Abstract:
A stent crimping tool for firmly and uniformly crimping a stent onto a balloon catheter is constructed from a crimping section holding the stent and the balloon catheter therein, wherein the crimping is actuated by a shaft having an input end and an output end, engaging the crimping section at the output end. The shaft has a detent formed into the input end. A gripping member has an internal cavity to receive the input end, and includes a hole proximate to the shaft, wherein a ball bearing and a compression spring are located within the hole to bias the ball bearing toward the shaft and to engage the detent. When a torque is applied to the gripping member, it is transmitted through the ball bearing to the shaft; if the torque exceeds a predetermined magnitude, it overcomes the force of the spring on the ball bearing causing the bearing to slide out of the detent thereby disconnecting the applied torque from the shaft. The crimping section can be a rubber tube having a lumen holding the stent and catheter. When the shaft compresses the rubber tube as it advances, the lumen collapses and crimps the stent onto the catheter. In another embodiment, the crimping section is a coiled filament suspended at both ends and having an axial space holding the stent and catheter. Rotating the shaft twists the filament which in turn constricts and crimps the stent onto the catheter.

Description:
This is a divisional application of co-pending application Ser. No. 09/072,925 now U.S. Pat. No. 5,974,652, filed May 5, 1998, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus for loading a tubular graft, such as a stent, onto the distal end of a catheter assembly of the kind used, for example, in percutaneous transluminal coronary angioplasty (PTCA) or percutaneous transluminal angioplasty (PTA) procedures. 
     In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the ostium. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient&#39;s coronary vasculature and the dilatation catheter is advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, a flexible and expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient&#39;s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty. 
     In angioplasty procedures of the kind referenced above, restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the development of restenosis and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery at the lesion. The stent is crimped tightly onto the balloon portion of the catheter and transported in its delivery diameter through the patient&#39;s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter. The stent also may be of the self-expanding type. 
     Since the catheter and stent travel through the patient&#39;s vasculature, and probably through the coronary arteries, the stent must have a small delivery diameter and must be firmly attached to the catheter until the physician is ready to implant it. Thus, the stent must be loaded onto the catheter so that it does not interfere with delivery, and it must not come off the catheter until it is implanted. 
     In procedures where the stent is placed over the balloon portion of the catheter, it is necessary to crimp the stent onto the balloon portion to reduce its diameter and to prevent it from sliding off the catheter when the catheter is advanced through the patient&#39;s vasculature. Non-uniform crimping can result in sharp edges being formed along the now uneven surface of the crimped stent. Furthermore, non-uniform stent crimping may not achieve the desired minimal profile for the stent and catheter assembly. Where the stent is not reliably crimped onto the catheter, the stent may slide off the catheter and into the patient&#39;s vasculature prematurely as a loose foreign body, possibly causing blood clots in the vasculature, including thrombosis. Therefore, it is important to ensure the proper crimping of a stent onto a catheter in a uniform and reliable manner. 
     This crimping is often done by hand, which can be unsatisfactory due to the uneven application of force resulting in non-uniform crimps. In addition, it is difficult to visually judge when a uniform and reliable crimp has been applied. 
     Some self-expanding stents are difficult to load by hand onto a delivery device such as a catheter. Furthermore, the more the stent is handled the higher the likelihood of human error, which is antithetical to a properly crimped stent. Accordingly, there is a need in the art for a device for reliably crimping a stent onto a catheter. 
     There have been attempts at devising a tool for crimping a stent onto a balloon delivery catheter. An example of such a tool comprises a series of plates having substantially flat and parallel surfaces that move in a rectilinear fashion with respect to each other. A stent carrying catheter is disposed between these surfaces, which surfaces crimp the stent onto the outside of the catheter by their relative motion 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 crimping of the stent. 
     Another stent loading tool design is comprised of a tubular member housing a bladder. The tubular member and bladder are constructed to hold a stent that is to be crimped onto a balloon catheter assembly. Upon placement of the stent over the balloon portion of the catheter, a valve in the loading tool is activated to inflate the bladder. The bladder compresses the stent radially inward to a reduced diameter onto the balloon portion of the catheter to achieve a snug fit. In this way, the stent is crimped onto the distal end of a balloon catheter with a minimum of human handling. The foregoing stent crimping tools are disclosed in, for example, U.S. Pat. Nos. 5,437,083 and 5,546,646 to Williams et al. 
     Yet another stent crimping tool is known in the art as the BARD XT, which is actually a stent loader. It is constructed from a rigid, tubular body with a ball at one end connected to a plurality of long, thin strips passing through the tubular body. An uncrimped stent is placed over the plurality of long, thin strips, which 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 are slid from beneath the stent and the stent is transferred onto the balloon portion. 
     Still another conventional stent crimping tool is manufactured by JOHNSON &amp; JOHNSON and appears similar to a hinged nutcracker. Specifically, the tool is comprised of two hand operated levers hinged at one end and gripped in the palm of the hand at the opposite end. A cylindrical opening holding a crimping tube is provided through the mid-portion of the tool to receive therein a stent loaded onto a balloon catheter. The crimping operation is performed by the user squeezing the handle thereby pressing the crimping tube which in turn pinches the stent onto the balloon catheter. 
     While the prior art devices are suitable for crimping stents onto balloon catheters, they suffer from problems such as non-uniform crimping forces, resulting in non-uniform crimps. Consequently, they are unsuitable for use by physicians in a cath lab who desire to crimp the stent onto the balloon catheter. 
     SUMMARY OF THE INVENTION 
     Both PTCA and PTA procedures have become commonplace in treating stenoses or lesions in blood vessels and coronary arteries. In approximately 35% to 40% of the procedures, restenosis may develop requiring a further angioplasty, atherectomy or bypass procedure to return the patency of the vessel. Intravascular stents are now being deployed after PTCA and PTA procedures, and after atherectomies, in order to help prevent the development of restenosis. Importantly, such stents, mounted on the balloon portion of a catheter, must be tightly crimped to provide a low profile delivery diameter, and to ensure that the stent stays on the balloon until the balloon is expanded and the stent is implanted in the vessel. The present invention is directed to a crimping tool that can repeatedly provide a uniform and tight crimp to ensure the low profile diameter of the stent on the balloon portion of the catheter, and to ensure that the stent remains firmly attached until it is implanted in the vessel by expanding the balloon. 
     The present invention is directed to a method and apparatus to obtain consistent crimping of a stent on a balloon catheter independent of the balloon profile. This is accomplished by limiting the amount of force that is applied to crimp the stent by using a clutch that disconnects the applied torque at a predetermined level. 
     In particular, the present invention is directed to a tool for crimping a stent onto a balloon catheter, comprising a crimping section holding the stent and the balloon catheter therein; a shaft having an input end and an output end, engaging the crimping section at the output end, which shaft when rotated actuates the crimping section to crimp the stent; a detent formed into the input end of the shaft; a gripping member having an internal cavity to receive the input end of the shaft, wherein the cavity includes a hole proximate to the shaft; a stop member; a biasing member disposed in the hole and biasing the stop member into engagement with the detent; whereby applying a torque to the gripping member beyond a predetermined level overcomes the force of the biasing member and slides the stop member out of the detent to disengage the applied torque from the shaft. 
     Rotation of the shaft halts, and the magnitude of the crimping force encountered by the stent levels off or drops off due to resilience or backlash in the system. Damage to the stent from excessive crimping force is avoided. 
     In one exemplary embodiment, the crimping section comprises a housing having an internal chamber with an enclosed first end, and an open second end having threads, wherein the output end of the shaft is partially disposed within the internal chamber through the open second end of the housing, and wherein the input end of the shaft includes threads that engage the threads of the internal chamber; and an elastic tubing having a lumen, wherein the tubing is disposed within the internal chamber adjacent the enclosed first end, and the output end of the shaft is disposed adjacent the tubing. Accordingly, the stent and balloon catheter are positioned within the lumen and rotation of the shaft advances the shaft into the tubing, compressing the tubing, and crimping the stent. 
     In another exemplary embodiment, the crimping section comprises a rigid chassis having a hollow interior enclosed by a closed back end and leading to an open front end, wherein the back end includes a threaded opening; an end cap enclosing the open front end, the end cap including a central opening; an elastic tube disposed within the hollow interior adjacent to the front end and having a length less than a length of the hollow interior to define a chamber adjacent to the back end; a piston slidably disposed within the chamber; wherein the shaft passes through the closed back end of the chassis and the shaft includes threads engaging the threads of the back end, and the output end of the shaft engages the piston so that the shaft when rotated displaces the piston to compress the elastic tube; whereby the stent is loaded onto the catheter and is inserted through the central opening into the elastic tube, and the compressed elastic tube squeezes the stent radially onto the catheter. 
     In yet another exemplary embodiment, the crimping section comprises a base having at least first and second spaced apart supports, wherein the shaft is rotatably disposed on the second support with the output end of the shaft extending toward the first support; a coiled filament having an axial space and being attached to the first support and the output end of the shaft and extending between the first and second supports; whereby inserting the stent and catheter into the axial space of the coiled filament and rotating the shaft reduces the diameter of the axial space thereby crimping the stent onto the catheter. 
     In conclusion, it is clear that the present invention tool can be adapted to a variety of stent crimping sections that are operated by application of torque. The clutch of the present invention ensures that the amount of force applied during the crimping process is controlled. This is achieved by disconnecting the gripping member from the shaft at a predetermined level of torque. Doing so disrupts the transfer of torque to the crimping section of the tool, which in turn levels the amount of crimping force exerted on the stent. 
     With precise control of applied crimping forces, the present invention tool is capable of homogeneously crimping a stent onto a balloon catheter. Such a crimping tool is highly useful to cardiologists, for example. Such physicians are often concerned with proper deployment of the stent within the patient that it is desirable to have a consistently and reliably crimped stent. The present invention tool is further a time saver, because the stent crimping procedure can be performed fairly efficiently and quickly. These and other advantages of the present invention will become apparent from the following detailed description thereof when taken in conjunction with the accompanying exemplary drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view, partially in section, depicting a stent that has been crimped onto a delivery catheter and disposed within a vessel. 
     FIG. 2 is a sectional view of a preferred embodiment of the present invention, showing the clutch mechanism and the crimping section of the tool. 
     FIG. 3 is a cross-sectional view of an alternative embodiment of the present invention tool shown in FIG.  2 . 
     FIG. 4 is a perspective view of an exemplary embodiment tool wherein the crimping section includes a coiled filament used to crimp the stent. 
     FIGS. 5 and 6 are simplified schematic diagrams depicting a stent crimping operation performed by the present invention tool. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates intravascular stent  10  which is mounted onto delivery catheter  11 . Stent  10  generally comprises a plurality of radially expandable cylindrical elements  12  disposed coaxially and interconnected by members  13  disposed between adjacent cylindrical elements  12 . Delivery catheter  11  has an expandable portion or balloon  14  for expanding stent  10  within coronary artery  15  or other vessel such as saphenous veins, carotid arteries, arteries, and veins. Artery  15 , as shown in FIG. 1, has dissected lining  16  which has occluded a portion of the arterial passageway. 
     Delivery catheter  11  onto which stent  10  is mounted is essentially the same as a conventional balloon dilatation catheter for angioplasty procedures. Balloon  14  may be formed of suitable materials such as polyethylene, polyvinyl chloride, polyethylene terephthalate and other like polymers. In order for stent  10  to remain in place on balloon  14  during delivery to the site of the damage within artery  15 , stent  10  is compressed onto balloon  14 . 
     An optional retractable protective delivery sleeve  20  may be provided to further ensure that stent  10  stays in place on balloon  14  of delivery catheter  11  and to prevent abrasion of the body lumen by the open surface of stent  10  during delivery to the desired arterial location. Other means for securing stent  10  onto balloon  14  may also be used, such as providing collars or ridges on the ends of the working portion, i.e., the cylindrical portion of balloon  14 . 
     In order to implant stent  10 , it is first mounted onto inflation balloon  14  on the distal extremity of delivery catheter  11 . Stent  10  is crimped down onto balloon  14  to ensure a low profile. The present invention addresses this crimping procedure. 
     The catheter-stent assembly can be introduced into the patient&#39;s vasculature through processes known in the art. Briefly, guide wire  18  is disposed across the arterial section where an angioplasty or atherectomy has been performed requiring a follow-up stenting procedure. In some cases, the arterial wall lining may be detached so that guide wire  18  is advanced past detached or dissected lining  16  and the catheter-stent assembly is advanced over guide wire  18  within artery  15  until stent  10  is directly under detached lining  16 . Prior to inflation of balloon  14 , optional delivery sleeve  20  is retracted to expose stent  10 . Depending on the balloon and stent assembly, a delivery sleeve may be unnecessary. Balloon  14  of delivery catheter  11  is then inflated using an inflation fluid. Expansion of balloon  14  in turn expands stent  10  against artery  15 . Next, balloon  14  is deflated and catheter  11  is withdrawn leaving stent  10  to support the damaged arterial section. As mentioned above, in order to ensure proper seating of stent  10  on balloon  14 , and to ensure proper deployment of stent  10  at the site of the damage within artery  15 , the stent crimping procedure is important. 
     FIG. 2 is a cross-sectional view of a preferred embodiment of the present invention stent crimping tool  22 . Stent crimping tool  22  as shown preferably has crimping section  24  and actuation section  26 . Actuation section  26  is rotated and torque is transmitted through shaft  28  to crimping section  24 . 
     In order to limit the amount of torque transmitted to shaft  28  and to thus limit the amount of crimping force, the present invention includes a clutch mechanism. In the preferred embodiment, the clutch mechanism includes compression spring  30 , ball bearing  32 , and detent  34  located on shaft  28 . As gripping member  36 , which can be a knob, crank, knurled spindle, or the like, is rotated, torque is transmitted through a stop member, here ball bearing  32 , to detent  34 . Spring  30  which is positioned within hole  38  biases ball bearing  32  into detent  34  with sufficient force to maintain the transfer of torque from gripping member  36  to shaft  28 . If, however, a predetermined amount of torque is exceeded, the axial force of compression spring  30  is overcome causing ball bearing  32  to slide out of detent  34  and to retract into hole  38 . Of course, this predetermined amount of torque can be adjusted by modifying the spring force, depth of the detent, size of the ball bearing, and other parameters known in the art. 
     At that instant, the linkage between gripping member  36  and shaft  28  is broken because ball bearing  32  is free to rotate and slide along the outer circumference of shaft  28 . The clutch mechanism thus limits the torque delivery through shaft  28  into crimping section  24 . 
     In the exemplary embodiment shown in FIG. 2, detent  34  is a semi-spherical cut-out formed in the input end  40  of shaft  28 . Input end  40  is also received within cavity  42  of gripping member  36 . Gripping member  36  may be formed in a cylindrical shape for easy gripping as shown, or may take other grippable shapes known in the art. Furthermore, a resilient piece of material may be used to replace spring  30  to bias ball bearing into shaft  28 . For example, a sponge-like material can be used that has compliance and a level of resilience needed to urge ball bearing  32  into detent  34  in order to transfer torque between gripping member  36  and shaft  28 . 
     At the opposite end of shaft  28  is output end  44  which is preferably located adjacent resilient tubing  46 . Shaft  28  further includes external threads  48  meant to engage internal threads  50  formed inside housing  52  of crimping section  24 . Resilient tubing  46  fits within hollow interior  54  of housing  52 , wherein the latter is sufficiently rigid to not expand or distort under pressure. At the opposite end of housing  52  is end cap  56  that encloses the back end. 
     Thus, as the user manually rotates shaft  28  through application of torque to gripping member  36 , shaft  28  advances into and compresses resilient tubing  46 . Within resilient tubing  46  is lumen  58  containing uncrimped stent  10  already loaded onto balloon  14  of catheter  11 . End cap  56  has an optional central opening  60  in communication with lumen  58 . Hence, delivery catheter  11  can be inserted through central opening  60  and advanced into alignment with uncrimped stent  10  inside lumen  58 . As compression of the resilient tubing  46  takes place, the length of resilient tubing  46  is shortened thereby causing lumen  58  to collapse and simultaneously crimp stent  10  onto delivery catheter  11 . After the crimping step, shaft  28  is rotated in the opposite direction to retract it away from resilient tubing  46 , which regains its original shape. Thereafter, the crimped stent and catheter assembly can be withdrawn through central opening  60 . 
     In an alternative embodiment, a through hole (not shown) can be formed through the length of shaft  28  and through gripping member  36 . After the crimping step, the crimped stent and catheter assembly can be advanced over a guide wire (not shown), passing through the through hole, and out the opposite end of the tool. Therefore, in this alternative embodiment, the crimped stent and catheter assembly can be immediately advanced over the guide wire to the patient for implantation after the crimping step. 
     During the crimping step, if maximum torque is exceeded, as explained above, ball bearing  32  slides out of detent  34 . On the other hand, if gripping member  36  is continuously rotated, ball bearing  32  can be reseated within detent  34  during a subsequent revolution of gripping member  36  about input end  40 , thereby re-engaging the linkage between shaft  28  and gripping member  36 . At that moment, torque can be reapplied by rotating the gripping member  36  in either direction to advance or retract shaft  28 . By alternately advancing and retracting shaft  28 , it is possible to repeat the crimping step and ensure a firm and consistent crimp of stent  10  on catheter  11 . To be sure, it is also possible to rotate delivery catheter  11  during each cycle of the crimping step. 
     FIG. 3 is an alternative embodiment of the exemplary embodiment shown in FIG.  2 . More precisely, FIG. 3 is a cross-sectional view showing crimping section  62  that is a modification of crimping section  24  from FIG.  2 . As seen in FIG. 3, torque is transferred between gripping member  36  and crimping section  62  through threaded shaft  64 . Crimping section  62  is similar to that disclosed in co-pending U.S. patent application entitled “Indeflator-Driven, Rubber-Compression Crimping Tool” by Stephen A. Morales, (ACS-42071) Ser. No. 09/063,905, filed Apr. 21, 1998, whose entire contents are incorporated herein by reference. 
     In this embodiment, crimping section  62  is constructed from cylindrical shape chassis  66  having open end  68  and closed end  70 . Open end  68  is sealed closed with optional end cap  72  that is bonded to open end  68  using adhesive  74  of a type known in the art. Optionally, end cap  72  may be attached to chassis  66  using threads, snaps, clamps, or other mechanical means known in the art. 
     Within cylindrical shape chassis  66  is hollow interior  76  that contains elastic tube  78  that is coaxially disposed within chassis  66 . Notably, elastic tube  78  has a length that is shorter than the length of hollow interior  76 . Because of this difference in length, and because elastic tube  78  is disposed adjacent open end  68 , chamber  80  is formed adjacent to closed end  70 . Slidably disposed within chamber  80  is movable piston  82 . Shaft  64  engages piston  82  as shown in FIG.  3 . 
     End cap  72  includes central opening  84  that is aligned and in communication with axial space  86  of elastic tube  78 . Central opening  84  allows the stent-catheter assembly to be inserted into crimping section  62  prior to undergoing the crimping procedure. 
     Leading up to the procedure, a user introduces stent  10  already loaded onto balloon portion  14  of catheter  11  into axial space  86  within elastic tube  78 . In the exemplary embodiment, the inside diameter of elastic tube  78  is slightly greater than the outside diameter of the uncrimped stent  10 , or uncrimped stent and balloon  10  and  14 , respectively. 
     As gripping member  36  is rotated, torque is transmitted through spring  30  to ball bearing  32  and to the walls of detent  34  formed in shaft  64 . Shaft  64  once in rotation advances piston  82  into elastic tube  78  as indicated by the arrow. As a result, elastic tube  78  is compressed axially or lengthwise. The elastic material of elastic tube  78  must maintain a constant volume due to its surface elasticity and containment within the confines of hollow interior  76 . Continuous compression of elastic tube  78  by piston  82  causes the material of elastic tube  78  to displace axially and then radially into axial space  86 , in effect collapsing that space. This decreases the diameter of axial space  86 . In turn, stent  10  contained inside axial space  86  is compressed radially onto balloon portion  14  of catheter  11 . 
     As in the previously described embodiment, exceeding a pre-determined torque on gripping member  36  disengages ball bearing  32  from detent  34  to disconnect the application of torque to shaft  64 . On the other hand, insofar as gripping member  36  and shaft  64  are linked through the clutch mechanism, it is possible to rotate and counter-rotate shaft  64  to advance and retract, respectively, piston  82 . Indeed, it is possible to cycle through the crimping step over and over as necessary. 
     In the various exemplary embodiments of the present invention crimping tool shown in FIGS. 2 and 3, the housing pieces, piston, shafts, gripping member, etc. can be made from a rigid, injection molded plastic material. Also, translucent and transparent materials can be used so that the task at hand can be visually monitored. The present invention design is well suited for fabrication from surgical steel, too. Resilient tubing  46  and elastic tube  78  of each embodiment can be made from rubber or other elastomers known in the art. 
     FIG. 4 is a perspective view of an alternative embodiment of the present invention tool. In this embodiment, stent crimping section  90  contains a filament used to constrict a stent onto a balloon catheter inserted within an axial space formed by the coiled filament. Torque is still applied through gripping member  36 , which is connected to shaft  92 . 
     As best seen in this figure, the surface of gripping member  36  may optionally be contoured or knurled by pattern  94  to provide a better gripping surface. 
     Stent crimping section  90  is similar to that disclosed in co-pending U.S. patent application entitled “Stent Crimping Tool and Method of Use” by Stephen A. Morales, (ACS-42070) Ser. No. 08/962,632, filed Nov. 3, 1997, the entire contents of which are incorporated herein by reference. In FIG. 4, stent crimping section  90  includes base  96 , first vertical support  98 , second vertical support  100 , wherein the two vertical supports  98  and  100  are spaced apart on base  96 . Shaft  92  rotatably passes through an opening in second vertical support  100 . Cam  102  is affixed on shaft  92  whereby the cam rotates with shaft  92 . 
     Cam  102  optionally includes an obstruction which, in the preferred embodiment, are teeth  104  located at the circumference of cam  102  and are designed to engage pawl  106 . Pawl  106  is positioned on base  96  and biased into teeth  104 . Together, cam  102 , teeth  104 , and pawl  106  form a ratchet mechanism that permits rotation in one direction yet prevents rotation of shaft  92  in the opposite direction. 
     Attached to output end  108  of shaft  92  is one end of coiled filament  110 . The opposite end of coiled filament  110  is connected to first vertical support  98 . In the preferred embodiment shown in FIG. 4, coiled filament  110  is a coiled tension spring with its ends hooked to pins  112  and  114 . 
     In FIG. 4, the present invention tool has fairly high extending vertical supports  98 ,  100 , such that shaft  92  passes through second vertical support  100  rather than just resting upon it. Optional bearing  116  is located inside second vertical support  100  to minimize rotational friction between shaft  92  and second vertical support  100 . 
     Also, through hole  118  is provided in first vertical support  98  and is in communication with axial space  120  that is defined by the collection of coils of coiled filament  110 . When the tool is used, through hole  118  allows the stent-catheter assembly to be passed therethrough into axial space  120 . 
     FIGS. 5 and 6 are simplified schematic diagrams of the preferred embodiment of the present invention shown in FIG. 4 to help explain the crimping operation. Specifically, FIG. 5 provides a side elevational view of the present invention whereby stent  10  and balloon  14  have been inserted within axial space  120 . Optional sheath  122  is shown covering the stent-catheter assembly. Inside gripping member  36 , ball bearing  32  has been biased by compression spring  30  into detent  34 . Gripping member  36  can be rotated to apply torque through shaft  92  thereby twisting coiled filament  110  in order to constrict the stent-catheter assembly inside axial space  120 . 
     FIG. 6 shows completion of the crimping step after coiled filament  110  has been twisted. Also shown in FIG. 6 is the instant when maximum torque has been exceeded so that ball bearing  32  has slid out of detent  34  and is riding on the outside diameter of shaft  92 . At this very instant, the applied torque from gripping member  36  is disconnected from shaft  92  and from constricted coiled filament  110 . The natural resiliency of coiled filament  110  at this moment tends to counter-rotate shaft  92 . However, pawl  106  biased by spring  124  engages cam  102  to prevent the counter-rotation. Of course, disengagement of pawl  106  from cam  102  would permit free rotation of shaft  92  in either direction. At input end  126  of shaft  92 , shaft  92  rotates independently of gripping member  36  until ball bearing  32  is again seated within detent  34  during one of the revolutions of shaft  92  relative to gripping member  36 . Upon re-engagement, gripping member  36  is again linked to shaft  92  to control its rotation. 
     In the preferred embodiment, parts forming crimping section  90  are made from Nylon or a comparable polymer known in the art. Coiled filament  110  can be a metal tension spring, a resilient polymer ribbon made from Mylar, for example, formed into a coil. The coiled filament can have a flat, polygonal, or round cross-sectional shape. 
     The present invention is preferably sterilized and intended to be used in a cath lab by a trained technician or cardiologist. As will be appreciated by those skilled in the art, the present invention crimping tool is designed both for single use applications in a cath lab by a physician, or for multiple use applications in a sterile environment in a high volume manufacturing facility. In such a manufacturing facility where sterile conditions exist, the present invention stent crimping tool can be used repeatedly to crimp stents onto balloons until the mechanism wears out. Thus, repeated uses of the present invention are contemplated for controlled, sterile environments, as are single use applications when operated by cath lab personnel. 
     Furthermore, the present invention crimping tool can be used with any stent that is released without a delivery system. The crimping tool may also be sold alone, because its design is robust enough to undergo many uses. 
     Other modifications can be made to the present invention without departing from the scope thereof. The specific dimensions, procedural steps, and materials of construction are provided as examples, and substitutes are readily contemplated which do not depart from the invention.