(19)
(11)EP 2 429 463 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
17.12.2014 Bulletin 2014/51

(21)Application number: 10720904.1

(22)Date of filing:  12.05.2010
(51)International Patent Classification (IPC): 
A61F 2/90(2013.01)
(86)International application number:
PCT/EP2010/056557
(87)International publication number:
WO 2010/130788 (18.11.2010 Gazette  2010/46)

(54)

STENT

STENT

ENDOPROTHÈSE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO SE SI SK SM TR

(30)Priority: 14.05.2009 GB 0908315
14.05.2009 US 178416 P

(43)Date of publication of application:
21.03.2012 Bulletin 2012/12

(73)Proprietor: Angiomed GmbH & Co. Medizintechnik KG
76227 Karlsruhe (DE)

(72)Inventor:
  • DREHER, Gael
    76227 Karlsruhe (DE)

(74)Representative: Hoffmann Eitle 
Patent- und Rechtsanwälte PartmbB Arabellastraße 30
81925 München
81925 München (DE)


(56)References cited: : 
EP-A2- 1 129 673
WO-A1-2008/025762
WO-A2-2008/028964
WO-A1-2007/035023
WO-A1-2009/003584
WO-A2-2008/119837
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Field of the Invention



    [0001] This invention relates to a stent formed by slitting a tube to create a matrix of struts which are separated from each other by no more than the width of the slit and which lie parallel to each other and to the longitudinal axis of the tube, the slitted tube being radially expandable to a stenting disposition in which the struts exhibit a zigzag pattern in successive loops around the circumference of the stent, the angle each strut makes with the longitudinal axis increasing as the stent diameter increases, the zigzag pattern exhibiting a cusp between any two adjacent struts, with selected tied cusps of any one loop being connected by a bridge to a facing cusp of the adjacent loop, the bridge extending in a direction parallel to the longitudinal axis of the tube, and with intervening free cusps, between any two bridge of a loop, not being connected to the adjacent loop, the zigzag pattern exhibiting a lengthwise staggering of circumferentially adjacent said slits to the extent that the lengths of two circumferentially adjacent struts on the zigzag pattern that flank a tied cusp are different and further such that, in the said stenting disposition, the free cusps of adjacent loops are circumferentially displaced from each other.

    Background Art



    [0002] Self-expanding stents for the arterio-vascular system need to demonstrate a predictable and lengthy resistance to fatigue failure. Furthermore, the process used to manufacture self-expanding stents needs to be rigorous and competitive. Applicant discloses in WO 2008/119837 an attractive stent design that lends itself to manufacture by laser cutting of a tube of stent material such as nickel titanium shape memory alloy. The slits that are cut in the tube by the laser are all straight and parallel to the axis of the tube, leaving the slits cut by the laser parallel with each other so that the struts of the stent, that lie between adjacent slits, are themselves also straight and parallel with the axis of the tube (at least in the moment that they are formed). Modelling of the stress distribution in the struts of the stent matrix is therefore a task that is relatively simple, by which we mean, simple when compared with a stent matrix in which the struts are not straight or not of constant cross section.

    [0003] Apart from fatigue performance, a stent design should be amenable to delivery through a tortuous bodily lumen, and then, for some applications, competent to endure severe bending, even after deployment, to follow without undue difficulty the changes of shape and configuration of the bodily lumen in which they are installed. Between adjacent struts of a zigzag turn around the stented bodily lumen, there are the "cusps" or "peaks" where two adjacent struts come together. In axially adjacent zigzag loops of the stent, after deployment, it is desirable that the peaks of the adjacent loops do not clash, "head-to-head" when the bodily lumen bends, and the stent with it. The above-mentioned WO 2008/119837 offers a stent design that, even though it is simple, achieves a configuration, upon deployment, in which the peaks of one ring face the valleys of the adjacent stenting loop, rather than its peaks. As stents are progressively installed, in ever more "bendy" lumens of the human body, there is an increasing requirement for such stents to undergo severe bending, after deployment, without that bending giving rise to any tissue damage in the stented lumen. Head-to-head clashes of cusps ought to be scrupulously avoided.

    [0004] Applicant's earlier WO 01/32102 provides capacity to bend, in a simple linear strut matrix, by sacrificing part of the surface area of the cylinder to so-called "scrap portions" of the cylinder that are cut out of it and discarded, to leave significant end to end gaps between facing cusps of struts. On the inside of the bend, when the stent cylinder takes up a banana shape, the facing cusps approximate. The gap gets smaller but does not close completely. It is time-consuming and expensive to remove the scrap portions during manufacture and removing them conflicts with the objective of using the maximum possible surface area of the stent to push on bodily tissue to keep the stented bodily lumen patent.

    [0005] WO2009/003584 is another publication of a self-expanding stent matrix with gaps between end to end facing cusps of colinear struts, which therefore suffers from the same disadvantages of the stent matrices disclosed in Applicant's aforesaid WO 01/32102.

    [0006] The present invention arises out of an appreciation by the present invention that the stent architectures disclosed in WO 2008/119837 are unexpectedly susceptible of further improvement. There is a further design simplification, that makes available enhanced design modelling, simpler manufacture and the chance to secure yet further improvements in stent performance after implantation.

    Summary of the Invention



    [0007] According to the present invention there is provided a stent in the field of this invention, in which a majority of the struts in any one of the successive loops share a first common length X, and any remaining struts in said one loop share a second common length Y, wherein Y < X.

    [0008] The loops of the stent can be endless, which is to say that the stent matrix exhibits a stack of endless loops arranged along a longitudinal axis of the stent, and each joined to the axially adjacent loop by one or more bridges. Alternatively, the loops of the stent can be the successive turns of a spiral that runs all the way from one end of the stent to the other. It is trite to observe that a chain is only as strong as its weakest link. With the invention, there being in the matrix no struts having a length longer than the common length X, there is present no individual strut that can pull down the performance of the struts of the strut majority. It is in this way that the difference between the stents of the present invention, and those of Applicant's earlier WO 2008/119837, can best be appreciated.

    [0009] Typically, each loop of a stent exhibits one or more repeat units that are constituted by a plurality of struts of the loop. Typically, with the present invention, there is only one strut of length Y, in each such repeating unit.

    [0010] The archetypal stent of the present invention exhibits struts that share a common thickness in the radial direction of the stent, and a uniform width, transverse to their length and thickness. However, stents in which the width of each strut varies, along the length of the strut, are also envisaged. One advantage of such architecture is that it can be used to optimize the distribution of stress in each one of the struts, the optimization being done by appropriate variation of the widths of the struts. Thus, for example, one might arrange for the level of stress after deployment, anywhere in the strut, to be at the same level, by providing that the struts are wider at their roots, close to a cusp of the zigzag ring, than they are along their length, midway between the respective cusps at each end of the strut in view.

    [0011] It may be desirable to provide the stent with end loops, one at each end of the length of the stent, that differ from the loops intermediate the two end loops. The case is also contemplated, where the loop at one end of the stent is a special end loop, but the loop at the other end of the stent is not special. Any such special end loops might exhibit a strut length that is greater than in the intermediate loops, resulting in the axial length of such an end loop of the stent, as such, being greater than the axial length of each of the intermediate loops of the stent.

    [0012] Further, it will likely be attractive to provide the stent with a plurality of radiopaque markers, likely located on one or both of the opposed ends of the stent. It might be attractive to locate the markers within the axial length of the end loop, so that they do not protrude beyond the length of the stent as such. Any such markers within the length of the stent can be asymmetric, in the sense that they are cantilevered from a cusp of the end loop of the stent, and are asymmetric about a mirror plane, parallel to the length of the stent and passing through the point where the marker is joined to the cusp of the end loop of the stent.

    [0013] The radiopaque markers are intended to be readily detectable by the radiologist and so will benefit from a relatively large surface area. It will generally be attractive for this large surface area to be part of the generally cylindrical envelope in which the stent matrix is located. In other words, each radiopaque marker will preferably have opposed major surfaces that are each part-cylindrical.

    [0014] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by an example, to the accompanying drawings.

    Brief Description of the Drawings



    [0015] 

    Fig. 1 is a plan view of part of a stent matrix, opened out flat; and

    Fig. 2 is a plan view of the same matrix (but a larger portion of it) after radial expansion, but again laid flat;

    Fig. 3 is a plan view like that of Fig. 1, but of a different stent matrix;

    Fig. 4 is a further plan view, of an end portion of the Fig. 3 matrix; and

    Fig. 5 is a plan view like that of Fig. 4, showing a variation with radiopaque markers;

    Fig. 6 is a plan view like that of Fig. 2, but showing the Fig. 3 matrix radially expanded; and

    Fig. 7 shows the matrix of Fig. 6, radially expanded, but not laid flat.


    Detailed Description



    [0016] Considering first what is shown in Fig. 1, the drawing shows a portion of the length of the stent (10), but the entirety of its circumference, yet laid out flat. The bridge (12) is parted along a notional parting line 14, that appears at both the top and the bottom of the drawing Figure, to divide the bridge (12) into a portion (12-1) on the top of the drawing and a portion (12-2) at the lower end of the drawing. Other bridges along that line of the length of the stent, (16, 18 and 20), are similarly split lengthwise notionally, for the purposes of the laid flat display in Fig. 1.

    [0017] Each endless loop (30, 32, 34, 36, 38 and 40) of the stent portion shown in Fig. 1 exhibits a zigzag sequence of 24 struts, of which 8 of the struts, designated 42, have a shorter length Y than the length X of the remaining 16 struts (44). There are 12 cusps (46) at one axial end of each zigzag ring, and a further 12 cusps (48) at the other axial end of each zigzag loop. Between any two adjacent cusps of each zigzag ring, there are three struts, two of these being of length X, and one of them being shorter, strut 42, of length Y. Distributed all over the stent matrix can be seen further bridges (12) that tie together two facing cusps of two adjacent zigzag rings, and which may be designated to "bridges" to join together adjacent loops of the stent matrix, with free cusps (46), not attached to the adjacent zigzag loop, lying in between any pair of the set of four bridges that join together any particular adjacent zigzag loops of the matrix.

    [0018] As can be seen from Fig. 2, when the stent matrix of Fig. 1 is radially expanded, any free cusp of any zigzag loop lies circumferentially in the gap between two cusps of the facing axial end of the next adjacent zigzag loop of the matrix. This effect is caused by the length differential of the struts, the shorter struts Y being somewhat more resistant to bending, when the radial expansion takes place, than the slightly longer struts (44) of length Y.

    [0019] Thinking about the performance in fatigue of the stent matrix shown in Fig. 2, what will characterize the fatigue life is the fatigue performance of the majority of struts (44) of length X. The shorter struts (42) enjoy a relatively favourable fatigue environment, because they can more easily carry the stress shared around the circumference of the stent, and so they are not the factor that limits the fatigue life of the matrix. Thus, calculation of the fatigue life based on the majority strut (44) will predict the fatigue performance of the stent as a whole. The matrix lacks any minority group of struts that have a poorer performance in fatigue than the strut majority.

    [0020] Moving on to Fig. 3, the difference to note is that the circumference includes a greater number of lengthwise slits cut by the laser, whereby each zigzag loop of the stent matrix exhibits 40 struts rather than 24. However, each zigzag loop is connected to the axially adjacent zigzag stenting loop by a set of four bridges (12), evenly distributed around the circumference of the stent, just as in the embodiment of Figs. 1 and 2.

    [0021] Figs. 6 and 7 show the Fig. 3 arrangement radially expanded, with Fig. 6 corresponding to Fig. 2, and Fig. 7 being useful in that it shows the stent in three dimensions whereby one can readily imagine the structure stenting surrounding bodily tissue and keeping open (patterned) the lumen inside the cylindrical stent matrix.

    [0022] Turning to Figs. 4 and 5, the concern is with how to bring the stent matrix to a close, at one end of the stent cylinder. From Fig. 4, it is immediately apparent that, in the end loop (50), the axial ends of that loop differ. At the axial end (52) all cusps lie in the same plane transverse to the long axis of the stent. However, at the other axial end of the end loop (50), where it faces the next adjacent stenting loop (56), the cusps are not all in the same plane but, instead, vary in axial position in order to face, head-to-head, the cusps of the adjacent loop (56). Thus, a minority of the struts of the end loop (50) are exhibiting a longer length that the majority of struts in the end loop (50). At a stenting site, there needs to be a transition length of the bodily lumen, between the stenosis, where the stent is working at full power, and the lumen just beyond the end of the stent, where it is not pressing on the lumen wall at all. The longer struts of the end loops provide such a transition length, where the stent, thanks to the greater length of the struts, imposes less force on the lumen wall. In this way, the stresses imposed on bodily tissue by the end loop of a stent are deliberately made less than those stenting loops nearer to the center of the length of the stent, which are doing the hard job of holding open the bodily lumen in that narrowed part of its length where it was stenosed and where the stent is needed to overcome the stenosis.

    [0023] Stents typically carry radiopaque markers at their ends in order that the radiologist may know with precision exactly where are the ends of the stent in relation to the length of the bodily lumen to be stented. Whereas such markers typically protrude beyond the axial length of the stent proper, Fig. 5 shows an embodiment in which the markers can be set into the length of the stent, located in circumferential gaps between spaced apart cusps in the end annulus (52) of the end ring (50).

    [0024] Until now it has been typical for such radiopaque markers to be cantilevered from a cusp of a stent matrix, with the marker being symmetrical about a mirror plane that passes through the point of connection of the marker to the cusp. This need not be the case, however, as can be seen from the way in which the markers (60) in Fig. 5 are attached to a cusp (62) which is not midway along the circumferential length of the marker (60).

    [0025] The present invention is not concerned with specific coatings of stents, or applications of stents. The skilled reader will not need to be told in this application what possibilities exist for covering a stent matrix with a graft material, or a medically active material, nor with what categories of bodily lumen the stent may be useful for. The skilled reader will also immediately appreciate the simplicity of the arrangements illustrated in the accompanying drawings, together with the performance characteristics evident from Figs. 2, 6 and 7 and the opportunities evident from Figs. 1, 3 and 5 to provide radiopaque markers as desired.

    [0026] Whereas the present description is in relation to stent matrices cut by laser from a starting tube of nickel titanium shape memory alloy, the principles of this invention are equally applicable to stents made of other materials (such as stainless steel) and from flat sheet as opposed to tube stock. There is a wealth of published knowledge in the field of stent designs, and all of this knowledge is available to those skilled in the art who wish to optimise the inventive concept disclosed in the present application. However, as stent matrix design becomes more sophisticated, and as performance enhancements become ever more difficult to achieve, a contribution that can enhance performance by yet another increment, however small, is not to be underestimated, or dismissed lightly, for it is a worthwhile, and non-obvious, contribution to the art.

    [0027] The archetypal stent is cylindrical when relaxed. However, the technical field of stents includes stent grafts and includes many proposals for a stent matrix which is a relaxed configuration is not strictly cylindrical. In particular, those skilled in the art are familiar with the so-called "flared" stents that exhibit at least a portion of the stent length not of constant diameter. Stents with outwardly flared ends are relatively common. All are within the scope of this invention.


    Claims

    1. A stent (10) formed by slitting a tube to create a matrix of struts (42, 44) which are separated from each other by no more than the width of the slit and which lie parallel to each other and to the longitudinal axis of the tube, the slitted tube being radially expandable to a stenting disposition in which the struts exhibit a zigzag pattern in successive loops around the circumference of the stent, the angle each strut makes with the longitudinal axis increasing as the stent diameter increases;
    the zigzag pattern exhibiting a cusp (46, 48) between any two adjacent struts;
    with selected tied cusps of any one loop being connected by a bridge (12) to a facing cusp of the adjacent loop, the bridge extending in a direction parallel to the longitudinal axis of the tube;
    and with intervening free cusps (46), between any two bridge of a loop, not being connected to the adjacent loop;
    and with the matrix of struts being free of significant end to end gaps between facing pairs of said intervening free cusps;
    the zigzag pattern exhibiting a lengthwise staggering of circumferentially adjacent said slits to the extent that the lengths of two circumferentially adjacent struts on the zigzag pattern that flank a tied cusp are different and further such that, in the said stenting disposition, the free cusps of adjacent loops are circumferentially displaced from each other;
    and characterized in that:

    a majority, but not all, of the struts (44) in any one of the successive loops share a first common length X, and all the remaining struts (42) in said one loop share a second common length Y, wherein Y < X.


     
    2. Stent as claimed in claim 1, the loops being endless.
     
    3. Stent as claimed in claim 1, the loops being successive turns of a spiral.
     
    4. Stent as claimed in any one of the preceding claims, wherein a calculated fatigue life of the said remaining struts, with common length Y, exceeds a calculated fatigue life of the struts of the majority, with common length X.
     
    5. Stent as claimed in any one of the preceding claims, in which each loop exhibits one or more repeat unit constituted by a plurality of struts of the loop, and there is only one strut of length Y, per repeat unit.
     
    6. Stent as claimed in any one of the preceding claims, in which the struts of length X and the struts of length Y share a common thickness in the radial direction of the stent.
     
    7. Stent as claimed in any one of the preceding claims, in which the struts of length X and the struts of length Y share a common width, transverse to their length.
     
    8. Stent as claimed in any one of the preceding claims, and including an end loop (50) at one or both ends of the axial length of the stent, in which end loop the strut length is greater than in the loops between the ends of the strut, whereby the axial length of the end loop as such is greater than the axial length of any other loops of the stent.
     
    9. Stent as claimed in any one of the preceding claims and including a plurality of radiopaque markers (60) located on at least one of the opposed ends of the stent.
     
    10. Stent as claimed in claim 9, wherein the markers are located on an annulus (52) that lies within the length of the end loop of the stent adjacent said markers.
     
    11. Stent as claimed in claim 10, wherein each said marker is an asymmetric cantilever.
     
    12. Stent as claimed in claim 9, 10 or 11, wherein said marker has opposed major surfaces that are each part-cylindrical.
     


    Ansprüche

    1. Stent (10), der durch Schlitzen eines Rohrs ausgebildet ist, um eine Matrix aus Streben (42, 44) zu erzeugen, die nicht mehr als die Breite des Schlitzes voneinander beabstandet sind und die zueinander und zu der Längsachse des Rohrs parallel liegen, wobei das geschlitzte Rohr radial zu einer Stentanordnung expandierbar ist, bei der die Streben ein Zickzackmuster in aufeinanderfolgenden Schlaufen um den Umfang des Stents ausbilden und der Winkel, den jede Strebe mit der Längsachse ausführt, ansteigt, während sich der Stentdurchmesser erhöht;
    wobei das Zickzackmuster einen Scheitelpunkt (46, 48) zwischen zwei beliebigen benachbarten Streben ausbildet;
    mit ausgewählten gebundenen Scheitelpunkten einer beliebigen Schlaufe über eine Brücke (12) mit einem zugewandten Scheitelpunkt der angrenzenden Schlaufe verbunden, wobei sich die Brücke in einer zu der Längsachse des Rohrs parallelen Richtung erstreckt;
    mit eingreifenden freien Scheitelpunkten (46) zwischen zwei beliebigen Brücken einer Schlaufe nicht mit der benachbarten Schlaufe verbunden;
    und mit der Matrix aus Streben zwischen sich zugewandten Paaren der eingreifenden freien Scheitelpunkte frei von signifikanten Ende-zu-Ende-Spalten;
    wobei das Zickzackmuster eine längsgerichtete Staffelung in Umfangsrichtung benachbarter Schlitze zu einem Ausmaß ausbildet, sodass sich die Längen der zwei in Umfangsrichtung benachbarten Streben bei dem Zickzackmuster, die einen gebundenen Scheitelpunkt flankieren, unterscheiden und zudem dass ferner die freien Scheitelpunkte benachbarter Schlaufen in der Stentanordnung in Umfangsrichtung zueinander versetzt sind;
    und dadurch gekennzeichnet, dass:

    eine Mehrzahl, aber nicht alle, der Streben (44) in einer beliebigen der aufeinanderfolgenden Schlaufen eine erste gemeinsame Länge X teilen und all die verbleibenden Streben (42) in der einen Schlaufe eine zweite gemeinsame Länge Y teilen, wobei Y < X.


     
    2. Stent nach Anspruch 1, bei dem die Schlaufen endlos sind.
     
    3. Stent nach Anspruch 1, bei dem die Schlaufen aufeinanderfolgende Windungen einer Spirale sind.
     
    4. Stent nach einem der vorstehenden Ansprüche, bei dem eine errechnete Lebensdauer der verbleibenden Streben mit einer gemeinsamen Länge Y eine berechnete Lebensdauer der Streben der Mehrzahl mit einer gemeinsamen Länge X überschreitet.
     
    5. Stent nach einem der vorstehenden Ansprüche, bei dem jede Schlaufe eine oder mehrere Wiederholeinheiten ausbildet, die durch eine Vielzahl an Streben der Schlaufen ausgebildet sind, und es nur eine Strebe der Länge Y pro Wiederholeinheit gibt.
     
    6. Stent nach einem der vorstehenden Ansprüche, bei dem die Streben der Länge X und die Streben der Länge Y eine gemeinsame Dicke in der radialen Richtung des Stents teilen.
     
    7. Stent nach einem der vorstehenden Ansprüche, bei dem die Streben der Länge X und die Streben der Länge Y eine gemeinsame Breite teilen, die quer zu Ihrer Länge ist.
     
    8. Stent nach einem der vorstehenden Ansprüche und einschließlich einer Endschlaufe (50) bei einem oder beiden Enden der axialen Länge des Stents, wobei bei der Schlaufe die Länge größer ist als bei den Schlaufen zwischen den Enden der Strebe, wodurch die axiale Länge der Endschlaufe als solche größer ist als die axiale Länge jeglicher anderer Schlaufen des Stents.
     
    9. Stent nach einem der vorstehenden Ansprüche und einschließlich einer Vielzahl röntgendichter Markierungen (60), die an zumindest einem der entgegengesetzten Enden des Stents angeordnet sind.
     
    10. Stent nach Anspruch 9, bei dem die Markierungen an einem Kranz (52) angeordnet sind, der in der Länge der Endschlaufe des Stents liegt, der benachbart zu den Markierungen ist.
     
    11. Stent nach Anspruch 10, bei dem jede Markierung ein asymmetrischer Krakarm ist.
     
    12. Stent nach Anspruch 9, 10 oder 11, bei dem die Markierung sich gegenüberliegende Hauptflächen aufweist, die jeweils teilzylindrisch sind.
     


    Revendications

    1. Endoprothèse vasculaire (10) formée par le fendage d'un tube en vue de créer une matrice d'entretoises (42, 44) séparées les unes des autres au maximum par la largeur de la fente et qui sont parallèles les unes par rapport aux autres et par rapport à l'axe longitudinal du tube, le tube fendu pouvant s'étendre radialement jusqu'à une disposition d'implantation d'endoprothèse dans laquelle les entretoises présentent un profil en zigzag en boucles successives autour de la circonférence de l'endoprothèse, l'angle formé par chaque entretoise avec l'axe longitudinal augmentant lorsque le diamètre de l'endoprothèse augmente ;
    le profil en zigzag présentant une cuspide (46, 48) entre deux entretoises adjacentes quelconques ;
    des cuspides liées sélectionnées de toute boucle étant reliées par un pont (12) à une cuspide en regard de la boucle adjacente, ledit pont s'étendant dans une direction parallèle à l'axe longitudinal du tube ;
    et les cuspides libres intermédiaires (46), entre deux ponts quelconques d'une boucle, n'étant pas reliées à la boucle adjacente ;
    et la matrice d'entretoises étant dépourvue d'espace significatif extrémité à extrémité entre les paires en regard desdites cuspides libres intermédiaires ;
    le profil en zigzag présentant un échelonnement en longueur desdites fentes circonférentiellement adjacentes tel que les longueurs de deux entretoises circonférentiellement adjacentes sur le profil en zigzag qui flanquent une cuspide liée sont différentes et, en outre, tel que dans ladite disposition d'implantation d'endoprothèse les cuspides libres de boucles adjacentes sont déplacées circonférentiellement l'une par rapport à l'autre ;
    et caractérisé en ce que :

    une majorité, mais pas la totalité, des entretoises (44) dans l'une quelconque des boucles successives partagent une première longueur X commune, et toutes les entretoises (42) restantes dans ladite boucle partagent une seconde longueur commune Y, dans laquelle Y < X.


     
    2. Endoprothèse selon la revendication 1, les boucles étant sans fin.
     
    3. Endoprothèse selon la revendication 1, les boucles étant des spires successives d'une spirale.
     
    4. Endoprothèse selon l'une quelconque des revendications précédentes, dans laquelle une durée de vie en fatigue calculée desdites entretoises restantes, avec une longueur commune Y, est supérieure à une durée de vie en fatigue calculée des entretoises de la majorité, avec une longueur commune X.
     
    5. Endoprothèse selon l'une quelconque des revendications précédentes, dans laquelle chaque boucle présente au moins une unité répétée constituée d'une pluralité d'entretoises de la boucle, et il n'y a qu'une seule entretoise de longueur Y par unité répétée.
     
    6. Endoprothèse selon l'une quelconque des revendications précédentes, dans laquelle les entretoises de longueur X et les entretoises de longueur Y partagent une épaisseur commune dans le sens radial de l'endoprothèse.
     
    7. Endoprothèse selon l'une quelconque des revendications précédentes, dans laquelle les entretoises de longueur X et les entretoises de longueur Y partagent une largeur commune, transversale à leur longueur.
     
    8. Endoprothèse selon l'une quelconque des revendications précédentes, et comprenant une boucle d'extrémité (50) au niveau de l'une des extrémités, ou des deux, de la longueur axiale de l'endoprothèse, dans laquelle boucle d'extrémité la longueur de l'entretoise est plus grande que dans les boucles entre les extrémités de l'entretoise, la longueur axiale de la boucle d'extrémité en tant que telle étant ainsi supérieure à la longueur axiale de toute autre boucle de l'endoprothèse.
     
    9. Endoprothèse selon l'une quelconque des revendications précédentes, et comprenant une pluralité de marqueurs radio-opaques (60) situés sur au moins l'une des extrémités opposées de l'endoprothèse.
     
    10. Endoprothèse selon la revendication 9, dans laquelle les marqueurs sont situés sur un anneau (52) qui repose dans la longueur de la boucle d'extrémité de l'endoprothèse adjacente auxdits marqueurs.
     
    11. Endoprothèse selon la revendication 10, dans laquelle chaque marqueur est un bras asymétrique.
     
    12. Endoprothèse selon la revendication 9, 10 ou 11, dans laquelle ledit marqueur a des surfaces principales opposées qui sont chacune en partie cylindriques.
     




    Drawing














    Cited references

    REFERENCES CITED IN THE DESCRIPTION



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    Patent documents cited in the description