Patent Publication Number: US-2017367862-A1

Title: Self-expandable stent delivery system

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/JP2016/054155 filed on Feb. 12, 2016, which claims priority to Japanese Application No. 2015-048759 filed on Mar. 11, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a self-expandable stent delivery system. 
     BACKGROUND ART 
     A stent is generally used for a treatment that expands a lesion portion, such as a stenosed site and a clogged portion, generated in body lumens such as blood vessels, bile ducts, trachea, esophagus, and urethra. 
     The stents can include a type which is expanded by a balloon having a stent mounted thereon (balloon expandable stent) and a type which expands by itself by removing a member which restricts expansion from the outside (self-expandable stent). 
     The self-expandable stent expands by itself without constraint and thus does not require an expanding operation such as that required for the balloon expandable stent. The self-expandable stent having a flexibility compared to stents that do not expand by themselves may be applied to lesion portions having a meandering shape or a curved shape, and are widely used in medical sites. When indwelling the self-expandable stent as described above in a lesion portion, a self-expandable stent delivery system for delivering the self-expandable stent to the lesion portion may be used. 
     For example, International Publication No. WO 2010/093017 A1 discloses a self-expandable stent delivery system configured to deliver a self-expandable stent in a state of being accommodated at a distal side of a catheter having an inner tube and an outer tube disposed in a periphery of the inner tube into a body lumen, move the outer tube to a proximal side by pulling a pull wire fixed to the outer tube to the proximal side by an operation on the operator&#39;s side, discharge the self-expandable stent from the catheter and expanding the self-expandable stent so that the self-expandable stent is indwelled at the lesion portion. 
     In the case where a configuration in which the outer tube is moved by a pushing and pulling operation of the pull wire as described above is employed, when the pull wire is pulled toward the operator&#39;s side (proximal side) by an operation unit, a pull force may act reversely to pull the pull wire toward an opposite side (distal side) to the pulling direction and thus the outer tube may inadvertently be moved. Therefore, in the self-expandable stent delivery system described above, occurrence of inadvertent movement of the outer tube can be prevented by imposing a limitation on rewinding (feeding) of the pull wire toward the distal side by imposing a limitation on the movement of the pull wire toward the distal side. 
     However, once the pull wire is pulled, the operation of moving the pull wire toward the distal side can be forcedly limited, and thus the pull wire cannot be fed toward the distal side again. For example, when indwelling the self-expandable stent in the body lumen, the pull wire may be pulled in a state in which the self-expandable stent is positioned in the vicinity of an indwelling position and then the pull wire may be moved back toward the distal side for adjusting the indwelling position (discharging position) again to achieve a state in which the self-expandable stent is accommodated in the outer tube again, and then subsequent operation may be performed continuously. However, in the case of the self-expandable stent delivery system of the related art, such an operation can hardly be achieved. For example, if the operation unit is capable of moving the pull wire reversibly toward the distal side and toward the proximal side when performing such an operation, the operability of the self-expandable stent delivery system will be further improved. 
     SUMMARY 
     Accordingly, in order to solve the above-described problem, a self-expandable stent delivery system is disclosed, which is capable of reversibly moving a pull wire toward a distal side of the self-expandable stent delivery system and toward a proximal side of the self-expandable stent delivery system to achieve an improvement of the operability of the self-expandable stent delivery system. 
     A self-expandable stent delivery system of the present disclosure includes: an inner tube provided with a guide wire lumen to which a guide wire is to be inserted; a self-expandable stent disposed around a distal side of the inner tube in a state of being compressed radially inward when being inserted into a body lumen and configured to be expandable outward to restore a shape before being compressed when being indwelled in the body lumen; an outer tube configured to be capable of accommodating the self-expandable stent in an inner lumen thereof by being disposed on an outer surface side of the inner tube and discharging the self-expandable stent accommodated in the inner lumen by being moved toward the proximal side with respect to the inner tube; a pull wire configured to be capable of pulling the outer tube toward the proximal side; and an operation unit that operates advancing and retracting movement of the pull wire. The operation unit includes: a holding portion configured to hold the pull wire so that the pull wire is movable toward the distal side and toward the proximal side; and a switching portion configured to be capable of switching the pull wire held by the holding portion between limitation of movement toward the distal side and release of the limitation. 
     An operation unit is disclosed that operates advancing and retracting movement of a pull wire for a self-expandable stent delivery system, the self-expandable stent delivery system including a self-expandable stent disposed around a distal side of an inner tube in a state of being compressed radially inward when being inserted into a body lumen and configured to be expandable outward to restore a shape before being compressed when being indwelled in the body lumen, and wherein the pull wire is configured to pull an outer tube accommodating the self-expandable stent in an inner lumen toward a proximal side of the inner tube, the operation unit comprising: a holding portion configured to hold the pull wire so that the pull wire is movable toward a distal side of the self-expandable stent delivery system and toward a proximal side of the self-expandable stent delivery system; and a switching portion configured to be capable of switching the pull wire held by the holding portion between limitation of movement toward the distal side of the self-expandable stent delivery system and release of the limitation. 
     A method is disclosed of indwelling a self-expandable stent into a living body, the method comprising: inserting a self-expandable stent delivery system into a lumen of the living body, the self-expandable stent delivery system including an inner tube provided with a guide wire lumen configured to receive a guide wire, the self-expandable stent disposed around a distal side of the inner tube in a state of being compressed radially inward when being inserted into a body lumen and configured to be expandable outward to restore a shape before being compressed when being indwelled in the body lumen, and an outer tube configured to be capable of accommodating the self-expandable stent in an inner lumen of the outer tube by being disposed on an outer surface side of the inner tube; advancing and retracting movement of a pull wire with an operation unit, the operation unit including a holding portion configured to hold the pull wire so that the pull wire is movable toward a distal side of the self-expandable stent delivery system and toward a proximal side of the self-expandable stent delivery system, and a switching portion configured to be capable of switching the pull wire held by the holding portion between limitation of movement toward the distal side of the self-expandable stent delivery system and release of the limitation; and discharging the self-expandable stent accommodated in the inner lumen by moving the outer tube toward a proximal side with respect to the inner tube with the pull wire. 
     According to the self-expandable stent delivery system configured as described above, the pull wire may not only be moved toward the proximal side by being pulled, but also be moved toward distal side again even after having been moved once toward the proximal side. Accordingly, a further improvement of the operability of the self-expandable stent delivery system can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general configuration drawing illustrating a self-expandable stent delivery system according to a first exemplary embodiment. 
         FIG. 2  is a cross-sectional view of a distal side portion of the self-expandable stent delivery system according to the first exemplary embodiment. 
         FIG. 3  is an explanatory drawing illustrating an internal structure of an operation unit of the self-expandable stent delivery system according to the first exemplary embodiment. 
         FIG. 4  is an exploded front view of the operation unit of the self-expandable stent delivery system according to the first exemplary embodiment. 
         FIG. 5  is a drawing illustrating a state in which the operation unit of the self-expandable stent delivery system according to the first exemplary embodiment is gripped. 
         FIGS. 6A and 6B  illustrate explanatory drawings of the operation unit of the self-expandable stent delivery system according to the first embodiment, in which  FIG. 6A  illustrates a state in which an engagement release portion is moved to the distal side, and  FIG. 6B  illustrates a state in which an engagement release portion applies a pressing force to an engaging portion. 
         FIGS. 7A and 7B  illustrate drawings of a self-expandable stent delivery system according to a comparative example, in which  FIG. 7A  illustrates a state in which a pull wire insertion tube is bent when the pull wire is pulled and  FIG. 7B  illustrates a state in which the self-expandable stent is released when removing the pull wire insertion tube. 
         FIGS. 8A and 8B  illustrate drawings of the self-expandable stent delivery system according to the first embodiment, in which  FIG. 8A  is a state in which the pull wire insertion tube is bent when the pull wire is pulled, and  FIG. 8B  is a state in which the bending of the pull wire insertion tube is released by feeding the pull wire to the distal side. 
         FIGS. 9A and 9B  illustrate explanatory drawings of an operation unit of a self-expandable stent delivery system according to a second exemplary embodiment, in which  FIG. 9A  illustrates a state in which an engagement release portion is moved to the distal side, and  FIG. 9B  illustrates a state in which the engagement release portion applies a pressing force to an engaging portion. 
         FIGS. 10A and 10B  illustrate explanatory drawings of an operation unit of a self-expandable stent delivery system according to a third exemplary embodiment, in which  FIG. 10A  illustrates a state in which an engagement release portion is moved to the distal side, and  FIG. 10B  illustrates a state in which the engagement release portion applies a pressing force to an engaging portion. 
         FIGS. 11A and 11B  illustrate explanatory drawings of an operation unit of a self-expandable stent delivery system according to a fourth embodiment, in which  FIG. 11A  illustrates a state of being restricted by a locking portion, and  FIG. 11B  illustrates a state in which restriction by the locking portion is released. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the attached drawings, embodiments of the present disclosure will be described. It should be noted that the following description is not intended to limit the technical scope or significance of terms described in Claims. Dimensional ratios of the drawings are exaggerated for the convenience of description and may be different from actual ratios. 
       FIG. 1  is a general configuration drawing illustrating a self-expandable stent delivery system  10  (hereinafter referred to as a “stent delivery system  10 ”) according to a first exemplary embodiment.  FIG. 2  is a cross-sectional view of a distal side portion of the stent delivery system  10  according to the first exemplary embodiment.  FIG. 3  is an explanatory drawing illustrating an internal structure of an operation unit  100  of the stent delivery system  10  according to the first exemplary embodiment.  FIG. 4  is an exploded front view of the operation unit  100  of the stent delivery system  10  according to the first exemplary embodiment.  FIG. 5  is a drawing illustrating a state in which the operation unit  100  according to the first exemplary embodiment is gripped.  FIGS. 6A and 6B  illustrate explanatory drawings of the operation unit  100  according to the first exemplary embodiment, in which  FIG. 6A  illustrates a state in which an engagement release portion  320  is moved to a distal side, and  FIG. 6B  illustrates a state in which the engagement release portion  320  applies a pressing force to an engaging portion  310 .  FIGS. 7A and 7B  illustrate drawings of a self-expandable stent delivery system  10 ′ (hereinafter, referred to as a stent delivery system  10 ′) according to a comparative example, in which  FIG. 7A  illustrates a state in which a pull wire insertion tube  70  is bent when the pull wire is pulled and  FIG. 7B  illustrates a state in which the self-expandable stent  30  (hereinafter, referred to as a “stent  30 ”) is released when removing the pull wire insertion tube  70 .  FIGS. 8A and 8B  illustrates drawings of the stent delivery system  10  according to the first exemplary embodiment, in which  FIG. 8A  is a state in which the pull wire insertion tube  70  is bent when the pull wire is pulled, and  FIG. 8B  is a state in which the bending of the pull wire insertion tube  70  is released by feeding the pull wire to a distal side. 
     As illustrated in  FIG. 1 , the stent delivery system  10  according to the embodiment can include: an inner tube  20  to which a guide wire is to be inserted, the stent  30  disposed in the periphery of a distal side of the inner tube  20 ; an outer tube  40  disposed on an outer surface side of the inner tube  20 ; pull wires  50   a,    50   b  that are capable of pulling the outer tube  40  to a proximal side; a distal end member  60  disposed on a distal-most end; the pull wire insertion tube  70  to which the pull wires  50   a,    50   b  are inserted; and an operation unit  100  that operates advancing and retracting movement of the pull wires  50   a,    50   b.  It should be noted that in the specification, a side which is inserted into a lumen in a living body is referred to as a distal side (a direction indicated by an arrow A in the drawings), and a side at which the operation unit  100  is provided and which comes to an operator&#39;s side is referred to as a proximal side (a direction indicated by an arrow B in the drawing). 
     The inner tube  20  is formed of a tube-shaped body having a guide wire lumen  20   a  that penetrates therethrough from a distal end to a proximal end as illustrated in  FIG. 2 . A guide wire (not illustrated) that guides the stent delivery system  10  to a lesion area in the body lumen is inserted to the guide wire lumen  20   a.    
     The distal end member  60  is disposed at a distal-most end of the inner tube  20 . The distal end member  60  is fixed to a distal end portion of the inner tube  20  with a stopper  22 . The stopper  22  is embedded in the distal end member  60  and prevents the distal end member  60  from coming apart. The stopper  22  preferably formed of a metal (for example, stainless steel). The distal end member  60  has a gradually tapered shape toward a distal end, and is formed to be inserted relatively easily into the body lumen. The distal end member  60  is provided with an opening  20   b  at a distal end thereof. It should be noted that the distal end member  60  may be formed of a member separate from the inner tube  20 , and may be integrally formed of the same member as the inner tube  20 . 
     A proximal side of the inner tube  20  is formed to be obliquely inclined toward the proximal side and is provided so as to capable of communication with a guide wire lead-out hole  43   d  of the outer tube  40  described later as illustrated in  FIG. 2 . Accordingly, guiding of the guide wire can be facilitated. 
     Preferably, a material that forms the inner tube  20  is a flexible material. For example, polyolefin such as polyethylene and polypropylene, polyester such as polyamide, polyamide elastomer and polyethylene terephthalate, polyester elastomer, fluorinated polymer such as ETFE, PEEK, and polyimide are preferably used. Among the resins described above, resins having especially thermoplastic property are preferably used. 
     Preferably, a material that forms the distal end member  60  is a flexible material. For example, synthetic resin-based elastomers such as olefin-based elastomer, polyamide elastomer, styrene-based elastomer, polyurethane, urethane-based elastomer, and fluorine resin-based elastomer, rubbers including synthetic rubbers such as urethane rubber, silicone rubber, and butadiene, and natural rubber such as latex rubber may be used. 
     In accordance with an exemplary embodiment, the stent  30  is a self-expandable stent. As indicated by a dot-and-dash line in  FIG. 2 , when being inserted into the body lumen, the stent  30  is disposed in a stent housing  41   a  described later, in a state of being compressed radially inwardly about a longitudinal axis of the outer tube  40 . When the outer tube  40  moves toward the proximal side, the stent  30  is exposed outward, and is discharged to a lesion area in the body lumen. Accordingly, the stent  30  is expanded radially outwardly and is restored to a shape before being compressed. In accordance with an exemplary embodiment, the stent  30  has a meshed shape having a number of openings, and is formed into a substantially cylindrical shape. It should be noted that a material that may be used as a material of the stent  30  is preferably, for example, a superelastic alloy such as a Ni—Ti alloy. 
     The pull wires  50   a,    50   b  are fixed respectively to a first outer tube  41  and a second outer tube  42  provided on the outer tube  40  described later, and pull the outer tube  40  toward the proximal side. Preferably, a material that forms the pull wires  50   a,    50   b  is a material having a relatively high rigidity. For example, metals such as Ni—Ti, brass, stainless steel, and aluminum, or resins having a relatively high rigidity, for example, polyimide, vinyl chloride, or polycarbonate may be used. 
     The pull wire insertion tube  70  is formed into a tube shape having a pull wire lumen  70   a  that penetrates therethrough from a distal end to a proximal end as illustrated in  FIG. 2 . The pull wires  50   a,    50   b  are inserted into the pull wire lumen  70   a,  and is guided to the operation unit  100 . A distal portion of the pull wire insertion tube  70  is disposed in a lumen of the outer tube  40 , and is fixed to a proximal portion of the inner tube  20 . A proximal portion of the pull wire insertion tube  70  is fixed to the operation unit  100 . 
     Preferably, a material that forms the pull wire insertion tube  70  is a flexible material. For example, polyolefin such as polyethylene and polypropylene, polyester such as polyamide and polyethylene terephthalate, fluorinated polymer such as ETFE, PEEK, and polyimide are preferably used. It should be noted that the pull wire insertion tube  70  may be coated with a resin having biocompatibility, especially antithrombotic on an outer surface thereof. In accordance with an exemplary embodiment, antithrombotic materials that may be used include, for example, a copolymer of poly-hydroxyethyl methacrylate, hydroxyethylmetaacrylate, and styrene. 
     The outer tube  40  is disposed on the distal side, and includes the first outer tube  41  that houses the stent  30 , the second outer tube  42  that is disposed so as to be proximity to the proximal side of the first outer tube  41 , and a third outer tube  43  disposed on the proximal side of the second outer tube  42  as illustrated in  FIG. 1  and  FIG. 2 . 
     In accordance with an exemplary embodiment, the first outer tube  41  can include a stent housing  41   a  that houses the stent  30  between the first outer tube  41  and the inner tube  20  in a state of being compressed radially inward. As illustrated in  FIG. 2 , the inner tube  20  is provided with a distal side movement limiting portion  23  that attaches a distal side of the stent  30  to impose a limitation on the movement toward the distal side and a proximal side movement limiting portion  24  that attaches a proximal side of the stent  30  to impose a limitation on the movement toward the proximal side, both fixed to the outer surface of the inner tube  20 . The distal side and proximal side movement limiting portions  23 ,  24  are formed around a longitudinal axis of the outer tube  40  into an annular shape. The stent housing  41   a  is formed of a portion surrounded by the proximal side movement limiting portion  24 , the distal side movement limiting portion  23 , and the first outer tube  41 . 
     After the stent housing  41   a  is arranged on a lesion area and then the first outer tube  41  is moved to the proximal side with respect to the inner tube  20 . At this time, a frictional force that makes an attempt to move toward the proximal side in association with the movement of the first outer tube  41  can be applied to the stent  30 . However, the stent  30  attaches the proximal side movement limiting portion  24  and thus is limited from moving toward the proximal side. Accordingly, the stent  30  can be discharged at the lesion area without being moved from the lesion area where the stent  30  is placed. The distal side movement limiting portion  23  can include at a proximal portion thereof a tapered surface that tapers towards the proximal side. Therefore, collection of the stent delivery system  10  after the discharge of the stent  30  can be facilitated without being hindered by the distal side movement limiting portion  23  when discharging the stent  30 . 
     As illustrated in  FIG. 2 , the first outer tube  41  is not fixed to the inner tube  20 . Therefore, the first outer tube  41  is movable relatively with respect to the inner tube  20  in a direction of the longitudinal axis of the outer tube  40 . The first outer tube  41  includes a fixed portion  41   b  to which distal ends of the pull wires  50   a,    50   b  are fixed. The pull wires  50   a,    50   b  are fixed to the fixed portion  41   b  by an adhesive agent. Epoxy resins, UV-curable resins, cyanoacrylate resins and the like may be preferably used as the adhesive agent. 
     In addition, the outer surface of the first outer tube  41  is preferably treated to provide lubricating property. As such a treatment, for example, a method of coating or fixing hydrophilic polymer such as polyhydroxyethyl methacrylate, polyhydroxyethyl acrylate, and polyvinyl pyrrolidone is exemplified. Alternatively, the inner surface of the first outer tube  41  may be coated or fixed with the above-described substances in order to achieve preferable sliding property of the stent  30 . The first outer tube  41  may be a combination having a two-layer structure (for example, polyamide on the outer surface and PTFE on the inner surface) as described above. 
     Preferably, a material that forms the first outer tube  41  is a resin having a flexibility, kink resistance, elasticity and the like. For example, polyester such as polyethylene, polypropylene, polyamide, and polyethylene terephthalate, fluorinated polymer such as polyimide, PTFE, and ETFE, and thermoplastic elastomer, and the like are used. It should be noted that although the first outer tube  41 , the second outer tube  42 , and the third outer tube  43  are formed of the same material in the embodiment, the present disclosure is not limited thereto and may be formed of different materials respectively. 
     As illustrated in  FIG. 2 , the second outer tube  42  includes a distal side cylindrical portion  42   a  having two tube-shaped bodies having different outer diameters, a reduced diameter portion  42   b,  a ring-shaped member  42   c  for fixing pull wires  50   a,    50   b,  and a main body portion  42   d.  The second outer tube  42  is movable toward the proximal side together with the first outer tube  41  by being pulled by the pull wires  50   a,    50   b.  The second outer tube  42  is not fixed to the first outer tube  41 . 
     The second outer tube  42  is provided in the lumen thereof with the reduced diameter portion  42   b  that restricts the movement of the ring-shaped member  42   c  toward the distal side thereof on the distal side of a portion where the ring-shaped member  42   c  is disposed. The reduced diameter portion  42   b  can impose a limitation on the movement of the ring-shaped member  42   c  toward the distal side by abutment of the ring-shaped member  42   c  therewith when the ring-shaped member  42   c  moves toward the distal side. 
     Since the ring-shaped member  42   c  is disposed in a loosely fitted manner with respect to the distal side cylindrical portion  42   a,  the ring-shaped member  42   c  is rotationally movable in a circumferential direction of the outer tube and is also movable in the direction of the longitudinal axis of the outer tube  40  by an amount corresponding to the gap. The pull wires  50   a,    50   b  are fixed to the ring-shaped member  42   c  by an adhesive agent. Preferably, a material that forms the ring-shaped member  42   c  is a material having a relatively high rigidity. For example, a metal and a resin may be used and, specifically, a metal may preferably be used. 
     The third outer tube  43  includes a distal side tube  43   a  having an inner diameter larger than that of the main body portion  42   d  of the second outer tube  42 , and a proximal side tube  43   b  fixed to a proximal side of the distal side tube  43   a  as illustrated in  FIG. 2 . 
     In accordance with an exemplary embodiment, the distal side tube  43   a  is not fixed to the main body portion  42   d,  and is accommodated by sliding the main body portion  42   d  towards the proximal side. The distal side tube  43   a  is provided with the second outer tube movement limiting portion  43   c  on the proximal side thereof. The second outer tube  42  is movable toward the proximal side until attaching the second outer tube movement limiting portion  43   c,  and further movement toward the proximal side is limited. 
     In the embodiment, the distal side tube  43   a  of the third outer tube  43  accommodates the main body portion  42   d  of the second outer tube  42 . However, the disclosure is not limited thereto, and a configuration in which the main body portion  42   d  may be accommodated in the distal side tube  43   a  by a sliding movement with a configuration in which an inner diameter of the main body portion  42   d  is larger than the outer diameter of the distal side tube  43   a.    
     The proximal side tube  43   b  includes a guide wire lead-out hole  43   d  that protrudes and opens in a radial direction and obliquely outward of the third outer tube  43  as illustrated in  FIG. 2 . The guide wire lead-out hole  43   d  is provided so as to be capable of communicating with the guide wire lumen  20   a  of the inner tube  20 , and may lead out the guide wire to the outside of the outer tube  40 . The pull wire insertion tube  70  is fixed to the lumen of the proximal side tube  43   b.    
     In accordance with an exemplary embodiment, the operation unit  100  is fixed to the proximal end of the pull wire insertion tube  70  to which the pull wires  50   a,    50   b  are inserted as illustrated in  FIG. 1 . The operation unit  100  includes a holding portion  200  that holds the pull wires  50   a,    50   b  so that the pull wires  50   a,    50   b  are movable toward the distal side and toward the proximal side, a switching portion  300  configured to be capable of switching between the limitation of the movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side and the release of the limitation, and an accommodation unit  400  that accommodates the holding portion  200  and the switching portion  300 , as illustrated in  FIG. 3 . 
     The holding portion  200  includes a rotating shaft  210  supported at both ends thereof by the accommodation unit  400 , and a rotating member  220  configured to be capable of moving rotationally about the rotating shaft  210  and to wind and feed the pull wires  50   a,    50   b  in association with the rotary movement as illustrated in  FIG. 3  and  FIG. 4 . 
     The rotating shaft  210  is provided so as to be substantially orthogonal to the direction of advancing and retracting movement of the pull wires  50   a,    50   b.  The rotating shaft  210  may have a rolling bearing such as a ball bearing and a roller bearing and a sliding bearing containing working fluid using oil, air and the like. Metals such as carbon alloy steel and stainless steel, resin, and the like may be used to form the rotating shaft  210 . 
     The rotating member  220  includes a disc-shaped rotating roller  221  configured to move rotationally about the rotating shaft  210  and having an irregular shape on a circumferential outer surface, a disc-shaped winding shaft portion  222  configured to rotationally move about the rotating shaft  210  in the same manner and wind and feed the pull wires  50   a,    50   b,  and a gear portion  223  that is capable of restricting and releasing the limitation of the rotary movement of the rotating roller  221 . 
     The rotating roller  221  includes a portion partly protruding outward of the accommodation unit  400 . Hereinafter, in the operation unit  100 , a side of the operation unit  100  where the rotating roller  221  protrudes is referred to as an upper side and the opposite side is referred to as a lower side. The rotating roller  221  is rotationally movable about the rotating shaft  210  by a user (operator) performing an operation for rotationally moving the protruding portion clockwise along a direction of an arrow R (a direction of winding the pull wires  50   a,    50   b ) or counterclockwise (a direction of feeding the pull wires  50   a,    50   b ) along a direction indicated by an arrow F. 
     In accordance with an exemplary embodiment, the rotating roller  221  has an irregular shape on the circumferential outer surface thereof. The irregular shape on a surface portion with which the user (operator) may touch when operating the rotating roller  221  serves as a slip resistance, and thus an operation of rotary movement is facilitated. The irregular shape is formed, for example, by a plurality of projections disposed at substantially regular intervals along the direction of advancing and retracting movement of the pull wires  50   a,    50   b  on a circumferential outer surface thereof. It should be noted that the slip-resistance function is not limited to the irregular shape, and surface treatments such as the circumferential outer surface of the rotating roller  221  may have a surface treatment such as knurling treatment, embossing treatment, high-resistance material coating, and the like. 
     In accordance with an exemplary embodiment, the winding shaft portion  222  has a cylindrical shape, and proximal portions of the pull wires  50   a,    50   b  are gripped by or fixed to the circumferential outer surface of the winding shaft portion  222 . The winding shaft portion  222  is integrally formed with the rotating roller  221  on one lateral face of the rotating roller  221 , and moves rotationally about the rotating shaft  210  along with the rotary movement of the rotating roller  221 . When the winding shaft portion  222  moves rotationally clockwise along the direction of the arrow R, the proximal portions of the pull wires  50   a,    50   b  gripped by or fixed to the circumferential outer surface are pulled, and the pull wires  50   a,    50   b  are wound around the outer surface of the winding shaft portion  222  and are moved to the proximal side. After the pull wires  50   a,    50   b  have been pulled by a predetermined amount, a repulsive force as counteraction of a tensile force applied by pulling is applied to an opposite side (distal side) from a pulling direction (proximal side). When the winding shaft portion  222  moves rotationally counterclockwise along a direction indicated by the arrow F, the pull wires  50   a,    50   b  are rewound from the winding shaft portion  222  and move to the distal side. 
     In accordance with an exemplary embodiment, the gear portion  223  has a disc shape, and is formed coaxially integrally with the rotating shaft  210  on a lateral face of the rotating roller  221  on the opposite side from the side where the winding shaft portion  222  is provided. The outer diameter of the gear portion  223  is smaller than the outer diameter of the rotating roller  221 , and a surface of the gear portion  223  on the winding shaft portion  222  side is integrally formed with the rotating roller  221 . The gear portion  223  is provided with a plurality of engaging teeth  223   a  on the circumferential outer surface at substantially regular intervals over the entire circumference along the direction of advancing and retracting movement of the pull wires  50   a,    50   b.  The engaging teeth  223   a  have a shape inclining with respect to a radial direction in a direction indicated by the arrow F. Accordingly, when engaging with the engaging portion  310  described later, the engagement is not released even though the gear portion  223  moves rotationally counterclockwise along the direction of the arrow F. However, the engagement is released to be rotationally movable when the gear portion  223  moves rotationally clockwise along the direction of the arrow R. 
     The rotating roller  221 , the winding shaft portion  222 , and the gear portion  223  are formed integrally. However, the disclosure is not limited thereto, and a configuration in which separate members follow and move rotationally along with the rotary movement of the rotating roller  221  may be employed. A method of transmitting the rotary movement of the rotating roller  221  may involve, for example, a gear system or a belt system. However, the disclosure is not limited thereto. Preferably, the material that is used for forming the rotating roller  221 , the winding shaft portion  222 , and the gear portion  223  is a material superior in abrasion resistance. 
     The switching portion  300 , as illustrated in  FIG. 3  and  FIG. 4 , can include an engaging portion  310  that restricts the rotary movement of the rotating member  220  by engaging with the rotating member  220  and an engagement release portion  320  that releases the limitation of the restriction of the rotary movement of the rotating member  220  by the switching portion  300 , by releasing the engagement between the rotating member  220  and the engaging portion  310 . 
     The engaging portion  310  includes a fixed shaft  311  fixed to the accommodation unit  400  and a reverse rotation preventing member  312  that moves rotationally about the fixed shaft  311 . 
     The reverse rotation preventing member  312  is provided so as to face engaging teeth  223   a  of the gear portion  223  and includes a depressed engaging portion  312   a  provided so as to be capable with engaging with one of the engaging teeth  223   a  by the one of the engaging teeth  223   a  being inserted thereto. The reverse rotation preventing member  312  is formed of a elastically deformable material, and is deformed by the engagement release portion  320  described later in a direction to move the engaging portion  312   a  away from the engaging teeth  223   a  of the gear portion  223  to disengage. It should be noted that the reverse rotation preventing member  312  is described to be formed of an elastically deformable material, but is not limited thereto, and may be formed to be elastically deformable by having an elastic member such as a spring. For example, a configuration in which a spring is provided on the fixed shaft  311 , and the reverse rotation preventing member  312  is rotationally movable in an elastic manner about the fixed shaft  311  is also applicable. 
     The engaging portion  312   a  includes a depression inclined with respect to the radial direction of the gear portion  223  in the direction indicated by the arrow F when engaging with one of the engaging teeth  223   a  of the gear portion  223 . Therefore, as described above, the engagement is not released even though the gear portion  223  moves rotationally in the direction of the arrow F. However, the engagement is released to be rotationally movable when the gear portion  223  rotates clockwise along the direction of the arrow R. Accordingly, when the engaging portion  312   a  and the engaging teeth  223   a  engage, the rotary movement of the rotating member  220  in a feeding direction is limited, while the rotary movement of the rotating member  220  in a winding direction of the pull wires  50   a,    50   b  is not limited and is allowed. In accordance with an exemplary embodiment, movement of the pull wires  50   a,    50   b  toward the distal side is preferably limited by the engagement between the rotating member  220  and the engaging portion  310 . 
     The engagement release portion  320  includes a sliding member  321  provided in the accommodation unit  400  so as to be capable of advancing and retracting in a direction of the direction of advancing and retracting movement of the pull wires  50   a,    50   b,  and a pressing member  322  provided so as to be movable toward and away from the engaging portion  310  and applying a pressing force in a direction to move the engaging portion  310  away from the rotating member  220  by moving toward the engaging portion  310  in association with the advancing and retracting movement of the sliding member  321 . 
     The sliding member  321  includes a rail-shaped guide member  321   a  and a movable member  321   b  movable by sliding on the guide member  321   a.  The guide member  321   a  extends from a proximal portion of the accommodation unit  400  on the upper side along a shape of an upper surface of the accommodation unit  400  in the direction of advancing and retracting movement of the pull wires  50   a,    50   b,  and extends further downward to the vicinity of a position above the reverse rotation preventing member  312 . Accordingly, the movable member  321   b  is configured to be capable of advancing and retracting from the upper proximal portion of the accommodation unit  400  on the upper side to the vicinity of a position above the reverse rotation preventing member  312  along the direction of advancing and retracting movement of the pull wires  50   a,    50   b.  It should be noted that the guide member  321   a  may be formed of a separate member from the accommodation unit  400 , or may be provided integrally from the same member as the accommodation unit  400 . 
     The movable member  321   b  includes a portion partly protruding outward of the accommodation unit  400 . The movable member  321   b  is configured to be movable in the direction of advancing and retracting movement of the pull wires  50   a,    50   b  by moving the protruding portion along the guide member  321   a.  The movable member  321   b  may be moved to the distal side along the guide member  321   a,  and then moved further downward to the vicinity of the position above the reverse rotation preventing member  312 , and then returned back to the proximal side before the movement again. 
     The pressing member  322  is provided at an end portion of the movable member  321   b  opposite to the protruding portion and is configured to move toward and press the reverse rotation preventing member  312  in association with the advancing and retracting movement of the movable member  321   b.  In accordance with an exemplary embodiment, the reverse rotation preventing member  312  may be deformed by pressing the reverse rotation preventing member  312 . Accordingly, by moving the engaging teeth  223   a  of the rotating member  220  and the engaging portion  312   a  of the engaging portion  310  relatively away from each other, the engagement between the engaging teeth  223   a  and the engaging portion  312   a  may be released. Since the movable member  321   b  may be moved to the vicinity of the position above the reverse rotation preventing member  312  along the guide member  321   a,  a distance between the portion that presses the movable member  321   b  and the reverse rotation preventing member  312  can be reduced. Therefore, a pressing force required for deforming the reverse rotation preventing member  312  may be reduced. 
     It should be noted that the pressing member  322  may be provided with a spring-shaped member having flexibility for alleviating an impact generating when pressing the reverse rotation preventing member  312 . The reverse rotation preventing member  312  is elastically deformable, and thus engages the rotating member  220  again when the pressing force by the pressing member  322  is removed, so that the movement of the pull wires  50   a,    50   b  toward the distal side is limited. Therefore, a stopper (not illustrated) that maintains a state in which the pressing member  322  presses the reverse rotation preventing member  312  may be provided. 
     The accommodation unit  400  is bent at a proximal side and a center portion and has a rounded shape to accommodate the holding portion  200  and the switching portion  300  as illustrated in  FIG. 3  and  FIG. 4 . In accordance with an exemplary embodiment, the accommodation unit  400  includes a first opening portion  410  opening at an upper surface, a finger hooking portion  420  on which a finger can be hooked when operating the pull wires  50   a,    50   b  via the holding portion  200 , a second opening portion  430  that exposes part of the engagement release portion  320 , bearing portions  440   a,    440   b,  and a coupling member  450 . 
     The first opening portion  410  is an opening provided on the upper surface of the accommodation unit  400 , and exposes part of the rotating roller  221  of the holding portion  200  to outside of the accommodation unit  400 . Since the rotating roller  221  may be operated from the outside of the accommodation unit  400 , the operation can be facilitated. An opening edge portion  410   a  and the rotating roller  221  are configured so that the accommodation unit  400  does not hinder the operation of rotary movement even when the rotating roller  221  is rotated. 
     The finger hooking portion  420  is formed on a lower surface of the accommodation unit  400 , and has a plurality of curved portions. The size of the curved portions is formed to follow curved surfaces of human fingers on a palm side. The finger hooking portion  420  can allow the user (operator) to hook his or her fingers when gripping the accommodation unit  400  as illustrated in  FIG. 5 , so that stable gripping of the accommodation unit  400  is achieved. It should be noted that the number of the curved portions is preferably at least four so as to allow all four fingers other than the thumb to be hooked thereon, but is not limited thereto. 
     The second opening portion  430  is formed at a position away from an extension line L (broken line in  FIG. 3 ) that connects the first opening portion  410  and the finger hooking portion  420  to a proximal side, and exposes part of the movable member  321   b  of the engagement release portion  320  to the outside of the accommodation unit  400 . Since the movable member  321   b  may be operated from the outside of the accommodation unit  400 , the operation is facilitated. Specifically, the second opening portion  430  is opened from the proximal portion of the accommodation unit  400  on the upper side to a position above the reverse rotation preventing member  312  on the proximal side with respect to the first opening portion  410 . Accordingly, as illustrated in  FIG. 5 , a protruding portion of the movable member  321   b  of the engagement release portion  320  may be disposed on the proximal portion of the accommodation unit  400  on the upper side, where the hand does not touch during the operation, so that inadvertent release of the limitation of rotary movement of the rotating member  220  by the switching portion  300  during the operation can be avoided. When the release of the limitation is desired, the movable member  321   b  of the engagement release portion  320  is moved to the vicinity of the position above the reverse rotation preventing member  312 , and is pressed against the reverse rotation preventing member  312  to release the limitation. 
     In accordance with an exemplary embodiment, the two bearing portions  440   a,    440   b  accommodate one end of the rotating shaft  210  of the rotating member  220  on the gear portion  223  side and the other end of the rotating shaft  210  on the winding shaft portion  222  side, respectively, as illustrated in  FIG. 4 . Accordingly, the rotating member  220  is accommodated in the accommodation unit  400  by being supported at both ends of the rotating member  220 . 
     The coupling member  450  includes a connector  451  that is interlocked with the pull wire insertion tube  70  and a seal member  452 . A distal portion of the connector  451  is fixed to the proximal portion of the pull wire insertion tube  70 . The seal member  452  is connected to a proximal portion of the connector  451 . 
     Hereinafter, a method of releasing the limitation of movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side by the switching portion  300  in the operation unit  100  of the first embodiment will be described. 
     In accordance with an exemplary embodiment, as illustrated in  FIG. 3 , before releasing the limitation of movement of the pull wires  50   a,    50   b  toward the distal side, the engagement release portion  320  is disposed on the proximal portion of the accommodation unit  400  on the upper side. At this time, the reverse rotation preventing member  312  of the engaging portion  310  engages the engaging portion  310  of the rotating member  220 , the rotary movement of the rotating member  220  to the feeding direction of the rotating member  220  (the direction indicated by the arrow F) is limited, and the movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side can be limited. 
     When release of the limitation of the movement of the pull wires  50   a,    50   b  is desired, first, the movable member  321   b  of the engagement release portion  320  is moved along the direction of advancing and retracting movement of the pull wires  50   a,    50   b  from the proximal portion of the accommodation unit  400  on the upper side to the position above the reverse rotation preventing member  312  on the distal side as illustrated in  FIG. 6A . Next, as illustrated in  FIG. 6B , the guide member  321   a  is pushed downward and then the reverse rotation preventing member  312  is pressed downward. With the pressing force, the reverse rotation preventing member  312  is deformed downward, and engagement is released by moving the engaging portion  310  relatively away from each other with respect to the gear portion  223  of the rotating member  220 . In this state, as the rotating member  220  is capable of moving rotationally in the feeding direction (the direction indicated by the arrow F), the movement of the pull wires  50   a,    50   b  toward the distal side is released from the limitation and thus is allowed. Accordingly, the limitation of movement of the pull wires  50   a,    50   b  toward the distal side may be released by an action of moving the members away from each other, and thus simple operation is achieved. In addition, with the operation as easy as pressing the reverse rotation preventing member  312 , the release of the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side may be achieved quickly. 
       FIGS. 7A and 7B  illustrate a stent delivery system  10 ′ according to a comparative example of the stent delivery system  10  according to the embodiment. The stent delivery system  10 ′ of the comparative example is provided with the engaging portion  310  that restricts the movement of the pull wires  50   a,    50   b  toward the distal side, but is not provided with the engagement release portion  320  that releases the limitation. 
     As illustrated in  FIG. 7A , when a distal side portion of the stent delivery system  10 ′ is inserted into a stenosed site (lesion area), a load (constraint force) may be applied to the distal side portion by the stenosed site radially inward (the direction indicated by arrows in  FIG. 7A ) that presses the outer tube  40 . When the inner diameter of the stenosed site is extremely narrow, the radially inward load is excessively high, and thus the movement of the outer tube  40  toward the proximal side following the pulling operation of the pull wires  50   a,    50   b  may be hindered. At this time, if an attempt is made to forcedly pull the pull wires  50   a,    50   b,  the distance between the outer tube  40  and an operation unit  100 ′ is decreased, but the position of the outer tube  40  does not change. Accordingly, the pull wire insertion tube  70 , to which the pull wires  50   a,    50   b  are inserted, on the proximal side of the outer tube  40  may be distorted by an amount corresponding to the reduction of the distance between the outer tube  40  and the operation unit  100 ′. In such a case, when the outer tube is moved to the proximal side by making an attempt to remove the distal side portion of the stent delivery system  10 ′, the outer tube  40  is suddenly opened from the constraint force applied thereto by the stenosed site. Accordingly, by a restoration force that tries to restore the distortion of the pull wire insertion tube  70 , a force in the direction of releasing the stent  30  to the distal side of the outer tube  40  is applied to the stent  30  so that the stent  30  may be discharged at an unintended timing as illustrated in  FIG. 7B . The user is obliged to perform an operation for removing the distal side portion of the stent delivery system  10 ′ while paying attention not to cause such discharge of the stent  30 , and thus an increased procedure time may result. 
     In the stent delivery system  10  illustrated in  FIGS. 8A and 8B , when the distal side portion is inserted into the stenosed site (lesion area) as illustrated in  FIG. 8A , a constraint force that presses the outer tube  40  radially inward at the stenosed site is applied in the same manner as the comparison example, so that the pull wire insertion tube  70  on the proximal side with respect to the outer tube  40  may be distorted. At this time, movement of the pull wires  50   a,    50   b  to the distal side is enabled by the engagement release portion  320  that releases the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side by the engaging portion  310 . As illustrated in  FIG. 8B , the state before being pulled is restored by moving the pull wires  50   a,    50   b  toward the distal side, so that the distortion of the pull wire insertion tube  70  may be solved. Since the distal side portion may be removed from this state, removal is facilitated, and the operability can be improved. 
     As described above, the operation unit  100  of the stent delivery system  10  according to the first embodiment includes the holding portion  200  that holds the pull wires  50   a,    50   b  in a state of being movable toward the distal side and toward the proximal side, the switching portion  300  configured to be capable of switching between the limitation of the movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side and the release of the limitation. 
     According to the stent delivery system  10  configured in this manner, the pull wires  50   a,    50   b  may not only be moved toward the proximal side by being pulled, but also be moved toward distal side again even after having been moved once toward the proximal side. Accordingly, a further improvement of the operability can be achieved. In addition, discharge of the stent  30  at an unintended timing may preferably be prevented even in the case where the constraint force that presses the outer tube  40  radially inward is applied in a stenosed site that is present in the body lumen, and convenience at the time of use can be improved. 
     In addition, the holding portion  200  is configured to be capable of moving rotationally and includes the rotating member  220  that winds and feeds the pull wires  50   a,    50   b  along with the rotary movement, and the switching portion  300  includes the engaging portion  310  that restricts the rotary movement of the rotating member  220  by engaging with the rotating member  220  and the engagement release portion  320  that releases the limitation by the switching portion  300  by releasing the engagement between the rotating member  220  and the engaging portion  310 . 
     According to the stent delivery system  10  configured as described above, the movement of the pull wires  50   a,    50   b  toward the distal side is preferably limited by the engagement between the rotating member  220  and the engaging portion  310 . The release of the limitation of the movement of the pull wires  50   a,    50   b,  may easily be achieved by releasing the engagement. 
     The engagement release portion  320  is configured in such a manner that engagement may be released in association with the relative movement of the rotating member  220  and the engaging portion  310  away from each other. 
     According to the stent delivery system  10  configured as described above, the engagement release portion  320  may release the limitation of movement of the pull wires  50   a,    50   b  toward the distal side by an action of moving the members away from each other, and thus a relatively simple operation can be achieved. 
     In addition, the accommodation unit  400  that accommodates the holding portion  200  and the switching portion  300  is further provided. The engagement release portion  320  includes a sliding member  321  provided in the accommodation unit  400  so as to be capable of advancing and retracting in the direction of advancing and retracting movement of the pull wires  50   a,    50   b,  and a pressing member  322  provided so as to be movable toward and away from the engaging portion  310  and applying a pressing force in the direction to move the reverse rotation preventing member  312  (the engaging portion  310 ) away from the rotating member  220  by moving toward the engaging portion  310  in association with the advancing and retracting movement of the sliding member  321 . 
     According to the stent delivery system  10  configured as described above, with the operation as easy as pressing the reverse rotation preventing member  312 , the release of the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side may be achieved relatively quickly. 
     In addition, the sliding member  321  includes a rail-shaped guide member  321   a  and a movable member  321   b  movable by sliding on the guide member  321   a,  and the pressing member  322  is provided at an end portion of the movable member  321   b.    
     According to the stent delivery system  10  configured as described above, since the movable member  321   b  may be moved to the vicinity of the position above the reverse rotation preventing member  312  along the guide member  321   a,  a distance between the portion that presses the movable member  321   b  and the reverse rotation preventing member  312  can be reduced. Therefore, a pressing force required for deforming the reverse rotation preventing member  312  may be reduced. 
     In addition, the accommodation unit  400  includes the first opening portion  410  that exposes part of the holding portion  200  to the outside, the finger hooking portion  420  on which a finger can be hooked when operating the pull wires  50   a,    50   b  via the holding portion  200 , the second opening portion  430  that exposes part of the engagement release portion  320  at a position away from the extension line L that connects the first opening portion  410  and the finger hooking portion  420  toward the proximal side. 
     According to the stent delivery system  10  configured as described above, the engagement release portion  320  may be disposed at a position where the hand does not touch during the operation, so that inadvertent release of the limitation of rotary movement of the rotating member  220  by the switching portion  300  during the operation is avoided. 
       FIGS. 9A and 9B  illustrate explanatory drawings of an operation unit  100   a  of a self-expandable stent delivery system  10   a  (hereinafter, referred to as a “stent delivery system  10   a ) according to a second exemplary embodiment, in which  FIG. 9A  illustrates a state in which an engagement release portion  520  is moved to the distal side, and  FIG. 9B  illustrates a state in which the engagement release portion  520  applies a pressing force to an engaging portion  310 . Referring to  FIGS. 9A and 9B , the stent delivery system  10   a  according to the second embodiment will be described below. 
     The stent delivery system  10   a  of the second embodiment is different from that of the first exemplary embodiment only in the configuration of the engagement release portion  520  of the operation unit  100   a,  and other configurations are the same as those of the first embodiment. Description of the same configurations as the first embodiment will be omitted below. It should be noted that members having the same configuration as the first embodiment will be described with the same reference numerals. 
     An engagement release portion  520  according to the second embodiment includes a sliding member  521  provided in an accommodation unit  400  so as to be capable of advancing and retracting in a direction of advancing and retracting movement of pull wires  50   a,    50   b,  and a pressing member  522  provided so as to be movable toward and away from the engaging portion  310  and applying a pressing force in a direction to move the engaging portion  310  away from a rotating member  220  by moving toward the engaging portion  310  in association with the advancing and retracting movement of the sliding member  521  as illustrated in  FIGS. 9A and 9B . 
     The sliding member  521  has a rod-shaped portion extending from the proximal portion of the accommodation unit  400  on the upper side to the position above the reverse rotation preventing member  312  along the direction of advancing and retracting movement of the pull wires  50   a,    50   b,  and the proximal portion is configured to attach an upper end portion of the pressing member  522 . In the same manner as the first embodiment, the sliding member  521  includes a portion partly protruding outward from a second opening of the accommodation unit  400 . The sliding member  521  is configured to be movable in the direction of advancing and retracting movement of the pull wires  50   a,    50   b  by moving the protruding portion inward and outward. 
     The pressing member  522  is provided at the vicinity of a position above the reverse rotation preventing member  312 . By the movement of the sliding member  521  toward the distal side, the upper side of the pressing member  522  attaches the distal side of the sliding member  521 . The distal side of the sliding member  521  and the upper side of the pressing member  522  are formed so as to be slidably movable with each other, and the pressing member  522  is configured to be movable downward by the sliding movement. By the operation to push the sliding member  521 , the pressing member  522  approaches the reverse rotation preventing member  312  and presses the same. 
     Hereinafter, a method of releasing the limitation of movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side by a switching portion  500  in the operation unit  100   a  of the second embodiment will be described. 
     As illustrated in  FIG. 9A , before releasing the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side, the sliding member  521  is disposed at a position on the proximal side that does not cause contact with the pressing member  522 . At this time, the reverse rotation preventing member  312  of the engaging portion  310  engages the engaging portion  310  of the rotating member  220 , the rotary movement of the rotating member  220  to the feeding direction of the rotating member  220  (the direction indicated by the arrow F) is limited, and the movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side is limited. 
     When the release of the limitation is desired, as illustrated in  FIG. 9B , the portion of the sliding member  521  protruding from the accommodation unit  400  is pushed to the distal side. The distal side of the sliding member  521  and the upper side of the pressing member  522  attach with each other, then the pressing member  522  is moved downward, so that the pressing member  522  presses the reverse rotation preventing member  312 . With the pressing force, the reverse rotation preventing member  312  is deformed downward, and engagement is released by moving the engaging portion  310  relatively away from each other with respect to the gear portion  223  of the rotating member  220 . In this state, as the rotating member  220  is capable of moving rotationally in the feeding direction (the direction indicated by the arrow F), the movement of the pull wires  50   a,    50   b  toward the distal side is released from the limitation and thus is allowed. Accordingly, with the operation as easy as pressing the reverse rotation preventing member  312 , the release of the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side may be achieved further quickly. In addition, since the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side may be released by a single action of pushing the sliding member  521  inward, the releasing operation may be performed in a relatively short time. 
     As described above, the operation unit  100   a  of the stent delivery system  10   a  according to the second embodiment has the accommodation unit  400  that accommodates the holding portion  200  and the switching portion  500  in the same manner as the first embodiment. The engagement release portion  520  includes a sliding member  521  provided in the accommodation unit  400  so as to be capable of advancing and retracting in the direction of advancing and retracting movement of the pull wires  50   a,    50   b,  and a pressing member  522  provided so as to be movable toward and away from the engaging portion  310  and applying a pressing force in the direction to move the reverse rotation preventing member  312  (the engaging portion  310 ) away from the rotating member  220  by moving toward the engaging portion  310  in association with the advancing and retracting movement of the sliding member  521 . 
     According to the stent delivery system  10   a  configured as described above, the release of the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side can be easily achieved with a simple operation of pressing the reverse rotation preventing member  312  in the same manner as in the first embodiment, further improvement of the operability can be achieved. 
     In addition, the distal side of the sliding member  521  and the upper side of the pressing member  522  are formed so as to be in slidable attachment with each other, and the pressing member  522  is configured to be movable downward by the sliding movement. According to the stent delivery system  10   a  configured as described above, since the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side may be released by a single action of pushing the sliding member  521  inward, the releasing operation may be performed in a relatively short time. 
       FIGS. 10A and 1B  illustrate explanatory drawings of an operation unit  100   b  of a self-expandable stent delivery system  10   b  (hereinafter, referred to as a “stent delivery system  10   b ”) according to a third exemplary embodiment, in which  FIG. 10A  illustrates a state in which an engagement release portion  620  is moved to the distal side, and  FIG. 10B  illustrates a state in which the engagement release portion  620  applies a pressing force to an engaging portion  310 . Referring to  FIGS. 10A and 10B , the stent delivery system  10   b  according to the third embodiment will be described below. 
     The stent delivery system  10   b  of the third embodiment is different from that of the first exemplary embodiment only in the configuration of a holding portion  200  of an operation unit  100   b,  the engagement release portion  620 , and the bearing portion, and other configurations are the same as those of the first embodiment. Description of the same configurations as the first embodiment will be omitted below. It should be noted that members having the same configuration as the first exemplary embodiment will be described with the same reference numerals. 
     The holding portion  200  according to the third exemplary embodiment includes a rotating shaft  210  supported at both ends thereof by an accommodation unit  400 , and a rotating member  220  configured to be capable of moving rotationally about the rotating shaft  210  and moving in the direction of the rotating shaft  210 , and to wind and feed pull wires  50   a,    50   b  in association with the rotary movement. It should be noted that the configurations of the components of the rotating member  220  of the stent delivery system  10   b  according to the third exemplary embodiment are the same as those of the first exemplary embodiment. 
     The rotating member  220  of the third exemplary embodiment is different from that of the first exemplary embodiment in being configured to be movable in the direction of the rotating shaft  210 . The direction of movement in the direction of the rotating shaft  210  is not specifically limited. However, in this embodiment, the respective components move integrally toward a winding shaft portion  222  with respect to a rotating roller  221 . 
     The structure of the rotating shaft  210  is not specifically limited. However, a configuration including a first rotating shaft  210   a  disposed on a gear portion  223  side and a second rotating shaft  210   b  disposed on the winding shaft portion  222  side is applicable. The first rotating shaft  210   a  and the second rotating shaft  210   b  have a slidable telescopic structure with respect to each other. The rotating member  220  is integrally assembled to an outer periphery of the first rotating shaft  210   a,  and is configured to move to retract in the axial direction together with the axial movement of the first rotating shaft  210   a.  The second rotating shaft  210   b  slides along with the movement of the first rotating shaft  210   a  in the axial direction and is housed in the interior of the first rotating shaft  210   a.  With the configuration described above, the rotating shaft  210  is capable of expanding in the axial direction. 
     The bearing portion that supports the rotating shaft  210  includes only a bearing portion  440   b  on the winding shaft portion  222  side for the rotating roller  221 , and on the other side, an insertion hole  460  to which the rotating shaft  210  is inserted is formed. 
     In accordance with an exemplary embodiment, the engagement release portion  620  according to the third exemplary embodiment includes a pressing member  622  capable of releasing the engagement along with a relative movement of the rotating member  220  and the engaging portion  310  away from each other in the direction of the rotating shaft  210  as illustrated in  FIG. 10A . 
     The pressing member  622  is provided coaxially with the rotating shaft  210  of the rotating member  220 . The pressing member  622  is fixed to one end portion of the rotating shaft  210  inserted into the insertion hole  460 . By pressing the pressing member  622  inward into the accommodation unit  400 , the rotating shaft  210  is pushed inward of the accommodation unit  400  from a lateral face side where the pressing member  622  is provided. Accordingly, the rotating shaft  210  is contracted. At this time, the other end portion of the rotating shaft  210  does not move in the axial direction by the bearing portion of the accommodation unit  400 . Accordingly, the rotating member  220  is configured to be movable in the direction of the rotating shaft  210 . 
     Hereinafter, a method of releasing the limitation of movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side by the switching portion  600  in the operation unit  100   b  of the third exemplary embodiment will be described. 
     First, as illustrated in  FIG. 10A , before releasing the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side, the engaging portion  310  is disposed on a plane of rotation of the gear portion  223 . At this time, the reverse rotation preventing member  312  of the engaging portion  310  engages the engaging portion  310  of the rotating member  220 , the rotary movement of the rotating member  220  to the feeding direction of the rotating member  220  (the direction indicated by the arrow F) is limited, and the movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side is limited. 
     When the release of the limitation is desired, as illustrated in  FIG. 10B , the pressing member  622  is pressed from the lateral face side where the pressing member  622  is provided to the other lateral face side. The pressing force applied by the pressing member  622  causes the rotating shaft  210  to contract. Along with the contraction, the rotating member  220  moves to the other lateral face side. The engagement is released by relatively moving the gear portion  223  away from the engaging portion  310  of the rotating member  220  in the direction of the rotating shaft  210 . In this state, as the rotating member  220  is capable of moving rotationally in the feeding direction (the direction indicated by the arrow F), the movement of the pull wires  50   a,    50   b  toward the distal side is released from the limitation and thus is allowed. Accordingly, the plane of rotation of the gear portion  223  and the motion area of the engaging portion  310  do not overlap with each other, inadvertent release due to an elastic deformation of the reverse rotation preventing member  312  may be avoided. Therefore, a further improvement of the operability can be achieved. In addition, by pulling back the pressing member  622 , the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side may be restored. 
     As described above, the engagement release portion  620  of the stent delivery system  10   b  according to the third exemplary embodiment is configured to be capable of releasing the engagement in association with the relative movement between the gear portion  223  of the rotating member  220  and the engaging portion  310  away from each other in the direction of the rotating shaft  210 . 
     According to the stent delivery system  10   b  configured as described above, the plane of rotation of the gear portion  223  and the motion area of the engaging portion  310  do not overlap with each other, inadvertent release due to the elastic deformation of the reverse rotation preventing member  312  may be avoided. Therefore, a further improvement of the operability is achieved. 
       FIGS. 11A and 11B  illustrate explanatory drawings of an operation unit  100   c  of a self-expandable stent delivery system  10   c  (hereinafter, referred to as a “stent delivery system  10   c ”) according to a fourth embodiment, in which  FIG. 11A  illustrates a state in which the restriction by a locking portion  730  is effected, and  FIG. 11B  illustrates a state in which the restriction by the locking portion  730  is released Referring to  FIGS. 11A and 11B , a stent delivery system  10   c  according to the fourth exemplary embodiment will be described below. 
     The stent delivery system  10   c  of the fourth exemplary embodiment is different from that of the first embodiment only in the configurations of an engagement release portion  720  and the locking portion  730 , and other configurations are the same as those of the first exemplary embodiment. Description of the same configurations as the first embodiment will be omitted below. It should be noted that members having the same configuration as the first exemplary embodiment will be described with the same reference numerals. 
     The stent delivery system  10   c  according to the fourth exemplary embodiment further includes the locking portion  730  that is switchable between a restriction of the releasing operation of a switching portion  700  that releases the limitation and release of the limitation. The locking portion  730  is provided on an upper side of an accommodation unit  400  so as to be slidably movable. The locking portion  730  further includes a locking member  730   a  that locks a pressing member  722 . 
     The engagement release portion  720  includes a pressing member  722  capable of releasing the engagement along with a relative movement of the rotating member  220  and the engaging portion  310  away from each other in the direction of a rotating shaft  210 . 
     Hereinafter, a method of releasing the limitation of movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side by the switching portion  700  in an operation unit  100   c  of the fourth embodiment will be described. 
     As illustrated in  FIG. 11A , before releasing the limitation of the movement of the pull wires  50   a,    50   b  toward the distal side, the pressing member  722  is disposed at a position above the reverse rotation preventing member  312 . In this state, the locking portion  730  locks the pressing member  722  by the locking member  730   a,  the downward movement of the pressing member  722  that presses the reverse rotation preventing member  312  is restricted. At this time, the reverse rotation preventing member  312  of the engaging portion  310  engages the engaging portion  310  of the rotating member  220 , the rotary movement of the rotating member  220  to the feeding direction of the rotating member  220  (the direction indicated by the arrow F) is limited, and the movement of the pull wires  50   a,    50   b  held by the holding portion  200  toward the distal side is limited. 
     When release of the limitation of the movement of the pull wires  50   a,    50   b  is desired, as illustrated in  FIG. 11B , the locking portion  730  is moved the locking member  730   a  away from the pressing member  722  to unlock by moving the locking portion  730  toward the proximal side so that the restriction by the locking portion  730  is released. Subsequently, the pressing member  722  is pushed downward. The pressing member  722  moves downward and the pressing member  722  presses the reverse rotation preventing member  312 . With the pressing force, the reverse rotation preventing member  312  is deformed downward, and engagement is released by moving the engaging portion  310  relatively away from each other with respect to the gear portion  223  of the rotating member  220 . In this state, as the rotating member  220  is capable of moving rotationally in the feeding direction (the direction indicated by the arrow F), the movement of the pull wires  50   a,    50   b  toward the distal side is released from the limitation and thus is allowed. Accordingly, if the releasing operation is not performed on the locking portion  730 , a releasing operation that releases the limitation applied by the switching portion  700  may not be performed. Therefore, irrespective of the disposition of the engagement release portion  720  of the switching portion  700  during the operation, the limitation on the rotary movement of the rotating member  220  may not be released inadvertently by the switching portion  700  during the operation, so that a further improvement of the operability can be achieved. 
     As described above, the stent delivery system  10   c  according to the fourth exemplary embodiment further includes the locking portion  730  that is capable of switching between the restriction of the releasing operation of the switching portion  700  for releasing the limitation and the release of the restriction. 
     According to the stent delivery system  10   c  configured as described above, irrespective of the disposition of the engagement release portion  720  of the switching portion  700 , the limitation on the rotary movement of the rotating member  220  may not be released inadvertently by the switching portion  700  during the operation, so that a further improvement of the operability can be achieved. 
     Although the stent delivery systems  10 ,  10   a,    10   b,    10   c  have been described through the embodiments thus far, the present disclosure is not limited to the configuration described in the embodiments, and may be modified as needed based on the description of the Claims. 
     For example, in all of the embodiments, the pull wires  50   a,    50   b  are wound when the rotating member  220  moves rotationally clockwise along the direction indicated by an arrow R, and the pull wires  50   a,    50   b  are fed when the pull wires  50   a,    50   b  is wound and move rotationally counterclockwise along the direction indicated by the arrow F. However, the disclosure is not limited thereto, and a configuration in which the pull wires  50   a,    50   b  are wound when moving rotationally in the direction indicated by an arrow F and are fed when moving rotationally clockwise along the direction indicated by the arrow R is also applicable. 
     The holding portion  200  includes the gear portion  223 , and the movement of the pull wires  50   a,    50   b  toward the distal side is limited by the engagement between the gear portion  223  and the engaging portion  310 . However, the present disclosure is not limited thereto. For example, a configuration provided with the winding shaft portion  222  and the engaging teeth  223   a  and engages the engaging portion  310  is also applicable. 
     As the first exemplary embodiment, the second exemplary embodiment, and the third exemplary embodiment have a configuration in which the pressing member  322  may be pressed against the engaging portion  310  once, and then restoration to the state before being pressed may be performed. However, the disclosure is not limited thereto, and may have a structure in which once pushed inward, the state in which the engaging portion  310  is pressed may not be released. 
     In addition, the configuration in which the locking portion  730  described as the fourth exemplary embodiment is applied is not limited to the corresponding embodiment, and may be applied, for example, to the stent delivery systems  10 ,  10   a,    10   b  in the first exemplary embodiment, the second exemplary embodiment, and the third exemplary embodiment. 
     In the first exemplary embodiment, the second exemplary embodiment, and the fourth exemplary embodiment, the pressing member  322  is described to release the engagement by pressing the reverse rotation preventing member  312  downward. However, the pressing direction is not limited thereto, and the reverse rotation preventing member  312  may be pressed from any direction. 
     Although the outer tube  40  includes the first outer tube  41 , the second outer tube  42 , and the third outer tube  43 , the disclosure is not limited thereto, and one or two outer tubes, or four or more outer tubes may be provided. 
     The detailed description above describes a self-expandable stent delivery system. The invention is not limited, however, to the precise embodiments and variations described. Various changes, modifications and equivalents can be effected by one skilled in the art without departing from the spirit and scope of the invention as defined in the accompanying claims. It is expressly intended that all such changes, modifications and equivalents which fall within the scope of the claims are embraced by the claims.