MXPA98009119A - Tool for folding endoprotesis and metodode - Google Patents

Abstract

A tool for stent folding, to firmly and uniformly fold a stent over a catheter. The stent folding tool is constructed of a base having two vertically projecting spaced supports and a coiled tension spring fixed to one end of an arrow and at the end opposite one of the vertical supports. When a stent is loaded into the balloon portion of a catheter, and the stent-catheter structure is inserted into an axial space within the coiled spring, the user can rotate the shaft to twist the coiled spring thereby restricting it, and its Once the restriction of the coiled spring folds evenly the endoprosthesis into the balloon catheter

Description

TOOL FOR FOLDING E DOPRÓTESIS AND METHOD OF USE BACKGROUND OF THE INVENTION The present invention relates to an apparatus for loading a tubular graft, such as a stent at the distal end of a catheter structure of the type employed as for example in methods of percutaneous transluminal coronary angioplasty (PTCA = Percutaneous Transluminal Coronary Angioplasty) or percutaneous transluminal angioplasty (PTA = Percutaneous Transluminal Angioplasty). In typical PTCA procedures, a guide catheter is inserted percutaneously into a patient's cardiovascular system through the brachial or femoral arteries and advanced through the vasculature until the distal end of the guide catheter is in the ostium. A guide wire and a dilatation catheter which has a balloon at the distal end, is inserted through the catheter, guide and the guidewire slides within the dilatation catheter. The guidewire is first advanced out of the guide catheter into the patient's coronary vasculature and the dilatation catheter is moved over the previously advanced guidewire until the dilatation balloon is properly placed through the arterial lesion. Once in position through the lesion, a flexible and expandable balloon is inflated to a predetermined size with a radio-opaque liquid at relatively high pressures to radially compress the atherosclerotic plaque in the lesion against the interior of the arterial wall and this way -dilating the lumen of the artery. The balloon is then deflated to a small profile, such that the dilatation catheter can be removed from the patient's vasculature and the flow of blood through the dilated artery resumed. As will be appreciated by those with skill in the art, while the procedure described above is typical, it is not the only method employed in angioplasty. In angioplasty procedures of the type referred to above, restenosis of the artery may arise over time, which may require another angioplasty procedure, a surgical bypass operation or some other method of repair or reinforcement of the area. To reduce the likelihood of the development of restenosis and to reinforce the area, a physician may implant an intravascular prosthesis to maintain the vascular opening, commonly known as a stent, within the artery in the lesion. The stent is tightly folded over the balloon portion of the catheter and transported at its delivery diameter through the vasculature of the patient. At the deployment site, the stent expands to a larger diameter, often by inflating the balloon portion of the catheter. The stent may also be of the self-expanding type. Since the catheter and stent travel through the patient's vasculature and probably through the coronary arteries, the stent should have a small delivery diameter and be firmly connected to the catheter until the doctor is ready to implant it. In this way, the stent should be loaded into the catheter, so that it does not interfere with the delivery and should not leave the catheter until it is implanted. In procedures wherein the stent is placed over the balloon portion of the catheter, it is necessary to fold the stent over the balloon portion to reduce its diameter and to prevent it from slipping out of the catheter, when the catheter is advanced through the vasculature of the patient. A non-uniform folding can result in sharp edges formed on the now non-uniform surface of the folded stent. In addition, non-uniform stent folding may not achieve the minimum profile desired for the stent and catheter structure. When the stent is not reliably folded over the catheter, the stent can slip out of the catheter and into the patient's vasculature prematurely as a loose foreign body, possibly causing blood clots in the vasculature, including thrombosis. Therefore it is important to ensure adequate stenting of a stent-over a catheter in a uniform and reliable manner. This folding is often done by hand, which can be insastifactory due to the non-uniform application of force resulting in non-uniform bends. In addition, it is difficult to judge visually when a uniform and reliable fold has been applied. Some self-expanding stents are difficult to load by hand on the delivery device such as catheter. In addition, the more the stent is handled, the greater the likelihood of human error that could be the antithesis of a properly folded endoprosthesis. Accordingly, there is a need in the art for a device to reliably fold a stent into a catheter. There have been attempts to design a tool for folding a stent over a balloon delivery catheter. An example of this tool comprises a series of plates having their substantially flat and parallel surfaces that move in a rectilinear fashion with each other. A catheter-carrying endoprosthesis is disposed between these surfaces, these surfaces fold the stent on the outside of the catheter by its relative movement and applied pressure. The plates have multiple degrees of freedom and may have force indicating transducers to measure and indicate the force applied to the catheter during stent folding. Another design of the tool for stent loading is constituted by a tubular member that houses a bladder. The tubular member and the bladder are constructed to hold a stent that is to be folded over a balloon catheter structure. By placing the stent over the portion of the catheter balloon, a valve is activated in the loading tool to inflate the bladder. The bladder compresses the stent radially inwardly at a reduced diameter over the balloon portion of the catheter to achieve a tight fit. In this way, the endoprosthesis is folded over the distal end of a balloon catheter with a minimum of human handling. Anterior stent folding tools are described, for example, in U.S. Pat. Nos. 5,437,083 and 5,546,646 granted to Williams et al. Still another stent folding tool is known in the art as the BARD XT, which is in fact a stent loader. It is constructed from a rigid tubular body with a ball at one end connected to a plurality of thin and long strips that pass through the tubular body. An unfolded stent is placed over the plurality of thin strips that hold the stent in an expanded state. The balloon portion of a catheter is inserted into the cylindrical space formed by the plurality of strips. When the user pulls the ball while holding the tubular body against the stent, the strips slide under the stent and the stent is transferred onto the balloon portion. Yet another conventional stent folding tool is manufactured by JOHNSON &; JOHNSON and appears similar to a hinged nutcracker. Specifically, the tool is constituted by two hand operated levers hinged at one end and held in the palm of the hand at the opposite end. A cylindrical opening holding a folding tube is provided through the middle portion of the tool to receive a stent loaded in the balloon catheter. The folding operation is performed by the user who compresses the handle by pressing in this way the folding tube which in turn tightens the stent on the balloon catheter. While prior art devices are suitable for folding stents in balloon catheters, they have problems such as non-uniform bending forces resulting in non-uniform folds. They are, incidentally, unsuitable for use by physicians in a catheter laboratory where it is desired to fold the stent into the balloon catheter. COMPENDIUM OF THE INVENTION Both PTCA and PTA procedures have become common. to treat stenosis or injury to blood vessels and coronary arteries. Approximately in 35 and 40% of the procedures, restenosis may arise requiring an additional procedure of angioplasty, atherectomy or bypass to return the opening of the vessel. Intravascular stents are now deployed after PTCA and PTA procedures, and after atherectomies to help prevent the development of restenosis. Importantly, these stents mounted on the balloon portion of a catheter must be folded tightly to provide a low profile delivery diameter and ensure that the stent remains in the balloon until the balloon expands and the stent is implanted in the balloon. glass. The present invention is directed to a folding tool that can repeatedly provide a uniform and tight fold to ensure the low profile diameter of the stent and the portion of the catheter balloon, and to ensure that the stent is firmly connected until it is implant in the glass when expanding the balloon.

The present invention is directed to a folding tool for folding a stent over a catheter comprising a base having first and second opposed vertical supports separated by a predetermined distance, a crank rotatably mounted on the second vertical support, wherein the crank includes an arrow extending through the first vertical support and a torque transmission member. The folding tool further includes a cam fixed to the crank between the first and second vertical supports, wherein the cam includes an obstruction in its circumference. The invention also comprises a ratchet arranged in the base and directed in engagement with the cam obstruction, to prevent free rotation of the crank, and a coiled filament having an axial space in which the coiled filament is connected to the first vertical support and the arrow of the crank extending between the first and second vertical supports, whereby inserting the endoprosthesis mounted on the catheter into the axial space within the wound filament and turning the crank causes the wound filament to restrict the endoprosthesis in the catheter. In the preferred embodiment, the torque transmitting member is a handle that is rotated by the user to twist the coiled filament. Also, in the preferred embodiment, the coiled filament is a coiled tension spring. The folding tool of the present invention is designed for a saphenous vein, carotid graft or any other stent product that is released without a delivery system. It is an ideal tool for any stent that is introduced to the market without this delivery system. All parts of the present invention are preferably made from nylon or a compatible polymer. The stent-folding tool of the present invention is intended to be used in a catheter laboratory to secure and repeatedly fold a stent into a balloon catheter. The folding tool of the present invention operates as follows. A catheter with a balloon having a mounted endoprosthesis is inserted into an axial space within the coiled filament. The user rotates the crank on the opposite end that rotates the cam and arrow of the crank. The rotating crank twists the kinked or wound filament, which at the opposite end is fixed to the first immobile vertical support. Continuous twisting of the wound filament restricts the filament on the endoprosthesis, this endoprosthesis in turn is compressed on the balloon.

In the preferred embodiment, the coiled filament is a tension spring which, when twisted, has a resilient tendency to turn the crank. Without However, the ratchet mechanism formed by an obstruction, which in the preferred embodiment are unidirectional teeth on the circumference of the cam engaging with the ratchet, prevent the resilience of the spring from uncurling and against turning the crank. When the spring has been manually wound or twisted to the point where it is restricted in its minimum diameter, the user can force the ratchet against its branch to detach the teeth of the cam. Once the ratchet mechanism is released, the natural resilience in the spring releases the restriction and discharges in the opposite direction, thus releasing the folded stent and balloon catheter. As a result of the above process, the crushing or decreasing diameter of the spring restricted in this way has compressed in a homogeneous and precise manner the spring on the balloon catheter. The system is repeatable because the tool is readjusted after the ratchet is released. The number of "clicks" by the ratchet can be counted or the number of rotations can be counted to provide accuracy and precision. In addition, the stent can not be folded homogeneously from the proximal to the distal end of the stent. A coil of smaller diameter can be used if this is desired. Larger diameter coils will increase the force required to drive the tool but will also increase fold uniformity and accuracy. Thus, the folding tool of the present invention is highly useful for cardiologists, for example. These doctors are constantly involved with the proper deployment of the stent in the patient, which is convenient to have a stent that is consistently and reliably folded. The tool of the present invention is also a time saver since the procedure of folding the stent can be performed in a substantially efficient and rapid manner. These and other advantages of the present invention will be apparent from the following detailed description thereof, when taken in conjunction with the accompanying exemplary drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elevation view, partially in section, illustrating a stent that has been folded over a delivery catheter and disposed within a damaged vessel.

Figure 2 is a perspective view of a preferred embodiment of the stent-folding tool of the present invention. Figure 3 is a side elevational view of the present invention drawn as a simplified schematic showing a stent mounted on a balloon catheter before being inserted into the axial space of the coiled filament. Figure 4 is a side elevation view of the present invention after the step illustrated in Figure 3, wherein the stent-catheter structure has been inserted into the axial space of the coiled filament. Figure 5 is a side elevational view of the present invention after the step illustrated in Figure 4 showing the rotation of the crank in restriction of the coiled filament, thereby causing the stent to fold over the balloon catheter. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Figure 1 illustrates stent 10 which is mounted on delivery catheter 11. Stent 10 generally comprises a plurality of radially expandable cylindrical elements 12, generally coaxially arranged and interconnected by members 13 disposed between adjacent cylindrical elements 12. The delivery catheter 11 has an expandable portion or balloon 14 for expanding the endoprosthesis 10 within the coronary artery 15 or another vessel such as saphenous veins, carotid arteries, arteries and veins. Artery 15, as illustrated in Figure 1, has a dissected liner 16 that has a portion of the arterial passage occluded. The delivery catheter 11 in which the stent 10 is mounted is essentially the same as the conventional balloon dilatation catheter for angioplasty procedures. The balloon 14 may be formed of suitable materials such as polyethylene, polyvinyl chloride, and other similar polymers. In order for the endoprosthesis 10 to be in place in the balloon 14 during delivery to the site of damage behind the artery 15, the stent 10 is compressed on the balloon 14. This compression step is referred to as folding. An optional retractable protective supply sleeve 20 may be provided to further ensure that the stent 10 remains in place in the balloon 14 of the delivery catheter 11 and to prevent abrasion of the body lumen by the open surface of the stent 10 during delivery to the arterial site. wanted. Other means for securing the stent 10 in the balloon 14 can also be employed, such as by providing collars or ridges at the ends of the working portion, ie the cylindrical portion of the balloon 14. In order to implant the stent 10, first - it is mounted on the inflation balloon 14 at the distal end of the delivery catheter 11. The endoprosthesis 10 is folded down on the balloon 14 to ensure a low profile. The present invention is directed to this folding process. The stent-catheter structure can be introduced into the vasculature of the patient through processes known in the art. Briefly, guide wire 18 is disposed through the arterial section where an angioplasty or atherectomy has been performed, requiring a follow-up procedure of stent placement. In some cases, the lining of the arterial wall can be detached such that the guide wire 18 is advanced beyond the detached or dissected liner 16 and the stent-catheter structure is advanced over the guidewire 18 within artery 15 to that the endoprosthesis 10 is directed under the detached liner 16. Before inflation of the balloon 14, the delivery sleeve 20 is retracted to expose the stent 10. from the balloon structure and stent, a delivery sleeve may be unnecessary. The balloon 14 of the delivery catheter 11 is then deflated using an inflation fluid. The expansion of balloon 14 in turn expands stent 10 against artery 15. Next, the balloon 14 is deflated and the catheter 11 is withdrawn leaving the stent 10 to support the damaged artery section. As mentioned above, in order to ensure proper seating of the endoprosthesis 10 in the balloon 14, and to ensure adequate deployment of the endoprosthesis 10 at the site of damage within the artery 15, the procedure of stent folding is important. Figure 2 provides a perspective view of a preferred embodiment of a stent-folding tool 22. In the preferred embodiment shown, the stent-folding tool 22 has several main components comprising the base 24, first vertical support 26, second vertical support 28, wherein the two vertical supports 26, 28 are spaced at the base 24. The crank 30 has the arrow 32 which rotates through an opening in the second vertical support 28. A cam 34 is fixed on the arrow 32 with which the cam rotates with the arrow 32. The cam 34 includes an obstruction which in the preferred embodiment are teeth 36 located on the circumference of the cam 34 and are designed to engage the pawl 38. The pawl 38 is placed on the base 24 and drift on the teeth 36. Together, the cam 34, the teeth 36 and the ratchet 38 form a ratchet mechanism allowing rotation in a non-directional direction -but avoids rotation of the arrow 32 in the opposite direction. Attached to the end 40 of the arrow 32 is an end of coiled filament 42. The opposite end of the coiled filament 42 is connected to the first vertical support 26. In the preferred embodiment shown in Figure 2, the coiled filament 42 is a tension spring. winding with its ends engaged to the pins 44, 46. In the exemplary embodiment of Figure 2, the present invention has substantially high vertical supports 26, 28, such that the arrow 32 passes through the second vertical support 28 instead of just leaning on him. An optional bearing 48 is located within the second vertical support 28 to minimize rotational friction between the arrow 32 and the second vertical support 28. Also, the through hole 50 is provided in the first vertical support 26 and is in communication with the axial space 52 which is defined by the coils of the coiled filament 42. Thus, when the stent-folding tool 22 is employed, the through-hole 50 allows the stent-catheter structure to be passed into the axial space 52 within the coiled filament 42. In the preferred embodiment, the through hole 50 is aligned with the open housing bearing 48; although it is recognized that the through hole 50 does not require alignment with the rotational axis of the bearing 48. Figures 3 to 5 are simplified schematic diagrams of a preferred embodiment of the present invention. In particular, Figure 3 provides a side elevational view of the endoprosthesis folding tool of the present invention 22, just prior to insertion of the stent-catheter structure. As seen in Figure 3, on the left side of the drawing, the stent 10 is loaded into the delivery catheter 11 such that the stent 10 superimposes the portion of the balloon 14 just prior to insertion of the structure into the through hole. 50 of the first vertical support 26. The arrow A shows the insertion direction of the stent-catheter structure in the axial space 52 within the coiled filament 42. As explained above one end of the coiled filament 42 is connected to the first vertical support 26 and the opposite end is anchored to the arrow 32 of the crank 30. In alternate embodiments of the present invention, the crank 30 may have a torque transmitting member such as a handle 54 as seen in FIG.

Figure 3, or textured wheel 56 as seen in Figure 2.

-Other torque transmission devices known in the art can be used equally. Figure 3 also shows the preferred embodiment of the ratchet device preventing counter rotation of the crank 30 during the folding procedure. The preferred embodiment of the ratchet mechanism of the present invention comprises the cam 34 having teeth 36 located on its circumference. Ratchet 38 is derived in engagement with teeth 36 for spring 58 or the like. A ratchet 38 can be operated by a lever which, when rotated, overcomes the spring branch 58 to release the ratchet 38 from the teeth 36; on the contrary, releasing the lever allows the spring to derive to reattach the pawl 38 with the teeth 36. In the exemplary embodiment illustrated in Figure 2, the pawl 38 can be made of a high resilience material and be formed into a plate that is derived in engagement with the teeth 36 of the cam 34. This type of contact coupling allows rotation of the arrow 32 in one direction however, it resists rotation in the opposite direction due to the obstruction of the pawl 38 against one or more teeth 36. Other ratchet mechanisms known in the art can be used here equally. For example, in an alternate embodiment, the outer circumference of the cam has a rough finish and the ratchet has a finish of equal high friction and engages the cam under spring bypass. In this alternative mode, the friction is used to avoid rotation of the cam and arrow. The ratchet will then serve as a brake against the rotating cam. In yet another alternate embodiment, the circumference of the cam may include a catch to catch the ratchet, which is derived on the cam. The detent profile may have an asymmetric sawtooth shape to allow the cam to continue to rotate in one direction by allowing the pawl to slide over the detent however solidly engage the pawl if the cam rotates in the opposite direction. Figure 4 is a side elevation view of the present invention, wherein the stent-catheter structure has been inserted into the axial space 52 within the coiled filament 42. With the pawl 32 detached from the teeth 36, the arrow 32 of the handle 30 is free to rotate in either direction clockwise or counterclockwise.

As previously mentioned, the optional bearing 48 is used to reduce the rotational friction between the arrow 32 and the second vertical support 28.

-It can be used equally lubricants or a low friction sleeve. When the handle 30 is rotated in the direction of the arrow B, the arrow 32 rotates and begins to twist the coiled filament 42, which at the opposite end is anchored to the first vertical support 26. As the coiled filament 42 is twisted, it restricts the stent-catheter structure contained within the axial space 52. Figure 5 shows this process continuation. As the user continuously rotates the handle 30, the restriction advances and the diameter of the wound filament 42 decreases uniformly, thereby uniformly compressing the stent 10 over the balloon portion 154 of the delivery catheter 11. As illustrated in the Figures 3 to 5, an optional sleeve or liner 20 overlays the stent 10 before and during folding for various reasons. The liner protects the stent until the stent is mounted on the balloon. Furthermore, as the coiled filament is compressed and its diameter is reduced, the compression forces are applied uniformly and constantly on the liner and on the stent. After folding, optional liner 20 can be removed or left in place to protect the stent during intravascular delivery. Any resilience in the winding filament -42 which displaces the arrow 32 to 'counter-rotate in a direction opposite to the arrow B, is resisted by the detent mechanism. Specifically, the ratchet 38 in Figure 5 engages the teeth 36 to prevent counter rotation. Of course, the detent mechanism can be removed and the counter-rotation manually resisted by the user using force against the crank 30. Torque is applied in the direction of the arrow B through the crank 30 until the amount is achieved desired folding. The folding process can be repeated by retracting the pawl 38 from contact with the teeth 36 and allowing free counter-rotation of the arrow 32 to unwind the coiled filament 42. At any time after the coiled filament 42 has begun to unwind, the crank 30 can be rotated in the direction of arrow B to again restrict the wound filament 42 in the stent-catheter combination. This process can be repeated again and again as required until the desired fold is achieved. Still further, the amount of torque applied to the crank 30 can slowly increase, decrease or remain uniform in magnitude. It is optional to keep the ratchet 38 Totally engaged on the teeth 36, until the previous folding process to resist the counter-rotation induced by resilience in the arrow. The ratchet 38 only requires detaching from the teeth 36 to allow counter rotation. in order to release the structure of • Folded stent-catheter or to restart the folding cycle. Undoubtedly, the folding cycle can be repeated again and again without coupling the ratchet 38, against the teeth 36 as long as the user maintains some level of torque on the crank 30. In the preferred embodiment, all parts of the present invention are made of nylon or a comparable polymer known in the art. The device is sterilized and intended to be used in the catheter laboratory by a trained cardiologist or technician. The coiled filament 42 can be a metal tension spring, a resilient polymer tape (for example mylar) formed in a coil, or the like made from a resilient material. Preferably, the coiled filament is a coiled spring having either a flat or round cross section. The filament can vary in thickness or diameter as required by the particular application.

As will be appreciated by those skilled in the art, the folding tool of the present invention 22 is designed for both utility applications - simple in a catheter laboratory by a doctor or for multiple uses in a sterile environment in a high-volume manufacturing facility. In this manufacturing facility where sterile conditions exist, the stent-folding tool 22 can be used to repeatedly bend stent-like balloons until the mechanism wears. In this manner, repeated uses of the present invention are contemplated for controlled, sterile environments, although applications of simple use are required, when used by personnel of catheter laboratories. In addition, the folding tool of the present invention can be used with any stent that is released without a delivery system. The folding tool can also be sold alone because its design is robust enough to support many uses.

Claims (23)

1. CLAIMS 1.- A tool for folding a stent in a catheter, characterized in that it comprises: a base that 'has at least first and second supports spaced apart; - a crank rotatably disposed in the second support and extending towards the first support; a coiled filament having an axial space and connected to the first support and the crank and extending between the first and second supports; whereby by inserting the endoprosthesis and catheter into the axial space of the wound filament and turning the crank, the diameter of the axial space is reduced thereby folding the endoprosthesis into the catheter.
2. 2. - The folding tool according to claim 1, characterized in that it also comprises a cam fixed to the crank that has an obstruction in a circumference; and a ratchet disposed at the base and directed in engagement with the cam obstruction to prevent free rotation of the crank.
3. 3. - The folding tool according to claim 2, characterized in that the obstruction includes a retainer formed in the cam.
4. 4. - The folding tool according to claim 2, characterized in that the obstruction includes a tooth.
5. 5. - The folding tool according to claim 2, characterized in that the obstruction includes a frictional surface on the circumference of the cam.
6. 6. - The folding tool according to claim 1, characterized in that the coiled filament includes a coiled spring.
7. 7. - The folding tool according to claim 6, characterized in that the coiled spring has a flat or round cross section.
8. 8. - The folding tool according to claim 1, characterized in that the first support includes an opening through which passes a stent and catheter when inserted into the axial space of the wound filament.
9. 9. - The folding tool according to claim 1, characterized in that the base includes a polymeric material.
10. 10. - The folding tool according to claim 1, characterized in that the coiled filament includes a flat cross-sectional shape.
11. 11. - The folding tool according to claim 1, characterized in that the coiled filament includes a circular cross-sectional shape.
12. 12. - The folding tool according to claim 1, characterized in that the endoprosthesis is covered by a lining in such a way that the forces of
13. -Folding of coiled filament are evenly distributed over the endoprosthesis. 13. - A tool for folding an endoprosthesis in a catheter, characterized in that it comprises: a base having first and second opposed vertical supports separated by a predetermined distance; a crank rotatably mounted on the second vertical support, wherein the crank includes an arrow extending to the first vertical support and a torque transmission member; a cam fixed to the crank between the first and second vertical supports, wherein the cam includes an obstruction in a circumference; a ratchet arranged at the base and directed in engagement with the cam obstruction to prevent free rotation of the crank; and a coiled filament having an axial space, wherein the coiled filament is connected to the first vertical support and the arrow of the crank and extends between the first and second vertical supports; whereby by inserting the endoprosthesis mounted in the catheter into the axial space within the coiled filament and turning the crank, the coiled filament is caused to fold the stent into the catheter.
14. 14. - The folding tool according to claim 13, characterized in that the torque transmission member includes a handle.
15. 15. - The folding tool according to claim 13, characterized in that the torque transmission member includes a wheel or a steering wheel.
16. 16. The folding tool according to claim 13, characterized in that the first and second vertical supports include first and second respective openings in which the arrow of the crank passes through the second opening.
17. 17. - The folding tool according to claim 16, characterized in that the second opening includes an inert bead.
18. 18. - Method for folding a stent in a catheter, characterized in that it comprises the steps of: providing a base having at least first and second supports spaced apart; providing a crank rotatably disposed in the second support extending towards the first support; stretching the coiled filament having an axial space from the first support to the crank; fixing a cam that has an obstruction in a circumference to the crank; deriving a ratchet arranged in the base in engagement with the cam obstruction to prevent free rotation of the cam; insert the endoprosthesis and catheter into the axial space of the wound filament; and turning the crank to overcome the - ratcheting of the ratchet against the cam to twist the wound filament; whereby twisting the coiled filament reduces the diameter of the axial space thereby folding the stent into the catheter.
19. 19. - The method according to claim 18, characterized in that the step of stretching the coiled filament includes a step of providing a coiled spring.
20. 20. The method according to claim 18, characterized in that the method further comprises the steps of detaching the ratchet from the cam obstruction and repeatedly rotating and releasing the crank.
21. 21. The method according to claim 18, characterized in that the method further comprises the steps of turning the crank, detaching the ratchet from the cam obstruction, coupling the ratchet against the cam obstruction and turning the crank.
22. 22. - The method according to claim 18, characterized in that the method further comprises the step of applying increased torque when the crank is rotated.
23. 23. The method according to claim 18, characterized in that the method further includes covering the endoprosthesis with a liner before the step of inserting the endoprosthesis and catheter into the axial space of the coiled filament such that as the coiled filament reduces the axial space, the imparted forces will be distributed uniformly and continuously over the stent to fold it to the catheter.