Note: Descriptions are shown in the official language in which they were submitted.
-2- 207452~
Device with a prosthesis for implantation in the body of a
patient
The invention relates to a device with a prosthesis, in the forrn of a
hollow body, which can be implanted in the body of a patient, especially in
5 a blood vessel or in another body cavity; the said prosthesis can be
compressed, by overcoming the action of shape-restoring spring forces, to a
reduced cross-sectionai size compared with its - expanded - size when in
use; once the forces holding the prosthesis in its compressed state are
removed, the prosthesis autornaticaliy expands to assume the cross
10 sectional dimensions appropriate to the site where it is used.
Devices of this type are already known and are used for the
percutaneous implantation of, in particular, vascular prostheses. Prostheses
with an enlargeable lumen which are introduced percutaneously can either
be expanded mechanically by means of a known balloon catheter from a
15 small radius to the larger radius in order to hold open the lumen in a vessel,
or, after being compressed prior to implantation, they expand again by
themselves under the action of the force exerted by compressed and
therefore pretensioned springs.
Various systems are know by means of which self-expanding spring-
20 loaded vascular prostheses can be introduced into the body of a patient andthen, by removing the restraining force, can be implanted and anchored in
the vessel.
In the most commonly used method, which is described in ~P-A-0
183 372, an endoprosthesis in the form of a tubular hollow body is
25 compressed to a reduced cross section and then, while still compressed, is
inserted using a pusher device through a catheter which has previously been
inserted into the vessel, until the prosthesis reaches its correct position in
the vessel. However, the disadvantage of this system is that a considerable
amount of force is needed to push the prosthesis through the catheter
30 because of the large frictional forces acting against it.
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i 207~52~
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ln another method (to which no reference could be found in the
patent literature) a sheath covering the endoprosthesis and keeping it
compressed is then retracted at the implantation site. Here again, it is
disadvantageous that large frictional forces have to be overcome. In
5 addition, the tubular system created by the sheath covering the pros~hesis is
extremely rigid and this makes it very difficult for the system to pass
through twists and turns in the vessel when it is being inserted.
In a further system (US Patent 4 732 152) a woven and resilient
prosthesis is held in the compressed state by a double sheath which is
10 seaied at the distal end. This sheath is withdrawn from the compressed
prosthesis in the same way that a person removes a sock from their foot. In
order to reduce the resulting friction, the space between the two sheaths
can be filled with a liquid. Although this system may at first appear elegant
because of the way in which it reduces the frictional resistance, it is in fact
15 extremely cumbersome to use and requires two persons to manipulate it.
In contrast, the purpose of the invention is to create a device, which
is particularly simple and easy to use, for implanting a prosthesis, and in
particular a vascular prosthesis, having the form of a hollow body.
This task has been solved in the following manner. In the device
20 described in the preamble to Patent Claim 1 the prosthesis is surrounded by
an unravellable cover, consisting of at least one continuous thread, and
compressed to a reduced cross section; and at least one unravelling line
extends away from the cover holding the prosthesis in iJIS radially
compressed position, and the thread of which the cover is made can be
25 retracted.
Therefore, in the device according to the invention, the prosthesis is
held in its radially compressed position by this externai cover and it does not
expand into its desired configuration, under the action of the pretensioning
force generated by the compression, until this unravellable cover is
30 removed.
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207~2~
The cover may in particular be a meshwork made by crocheting,
tying, knotting or some other means of making meshes.
Advantageously, the prosthesis, which i5 held in the radially
compressed state by means of an unravellable cover, can be mounted and
5 advanced on a probe, such as a flexible guide wire. Using a device o~ ~his
configuration, implantation is carried out by inserting the guide wire in the
known manner into a vessel an~ then advancing the prosthesis, while
radially cornpressed, along the guide wire; this can be done, for example, by
using a sleeve, which is also advanced along the guide wire and which
10 engages against the end of the prosthesis opposite from the leading end of
the prosthesis.
In another embodiment, on the other hand, the prosthesis, which is
held radially compressed by the unravellable cover, is mounted in an axially
fixed manner on the leading end of a probe. Th;s probe may be, in
15 particular, a catheter which is advanced along a guide wire.
Even when the compressed prosthesis is axially firmly mounted on
the leading end of a probe or a catheter, it is still simple to carry out the
implantation ~y advancing the probe or catheter, with the prosthesis
mounted at its tip, for example while monitoring progress on an X-ray
20 screen, until the implantation site is reached; here the cover, which is made for example of an encircling meshwork, is unravelled, the prosthesis is
released, and it expands automatically to assume its correct implanted
posltlon .
When the prosthesis is arranged at the leading end of a probe or a
25 catheter, it has proved advantageous to mount the prosthesis on a non-slip
substrate surrounding the probe or the catheter, so that no undesired
slipping or sliding can occur while the thread material of which the
meshwork is formed is being removed.
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207~21
-5-
Advantageously, the self-expanding prosthesis may be a tubular
structure made by crocheting or knitting or by some other method of
producing a mesh fabric, using metal or plastic thread material which is well
tolerated by body tissues. This tube is compressible against the action of
5 pretensioning forces and, once the restraining ~orces have been removed, it
expands automatically into and retains its expanded shape at the
implantation site.
In a further logicai refinement of a prosthesis having a mesh
structure, successive rows of meshes can be made alternately of resorbable
10 and non-resorbable thread material. In this way, within a predetermined time
following impiantation, the resorbable material dissolves and only the parts
of the prosthesis made of non-resorbable thread material are left behind in
the body of the patient. These remaining sections form rings of successive
open loops. This avoids any thread crossings which could exert undesired
15 shear forces on the tissues surrounding and growing around the prosthesis.
In the case of this last discussed refinement, it is also possible to
embed medication in the resorbable thread material so that the prosthesis
forms a depot for medication which is gradually released as the resorbable
thread material progressively dissolves.
A particularly advantageous embodirnent of the invention is
characterized by the design of the tubular meshwork which holds the
prosthesis in th0 compressed state, wherein after each encirclernent of the
prosthesis the rows of meshes change direction, and when successive rows
of meshes are unravelled the thread sections which form the stitches detach
themselves from the prosthesis by unravelling alternately from left to right
and from right to left.
The advantage of this embodiment is that the successive rows of
meshes, encircling the prosthesis alternately from left to right and from right
to left, can be unravelled without the thread material becoming wrapped
around the prcbe or catheter on which the prosthesis is mounted, or
~: .: . . .
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-6- ~074521
without becoming twisted, which would create friction and thus make it
difficult to continue withdrawing the thread material.
In the aforementioned embodi~ent, it has also proved advantageous
if the unravellable loops or knots of the successive rows o~ meshes
5 surrounding the prosthesis are arranged opposite each oth~r or sne behind
the other in a substantially axial row.
In another important embodiment of the invention, the unravelling line
extends from the mesh surrounding the leading end of the prosthesis and
thus the prosthesis progressively expands into its implanted position,
10 starting at its distal end, as the meshwork is unravelled.
In this further embodiment of the invention, the thread material can
never come between the already expanded section of the prosthesis and, for
example the wall of a vessel, as the meshwork is unravelled and the thread
withdrawn. Instead, the thread material runs at all times along the still intact15 meshwork and thus in the zone where the prosthesis is still compressed.
The ends of the thread material of which the meshwork is made up
can be secured by means of untieable knots, such as slip-knots, and thus be
held in place regardless of the fact that they can be undone. One particularly
simple means of axially fixing the prosthesis on a probe, or on a catheter
20 acting as a probe, consists of elamping the end of the thread forming the
meshwork and one end mesh in holes on the probe or on the catheter, but
in such a way that they can be released from this position by pulling on the
unravelling line. However, the start of the thread may also be clamped
between the probe and a sleeve mounted thereon.
The meshwork is particularly securely held, but nonetheless easy to
unravel, if a loop extends from the knot of the first mesh on the unraveiling
side of the meshwork and passes throu~h a hole; and in the area of the said
knot one end of this loop merges into the unravelling line. In this way, the
.
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7 2074521
said loop can be pulled through the aforernentioned knot and thereafter all
the meshes making up the meshwork can be unravelled one after the other.
According to another logical embodiment oF the invention, the
prosthesis can also be held in its radially compressed position by means of
5 meshwork fitted Trom the distal end of the probe or catheter and ext~ndiny
over the tip of the prosthesis, and by means of another meshwork fitted in
the opposite direction, namely from the proximal end, and extending over
the end meshes of the first meshwork. It has proved advantageous, in this
case, for the two meshworks to be unravelled in opposite directions by the
10 unravelling lines, starting in each case from their loop-shaped end meshes.
With such a configuration, when the prosthesis mounted on a probe
or catheter has been correctly positioned in a vessel, the meshwork fitted
from the distal end is unravelled first, starting by removing the end mesh
furthest away from the distal end and proceeding gradually until this
15 meshwork has been completely unravelled and the thread material has been
withdrawn. Next, the meshwork applied from the proximal end is unravelled,
starting with the end mesh pointing towards the distal end, and then
progressing towards the proximal end. It can be seen that when the two
meshworks are unravelled in this manner, the self-expanding prosthesis
20 gradually and progressively expands, from its distal to its proximal end, to
occupy its intended implantation site.
In another important configuration, the cover holding the prosthesis in
its radially compressed position consists of axially spaced loops encircling
the prosthesis, wherein thread material from a thread running longitudinally
25 through the inside of the prosthesis is passed at intervals through a hole inthe prosthesis, and the ends of the loops are taken back into ~he interior of
the prosthesis through other holes peripherally adjacent to the first holes,
and a warp thread also running longitudinally inside the prosthesis is passed
through the ends of the IQOPS, thereby holding them in their encircling
30 position. It can be seen that, in this configuration, the prosthesis is released
by withdrawing the warp thread from the end sections of ~he loops and
207~521
-8-
finally the thread material forming the ioops, as well as the warp thread, can
be simp!y withdrawn.
In a similar embodiment of the invention, the cover retaining the
prosthesis in its radially compressed position consists of axially spaced
5 loops encirclin~ the prosthesis, wherein thread material From a thrcad
running longitudinally through the prosthesis is drawn through holes in ~he
prosthesis, and the ends of the loops are taken back in~o the interior of the
prosthesis through holes axially spaced from the first-mentioned holes, and
are secured in position by passing through the end of each loop extending
10 into the interior oF th~ prosthesis another loop, formed by the thread
material runnin~ inside the prosthesis; this second loop is then taken to the
outside of the prosthesis by passing it through the next hole following in the
axial direction, and it is then again passed around the prosthesis and the end
of the loop is passed in the same way back through a hole and into the
15 prosthesis and is secured in this position. In this configuration, as well, it is
a simple matter to unravel the cover holding the prosthesis in its radially
compressed position by means of the thread, of which the loops encircling
~he prosthesis are made up, which extends from the last loop.
In the interest of ensuring particularly tight encirclemen~ and thus
20 compression of the prosthesis, it has also proved advantageous to make the
meshwork from shrinkable thread material. The unravellable meshwork may
also consist of several threads running parallel to each other.
In another important embodiment of the invention, at least one other
cover is provided between the prosthesis and the cover holding the
25 prosthesis in the radially compressed state; this other cover loosely
surrounds the prosthesis and, when the outer cover is unravelled, it permits
partial expansion of the prosthesis and can itself then be unravelled.
In this embodiment, therefore, a cover, which may take the form of a
meshwork, is directiy but loosely fitted, i.e. with a sertain amount of play,
30 on the prosthesis; and the prosthesis and this inner cover are tightly
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surrounded by an outer cover which holds the prosthesis, together with the
other sheath fitted directly over it, in the radially compressed position.
Consequently, the prosthesis is, as it were, wrapped in tWD layers and once
the outer cover has been unravelled the prosthesis may expand only within
5 the limits allowed by the inner cover. Final implantation is then achi~ved by
unravelling the inner cover, i.e. in stages.
It goes without saying that it is possible to provide several
meshworks, each surroundillg the others with a certain amount of play, so
that the prosthesis can be allowed to expand in several successive stages.
Within the scope of the invention, the intervening spaces between the
meshes in a meshwork surrounding the prosthesis and holding it in the
compressed state may be filled and smoothed out with gelatine, or a similar
substance, which dissolves in the body of a patient. This makes it easier to
insert such a device.
According to another embodiment, at least ons end of the prosthesis
can be encircled in the compressed state by a sleeve; because of the axial
shortening of the prosthesis which occurs when the latter expands, this end
is then pulled out of the sleeve encircling it. Such a sleeve may be firmly
mounted on the probe or on a catheter with its open side facing towards the
20 prosthesis, e.g. at the distal end. This achieves a smooth transition at the
front end of the prosthesis, seen in ths direction of insertion, and it
simplifies the insertion of the prosthesis.
In the interest of obtaining better fixation of the prosthesis on a prohe
or on a catheter used for that purpose, the end of the prosthesis facing
25 away from the leading end may abut against a radially projecting step or
shoulder or against a sleeve mounted on the probe or catheter.
in another embodiment of the invention, in which a catheter is used
as the probe, the unravelling lins is passed through a hole in the wall of the
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207~521
-10-
catheter near the end of the prosthesis and into the lumen of the catheter,
then runs through ~he lumen and extends beyond the end of the catheter.
However, it is also possible to use a double-lumen catheter as the
probe, wherein one lumen is used for advancing the catheter alon~ a guide
5 wire and the unravelling line is passed through the other lumen.
When a single- or double-lumen catheter is used as the probe,
wherein the unravelling line passes through the lumen of the catheter, there
is no possibility of the walls of the vessels or other body cavities into which
the prosthesis is implanted being damaged by the unraveliing line or by the
10 thread material which is withdrawn through the catheter lumen when the
meshwork is unravelled.
It has aiso proved advantageous to provide the unravelling line and/or
thread material of the meshwork with a friction-reducing lubricant.
Also, at least the unravelling line may be made from a metal thread,
15 or it may be treated with an admixture of metal so that it shows up well on
an X-ray image.
Finally, according to another embodiment, the prosthesis which is
held in its radially compressed position by means of the unravellable cover
may also - in the expanded state after removal of the sheath - assume a
20 trumpet-shaped configuration at its proximal end. This configuration of the
prosthesis is important when the latter is implanted at a point where one
vessel branches from another, because there is always a risk of the
prosthesis sliding into the branching vessel. But, the trumpet-shaped
enlargement at the proximal end effectively prevents such slippage during
25 implanting, when the cover surrounding the prosthesis is unravelled, starting at the proximal end.
207~21
An embodiment of the device according to the invention will be
explained below on the basis oF the attached drawing. The diagrammatic
views presented are as follows:
Fig. 1: depicts a catheter with a vascular prosthesis mounted on its
distal end and held radially pretensioned in a compressed
position by a cover in the form of a tubular, unravellable
crocheted meshwork;
Fig. 2: illustrates the formation of an initial mesh in the crocheted
cover surrounding the prosthesis, using a loop brought around
the vascular prosthesis from the Fight-hand side;
Fig. 3: is a diagram similar to Fig. 2 and illus~rates the formation of the
next mesh linking up with the starting mesh and encircling the
vascular prosthesis from the left-hand side;
Fig. 4: in a view similar to Fig. 1 depicts a device in which the
vascular prosthesis mounted on the catheter is held radially
pretensioned in its compressed position by means of
unravellable crocheted covers fitted frorn the distal and
proximal ends respectively;
Fig. 5: shows the device as seen in Fig. 4, but simply with the
crocheted cover Fitted from the distal end;
Fig. 6: shows the device as seen in Fig. 4 merely with the crocheted
cover fitted from the proximal end, and omitting the crocheted
cover shown in Fig. 5;
Fig. 7: depicts, by itself, a vascular prosthesis held in a radially
compressed position by means of encircling loops;
207~521
-12-
Fig. 8: is a view, similar to that in Fig. 7, of a prosthesis, wherein the
loops holding the latter in a radially compressed position are
formed by crocheting, and
Fig. 9: is a view of an unrolled s~ction of a vascular prosthesis made
of knitted fabric
In the device 10 illustrated in Fig. 1, an elongated catheter 11 with a
continuous lumen is used as the probe; and the ca~heter is advanced by
means of the lumen, along a guide wire inserted in known manner into a
10 vessel. Near the distal end 12 of the catheter 11 is mounted a prosthesis 15
which is held in a compressed position under radial pretension by means of
a crocheted meshwork covering 14; after the restraining force of the
meshwork has been removed, the prosthesis expands au~omaticaliy to
assume its intended irnplanted position. The prosthesis may, for example,
15 consist of a knitted tube which can be compressed radially, against a
restorative spring force into a position where it ~ightly encloses the catheter
close to its distal end.
The prosthesis 15 is enclosed by a crocheted meshwork 14, made
from one continuous thread, in which the successive meshes encircle the
20 prosthesis alternately on one side and then the other, i.e. alternately from
right to left or left to right. The initial section 17 of the thread material,
which is arranged ahead of the first mesh 16 at the distal end 12 of the
catheter 11, is drawn through a slit 18 in the wall of the catheter; it is
wedged in the said slit and then taken through the lumen of the catheter
25 and led out beyond the distai end of the catheter. An unravellable loop 22 isdrawn through a knot 21 which ties off the final rnesh 20 at the opposite
end from the distal end; the said loop is drawn through two axially spaced
slits 23, 23' in the wall of the catheter, and thus is also axially tightly
clamped .
30The free end of the thread drawn through the knot 21 of the said final
mesh 20, forms an unravelling line 24, running along the length of the
.
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207~2~
-13-
catheter 11, by means of which the loop 22 hetd clamped in the catheter is
unravelled by drawing it through the said end knot, and then gradually the
meshes of the crocheted meshwork encircling the prosthesis and keeping it
compressed can also be unravelled. Since the meshes enclrcle the
5 prosthesis 15 from right to left and left to right, the thread detaches itselffrom the mesh knots alternately on the right and Icft side of the catheter as
the mesh unravels; and after the last mesh at the distal end is unravelled,
the initial section 17 of the thread material can be withdrawn from the slit
18 where it is clamped at the distal end 12 of the catheter 1 1.
Figs. 2 and 3 show in enlarged view the way in which the meshes are
formed, with the catheter 15 being encircled alternatingly from the back and
from the front; for the sake of simplicity, in these Figures the catheter is
shown as a rigid tubular object. After the initial section 17 of the thread
material has been secured by clamping it in the slit 18, as shown in Fig. 1,
15 the thread is wrapped around the catheter, then a loop 26 is pulled through
under the thread; then, from the free thread material 27 a mesh is forrned,
taken around the back of the catheter and then drawn through the loop 26;
the section of mesh drawn through the aforementioned loop 26 forms in
turn a loop 28 for making the next mesh in ~he sequence. Fig. 2 shows in
20 solid lines the free thread material 27 before it is drawn through the loop
26, and the broken lines depict it after it has been pulled through this loop,
and they also depict the formation of loop 28 for the next mesh.
To form the next mesh, which is shown in Fig. 3, the free thread
material, taken from position 31 in fact of the catheter, is drawn through
25 the previously formed loop 28, thereby forming ano~her loop 30 in the
manner indicated by the dotted lines; this method of forming loops and
meshes by means of thread material drawn alternately behind and in front of
the catheter and through the appropriate loop, is continued until the
prosthesis mounted on the catheter is covered over its entire length by a
30 crocheted meshwork.
~07~521
-14-
The end mesh 20 is formed by drawing the loop 22 through the
associated end loop or through a knot 21 formed by tightening this loop;
then, as illustrated schematically in Fig. 1, the loop 22 is drawn through and
clamped in the two slits 23, 23' spaced a certain axial distance apart in the
5 wall of the catheter. The remaining thread material then forms the
unravelling line 24 which extends from the loop of the end mesh 20 and
permits ~he encircling crocheted meshwork to be unravelled; when this
happens, the thread material from the unravelled meshes detaches itself
alternately first on the one side and then on the other side of the prosthesis
10 15, and as a result the prosthesis is released and permitted to expand under
the action of the pretension ~uilt up by the radial compression caused by
the fitting of the meshwork covering.
Also in the embodiment 40 shown in Fig. 4, a prosthesis 45 is
mounted near the distal end 42 of an elongated catheter 41 and is held
15 compressed under radial pretension. This is achieved by the crocheted
meshworks 46, 47, each shown separately in Figs. 5 and ~ respectively.
Like the catheter 11 in the embodiment shown in Fig. 1, the catheter 41 is
also advanced along a ~uide wire which has been previously positioned in
the vessel, and in this manner the prosthesis 45 mounted on the catheter
20 can be positioned correctly in the vessel before being implanted by
unravelling the meshwork.
The two crocheted meshworks shown holding the prosthesis 45
compressed in Fig. 4 are applied one after the other, starting with
meshwork 46 frorn the distal end. The other meshwork 47 is fitted from the
25 proximal end and then covers the end of the first meshwork 46.
Fig. 5 shows that the catheter 41 is fitted at its distal end vvith a
silicon sleeve 43 which serves to fix the starting section 48 of the thread
from which the first meshwork is crocheted. For this purpose, the starting
section 48 of this thread is drawn under the silicon sleeve 43. Next, the first
30 rneshes 49 are crocheted onto the calheter 41 in the manner described
above in conjunction with Figs. 1 to 3, and these meshes provide a firm
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207~2~
-15-
anchorage on the catheter for the first meshwork.The subsequent meshes
5û extend over the end of the prosthesis 41 pointing towards the distal end
of the catheter, compressing this end of ~he prosthesis under radial
pretension, while simultaneously axially fixing the prosthesis on the
5 catheter, as shown in Fig. 5. A last mesh 51 of this crocheted meshwork
46 is then laid down on the outside of ~he prosthesis 45, and from this
mesh extends the thread 52 which serves as a line for unravelling the
meshes in the said meshwork.
Fig. 6 illustrates the fitting of the second crocheted meshwork 47
10 starting from the proximal end. The start 55 of the thread material of which
this meshwork is made up is again fixed by passing it under a silicon sleeve
54 fitted on the catheter 41. Next some meshes 56 are crocheted onto the
catheter towards the distal end, and these are followed by further meshes
57 which encircle the prosthesis 41, while simultaneously compressing it
15 radially, and they extend over and thereby secure the meshes 50, 51 of the
first meshwork 46 facing away from the distal end of the meshwork 46. A
last mesh 58 of the meshwork 47 applied from the proximal end is then
drawn under the silicon sleeve 43 fitted at the distal end of the catheter and
thus secured. Furthermore, the thread ~0 extends away from the distally
20 oriented end mesh of the meshwork 47, which is applied from the proximal
end, ànd this thread is used to unravel the meshes of the crocheted
meshwork.
The prosthesis 45 in the embodiment illustrated in Figs. 4 to 6, like
the embodiment seen in Figs. 1 to 3, is held compressed under radial
25 pretension on the catheter 41, and once the crocheted meshworks 46, 4
have been removed, it expands automaticaliy to occupy its intended
location. Once the prosthesis mounted on the catheter has been introduced
into a vessel and correctly positioned therein, it is implanted by first
removing the meshwork 46 which has been applied from the distal end.
30 This is done by unravelling the meshes in this meshwork by means of the
unravelling line 52, so that first the mesh 51, which is overlain by the distal
end of the meshwork applied from the proximal end, and then gradually the
2074521
-1 6-
meshes 50 and 49 adjoining towards the distal end are unravelled, until
finally the first mesh adjacent to the silicon sleeve 43 is unravelled and the
start of the thread 48 is withdrawn from beneath the silicon sleeve.
The end of the prosthesis 45 pointing towards the distal end o~ the
5 catheter is released by unravelling the meshwork 46 which is applied from
the distal end; when this happens, this end of the prosthesis expands
radially due to the pretensioning forces inherent in the prosthQsis, while the
remainder of the prosthesis is still held compressed by the crochete~
meshwork 47 applied from the proximal end. The partially expanded
10 prosthesis 45 is axially fixed on the one hand by the adhesion between the
catheter and the prosthesis, and on the other by a silicon sleeve 62, against
which the prosthesis is axially supported, mounted at the proximal end of
the prosthesis 45 on the catheter ~1.
Once the first croclleted meshwork 46 is unravelled, the meshwork
15 47 applied from the proximal end is also unravelled, namely by means of the
unravelling line 60 extending away from the end mesh 58 at the distal end.
It can be seen that by pulling on the unravelling line, to start with the loop
58 held beneath the silicon sleeve 43 at the distal end will be unravelled and
the meshes 57 and 56 will be progressively unravelled from the distal end to
20 the proximal end, and the prosthesis 45 will expand radially and come to
rest against the walls o~ a vessel which requires to be fitted with a
prosthesis. Once the unravelling process is complete, the end 55 of the
thread hetd beneath the silicon sleeve 54 at the proximal end is withdrawn.
The prosthesis 45 is then detached ~rom the catheter and the latter can be
25 withdrawn in a simple manner from the vessel.
The prosthesis 70 illustrated in Fig. ~ is also tubular in shape and selF-
expanding. It may be made of a mesh fabric, e.g. of knitted structure. The
prosthesis is provided with pairs of holes 71, 72 arranged at approximately
equal axia! distances from one another. Loops 74 encircle the prosthesis on
30 the outside and serve to hold the prosthesis in its radially compressed state.
Each loop consists of thread material from a thread 7~ running Isngitudinal!y
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2~7~
- -17-
inside the prosthesis and drawn through holes 71; the thread then forms a
loop which tightly encircles the prosthesis and the end of the loop 76 is
then drawn back inside the prosthesis through a hole 72 paired with the
corresponding hole 71. The loops are secured in the encircling posi~ion
5 shown in Fig. 7 by means of a warp thread 78 passing throu0h the ends o~
the loops 76 inside the prosthesis.
The advantage of the embodiment according to Fig. 7 is that the
prosthesis 70 is radially compressed by these encircling loops 74, which are
spaced at substantialiy equal axial distances frorn each o~her and have no
10 external knots, but instead are form~?d by a thread 75 running longitudinallyinside the prosthesis and held tightly in place by means of the warp thread
78 also running longitudinally inside the prosthesis.
The prosthesis according to Fig. 7 is mounted, radially compressed,
near the distal end of a catheter in the same way as described above in
15 conjunction with Figs. 1 to 6 and it is implanted in a vessel ~y advancing
the catheter. Once it has been correctly positioned in the vessel, the
prosthesis is implanted in a simple manner by Yvithdrawing the warp thread
78 from the ends 76 of the loops 74, whereupon the prosthesis 70 expands
radially under its own pretensioned spring force to assume its intended
20 implanted position. The thread 75 used to form the loops can then also be
withdrawn in a simple manner.
The embodiment illustrated in Fig. 8 differs from the embodiment
according to Fig. 7 in that the axially spaced loops 7~' encircling the
prosthesis 70' are formed by crocheting. For this purpose, thread rnaterial
25 from the thread 75 running longitudinally inside the prosthesis is drawn out
through a hole 71' in the prosthe~is and wrapped around the prosthesis as a
loop 74', and also the loop end 76' of the thread is again taken back inside
the prosthesis through a hole 72' axially spaced from the aforementioned
hole 71. Thread material is then drawn through the end of the loop 76'
30 inside the prosthesis to form a further loop which is then taken to the
exterior through a hole 71' following in the axial direction, and it is then also
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207~521
-18-
wrapped around the prosthesis as loop 74', and the loop end which is taken
back inside the prosthesis through a further hole 72' ;s secured in the same
way as in the case of the first loop.
Fig. ~ illustrates an unrolled section of a vascular prosthesis ~0 made
5 of a knitted fabric in which alternatingly a thread 81 made frorn resorbable
material and a thread 82 made of non-resorbable material are knitted
together with each other. The non-resorbable thread material may, for
example, be tantalum.
The advantage of such a prosthesis is that, after a certain amount of
10 time has elapsed following implantation, the resorbable thread material will
be dissolved and all that is left behind in the patient's body are the non-
biodegradable components. These remaining components form encircling
rings consisting of a series of open loops. This design avoids thread
crossings which might exert unnecessary shear forces on the tissues
15 surrounding and growing around the prosthesis.
Prostheses according ~o Fig. 9 may also be designed in a simple
manner to act as medication depots, by embedding in the resorbable thread
material medical agents which are released when this material breaks down.
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