rotation of advancer  64  displaces catheter  52  relative to inner member  57 ′, causing tensile or compressile forces to be transmitted through retainers  55   p ,  55   d  and tabs  16  to implant  54  and balloon  59 ′. In one embodiment manifold  56  is comprised of one or more indicators which display one or more of implant stretched, nominal, or compressed length. 
     Y-fitting  63 ′, advancer  64 , and flange  65 ′ have substantially the same construction, dimensions, and function as Y-fitting  63 , advancer  64 , and flange  65  respectively described above in conjunction with  FIGS. 5A to 5C . Optional strain relief, access port and sealing means, or both may be provided on flange  65 ′ as described above in conjunction with  FIG. 6 . Seal  67  may be comprised of elastomeric materials such as butyl rubber, silicone rubber, Viton, C-flex, PVC, polyurethane, or other materials and may be molded, cut from sheet, or made using other processes known in the art. 
     Exemplary methods of using stretchable implant system  50 ′ in a body of a patient are identical to those for stretchable implant system  50  with the following exceptions. When advancer  64  is rotated both the stent  54  and the balloon  59 ′ will be stretched or contracted. Also, the initial balloon will expand substantially all of the length of the stretchable stent due to the length change of the balloon when the advancer is rotated. For this reason catheter  51 ′ may not need to be repositioned to effect satisfactory stent contact with lumenal wall of vessel V. 
       FIGS. 8A and 8B  illustrate the distal and proximal ends respectively of an alternate embodiment of a stretchable implant system. Stretchable implant system  70  is comprised of catheter  71  having stretchable stent  74  mounted on distal region  70   d  of catheter. Catheter  71  is comprised of catheter shaft  72 , proximal retainer  75   p , and manifold  76 . Working length of catheter, defined as the catheter length distal to manifold  76 , is contemplated to be from 60 to 200 cm. Catheter  71  is further comprised of inner member  77  having single lumen proximal tube  77   b , single lumen extension tube  77   s , bitumen distal tube  77   g  having balloon inflation lumen  82 , having guidewire lumen  81  and having balloon  79  sealingly attached thereto at bonds  79   p  and  79   d , track  77   j , tip  78 , and distal retainer  75   d . Tip  78  and distal retainer  75   d  are fixedly attached to distal tube  77   g . Single lumen proximal tube  77   b , single lumen extension tube  77   s , and bitumen distal tube  77   g  are fixedly attached to track  77   j . Lumen  82  is in fluid communication with interior of balloon  79 . Proximal retainer  75   p  is slideable over track  77   j  and extension tube  77   s  is slideable within lumen  72   b  of bitumen distal portion of catheter shaft  72 . Guidewire lumen  81  extends from distal region  70   d  of catheter to catheter port  72   s . Stretchable stent  74  has proximal end  74   p , distal end  74   d , is balloon expandable, and is secured to catheter shaft  72  by crimping the stent to a delivery diameter onto balloon  79  with interlock of stent tabs  16  into pockets of retainers  75   p  and  75   d . Stretchable stent  74  may be but is not limited to any of the stretchable stents  10 ,  20 A,  20 B,  20 C,  20 D, or  20 F discussed previously and unstretched stent lengths of from 20 mm to 400 mm are contemplated. Manifold  76  is attached to proximal region  70   p  of catheter and provides means for attachment of a stent expansion device and means for stretching stent  74 . 
     Catheter shaft  72 , retainer  75   p , inner member  77  (including tubes  77   b ,  77   g ,  77   s  and track  77   j ), lumen  81 , balloon  79 , bonds  79   p  and  79   d , tip  78 , and retainer  75   d  have substantially the same construction, dimensions, and function as catheter shaft  52 , retainer  55   p , inner member  57 , lumen  61 , balloon  59 , bonds  59   p  and  59   d , tip  58 , and retainer  55   d  respectively described above in conjunction with  FIGS. 5A to 5C . Track  77   j  may be comprised of polymers and may be manufactured using processes such as insert molding or reflow techniques. 
       FIG. 8B  illustrates manifold  76  at proximal region  70   p  of stretchable implant system  70 . Manifold  76  is comprised of fitting  83 , advancer  84 , and flange  85 . Outer surface of proximal portion of tube  77   b  is sealingly attached to inner wall  83   b  of fitting  83 . Lumen  82  of tube  77   b  is in fluid communication with lumen  82   a  of fitting  83 . Fitting  83  is comprised of standard luer fitting  86   b  at proximal end of lumens  82   a . Shaft  72  is fixedly attached to flange  85 , flange is held captive within groove  84   a  of advancer  84 , flange is slideable within groove  84   a  and flange is slideable over tube  77   b  by means of through hole  85   a . In an alternate embodiment where length of stretchable stent is changed by applying torque to the stent, flange  85  is fixedly bonded to advancer  84 . Advancer is slideably attached to fitting  83  by means of threads  84   t  and  83   t  integral with advancer  64  and fitting  83  respectively. Rotation of advancer  84  displaces shaft  72  relative to inner member  77 , causing tensile or compressile forces to be transmitted through retainers  75   p ,  75   d  and tabs  16  to implant  74 . 
     Fitting  83 , advancer  84 , and flange  85  have substantially the same construction, dimensions, and function as Y-fitting  63 , advancer  64 , and flange  65  respectively described above in conjunction with  FIG. 6 . Tube  77   b  and shaft  72  are attached to fitting  83  and flange  85  respectively in substantially the manner as inner member  57  and catheter  52  are attached to Y-fitting  63  and flange  65  respectively described above in conjunction with  FIG. 6 . Optional strain relief, access port and sealing means, or both may be provided on flange  85  as described above in conjunction with  FIG. 6 . 
     Exemplary methods of using stretchable implant system  70  are the same as the exemplary methods described above for using stretchable implant system  50 . 
       FIGS. 9A ,  9 B and  9 C illustrate the distal and proximal portions respectively of an alternate embodiment of a stretchable implant system. Stretchable implant system  90  is comprised of catheter  91  having stretchable stent  94  mounted on distal region  90   d  of catheter. Catheter  91  is comprised of catheter shaft  92 , retainer  95   p , manifold  96  and sheath  93 . Catheter shaft  92  is fixedly attached to retainer  95   p . Working length of catheter  91 , defined as the catheter length distal to handle  106 , is contemplated to be from 60 to 200 cm. Catheter  91  is further comprised of inner member  97  having guidewire lumen  101 , tip  98 , and distal retainer  95   d . Tip  98  and distal retainer  95   d  are fixedly attached to inner member  97 . Retainer  95   p  is slideable over inner member  97  and sheath  93  is slideable over catheter shaft  92  and stent  94 . Guidewire lumen  101  extends from distal region  90   d  of catheter to manifold  96 . Stretchable stent  94  has proximal end  94   p , distal end  94   d , is self expandable, and is secured to catheter  91  by compressing the stent to a delivery diameter within sheath  93  with interlock of stent tabs  16  into pockets of retainers  95   p  and  95   d . Stretchable stent  94  may be but is not limited to any of the stretchable stents  10 ,  20 A,  20 B,  20 C,  20 D, or  20 F discussed previously and unstretched stent lengths of 20 mm to 400 mm are contemplated. Manifold  96  is attached to proximal region  90   p  of catheter, provides means for withdrawal of sheath  93  from stent  94 , and provides means for stretching stent  94 . 
     Catheter shaft  92 , retainer  95   p , inner member  97 , lumen  101 , tip  98 , and retainer  95   d  have substantially the same construction, dimensions, and function as catheter shaft  52 , retainer  55   p , inner member  57 , lumen  61 , tip  58 , and retainer  55   d  respectively described above in conjunction with  FIGS. 5A to 5C . Sheath is fixedly attached to handle  106 , has sufficient distal hoop strength to constrain self expanding stent  94  at a delivery diameter, has sufficient axial strength to be slid proximally off of stent  94  without damage or tensile failure, and sufficient flexibility to be advanced as part of system  90  through tortuous vessels. Sheath  93  may be comprised of polyester, nylon, PEEK, liquid crystal polymer, polyimide, metal reinforcement, or other materials and may be manufactured at least in part by extrusion, braiding, joining of tubing lengths, or other processes known in the art. 
       FIG. 9B  illustrates manifold  96  at proximal region  90   p  of stretchable implant system  90 . Manifold  96  is comprised of fitting  103 , advancer  104 , and flange  105 . Outer surface of inner member  97  is sealingly attached to inner wall  103   b  of fitting  103 . Lumen  101  of inner member  97  is in fluid communication with lumen  102   a  of fitting  103 . Fitting  103  is comprised of standard luer fitting  106   b  at proximal end of lumen  102   a . Shaft  92  is fixedly attached to flange  105 , flange is held captive within groove  104   a  of advancer  104 , flange is slideable within groove  104   a  and flange is slideable over inner member  97  by means of through hole  105   a . In an alternate embodiment where length of stretchable stent is changed by applying torque to the stent, flange  105  is fixedly bonded to advancer  104 . Advancer is slideably attached to fitting  103  by means of threads  104   t  and  103   t  integral with advancer  104  and fitting  103  respectively. Rotation of advancer  104  displaces shaft  92  relative to inner member  97 , causing tensile or compressile forces to be transmitted through retainers  95   p ,  95   d  and tabs  16  to implant  94 . Handle  106  houses seal  107  that is sealingly slideable over shaft  92 . In a transport position, handle  106  and advancer  104  are spaced apart and sheath  93  covers stent  94  to prevent premature deployment of stent  94 . When handle  106  and advancer  104  are moved toward each other, sheath  93  slides proximally relative to catheter  92  and inner member  97 , uncovering self expanding stent  94 , thereby permitting stent to deploy by radially expansion. Optionally, handle  106  may be provided with a lock (not shown) to limit axial movement of handle relative to catheter shaft  92  prior to deployment of stent  94 . 
     Fitting  103 , advancer  104 , and flange  105  have substantially the same construction, dimensions, and function as Y-fitting  63 , advancer  64 , and flange  65  respectively described above in conjunction with  FIG. 6 . Handle  106  may be comprised of the same materials as fitting  103 , advancer  104 , or flange  105  and may comprise an annular groove along the inner diameter to house seal  107 . Seal  107  may be comprised of elastomeric materials such as butyl rubber, silicone rubber, Viton, C-flex, or other materials and may be molded, cut from sheet, or made using other processes known in the art. Inner member  97  and shaft  92  are attached to fitting  103  and flange  105  respectively in substantially the manner as inner member  57  and catheter  52  are attached to Y-fitting  63  and flange  65  respectively described above in conjunction with  FIG. 6 . Optional strain relief, access port and sealing means, or both may be provided on flange  105  or handle  106  as described above in conjunction with  FIG. 6 . 
     Optionally, system  90  is comprised of stretchable stent retainer  95   s  as illustrated in  FIG. 9C . Stretchable stent retainer influences stretching characteristics of stent  94 . Stretchable stent retainer is fixedly attached to distal retainer  95   d  and proximal retainer  95   p  by molding, fusing, adhesive bonding, welding, or other means. Stretchable stent retainer is slideably attached to stent  94  by means of tabs  99 . In some embodiments, tabs  99  protrude from surface of retainer  95   s  and into cells  18 ,  18   a ,  18   b ,  18   c ,  18   d , or  18   f  of stents  10 ,  20 A,  20 B,  20 C,  20 D, or  20 F respectively. Stretchable retainer  95   s  is axially stretches uniformly along its length, preferentially along one or more localized region along it&#39;s length, or at different rates along one or more localized region along it&#39;s length. Stretchable stent retainer may be comprised of polymers such as nylon, PEBAX, polyester, PEEK, of metals such as stainless steel, nitinol, or of other materials and may be fabricated using processes such as molding, extrusion, or other processes. In one embodiment retainer  95   s  is a coextruded tube comprised of nylon 12 tabs  99  and outer shell with a  72 D PEBAX inner shell. Stretch rate of retainer  95   s  may be adjusted by varying the wall thickness of the retainer at various regions along the length of the retainer. In one embodiment retainer  95   s  has a uniform wall thickness over its length and undeployed stent  94 /retainer  95   s  combination uniformly stretches along it&#39;s length prior to stent deployment. In another embodiment retainer  95   s  has a locally thin wall thickness over the distal and proximal thirds of its length and undeployed stent  94 /retainer  95   s  combination preferentially stretches along the distal and proximal regions of retainer prior to stent deployment. In yet another embodiment retainer  95   s  has more one or more distinct regions of locally thin wall thickness over its length and undeployed stent  94 /retainer  95   s  combination preferentially stretches at pre-programmed discrete regions along the length of the stent/retainer combination prior to stent deployment. 
     Exemplary methods of using stretchable implant system  90  in a body of a patient are now described. While a stent is chosen as the exemplary implant in the method it is understood that the disclosure is not limited to stent implants. 
     Using techniques well known in the art, a guidewire GW is percutaneously inserted into a patient&#39;s blood vessel V and advanced to a region of interest in the patient&#39;s body. Using imaging techniques such as fluoroscopy the diseased portion of the vessel is identified and a stretchable stent system comprised of a stretchable stent  94  having the correct length range and diameter range for treating the diseased portion is chosen. Stretchable implant system  90  is advanced over the guidewire to the treatment site and by using imaging techniques such as fluoroscopy markers  17  at distal end  94   d  of stent  94  are positioned at a correct location relative to the diseased portion. Markers  17  at proximal end  94   p  of stent  94  are then imaged and stent  94  is stretched or contracted to the correct length by rotating advancer  104  as evidenced by positions of proximal and distal markers relative to disease length. 
     Fitting/advancer of stretchable implant system  90  is held stationary and sheath  93  is withdrawn proximally to uncover stent  94  thereby permitting stent to deploy by radial self expansion. System  90  is then withdrawn from vessel. 
     In an alternative method, stretchable implant system  90  may be used according to the exemplary method described for using stretchable implant system  110 . 
       FIGS. 10A and 10B  illustrate the distal and proximal portions respectively of an alternate embodiment of a stretchable implant system. Stretchable implant system  110  is comprised of catheter  111  having stretchable stent  114  mounted on distal region  110   d  of catheter. Catheter  111  is comprised of catheter shaft  112 , extension rod  116 , proximal retainer  115   p , inner member  117 , manifold  116  and sheath  113 . Catheter shaft  112  is fixedly attached to extension rod  116  and extension rod  116  is fixedly attached to retainer  115   p . The working length of catheter, defined as the catheter length distal to handle  126 , is contemplated to be from 60 to 200 cm. Inner member  117  is further comprised of core rod  117   c , track  117   a , distal tube  117   b , extension tube  117   s , tip  118 , and distal retainer  115   d . Tip  118  and distal retainer  115   d  are fixedly attached to distal tube  117   b , distal tube  117   b  is fixedly attached track  117   a , and track  117   a  is fixedly attached to extension tube  117   s  and core rod  117   c . Guidewire lumen  121  extends from distal region  110   d  of catheter to sheath port  113   s . Sheath  113  is comprised of a single lumen over much of its length as well as a short bilumen portion in the vicinity of lumen  113   b . Proximal retainer  115   p  is slideable over track  117   a , single lumen extension tube  117   s  is slideable within lumen  113   b  of sheath  113 , and sheath  113  is slideable over catheter shaft  112 , retainer  115   p  and stent  114 . Stretchable stent  114  has proximal end  114   p , distal end  114   d , is self expandable, and is secured to catheter  111  by compressing the stent to a delivery diameter within sheath  113  with interlock of stent tabs  16  into pockets of retainers  115   p  and  115   d . Stretchable stent  114  may be but is not limited to any of the stretchable stents  10 ,  20 A,  20 B,  20 C,  20 D, or  20 F discussed previously and unstretched stent lengths of 20 mm to 400 mm are contemplated. Manifold  116  is attached to proximal region  110   p  of catheter and provides means for withdrawal of sheath  113 , thereby allowing stent self-expansion, and provides means for stretching stent  114 . Optionally, a stretchable inner member (not shown) is fixedly attached to retainers  115   p ,  115   d  and slideably attached to stent  114  as described for stretchable implant system  90 . 
     Catheter shaft  112 , retainer  115   p , lumen  121 , tip  118 , and retainer  115   d  have substantially the same construction, dimensions, and function as catheter shaft  52 , retainer  55   p , lumen  61 , tip  58 , and retainer  55   d  respectively described above in conjunction with  FIGS. 5A to 5C . Distal tube  117   b  and extension tube  117   s  have substantially the same construction, dimensions, and function as inner member  57  described above in conjunction with  FIGS. 5A to 5C . Sheath  113  has substantially the same construction, dimensions, and function as Sheath  93  described above in conjunction with  FIGS. 9A to 9B . Track  117   a  may be comprised of polymers and may be manufactured using processes such as insert molding or reflow techniques. Extension rod  116  and core rod  117   c  may be comprised of metal, engineering polymer, or other materials intended to resist axial tensile and axial compressive deformation including but not limited to stainless steel, nitinol, liquid crystal polymer, PEEK, polyimide, metal reinforced materials, fiber reinforced materials, or other materials. Sheath is fixedly attached to handle  126 , has sufficient distal hoop strength to constrain self expanding stent  114  at a delivery diameter, has sufficient axial strength to be slid proximally off of stent  114  without damage or tensile failure, sufficiently low coefficient of friction to allow for movement of the sheath across the compacted stent, and sufficient flexibility to be advanced as part of system  110  through tortuous vessels. Sheath  113  may be comprised of polyester, nylon, PEEK, liquid crystal polymer, polyimide, metal reinforcement, or other materials and may be manufactured at least in part by extrusion, braiding, or other processes known in the art. 
       FIG. 10B  illustrates manifold  116  at proximal region  110   p  of stretchable implant system  110 . Manifold  116  is comprised of fitting  123 , advancer  124 , and flange  125 . Outer surface of core rod  117   c  is fixedly attached to fitting  123 . Fitting  123  is comprised of handle  126   b  at proximal end of fitting  123 . Shaft  112  is fixedly attached to flange  125 , flange is held captive within groove  124   a  of advancer  124 , flange is slideable within groove  124   a  and flange is slideable over core rod  117   c  by means of through hole  125   a . In an alternate embodiment where length of stretchable stent is changed by applying torque to the stent, flange  125  is fixedly bonded to advancer  124 . Advancer is slideably attached to fitting  123  by means of threads  124   t  and  123   t  integral with advancer  124  and fitting  123  respectively. Rotation of advancer  124  displaces shaft  112  relative to core rod  117   c , causing tensile or compressile forces to be transmitted through retainers  115   p ,  115   d  and tabs  16  to implant  114 . Handle  126  houses seal  127  that is sealingly slideable over shaft  112 . In a transport position, handle  126  and advancer  124  are spaced apart and sheath  113  covers stent  114  to prevent premature deployment of stent  114 . When handle  126  and advancer  124  are moved toward each other, sheath  113  slides proximally relative to catheter  112  and core rod  117   c , uncovering self expanding stent  114 , thereby permitting stent to deploy by radial expansion. Optionally, handle  126  may be provided with a user activated mechanical lock (not shown) to limit axial movement of handle relative to catheter shaft  112  prior to deployment of stent  114 . 
     Fitting  123 , advancer  124 , and flange  125  have substantially the same construction, dimensions, and function as Y-fitting  63 , advancer  64 , and flange  65  respectively described above in conjunction with  FIG. 6 . Handle  126  may be comprised of the same materials as fitting  123 , advancer  124 , or flange  125  and may comprise an annular groove along the inner diameter to house seal  127 . Seal  127  may be comprised of elastomeric materials such as butyl rubber, silicone rubber, Viton, C-flex, or other materials and may be molded, cut from sheet, or made using other processes known in the art. Core rod  117   c  and shaft  112  are attached to fitting  123  and flange  125  respectively in substantially the manner as inner member  57  and catheter  52  are attached to Y-fitting  63  and flange  65  respectively described above in conjunction with  FIG. 6 . Optional strain relief, access port and sealing means, or both may be provided on flange  125  or handle  126  as described above in conjunction with  FIG. 6 . 
     Exemplary methods of using stretchable implant system  110  in a body of a patient are now described. While a stent is chosen as the exemplary implant in the method it is understood that the disclosure is not limited to stent implants. 
     Using techniques well known in the art, percutaneous access to a patient&#39;s blood vessel V is established. Using imaging techniques such as fluoroscopy the diseased portion of the vessel is identified and a stretchable stent system comprised of a stretchable stent  114  having the correct length range and diameter range for treating the diseased portion is chosen. A guidewire is either back-loaded or front-loaded into lumen  121  of stretchable implant system  110  and the position of the guidewire is adjusted such that a short length (typically 10-20 cm) of the guidewire extends distally of tip  118 . The system/guidewire combination is advanced through the patients vessel to a region of interest in the patient&#39;s body. The combination is advanced to the treatment site and by using imaging techniques such as fluoroscopy markers  17  at distal end  114   d  of stent  114  are positioned at a correct location relative to the diseased portion. Alternatively, the diseased portion is initially crossed by further advancement of the guidewire alone, stretchable implant system  110  is subsequently advanced over the guidewire to the treatment site and by using imaging techniques such as fluoroscopy markers  17  at distal end  114   d  of stent  114  are positioned at a correct location relative to the diseased portion. Markers  17  at proximal end  114   p  of stent  114  are then imaged and stent  114  is stretched or contracted to the correct length by rotating advancer  124  as evidenced by positions of proximal and distal markers relative to disease length. 
     Fitting/advancer of stretchable implant system  110  is held stationary and sheath  113  is withdrawn proximally to uncover stent  114  thereby permitting stent to deploy by radial self expansion. System  110  is then withdrawn from vessel. 
     In an alternative method, stretchable implant system  110  may be used according to the exemplary method described for using stretchable implant system  90 . 
     In a further alternative method, stretchable implant system  50 ,  70 ,  90 ,  110  may be used advantageously during delivery of an implant through a tortuous path, for example, to a treatment site in the brain. While a stent is chosen as the exemplary implant in this method it is understood that the disclosure is not limited to stent implants. A stretchable implant system comprised of a stretchable stent of a length suitable for treatment of a diseased vessel is chosen. The stent is stretched before introduction of the system into the tortuous path so as to increase the bending flexibility of the system in the region of the unexpanded stent. For example, a stent similar to implant  20 C, when stretched, will be more flexible than when in an unstretched state due to increases in gaps  23 . The stretchable implant system is then advanced through tortuosity to the treatment site and the stent is axially contracted to the length suitable for treatment of the diseased vessel. The stent is then deployed and the system is withdrawn from the patient. 
       FIG. 11  illustrates the distal portion of an alternate embodiment of a stretchable implant system. Stretchable implant system  120  is comprised of catheter  121  having stretchable stent  54  mounted on distal region  120   d  of catheter, short balloon  129  mounted on distal region of inner member  57 , and manifold  56  (illustrated in  FIG. 6 ). Aside from the shortened length of balloon  129  as compared to balloon  59 , all components of system  120  have substantially the same construction, dimensions, and function as all components of system  50  described above in conjunction with  FIGS. 5A to 5C  and  FIG. 6 . 
     Exemplary methods of using stretchable implant system  120  in a body of a patient are now described with the assistance of schematic illustrations in  FIGS. 12A to 12C . While a stent is chosen as the exemplary implant in the methods it is understood that the disclosure is not limited to stent implants. 
     Using techniques well known in the art, percutaneous access to a patient&#39;s blood vessel V is established. Using imaging techniques such as fluoroscopy the diseased portion of the vessel is identified and a stretchable stent system comprised of a stretchable stent  54  having the correct length range and diameter range for treating the diseased portion is chosen. A guidewire is either back-loaded or front-loaded into lumen  61  of stretchable implant system  120  and the position of the guidewire is adjusted such that a short length (typically 10-20 cm) of the guidewire extends distally of tip  58 . The system/guidewire combination is advanced through the patients vessel to a region of interest in the patient&#39;s body. The combination is advanced to the treatment site and by using imaging techniques such as fluoroscopy markers  17  at distal end  54   d  of stent  54  are positioned at a correct location relative to the diseased portion. Alternatively, the diseased portion is initially crossed by further advancement of the guidewire alone, stretchable implant system  120  is subsequently advanced over the guidewire to the treatment site and by using imaging techniques such as fluoroscopy markers  17  at distal end  54   d  of stent  54  are positioned at a correct location relative to the diseased portion. If desired, stent  54  can be stretched by rotating advancer  64  prior to initial deployment. Distal end of stent  54  is then deployed by inflating balloon  129 . Stent  54  is then stretched in-situ by pulling catheter  120  proximally so that stent  54  becomes tensioned between deployed segment (which is anchored to the vessel in an expanded form) and proximal retainer  55   p . A stretched portion of stent  54  is then deployed over region D 1  by adjusting position of balloon  129  relative to stent and then inflating balloon  129  ( FIG. 12A , with one alternate balloon position shown in phantom). Stent  54  is then contracted in the vicinity of disease D 2  and the contracted portion of stent  54  is then deployed by adjusting position of balloon  129  relative to stent and then inflating balloon  129  ( FIG. 12B  with contracted portion of stent shown by heavy line). Stent  54  is then again stretched in-situ and proximal most stretched portion of stent  54  is then deployed by adjusting position of balloon  129  relative to stent and inflating balloon  129  ( FIG. 12C , with one alternate balloon position shown in phantom). System  110  is then withdrawn from vessel. Optionally, fully deployed stent  54  is further expanded using a balloon long enough to extend over the entire length of the expanded stent. 
     In an alternate exemplary method, May-Thurners syndrome is treated by deploying compressed stent  54  in the region of crushed vein and deploying stretched stent  54  in the region of un-crushed vein. 
     While the various embodiments of the present disclosure have related to stents and stent delivery systems, the scope of the present disclosure is not so limited. It will be appreciated that the various aspects of the present disclosure are also applicable to systems for delivering other types of expandable implants. By way of non-limiting example, other types of expanding implants include anastomosis devices, blood filters, grafts, vena cava filters, percutaneous valves, aneurism treatment devices, occlusion coils, or other devices. 
     It has been shown how the objects of the disclosure have been attained in a preferred manner. Modifications and equivalents of the disclosed concepts are intended to be included within the scope of the claims. Further, while choices for materials and configurations may have been described above with respect to certain embodiments, one of ordinary skill in the art will understand that the materials and configurations described are applicable across the embodiments.

Technology Category: 1