Patent Publication Number: US-11026821-B2

Title: Device for catheter sheath retraction

Description:
PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 14/793,659, filed Jul. 7, 2015, now U.S. Pat. No. 10,206,800, which is a continuation of U.S. patent application Ser. No. 13/958,460, filed Aug. 2, 2013, now U.S. Pat. No. 9,421,115, which is a continuation of U.S. patent application Ser. No. 12/668,613, filed Feb. 19, 2010, now U.S. Pat. No. 8,500,789, filed as a U.S. national stage application under 35 USC § 371 of International Application No. PCT/EP2008/059040, filed Jul. 10, 2008, claiming priority to Great Britain Patent Application No. 0713497.6, filed Jul. 11, 2007, each of which is incorporated by reference in its entirety into this application. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device for moving an elongate member relative to an elongate body through which it at least partially extends, to a device for moving an elongate member by a predetermined distance relative to an elongate body through which it at least partially extends, thereby to release a stent at the distal end of the elongate body, and to surgical apparatus including such devices. More specifically, the invention is concerned with medical transluminal catheters such as those used to deliver a stent to a vascular treatment location, and the devices by which a medical practitioner operates such catheters from a location external of the patient. 
     BACKGROUND OF THE INVENTION 
     It has long been desirable to reduce the degree of trauma caused by, and attendant risks associated with, surgical procedures. In order to further this aim, there have been a large number of technical advances in recent times to enable various surgical procedures to be carried out using minimally invasive techniques. 
     One particular form of treatment to have benefited from advances in minimally invasive surgical procedures is the treatment of cardiovascular diseases. Whereas in the past it would have been necessary to conduct an open procedure in order to access the heart or a portion of the venous system, minimally invasive techniques have now been developed in which a catheter-based piece of surgical equipment can be deployed to a treatment location within a patient&#39;s cardiovascular system from a remote location external to the patient. Specifically, an elongate endoluminal catheter is inserted percutaneously through an incision in a patient&#39;s skin and is then advanced transluminally through the patient&#39;s vasculature from the incision location to a treatment location. A control device, mounted at the proximal end of the surgical catheter, is used to control the equipment mounted at the distal end of the surgical catheter, which has been advanced to the treatment location, from a remote location external to the patient&#39;s body. 
     In one particular technique, a stent is mounted on a distal end portion of the surgical catheter in a reduced-diameter configuration. The surgical catheter includes a retractable sheath which extends along at least the distal portion of the catheter to enclose the stent and to retain the stent in the reduced-diameter configuration. When the catheter distal portion has been advanced to the treatment location, the sheath is retracted to expose the stent. The stent is then caused to expand to an increased-diameter configuration at the treatment location, so that its abluminal surface engages the vessel inner wall, and thereafter serves to maintain an open fluid passageway through the vascular treatment location. The surgical catheter is then retrieved from the patient, leaving the stent in place. Preferably the stent is a so-called self-expanding stent, typically manufactured from a shape memory alloy, such as Nitinol, and being configured to expand from the reduced diameter configuration to the increased-diameter configuration due to the memorized molecular configuration of the alloy at body temperature. When the sheath is retracted, such a stent therefore adopts the increased-diameter configuration without further intervention by the medical practitioner. Balloon-expandable stents, and other configurations, are also known, however, which require intervention by the medical practitioner to cause the stent to expand from the reduced-diameter configuration to the increased-diameter configuration. 
     In order to be insertable through the tortuous vasculature of a patient, from the incision location to the treatment site, a surgical catheter must be flexible transverse to its longitudinal axis. This allows the catheter to follow the narrow and twisting passageways through the patient&#39;s venous system. On the other hand, such catheters must be relatively incompressible in the lengthwise direction, so as to facilitate catheter advancement by providing a driving force to guide the catheter into the vasculature from the proximal end, and so as to resist compression during retraction of the catheter sheath when a stent is to be released. For this purpose, it is not uncommon to provide a means of reinforcing the inner tubular portion of the surgical catheter, such as by providing a coil spring along the length thereof from the proximal end to the distal portion. Such a coil spring is closely wound, with adjacent turns of the coil being substantially in contact with one another, to resist compressive forces but provides the requisite degree of flexibility transverse to the coil&#39;s central axis. A so-called stent pusher may be provided at the coil distal end, configured to engage the stent and to prevent proximal displacement of the stent when a retaining sheath is withdrawn for stent release. 
     The sheath provided to restrain the stent in the reduced diameter configuration may be provided so as to extend along the entire length of the surgical catheter, from the proximal end to the distal tip. On the other hand, the sheath need only be provided in a region at the distal portion of the catheter, sufficient to enclose the stent along its length, and being retractable to fully expose the stent. In either case, a sheath retraction wire may be provided by which to withdraw the sheath proximally along the catheter, thereby exposing the stent at the catheter distal end portion. Typically, as noted, the stent will be self-expanding, so as to place the sheath under a circumferential pre-tension. In order to allow the sheath to slide over the catheter, the catheter and sheath are usually constructed from low-friction materials, and provided with a lubricant or lubricious surface treatment there-between. 
     At the proximal end of the surgical catheter, a device is provided for retracting the sheath over the catheter. Typically, such a device includes a housing by which a medical practitioner can grip the device, and to which the catheter is rigidly connected. In particular, any reinforcing member, such as a coil spring, is attached to the device distal end by a hub, by which to hold the reinforcing member in place. A retraction wire is typically provided, attached at its distal end to one end of the catheter sheath, by which to withdraw the sheath. Typically, the retraction wire extends from the connection point with the sheath, into and through a lumen inside the catheter, to extend from the proximal end of the catheter inside the device housing. An actuator is provided, operable by the medical practitioner using the device, by which the sheath wire is retracted to withdraw the sheath and expose the distal portion of the catheter. In alternative configurations, a retraction wire is not necessitated, and the sheath may be connected directly to a portion of the actuator mechanism within the housing. In most applications, the catheter sheath is configured to be withdrawn proximally along the catheter, but distal withdrawal is not impossible. The reinforcing member serves to resist compression due to the tensile stresses in the catheter sheath and retraction wire. The resulting compressive stresses are transferred from the reinforcing member to the device via the connection hub by which they are joined. 
     WO 2002/087470 discloses a sheath retraction device for proximally withdrawing a catheter sheath. The sheath is in the form of an outer tube  16  connected at its proximal end to a slider  24  in the device housing. As the slider  24  is proximally withdrawn, the sheath is retracted. The retraction device in WO 2002/087470 provides two actuation mechanisms by which the sheath may be withdrawn. The first is to provide a finger engagement portion (a button) on the slider  24 , by which the slider and the connected outer tube  16  may be directly proximally withdrawn by retracting the slider along slider tracks provided. The second mechanism by which the sheath may be withdrawn is actuated by a finger trigger  34 . A pull wire  30  extends proximally from the slider  24  to a take-up reel  32 . The take-up reel is connected to a toothed gear  35 , which engages with ratchet teeth  36  of the trigger  34 . When the trigger is depressed, the ratchet teeth rotate the toothed gear  35  so as to wind the pull wire  30  on the take-up reel  32 , thereby retracting the slider and connected sheath proximally in the housing. Because the teeth  36  are ratchet teeth, the take-up reel may only be rotated in one direction by successive pulls of the trigger. The length of a retraction stroke possible with the device of WO 2002/087470 is restricted by the length of the track provided for the slider  24  in the housing. 
     A similar device is disclosed in WO 2007/022395. In this device, a catheter outer sheath  262  is rigidly attached to a slider block  624  in the device housing. A belt  670  is provided, connected to the slider block  624  and passing around a proximal idle pulley  638  to be connected at its other end to a take-up pulley  656 . Take-up pulley  656  may be rotated by an operator via a knob  640 ,  650 , in order to wind the belt  670  onto the reel  656 . As the belt is wound onto the reel, the hub  624  is retracted so as to withdraw the outer sheath  262 . As the belt is wound onto the take-up pulley  656 , the winding diameter of the pulley increases, thereby reducing the mechanical advantage afforded, simultaneously increasing the degree of retraction for a given rotation of the knobs  640 ,  650 . A lock  646  may be provided so as to inhibit rotation of the knobs  640 ,  650  during shipping, although explanation of the operation of this lock is not given. The length of a retraction stroke of the device is again limited by the length of the track provided for sliding the proximal hub  624  within the device housing. 
     Several sheath retraction devices are disclosed in WO 2005/039448. In the first illustrated embodiment of  FIGS. 1 to 5 , a wire  160  is provided, connected to the outer tube (sheath)  130 . The wire is connected to a cam  190  in the device housing. The cam is coupled to a thumbwheel  180 , which may be rotated by a medical practitioner when using the device. Rotation of the thumbwheel  180  causes the wire  160  to be wound onto the surface  192  of the cam  190  so as to withdraw the outer tube  130  proximally with respect to the catheter inner tube  140 . Since the radius of the cam  190  increases around the cam&#39;s surface  192 , the mechanical advantage provided for retracting the outer tube  130  decreases as the wheel  180  rotates, with the degree of retraction for a given amount of rotation of the thumbwheel  180  correspondingly increasing as the thumbwheel  180  rotates. The device of WO 2005/039448 is configured to achieve only a single rotation of the thumbwheel  180 , thereby limiting the retraction stroke to a distance equal to the circumference of the cam outer surface  192 . 
     For minimally invasive surgical procedures utilizing a catheter, as with any surgical procedure, hygiene is of paramount importance. Regardless of the level of trauma caused by the surgical operation, the risks of infection must be minimized or neutralised, to ensure and aid a patient&#39;s recovery. For this reason, surgical catheter devices are usually provided with a control device already attached to the catheter&#39;s proximal end, and, in the case of a stent delivery catheter, with the stent already loaded in the catheter distal end. The surgical apparatus is typically packaged in sterile packaging, ready for use when first exposed from the packaging. 
     Because a surgical catheter is typically several times longer than the associated control device, the catheter is normally packaged in a rolled, folded or bent configuration, rather than in a fully elongated, straight configuration. This is enabled by the inherent flexibility of such catheters. In order to use the surgical apparatus, the catheter is straightened for insertion transluminally into a patient, and is then guided to the treatment site within a patient&#39;s vasculature. Typically, a guide-wire is provided, along which the catheter is run, to bring the distal end of the catheter to the treatment location. 
     Both when folding and unfolding the catheter for packaging and distribution purposes, and also when running the catheter along a guide-wire to follow a tortuous passage way, localised relative motion necessarily occurs between the catheter and the sheath. In particular, the sheath is necessary relatively inextensible in the lengthwise axial direction, to enable controlled withdrawal in use. The catheter material is typically moderately elastic, so as to provide the necessary lateral flexibility, with rigidity provided by a coil spring or other reinforcing support member as described above. As the catheter bends and flexes, localised movement between the catheter and sheath can thus occur. So that this will not result in accidental premature retraction of the sheath, the sheath distal end may be formed to extend over the end of the catheter to form an atraumatic distal tip. In other known catheters, an atraumatic tip may simply be provided on the distal end of the catheter. An element of slack or flexibility is also typically provided in the sheath retraction wire, which is itself substantially inextensible, so as to accommodate relative motion of the sheath proximal end with respect of the catheter. 
     The overall effect of the tolerances provided to allow such flexibility and relative motion means that when the operator comes to retract the sheath, the initial stages of sheath retraction may not deliver a controlled or expected degree of motion in the sheath, as the slack is taken up. In particular, at the initial stages of stent deployment, it is essential to have full control of the positioning and placement of the stent at the distal end of the surgical catheter device, to prevent accidental movement of the stent relative to the treatment site, which could result in an unintentional patient trauma. 
     There is also typically some inherent lengthwise compressive flexibility in the catheter, and some lengthwise tensile flexibility in the sheath, upon initial delivery to the treatment site, before any residual compressibility or extensibility can be taken up by proximal lengthwise tensioning of the sheath wire to place the catheter under compression along the catheter length. This initial catheter compression can produce undesirable preliminary motion at the catheter distal end as the sheath retraction device is first actuated. 
     Whilst prior art devices including two or more separate retraction mechanisms for delivering different mechanical advantages have been provided, so as to achieve slow initial sheath withdrawal for accurate placement of the stent distal end and fast subsequent sheath withdrawal for quickly releasing the stent when placed, no device has yet been produced to specifically account for the inherent residual tolerances and material resilience of the surgical catheter construction. It would therefore be desirable to provide a sheath withdrawal device constructed and arranged to accommodate specifically such residual tolerances and the material resilience of the surgical catheter construction. 
     It would also be desirable to provide indication to the user of such devices of when the sheath has been fully retracted, to ensure proper and accurate stent release and to indicate when the catheter may be retracted from the patient. 
     WO 2006/104143 discloses a body organ expansion instrument  1  having a tubular member  5  capable of sliding in a proximal direction at the distal end of a distal tube  2 . A pulling wire  6  is attached at the proximal end to a winding shaft portion  63  which retracts the wire  6  by winding wire  6  thereon. A linear member  71  is also provided to be wound onto shaft portion  63  also. The linear member is fed out from a bobbin  73 , around which it is initially wound, as the linear member  71  is wound onto shaft portion  63 . When linear member  71  is all fed out, the bobbin  73  is nonrotatable, thereby making rotational roller  61 , which winds the shaft portion  63  to retract wire  6 , incapable of further rotating. The end  71   a  of the linear member  71  is inserted into a slit  72  to be held on the shaft portion  63 . The shaft portion  63  is, however, provided only with a single slit  72 , and the length of linear member  71  must therefore be made in accordance with the length of the specific stent to be held by tubular member  5  at the distal end of distal tube  2 . 
     It would be desirable to provide means whereby the same device, or devices having substantially identical construction, can be adapted for retracting the sheath by amounts corresponding to different lengths of stents to be released, and to provide indication of full and proper sheath retraction appropriate to the length of each stent being released. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a device for moving an elongate member relative to an elongate body through which it at least partially extends, the device comprising a housing connectable to the elongate body; a mover associated with the housing and connectable to the elongate member for moving the elongate member relative to the housing and relative to a connected elongate body; and a pre-mover for adjusting an elongate member connected to the mover relative to an elongate body connected to the housing in preparation for moving the elongate member with the mover. 
     In preferred embodiments, the pre-mover resists movement of the elongate member by the mover prior to adjusting the elongate member. 
     In further preferred embodiments, the pre-mover is configured for adjusting the elongate member relative to the elongate body to reduce slack between the elongate member and the elongate body to ensure direct subsequent relative movement therebetween by the mover. 
     In yet further preferred embodiments, the pre-mover is configured to adjust the mover relative to the housing so as to relatively adjust the elongate member and the elongate body respectively connected thereto. 
     In even further preferred embodiments, the pre-mover is configured to effect a predetermined relative adjustment between the elongate member and the elongate body. 
     In yet even further preferred embodiments, the pre-mover is configured to become inoperable following adjustment of the elongate member. 
     In more preferred embodiments, the mover is operable to move the elongate member only in a first direction relative to the elongate body. 
     In yet more preferred embodiments, the device is configured for the mover to move the elongate member towards the housing relative to the elongate body, which is fixedly connected to the housing. 
     In even more preferred embodiments, the device further comprises an accumulator, by which the elongate member is connectable to the mover and a portion of the elongate member is formed as an accumulation in the housing. 
     In yet even more preferred embodiments, the device further comprises a limiter for limiting the extent of movement of the elongate member relative to the elongate body. In such embodiments, the limiter may comprise a band of substantially inextensible material which is connected at one end to, and is wound on, a spool which is mounted to the housing, the band being connected at the other end to a winding member of the mover onto which the band is wound from the spool as the mover moves the elongate member, thereby permitting movement of the mover until the band is fully unwound from the spool and thereafter preventing further movement of the elongate member by the mover. 
     In still further preferred embodiments, the elongate body comprises a surgical catheter configured for insertion into a bodily lumen, and which includes a sheath which surrounds at least a distal end portion of the catheter; the elongate member is a wire for moving the sheath relative to the catheter; and the housing is connectable to a proximal end of the catheter. 
     In yet still further preferred embodiments, the mover comprises a take-up reel mounted to rotate relative to the housing onto which the elongate member is wound to effect movement thereof. 
     In still even further preferred embodiments, the mover includes an actuator by which a user of the device may actuate the mover to move the elongate member. In such embodiments, the actuator may include a trigger pivotally mounted to the housing to pivot between an extended position and a depressed position and configured to rotate a trigger gear by which to actuate the mover. More preferably, the trigger may include a planetary gear by which to rotate the trigger gear. Even more preferably, the trigger gear is coupled to a drive shaft of the mover by a one-way clutch so as to enable the trigger gear to rotate the drive shaft when depressed towards the depressed position but preventing the trigger gear from rotating the drive shaft when returned towards the extended position, the trigger being biased towards the extended position. 
     In still more preferred embodiments, the mover includes: a toothed gear mounted to rotate relative to the housing; and a leaf spring fixedly mounted to the housing and arranged so that one end thereof engages with the teeth of the toothed gear at a non-radial angle of incidence to the gear, the leaf spring being resiliently flexible to disengage from the gear teeth and allow rotation of the toothed gear in one direction and to engage the gear teeth and substantially resist rotation of the gear in the other direction, so as to effect a ratchet arrangement to permit actuation of the mover to move the elongate member only in one direction relative to the elongate body. 
     In yet still more preferred embodiments, the pre-mover includes a rack gear configured to engage initially with a pinion gear of the mover, so that adjustment of the elongate member relative to the elongate body is effected by actuation of the rack gear to rotate the pinion gear of the mover. 
     In still even more preferred embodiments, the rack gear is mounted to a slider arm which is connected at one end to a button which is mounted to slide relative to the housing and is arranged to be actuated by a user to effect actuation of the rack gear. 
     In yet still even further embodiments, the housing forms a sealed unit in which the mover and pre-mover are mounted to be actuated by a user. In such embodiments, preferably the housing is sized and configured, and an actuator of the mover and of the pre-mover are arranged, so as to facilitate operation of the device with a single hand by a user. 
     According to a second aspect of the present invention, there is provided a device for moving an elongate member by a predetermined distance relative to an elongate body through which it at least partially extends, thereby to release a stent at the distal end of the elongate body, the device comprising: a take-up reel onto which the elongate member is wound when it is moved; and a limiter that is configured to limit further rotation of the take-up reel after a length of the elongate member has been taken up on the reel to move the elongate member said pre-determined distance, wherein the limiter comprises a tethered line, which is configured to be progressively consumed when the take-up reel is rotated until the tethered line anchors the take-up reel against further rotation, one end of the tethered line being provided with a line connector by which it may be attached to a limiter reel on which it is to be taken up to be consumed, and wherein the limiter reel is provided with plural reel connectors to which the line connector may be connected to attach the tethered line to the limiter reel. 
     In preferred embodiments, the line connector is a male connector and the reel connectors are female connectors into which the male connectors can be connected. More preferably, the line connector is a ball or cylinder joined onto the end of the tethered line. Yet more preferably, the tethered line has a total length, of which a consumable length corresponding to the length of said elongate member to be taken up may form all or a portion, the limiter being adjustable to set the consumable length to correspond to the length of said elongate member to be taken up prior to use of the device for effecting the predetermined relative movement between the elongate body and the elongate member, preferably during manufacture-and-assembly of the device. 
     According to a third aspect of the present invention, there is provided a device for moving an elongate member by a predetermined distance relative to an elongate body through which it at least partially extends, thereby to release a stent at the distal end of the elongate body, the device comprising: a take-up reel onto which the elongate member is wound when it is moved; and a limiter that is configured to limit further rotation of the take-up reel after a length of the elongate member has been taken up on the reel to move the elongate member said pre-determined distance, wherein the limiter comprises a tethered line, which is configured to be progressively consumed when the take-up reel is rotated until the tethered line anchors the take-up reel against further rotation, wherein the tethered line to be consumed has a consumable length corresponding to the length of said elongate member to be taken up, and wherein (i) a plurality of tether lines are provided having different respective consumable lengths, from which the tethered line to be consumed is selected having a consumable length which corresponds to the length of said elongate member to be taken up, or (ii) a tether line is provided having reference markings along its length indicating different consumable lengths corresponding to different lengths of said elongate member which can be taken up, the consumable length being set by the tether line being consumed, prior to moving the elongate member, up to the reference marking which indicates a remaining consumable length corresponding to the length of said elongate member to be taken up. 
     Preferably, the tethered line is consumed by being taken up on a limiter reel. More preferably, the tethered line is carried on a tether spool, and is unspooled from the tether spool while being progressively consumed during rotation of the take-up reel. 
     In further preferred embodiments, the elongate body is a catheter and the elongate member is a sheath retraction wire for proximally retracting a sheath that surrounds the abluminal surface of the stent to be released at the catheter distal end. 
     The present invention also provides a surgical apparatus including a device as set forth above and having an elongate body connected to the housing and an elongate member connected to the mover. 
     In preferred embodiments, the surgical apparatus further includes a stent carried by the elongate body for delivery to a target site of a patient and releasable from the elongate body at the target site by movement of the elongate member relative to the elongate body. Preferably, the stent is a self-expanding stent suitable to be implanted at a treatment location in a bodily lumen, and the device is configured to effect a pre-movement adjustment of the elongate member relative to the elongate body, said adjustment including a preliminary movement of the elongate member relative to the elongate body insufficient to release any portion of said stent to an expanded diameter permitting circumferential engagement with the inner wall of the bodily lumen at the intended treatment location. More preferably, said preliminary movement is insufficient to release any portion of said stent from the elongate body. Most preferably the stent is a self-expanding stent, and the device is configured to effect a pre-movement adjustment of the elongate member relative to the elongate body, said adjustment including a preliminary movement of the elongate member relative to the elongate body insufficient to release any portion of the stent to an expanded diameter of more than 110% of the stent unreleased diameter, preferably 105% or less of the stent unreleased diameter. 
     According to a fourth aspect of the present invention, there is provided a stent delivery device, comprising: a housing connectable to an elongate body; a mover coupled to a housing and connected to an outer sheath disposed over a stent compressed about a distal end of the elongate body; and a pre-mover associated with the housing having a locked position engaging the mover and an unlocked position in which the mover is released, wherein movement of the pre-mover from the locked position to the unlocked position prepares the outer sheath for deployment of the stent. 
     According to a fifth aspect of the present invention, there is provided a stent delivery device, comprising: a take-up reel onto which a sheath retraction line is wound when an outer sheath which surrounds a compressed stent at a distal portion of the delivery device is retracted; and a limiter which limits the length of the sheath retraction line which may be taken up on the reel so as to limit retraction of the outer sheath, wherein the limiter comprises a limiter reel and a tethered line which is progressively consumed by the limiter reel when the take-up reel is rotated and which anchors the take-up reel against further rotation when fully consumed, one end of the tethered line being provided with a line connector attached to the limiter reel, and wherein the line connector is connected to one of plural reel connectors disposed around the limiter reel. 
     According to a sixth aspect of the present invention, there is provided a stent delivery device, comprising: a take-up reel onto which a sheath retraction line is wound when an outer sheath which surrounds a compressed stent at a distal portion of the delivery device is retracted; and a limiter which limits the length of the sheath retraction line which may be taken up on the reel so as to limit retraction of the outer sheath, wherein the limiter comprises a limiter reel and a tethered line connected to the limiter reel, which is progressively consumed by the limiter reel when the take-up reel is rotated, wherein the tethered line has a consumable length corresponding to the retraction limit of the outer sheath, and wherein (i) one or more further tether lines are provided having respective consumable lengths different from the length of the tethered line connected to the limiter reel, or (ii) the tether line connected to the limiter reel has reference markings along its length indicating different available consumable lengths, the consumable length which corresponds to the retraction limit of the outer sheath being indicated by one said reference marker. 
     Embodiments of the first and fourth aspects of the invention set forth above are able to provide adjustment prior to bulk actuation of the mover, ensuring that tolerances are accommodated and that motion between the mover and housing translates directly into proportional motion between the elongate member and elongate body, thereby improving control accuracy with the device. 
     In particular for stent delivery catheter embodiments, unexpected deflection at the catheter tip as the sheath retractor is first activated can be reduced or eliminated. 
     Furthermore, an effective locking mechanism may be achieved, with certain embodiments, to prevent premature or accidental actuation of the mover. 
     Preferred embodiments are also able to accommodate different stroke length requirements, as the stroke length need not be restricted by the length of the housing or its components. 
     Embodiments of the second, third, fifth and sixth aspects of the invention set forth above can indicate to the user of the device, when a stent at the elongate body distal end has been fully released, preventing premature catheter withdrawal or unnecessary further movement of the elongate member, and are readily adaptable to different lengths of stent which the devices may be employed to release. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To enable a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:— 
         FIG. 1  shows an exploded perspective view of a catheter sheath retraction device as one embodiment of a device in accordance with the present invention, detailing the major internal and external component parts of the device; 
         FIG. 2  shows a cross-sectional left-hand-side view of the catheter sheath retraction device of  FIG. 1 ; 
         FIG. 3  shows a plan view of the main internal components forming the sheath retraction mechanism of the catheter sheath retraction device of  FIG. 1  and  FIG. 2 ; 
         FIG. 4  shows a similar plan view of the components of  FIG. 3 , with the planetary gear omitted, indicating how a trigger gear is connected to the main shaft of the sheath retraction mechanism by virtue of a one-way clutch; 
         FIG. 5  shows a left-hand-side view of the working components of the retraction mechanism of the catheter sheath retraction device of  FIGS. 1 to 4 ; 
         FIG. 6  shows a right-hand-side view of the retraction mechanism of the catheter sheath retraction device of  FIGS. 1 to 5 ; 
         FIG. 7  shows a perspective exploded view of the components of  FIGS. 5 and 6 ; 
         FIG. 8  shows a detailed view of the trigger actuator components of the catheter sheath retraction device of  FIGS. 1 to 7 ; 
         FIG. 9  shows a view of the components of a pre-mover assembly of the catheter sheath retraction device of  FIGS. 1 to 8 ; and 
         FIG. 10  shows an exploded perspective view of the main rotational shaft at the center of the catheter shaft retraction device of  FIGS. 1 to 9 , and the rotary components to be mounted thereto. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is directed to a specific example of a catheter sheath retraction device, suitable for connection to the proximal end of a stent delivery catheter (elongate body) for retracting the catheter outer sheath, by virtue of a sheath retraction wire (elongate member), so as to expose a stent at the distal end of the catheter. It will be appreciated, however, that the utility of the disclosed device and the components of the actuator mechanism may find utility in alternative applications where actuation to achieve relative motion between two elongate components is required. 
     In the present specification, as is usual in this technical field, the term “proximal” refers to the direction or end of the device which, when in use, is generally towards the medical practitioner, and the term “distal” refers to the opposite sense, i.e. towards the patient or away from the medical practitioner. 
     The following description is made with reference to  FIGS. 1 to 10  generally, and with reference to specific ones of the figures, where appropriate. The catheter sheath retraction device  1  generally includes a housing  10 , a mover  20 , a trigger  30 , a pre-mover  40  and a limiter  50 . 
     As shown in  FIG. 1 , the housing  10  is formed of a left housing  11 , a right housing  12  and a lower housing  13 , which together form an outer shell of the catheter sheath retraction device  1 . The housing components will typically be formed of any suitable surgically compatible material to provide a substantially rigid outer shell. The housing is formed in an ergonomic shape, including ridged regions to provide grip for a user&#39;s hand. The housing is shaped so as to rest comfortably within one hand of a user, and to allow actuation of the trigger  30  with a single hand by a user. The device is furthermore configured to be substantially symmetric along its longitudinal axis, to permit facile use with either hand. The left  11 , right  12  and lower  13  housing components are preferably moulded separately before being joined together. The joints may be effected using suitable adhesive means, to form a sealed housing unit containing the components of the sheath retraction mechanism therein. Preferably, the housing components  11 ,  12  and  13  are provided with resilient male/female connecting portions, which allow the housing components to be clipped together, as well as the joints being glued. 
     As is apparent from  FIG. 2 , the housing is provided with a rear connector  15  and a front connector  16 , by which to provide a fluid-tight connection between the housing and a surgical catheter to be held therein. Connectors  15  and  16  preferably provide external access to the internal fluid passageways of the surgical catheter, for example, so as to introduce flushing fluid into the catheter prior to use, and to allow insertion and retraction of a guide wire through the catheter. 
     A conical nose or strain relief element  18  is provided at the distal end of the housing  10 , to provide a rigid connection with the proximal end of a catheter. The strain relief element  18  enables the user to apply controlled forces to the surgical catheter, and relieves localised compression and bending forces at the catheter proximal end where it is connected to the housing  10 . Front connector  16  and pusher  18  form the distal hub by which a reinforcing member of the surgical catheter is held in place relative to housing  10  to transfer compressive stresses to the housing. 
     When a surgical catheter is connected to the catheter sheath retraction device  1 , the connector  16  is configured to allow a sheath pull wire to extend distally into the housing from the catheter. The sheath retraction device  1  is provided with a mover  20  for retracting the sheath pull wire proximally into the housing  10 . 
     As described in WO 2005/053574, the sheath pull wire can be connected to the sheath by, for example, first and second metal rings, one inside the other, and sandwiching the sheath so that one of the metal rings is inside the sheath annulus and the other is outside the sheath annulus. The inside metal ring would normally be welded, soldered or brazed to the distal end of the sheath pull wire (adhesives being generally disfavoured in failure-critical applications in such stent delivery devices), while the outer metal ring can be swaged down onto the sheath to press the sheath onto the inner metal ring. 
     As best seen in  FIG. 3 , the mover  20  is provided with a mover reel  21 , onto which the sheath pull wire is to be wound as the mover reel  21  rotates. As can be seen, the mover reel  21  is formed with a circumferential V-shaped groove into which the sheath pull wire is received. The mover reel  21  is provided with slots or notches around its circumference, into which an end connector of the sheath pull wire can be received, to connect the sheath pull wire to the mover reel  21 . 
     Although a sheath pull wire is mentioned as a specific, preferred example of an elongate member by which to retract the catheter sheath, it is of course possible in alternative configurations to utilise a band, chain or other flexible member to connect the sheath to the mover  20 . As the mover reel  21  is rotated, the sheath pull wire is wound onto the mover reel  21 , in the V-shaped groove, thereby retracting the sheath and accumulating the sheath pull wire on the mover reel  21 . Accordingly, as the sheath wire is retracted into the housing and wound on the mover reel  21 , the sheath is retracted towards the catheter proximal end, as the catheter itself is held in place by the housing  10  and strain relief element  18 . 
     As shown in  FIG. 3 , in particular, the mover reel  21  is mounted on a mover shaft  24  along with a number of further components. To enable the mover shaft  24  to rotate in the centre of the housing, it is mounted between a pair of left and right support frames  28  and  29 , respectively. Holes are provided in support frames  28  and  29  to support the shaft  24 , and to allow the shaft  24  to rotate substantially freely. Left and right support frames  28  and  29 , respectively, are configured to be fixedly mounted in the respective left and right housing portions  11  and  12 . 
     As shown in  FIG. 3 , the mover reel  21  and mover shaft  24  are provided, on the left side of the catheter sheath retraction device  1 , with a mover toothed gear  22 . Mover toothed gear  22  is rigidly coupled with the mover reel  21 , either via the mover shaft  24 , or through being constructed as a unitary component therewith. In the present example, as shown in  FIG. 10 , the mover reel  21  and mover toothed gear  22  are formed as a unitary component, along with a limiter reel  53 , to be described further below. The mover reel  21  and toothed gear  22  are directly coupled to the shaft  24 , to rotate together therewith. 
     The mover shaft  24  is further provided with a trigger gear  26 . As shown in  FIG. 4 , trigger gear  26  is not coupled directly to the mover shaft  24 , but is engaged therewith via a one-way clutch arrangement. Specifically, a one-way clutch  25  is provided on mover shaft  24 . Clutch  25  is a standard component for providing a rigid connection for transmitting forces from the trigger gear  26  to the mover shaft  24  in a driving direction, and for allowing the trigger gear  26  to rotate freely of the mover shaft  24  in the opposite direction. 
     As best seen in  FIG. 10 , for example, the trigger gear  26  is formed with a cylindrical through-hole  27  into which the one-way clutch  25  is press-fitted. Grooves in the one-way clutch  25  outer surface deform the inner surface of through-hole  27  to fixedly engage the clutch  25  in the trigger gear  26 . 
     The one-way clutch  25  is configured to engage with mover shaft  24  so as to transmit drive from the trigger gear  26  to the mover shaft  24  in a first, winding direction (anti-clockwise as shown in  FIGS. 1, 2, 5, 7 and 9  and clockwise as shown in  FIGS. 6, 8 and 10 ). When rotated in this winding direction, the internal components of one-way clutch  25  engage mover shaft  24  to transmit drive from the trigger gear  26  to the mover shaft  24 . When the trigger gear  26  is rotated in the opposite sense, the internal components of one-way clutch  25  are configured to disengage from mover shaft  24 , allowing the trigger gear  26  to rotate separately from the mover shaft  24 . 
     Accordingly, the trigger gear  26  may be rotated so as to cause the mover reel  21  to rotate in a first, winding direction, thereby to wind the sheath pull wire onto the mover reel  21 . The trigger gear  26  will not, however, cause the mover reel  21  to rotate in the reverse direction, thereby unwinding the sheath pull wire from the mover reel  21 . 
     Of course, in practice, the one-way clutch  25  is capable of transmitting some torque to the mover shaft  24 , even in the non-winding direction. To prevent these unavoidable minimal forces from transmitting drive from the trigger gear  26  to the mover shaft  24  in the reverse direction, the catheter sheath retraction device  1  is provided with a leaf spring  23 , as shown in  FIGS. 1 and 3 . The leaf spring  23  is mounted to the housing  10 , in the present example to the left housing  11 , to be rigidly and fixedly supported at one end thereof. The leaf spring  23  is mounted so that the other, free end thereof is in contact with the teeth of the mover toothed gear  22 , and projects into the toothed region at an angle oblique to the radial direction of the toothed gear  22 . By this arrangement, the leaf spring  23  is configured to allow the toothed gear  22  to rotate in a first direction (anti-clockwise, as shown in  FIGS. 1, 2, 5, 7 and 9 ), due to the teeth of the fixed gear  22  deflecting the resilient leaf spring  23  radially outwardly with respect to the toothed gear  22  so as to disengage it from the teeth as the toothed gear  22  rotates. 
     As best seen in  FIG. 9 , however, when the toothed gear  22  attempts to rotate in the opposite sense (clockwise, as shown in  FIG. 9 ), the oblique interface of the free end of the leaf spring  23  with the teeth of the toothed gear  22  causes the teeth of the toothed gear  22  to engage the leaf spring  23  in a longitudinally compressive sense, rather than in a direction transverse to the leaf spring  23  long axis. Accordingly, the leaf spring  23  is not caused to deflect radially outwardly, and instead engages positively with the teeth of the toothed gear  22 , preventing rotation in the reverse, non-winding direction. 
     Accordingly, by the combined operation of the one-way clutch  25  and the ratchet effect produced by the leaf spring  23 , a drive system is configured for providing uni-directional drive in the winding direction of the mover reel  21  via the mover shaft  24 . Furthermore, the degree of rotation of the mover shaft  24  imparted by rotation of the trigger gear  26  in the winding direction is not disturbed by subsequent reverse rotation of the trigger gear  26 , such as when the trigger  30  is released. 
     As shown in detail in  FIGS. 6, 7 and 8 , the catheter sheath retraction device  1  is provided with a trigger  30 . Trigger  30  includes a user-engagement portion  33  which projects through an opening in the housing  10  for engagement and manipulation by a user of the catheter sheath retraction device  1 . The trigger  30  is pivotally mounted in the housing  10  by a trigger pivot shaft  31 , about which the trigger  30  prescribes a part-circular, arcuate path. The trigger pivot shaft  31  may be mounted in the housing  10  either in further holes provided in the left and right support frames  28  and  29 , or, as in the present example, directly mounted in a shaft receiving hole in each of the left and right housings  11  and  12 . 
     The trigger user engagement portion  33  is connected to a planetary gear  32 , which is also constrained to follow a part-circular arcuate path as the trigger  30  is depressed by a user pressing on the trigger user engagement portion  33 . The trigger  30  is mounted in the housing  10  so that the planetary gear  32  engages with the trigger gear  26  mounted on the mover shaft  24 , as seen in  FIGS. 3 and 8 , for example. Accordingly, each depression of the trigger  30  rotates the trigger gear  26  in the winding direction, so as to wind the mover reel  21  by a certain amount. The trigger  30  is also provided with a trigger spring  34  for biasing the trigger from a fully depressed position to an extended position fully projected, within the trigger&#39;s arc of travel, from the housing  10 . After the trigger  30  has been depressed from the extended position to the depressed position, and then released, the spring  34  returns the trigger  30  to the extended position through its biasing action. Although a coil spring is specifically exemplified in the illustrated embodiment, any suitable biasing means may be used to return the trigger to the extended position after each depression. This trigger return motion causes the trigger gear  26  to reverse in the opposite sense to the winding direction. However, as noted above, no drive is transmitted to the mover reel  21  in the unwinding direction, by virtue of the one-way clutch  25 . Again, as noted, any minimal forces attempting to rotate the mover shaft in the unwinding direction are resisted by the leaf spring  23  engaging with the teeth of the fixed gear  22 . 
     In this way, a plurality of sequential depressions of the trigger  30  can be used to fully retract the catheter sheath by winding the sheath pull wire on the mover reel  21 . Each full depression of the trigger  30  will retract the sheath pull wire by a substantially constant pre-determined amount. Within practical limits, the trigger  30  can be utilised to wind up a sheath pull wire of substantially any length, unconstrained by the physical length of the housing  10 . Accordingly, the same housing  10  and retraction mechanism, comprising the mover  20  and trigger  30 , can be utilised to retract a catheter sheath by substantially any given length, without needing to modify the components of the housing  10 , mover  20  or trigger  30 . 
     The distance by which any sheath must be retracted is essentially the same as the length of the stent to be deployed, typically 20 mm to 200 mm. The sheath may run along substantially the entire length of the catheter, which would have a typical length from 60 cm to 135 cm, although catheter lengths up to 200 cm are also known, for endoscopic applications and such like. Alternative sheath designs include a sheath only along the distal portion of the catheter delivery system, in which case the length of such a sheath would normally be from 100 mm to 400 mm, suitable for use with the existing standard lengths of stents to be deployed. 
     On the other hand, it is preferable for the operator of the catheter sheath retraction device to have an indication of when the sheath at the distal portion of the catheter has been fully retracted, such that a stent mounted at the distal end of the catheter has been released. To this end, a limiter  50  is provided. Limiter  50  is mounted, in the present example, in a proximal portion of the housing  10 . The limiter includes a tethered line, which is realised in this example by a spool  51  on which a band  52  is wound. In a preferred embodiment, the limiter band  52  is provided of a fixed length, with reference markings to indicate particular positions along the band  52  which each denote an amount by which the band  52  is to be unwound (and rolled-up onto limiter reel  53 ). The amount provided by each marker provides for a consumable length of the band  52  remaining spooled on the limiter spool  51  which corresponds to (but is not necessarily equal to) the distance by which a particular sheath to be retracted by the catheter sheath retraction device  1  is to be retracted. During manufacture or set-up of the catheter sheath retraction device  1 , the band  52  is unspoiled from spool  51  and around onto limiter reel  53  until the marker corresponding to the required sheath retraction distance is revealed, leaving the spooled portion of band  52  with a remaining consumable length corresponding to said required sheath retraction distance. 
     In practice, there are twelve standard lengths of stent (there are twelve stent lengths commonly adopted within the medical devices industry, as an informal standard, ranging from 20 mm to 200 mm). Accordingly, each band  52  may be provided with eleven or twelve such markers, allowing accurate adjustment of the band  52  consumable length to any one of the twelve standard lengths. Stents up to 300 mm in length are also contemplated, and bands of appropriate length having any number of suitable markers may of course be provided to accommodate any such other stent length. Most preferably, the adjustment of the band  52  consumable length is undertaken during manufacture and assembly of the catheter sheath retraction device  52 . As an alternative, a specific limiter band  52  may be selected which has a particular length, in particular including a consumable portion having a length corresponding (but not necessarily equal) to the distance by which a particular sheath is to be retracted by the catheter sheath retraction device  1 . 
     The unspooled free end of the limiter band  52  is provided with a connector, such as a ball or cylinder welded or otherwise joined onto the end of the band  52 , for example. The band  52  is substantially inextensible in its lengthwise direction. The free end of the limiter band  52  provided with the connector is attached to the limiter reel  53 , which is provided in the present example mounted on the shaft  24  between the mover reel  21  and the toothed gear  22 . 
     As visible in  FIGS. 3, 4, 6, 7, 8, and 10 , the limiter reel  53  is provided with one or more female connector portions around its circumference, into which the connector on the free end of the limiter band  52  may be inserted and retained. Preferably, the limiter reel  53  is provided with plural female connector portions, which enable the free end of the limiter band  52  to be attached at a variety of positions around the limiter reel. This enables the mover reel  21  to be rotated to a suitable initial position in dependence on the initial winding-on of the sheath pull wire onto the mover reel  21 , and for connecting the limiter band to the limiter reel to provide the correct consumable length independently of the rotational position of the mover reel  21 . The length of the limiter band to be consumed can therefore be adjusted with greater freedom, unconstrained by the position of the sheath pull wire. 
     In operation of the catheter sheath retraction device, as the mover shaft  24  rotates to wind the sheath pull wire onto the mover reel  21 , the limiter band  52  is similarly wound onto the limiter reel  53 , as it is unspooled from the spool  51 . When the pre-determined length of the limiter band  52  has been unspooled from the spool  51  and wound on the limiter reel  53 , the inextensible limiter band  52  prevents further rotation of the limiter reel  53 , and consequently prevents further rotation of the mover shaft  24  and mover reel  21 . This indicates to the user that the catheter sheath retraction device  1  has fully retracted the catheter sheath. 
     Accordingly, by simply adjusting the consumable length of limiter band  52  during manufacture or set-up of the retraction device, or by substituting the limiter band  52 , according to the length of sheath to be retracted, the further components of the catheter sheath retraction device  1  can be left unaltered, regardless of the length of the catheter sheath to be retracted, thereby rendering identical (or virtually identical) ones of the device applicable to numerous sheath withdrawal applications with only this minor modification. 
     Turning now to  FIG. 9 , in particular, a pre-mover  40  of the catheter sheath retraction device  1  will be described. The pre-mover  40  is preferably a separate and distinct mechanism from any actuator device, such as trigger  30 , for effecting retraction of the sheath, and is dissimilar in operation from incremental or bulk retraction actuators known in the prior art. 
     The illustrated pre-mover  40  includes a slider arm  43  provided with a slider arm groove  44  extending partially along the length thereof. Slider groove  44  is mounted on a slider pin  47  provided in the housing  10 . Slider pin  47  may be formed as part of the left housing  11 , or may form part of the left support frame  28 . Slider arm  43  is thus constrained to move so that the slider groove  44  travels along slider pin  47 . 
     The slider arm  43  is provided at its proximal end with a pre-mover rack gear  45 . Rack gear  45  is configured to engage with the mover toothed gear  22 , so that movements of the slider arm  43  in the proximal direction (in the right-hand direction as shown in  FIG. 9 ) will cause the rack gear  45  to rotate the toothed gear  22  in the winding direction (anticlockwise in  FIG. 9 ). 
     The pre-mover  40  is provided at the distal end with a pre-mover finger button  41 , which is mounted on a pre-mover button slider  42 . The pre-mover button slider  42  is pivotally connected to the distal end of the slider arm  43 , mounted on a pivot shaft  46  of the slider arm  43  (see  FIG. 6 ). 
     The pre-mover button slider  42  is mounted in a track provided in the housing  10 , as shown in  FIGS. 1 and 2 . The button slider  42  is slidable along the track in the housing between a distal, locking position and a proximal release position. The pre-mover finger button  41  is configured to project outside the housing  10  when the button slider  42  is mounted in the track of the housing, as shown in  FIG. 2 , to enable manipulation by a user of the catheter sheath retraction device  1 . The finger button  41  is configured for retraction by a user&#39;s single digit in the proximal direction. 
     As visible in  FIG. 1 , notches or dimples may be provided along the track in which the button slider  42  is mounted. In particular, a first notch, or pair of notches, is provided near to the distal end of the track and a second notch, or pair of notches, is provided near to the proximal end of the track. These notches provide a tactile indication to a user of the catheter sheath retraction device  1  to indicate, firstly, when the slider button has been retracted from the distal locking position so as to effect initial release of the button slider  42  from the locking position, and, secondly, when the slider button  42  has been fully retracted. 
     With the button slider  42  in the distal locking position, the pre-mover rack gear  45  is engaged with the teeth of the toothed gear  22  of the mover  20 . The inclination of the track along which the button slider  42  can travel, in combination with the provision of the distal notches in the slider track, means that, with the pre-mover in the locking position, slider arm  43  is immobilised so that the toothed gear  22  is substantially locked against rotation due to the pre-mover rack gear  45  holding the toothed gear  22  stationary. Accordingly, the pre-mover  40  functions as a locking device to prevent premature unintentional depression of the trigger  30  and consequential retraction of the sheath pull wire through rotation of the mover reel  21 . 
     The pre-mover finger button  41  may readily be used, however, due to its different alignment to slider arm  43 , to proximally retract the button slider  42  along the track provided in the housing, thereby causing slider arm  43  to move proximally, with groove  44  tracing along the pre-mover slider pin  47 . This causes the rack gear  45  to rotate the toothed gear  22 , at the same time rotating the mover shaft  24  and mover reel  21 , in the winding direction. 
     The track along which button slider  42  is configured to run, and the pre-mover rack gear  45 , both have a short fixed length. When the finger button  41  has been retracted to the proximal release position, the slide arm  43  has been displaced proximally to a position in which the rack gear  45  is disposed entirely proximally of the toothed gear  22 , and is disengaged therefrom, allowing the toothed gear  22  and mover shaft  24  thereafter to rotate freely of the rack gear  45 . (In alternative embodiments where the pre-mover is not implemented by a linear slider, other means may be provided by which to disengage the pre-movement mechanism from the toothed gear  22  or equivalent component. For example, were a pivotally-mounted rack gear to be used, the rack gear might be disengaged by being pivoted downwardly out of mesh with the toothed gear  22  teeth, or in other arrangements might be displaced out of mesh by moving the rack and toothed gear along the toothed gear  22  axis relative to each other.) 
     The pre-mover  40  is provided in order to effect a small pre-determined rotation of the toothed gear  22  in the winding direction, preferably without effecting any notable retraction or peeling at the sheath distal end or tip. The purpose of the pre-mover  40  is not to effect any bulk movement or retraction of the catheter sheath by winding any substantial portion of the sheath pull wire onto the mover reel  21 . Instead, the pre-mover  40  is configured to effect a pre-movement adjustment of the pull wire and catheter sheath relative to the catheter, in preparation for retraction of the sheath using the trigger  30 . This adjustment of the sheath pull wire by pre-winding the mover reel  21  by a pre-determined small amount has two effects. Firstly, the initial movement can take up any slack in the sheath pull wire which may have resulted from, or is provided to allow, the flexible bending movements which the catheter undertakes when being folded or inserted into a bodily lumen. Accordingly, any slack in the sheath pull wire is taken up to ensure a taut direct connection between the mover reel  21  and the catheter sheath to be retracted. Secondly, the pre-movement adjustment can further function to pre-tension the catheter, by pre-tensioning the pull wire and the catheter sheath at the distal portion of the catheter, thereby producing a corresponding compressive force along the catheter length, so as to reduce any remaining compressive flexibility along the catheter length. This serves to pre-tension the retraction mechanism, with the sheath pull wire being pulled taut between the sheath and the mover reel  21 . With the sheath pull wire pre-tensioned, and with the pre-mover in the proximal release position, the leaf spring  23  functions to prevent motion of the mover reel  21  in the unwinding direction (due to tension in the pull wire), and to maintain the sheath and pull wire in the adjusted pre-tensioned state. 
     Accordingly, by providing the pre-mover  40 , a preliminary adjustment of the sheath pull wire can be effected, to prepare the catheter for sheath retraction. This ensures that subsequent actuation of the trigger  30  will result in a direct corresponding motion of the sheath, as the mover reel  21  winds the sheath pull wire to proximally retract the catheter sheath. This direct pre-tensioned condition provides greater tactile feel for a medical practitioner using the catheter sheath retraction device  1 , and improves the accuracy by which the stent being released at the distal end of the device can be positioned and released at the treatment site. The pre-mover  40  further functions to operate as a locking device, securing the retraction mechanism of the catheter sheath retraction device  1  against accidental, premature retraction of the sheath pull wire, such as during transport and during insertion of the catheter into a patient. 
     From the foregoing, it will be appreciated that the pre-movement adjustment is effected to prepare the stent delivery device provided with such a catheter sheath retraction device for bulk sheath withdrawal and stent release. Although in an ideal configuration the pre-movement adjustment would not cause the catheter sheath to be retracted relative to the catheter, in practice some retraction of the sheath may occur, even to the extent that the stent extreme distal end may become exposed at the catheter distal end portion. 
     This is to be contrasted, however, with the arrangement in two-stage catheter sheath retraction systems. In such systems, the catheter sheath is firstly partially withdrawn, part way along the stent, using an actuator with a high mechanical advantage so as to effect a controlled withdrawal at a slow rate. By this process, the stent distal end is gradually released from the catheter sheath to expand into contact with the wall of the bodily lumen into which the stent is being implanted, allowing the stent distal end to be positioned at the treatment location with high precision. When the stent distal end has been positioned, the catheter sheath is then secondly withdrawn the remaining distance to fully release the stent, using an actuator with a low mechanical advantage to effect sheath withdrawal at a fast rate. This ensures that once the stent distal end is positioned the stent can be quickly fully released, to reduce the chances of inadvertently causing trauma to the patient through relative movement between the stent and the vessel wall after the stent distal end is engaged with the bodily lumen. 
     With the pre-movement adjustment presently provided, any sheath retraction is preferably insufficient to expose the stent distal end portion from beneath the sheath. Even if the stent extreme distal end portion is partially exposed, the degree of exposure will be insufficient to allow the stent to expand into circumferential engagement with the wall of the bodily lumen into which the stent is to be implanted. In terms of the stent diameter, the stent is preferably exposed during pre-movement adjustment only by an amount permitting radial expansion by up to 10% or less of the delivery diameter of the stent, more preferably by up to only 5% or less. For typical catheter and stent dimensions, the pre-movement adjustment will represent a maximum sheath withdrawal of 5 mm to 10 mm at the distal end. 
     Although a specific example of a catheter sheath retraction device  1  has been described and illustrated, it will be appreciated that numerous modifications may be effected based upon the same operational principles by which the described device functions. 
     For example, the pre-mover  40  may be provided by alternative means for adjusting the sheath pull wire prior to bulk retraction of the sheath relative to the catheter, other than by using a slider arm  43  and rack gear  45 . Even if a rack gear based mechanism is utilised, the slider arm need not be configured to provide a secure locking function, and alternative locking devices may be utilised. Similarly, the pre-mover button could be mounted at the proximal end of the catheter sheath retraction device, to adjust the mover  20  by a proximal pulling retraction, rather than a proximal pushing retraction of the rack gear  45 . Numerous further alternatives are clearly possible. 
     Similarly, the advantages achieved by the pre-mover  40  are not restricted to embodiments utilising a trigger  30  for actuating the mover reel  20  to retract the sheath pull wire. Various actuation mechanisms utilizing thumb wheels, knobs, triggers and sliders are known for retracting a sheath pull wire, of which the skilled reader will be fully aware. 
     A number of published documents have been mentioned above. Many of these are from the present proprietor, and represent steps along the way to the present invention. It is intended that the disclosures of these mentioned earlier documents are incorporated by reference in their entirety into the teaching and disclosure of the present specification, as if each individual publication or patent application were specifically and individually put forth herein.