Abstract:
A ureter stent designed for assisting the draining of urine with calculus fragments. The ureter stent includes a first holding portion, a second holding portion and a junction portion. The first holding portion has a pigtail shape for holding itself in a kidney. The second holding portion has a pigtail shape for holding itself in a bladder. The junction portion joins the first holding portion and the second holding portion and placed in a ureter. The junction portion is made of a metal round wire having no internal flow path. Urine flows outside the ureter stent.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a ureteral stent placed between a kidney and a bladder. 
   2. Description of the Related Art 
   A process for placing a ureteral stent in a ureter in order to protect the ureter from being narrow and reserve a flow path of urine. The ureteral stent has been requested for reducing the burden on a patient and reserving the flow path of the urine. 
   When a calculus appears in the kidney or ureter, a process is often performed for using ESWL (Extracorporeal Shock-Wave Litotripsy), and chopping the calculus and then discharging the chopped calculus pieces through the ureter from a body. After the calculus is chopped, the ureteral stent is placed to reserve the urine path. 
   Japanese Laid-Open Patent Application (JP-A-Heisei, 6-238007) discloses a ureteral stent characterized by having a lead portion, a main body and a tail portion and having a lumen therein, wherein the main body is at least constituted by a super-elastic metal tube and an outer diameter (φ 0 ) and an inner diameter (φi) of the super-elastic metal tube are defined so as to satisfy the following equations (1) and (2).
 
φ 0 ≦3000 μm  (1)
 
200 μm≦(φ 0 −φ i )/2≦150 μm  (2)
 
   PCT application WO/2002/053065 discloses a radially expanding ureteral device. The ureteral device is provided for facilitating stone passage through a ureter or duct. An exemplary ureteral device includes a flexible, elongate body that defines a plurality of cages along the body. In a contracted state the cages have a reduced diameter. When an activation force is applied, the cages transform to an expanded state, thereby defining a plurality of void spaces. The void spaces are configured to receive an obstruction, such as a stone. 
   Japanese Laid-Open Patent Application (JP-P2003-19211) discloses a stent. The stent is disintegrated in a living body after staying in the body for a time appropriate for a therapeutic purpose. 
   Japanese Patent (JP2888979-B2) discloses a stent for removing calculus and its fragments. The stent includes an elongate and flexible tube. 
   SUMMARY OF THE INVENTION. 
   An object of the present invention is to provide a ureteral stent for enhancing the discharge of calculus fragments. 
   Another object of the present invention is to provide a ureteral stent which is preferably used even for a ureter including narrow portion. 
   Still another object of the present invention is to provide a ureteral stent having reduced burden on a human body. 
   In an aspect of the present invention, the ureteral stent includes: a first holding portion configured to prevent the stent from displacing from a kidney by hanging a junction of renal pelvis and ureter when placed in the renal pelvis; a second holding portion configured to prevent the stent from displacing from a bladder by hanging a ureterovesical junction when placed in the bladder; and a junction portion having a solid-core round wire which joins the first holding portion and the second holding portion. The longitudinal direction is substantially conforming with the ureter when placed in the ureter. 
   Preferably, the round wire is made of metal. The cross section of the round wire in a direction perpendicular to a longitudinal direction of the round wire forms a convex domain. The size of the round wire is equal to or less than 4 French. 
   Preferably, the round wire is covered by a winding wire or braided material. 
   In another aspect of the present invention, the ureter stent further includes an auxiliary wire fixed to the round wire at a first point and a second point. The length between the first point and the second point along the auxiliary wire is larger than the length between the first point and the second point along the round wire. 
   In further another aspect of the present invention, the ureter stent further includes a wavy round wire joined to the round wire at a first point near the first holding portion and at a second point near the second holding portion. The shape of the wavy round wire is waveform, the direction of the amplitude of the waveform is substantially perpendicular to a longitudinal direction of the round wire. 
   In further another aspect of the present invention, the junction portion includes a helical portion. The central axis of helix included in the shape of the helical portion is substantially parallel to the line connecting the junction of the junction portion and the first holding portion and the junction of the second holding portion and the junction portion. 
   Preferably, the area contacting with the renal pelvis surface is covered by fluoride resin. 
   Preferably, the surface of the ureter stent of the present invention has a chromatic stripe pattern. 
   Preferably, the shape of the first holding portion is a pig tail shape. 
   In further another aspect of the present invention, the shape of the first holding portion is helical. The central axis of the helical shape of the first holding portion is substantially parallel to a longitudinal direction of the round wire when the ureter stent is free from external force. Or the central axis of the helical shape of the first holding portion is substantially perpendicular to a longitudinal direction of the round wire when the ureter stent is free from external force. 
   In an aspect of the present invention, a ureter stent set includes: a ureter stent according to the present invention; a sleeve; and a pusher. The sleeve is configured to have a tube shape having an internal path through which the ureter stent is guided into a human body and the first holding portion is guided into a kidney, and the pusher is configured to push the ureter stent along the internal path. 
   Preferably, the ureter stent set further includes a tube-shaped second ureter stent having a flow path through which urine flows, and an external surface of the ureter stent is slidably fit into an internal path of the second ureter stent. 
   According to the present invention, the ureteral stent for enhancing the discharge of the calculus fragments is provided. 
   Also according to the present invention, the ureteral stent which is preferably used even for the ureter including narrow portion. 
   Also according to the present invention, the ureteral stent having reduced burden on the human body is provided. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a state where a ureteral stent is placed inside a body; 
       FIG. 2  shows a configuration of the ureteral stent; 
       FIG. 3  shows a configuration of the ureteral stent; 
       FIG. 4  shows a configuration of the ureteral stent; 
       FIG. 5  shows a configuration of the ureteral stent; 
       FIG. 6  shows a configuration of the ureteral stent; 
       FIG. 7  shows a configuration of the ureteral stent; 
       FIG. 8  shows a configuration of the ureteral stent; 
       FIG. 9  shows a configuration of the ureteral stent; 
       FIG. 10  shows a configuration of the ureteral stent; 
       FIG. 11  shows a configuration of the ureteral stent; 
       FIG. 12  shows a configuration of a ureteral stent system; 
       FIG. 13A  shows a closeup view of the core wire; 
       FIG. 13B  shows a schematic view of the cross section of the ureteral stent; and 
       FIG. 14  shows a configuration of a ureteral stent having stripe pattern. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The embodiment of a ureteral stent according to the present invention will be described below with reference to the drawings.  FIG. 1  shows the ureteral stent placed inside a human body. A renal pelvis of the kidney  2  is connected to an end of the ureter  4 . The other end of the ureter  4  is connected to the bladder  6 . The ureteral stent  8  is placed inside the ureter  4  in the state that one end is located at a space of the renal pelvis and the other end is located at a space inside the bladder. 
     FIG. 2  shows the configuration of the ureteral stent  8 . The ureteral stent  8  includes a wire (called “core wire”) as a main component. The wire can be made of resin. The wire can be made of resin. In this embodiment, the wire made of metal is desirable. By using metallic core wire, the load on the body of a patient is suppressed; the uncomfortable feeling sensed by the patient is small; the manufacturing process is simple; and generally stronger than the wire of same size and made of resin. Specifically, the metal that is kink-inhibiting and is resist rust is preferably adopted as the wire material. As such metals, stainless and nitinol can be preferably exemplified. 
   The portion near a first end  11  of the ureteral stent  8  is a first holding portion  10  that is processed to the shape of the “pig tail”, namely, the shape having a curling for preventing the end from dropping out of a certain cavity inside a body and slipping out of a vessel connected to the cavity. A portion near a second end  15  of the ureteral stent  8  is a second holding portion  14  that is processed to the shape of the pig tail. The first holding portion  10  and the second holding portion  14  are connected through a connecting portion  12 . By the first holding portion  10 , one end of the ureteral stent  8  is hooked at the junction of renal pelvis and ureter and held inside the kidney. By the second holding portion  14 , the other end of the ureteral stent  8  is hooked at a junction of ureter with bladder and held inside the bladder. As a result, the connecting portion  12  is held inside the ureter  4 . Since the first holding portion  10  has the shape of the pig tail, the possible load on the body caused by the first end  11  contacting to the kidney is suppressed. Since the second holding portion  14  has the shape of the pig tail, the possible load on the body caused by the second end  15  contacting to the bladder  6  is suppressed. 
   The variation in the configuration of the ureteral stent  8  will be explained below with reference to  FIGS. 3 to 9 ,  13 A,  13 B and  14 .  FIG. 3  shows a ureteral stent  8   a  whose surface is processed so that the surface of the core wire is covered with a wire-wrapping, mesh or braid. The ureteral stent  8   a  has a core wire  16 . The core wire is flexible and hard to kink. The core wire remains in an elastic deformation region when the shape of the ureter  4  is deformed by the maximum motion of the human body. 
   The core wire  16  is a solid-core wire. Namely, it does not have therein a groove or a path where fluid (typically, urine) flows. The urine flows outside the core wire  16 . The ureteral stent  8 , which is made of metal and has the solid core wire, can be made strong and thin. For example, the sufficient strength and elastic force can be achieved even in the size of 4 F (4 French) or thinner. Moreover, the core wire can be made such that its diameter is 1 mm or less. 
     FIG. 13A  shows the closeup view of a fragmentary view of the connecting portion  12  of the ureteral stent  8 . In this case, the surface of the core wire  16  is covered by an overwinding material made of a metallic round wire  19 . Namely, the connecting portion is made of a wound string. 
     FIG. 13B  shows a cross section of the core wire  16 . The core wire  16  is not a tube but a solid round wire. Preferably, the cross section  17  of the core wire  16  in a direction perpendicular to the longitudinal direction of the core wire  16  forms a convex domain. Namely, the core wire  16  has no groove or flow path on its surface thorough which the urine flows. Such a core wire is simple and strong. Also the clogging caused by the fragments of the calculus or the like is suppressed because of the convexity of the surface. 
   In the core wire  16 , the portions near its both ends are thinner than its center portion. That is, the first holding portion  10   a  and the second holding portion  14   a  of the core wire  16  are thinner than the connecting portion  12   a . When the ureter stent is placed in the ureter, because the connecting portion  12   a  is thicker, a stronger elastic force is generated so that the urinary flow path in the ureter is straightened and the smoothness of the ureter flow is improved. On the other hand, because the first holding portion  10   a  and the second holding portion  14   a  are thinner, the elastic force is weak and the holding portions can be deformed easily. 
   The portion in contact with the human body when the ureteral stent  8   a  is placed inside the body is coated with fluoro-resin exemplified by poly-tetra-fluoro-ethylene. 
   For the safety, the cut edge of the first end  11   a  of the core wire  16  is smoothed by welding. The portion close to the first end  11   a  of the ureteral stent  8   a  is the first holding portion  10   a  processed to the shape of the pig tail. The portion close to the second end  15   a  is the second holding portion  14   a  processed to the shape of the pig tail. The surface of the core wire  16  is covered by a covering wire  18  which forms a braid. In  FIG. 3 , the covering wire  18  is symbolically drawn. Although it is away from the core wire  16  on the drawing, it is in contact with and fixed to the core wire  16  in the actual configuration. Covered string is preferably used instead of the braid-processing. The surface of the covering wire  18  is hydrophilic. Preferably, the covering wire  18  is made of metal. The covering wire  18  is welded together with the core wire  16 , at the first end  11   a  and the second end  15   a . A stripe pattern vertical to the extension direction of the connecting portion  12   a  is preferred to be drawn on the surface (portion visible from outside) of the connecting portion  12   a  of the ureteral stent  8   a.    
     FIG. 12  shows the configuration of the stent set  40  including the ureteral stent  8  exemplified by the ureteral stent  8   a . The stent  40  contains the ureteral stent  8 , a sleeve  44  and a pusher  46 . 
   Preferably, the stent set  40  further includes a ureteral stent  42 . The ureteral stent  42  is a conventional stent having a shape of a tube made of resin, having a urinary flow path therein. The inner circumference of the ureteral stent  42  slidably fits the outer circumference of the ureteral stent  8 . 
   The ureteral stent  8   a  is used as follows. The calculus located in the kidney  2  or ureter  4  is fragmented by using the process such as the ESWL (Extracorporeal Shock-Wave Lithotripsy) and the like. Before or after the process, the ureteral stent  8   a  is guided into the body. 
   The ureteral stent  8   a  is guided into the body as follows. The sleeve  44  and pusher  46  for guiding the stent  8   a  are prepared. The sleeve  44  has the shape of a tube having a path both ends of which are opened. The sleeve  44  is guided from the urethra through the bladder  6  to an inlet of the kidney  2 . 
   The ureteral stent  8   a  is guided by the path of the sleeve  44  and introduced into the urethra from the external urinary meatus side. At this time, the first holding portion  10  and the second holding portion  14  are elastically deformed and become the shapes along the path of the sleeve  44 . Following to the ureteral stent  8   a , the pusher  46  is inserted into the path of the sleeve  44  from the external urinary meatus side. In the path of the sleeve  44 , the ureteral stent  8   a  is pushed by the pusher  46  and moved toward the kidney along the sleeve  44 . Since the surface of the ureteral stent  8   a  is coated with fluoride, the friction is small and the ureteral stent  8   a  smoothly moves along the path of the sleeve. 
   Pushed by the pusher  46 , the first holding portion  10   a  goes outside the sleeve  44  (inside the kidney) from the end of the sleeve  44 . The first holding portion  10   a  is elastically deformed and returns to the shape of the pig tail. The sleeve  44  is pulled out from the side of the urethra. The ureteral stent  8   a  is hooked by an outlet of the kidney to the ureter  4  and remains at that position. When the sleeve  44  is pulled out, the second holding portion  14   a  is elastically deformed and returns to the shape of the pig tail and remains in the bladder  6 . In this way, the ureteral stent  8   a  is placed. If the stripe pattern is drawn on the surface of the connecting portion  12   a , the insertion depth of the ureteral stent  8   a  guided into the ureter can be easily recognized. 
   The longitudinal direction of the core wire  16  is substantially conforming with the ureter when the ureteral stent  8   a  is placed in the renal pelvis. 
   The operation of the ureteral stent  8   a  is explained as follows. The elastic force of the connecting portion  12   a  causes the ureter  4  to approach the shape of a straight line. This makes the flow of the urine smoother. Moreover, the ingredients or the fragmented pieces of the calculus included in the urine are easy to flow. Moreover, since the covering wire  18  is installed, a lot of gaps are existed in the portion where the ureteral stent  8   a  (having hydrophilic surface) and the ureter are in contact with each other, and the urine flows more smoothly. 
   The ureteral stent  8   a  is not hollow but solid. A flow path does not exist in the center of the ureteral stent  8   a . Thus, the cross section of the ureter  4  outside the stent is larger than that of the hollow stent, supposing that the amount of the substance included in the solid ureteral stent  8   a  is same with that of the hollow stent. Hence, the ingredients and the fragmented pieces of the calculus are easy to flow. In particular, the relatively large calculus and fragmented pieces are easy to flow. 
   Conventionally, the ureteral stent  42  that has a tube shape, namely, having the path in which the urine flows is usually used. After the ureteral stent  8   a  of this embodiment is placed in the body, if there is a need to exchange the stent  8   a  for the conventional ureteral stent  42 , the second holding portion  14  of the ureteral stent  8   a  is pulled outside the body from the urethra, and the flow path placed in the core of the conventional ureteral stent  42  is fitted with the ureteral stent  8   a . And the ureteral stent  42  is inserted into the body guided by the ureteral stent  8   a  and placed in the renal pelvis. After that, the ureteral stent  8   a  is extracted from the external edge of the ureteral stent  42 . That is, since the ureteral stent  8   a  can be used as the guide, the exchanging procedure is easy, which reduces the load on the patient. For this reason, the ureteral stent  8   a  is preferred to be used as the stent system  40  including the conventional ureteral stent  42 . 
     FIG. 14  is another example of the ureteral stent  8 - 1 . The connecting portion  12 - 1 , the first holding portion  10 - 1  and the second holding portion  14 - 1  which are made of a single core wire. The surface of the core wire has colored zones. The colored zones are placed periodically in the length direction of the core wire. Each of the color zones has a first color zone  21 - 1  and a second color zone  21 - 2 . They are placed adjacently in the length direction. The color of the second color zone  21 - 2  is different from that of the first color zone. For using the ureteral stent having such colored zones, in inserting to or withdrawing from the body, it is easy for the doctor to recognize the inserting depth of the ureteral stent. 
   Another configuration of the ureteral stent  8  will be described below with reference to  FIGS. 4 to 9 .  FIG. 4  shows a ureteral stent  8   b  having auxiliary wires. The ureteral stent  8   b  has the core wire  16  similar to that of  FIG. 3 . The ureteral stent  8   b  further has auxiliary wires  20 . One end of the auxiliary wire  20  is welded together with the core wire  16 , in a first end  11   b . The other end is welded together with the core wire  16  in a second end  15   b . The auxiliary wire  20  is longer than the core wire  16 . That is, the length along the auxiliary wire  20  between the first end  11   b  and the second end is larger than the length along the core wire  16 . Connected to the core wire  16  in both ends, the auxiliary wire  20  is elastically deformed so that the shape of the auxiliary wire  20  is convex. 
   The position where the auxiliary wire  20  is fixed to the core wire  16  can be also set as follows. That is, one end of the auxiliary wire  20  is fixed at the junction of the first holding portion  10   b  and the connecting portion  12   b , and the other end is fixed at the junction of the second holding portion  14   b  and the connecting portion  12   b.    
   Preferably, two or more auxiliary wires  20  are connected to the core wire  16 . In the case of the two auxiliary wires  20 , when any external force is not applied, it is desirable that the two auxiliary wires  20  are connected to the core wire  16  so that the core wire  16  and the two auxiliary wires are placed on the same flat surface. Namely, the first auxiliary wire and the second auxiliary wire are connected to the core wire  16  at the sides opposite to each other. 
   According to the ureteral stent  8   b , the ureter  4  is pushed and spread by the elastic force of the auxiliary wire  20 , and wide path for the urine flow is maintained. The portions where the plurality of auxiliary wires  20  are convex are moved independently of each other. For example, in the renal pelvis, when the first auxiliary wire  20  is convex in the portion near the first holding portion  10   b , the second auxiliary wire  20  is convex in the portion near the second holding portion  14   b . Such deformation reserves the urine path while protecting the excessive force from being applied to the ureter  4 . 
     FIG. 5  shows a ureteral stent  8   c  having wave-shaped auxiliary wires. The ureteral stent  8   c  has the core wire  16  similar to that of  FIG. 3 . The ureteral stent  8   c  further has auxiliary wires  22  each of which is made of round wire. One end of the auxiliary wire  22  is welded together with the core wire  16  in a first end  11   c . The other end is welded together with the core wire  16  in a second end  15   c . When the core wire  16  is straightly extended, the auxiliary wire  22  is wave-shaped. 
   The position where the auxiliary wire  22  is fixed to the core wire  16  can be also set as follows. That is, one end of the auxiliary wire  22  is fixed to the junction of the first holding portion  10   c  and the connecting portion  12   c , and the other end is fixed to the junction of the second holding portion  14   c  and the connecting portion  12   c.    
   Two or more auxiliary wires  22  are preferred to be installed. In the case that the number of the auxiliary wires  22  is two, when the force is not applied, the core wire  16  and the two auxiliary wires  22  are preferred to be installed so as to be located on the same flat surface. 
   Such a ureteral stent  8   c  provides the effect similar to the ureteral stent  8   b  in  FIG. 4 . From the viewpoint of protecting the urine path from being narrow in any portion of the ureter  4 , the configuration that the auxiliary wire  22  is wave-shaped is preferable. 
     FIG. 6  shows a ureteral stent  8   d  having a helical wire. The ureteral stent  8   d  has the helical shape which is centered on a central line  24  for connecting: a point where a first holding portion  10   d  and a connecting portion  12   d  are linked; and a point where the connecting portion  12   d  and a second holding portion  14   d  are linked, when external force is not applied. 
   With the ureteral stent  8   c , the ureter  4  is held in the shape close to a cylindrical shape, and the urine path is maintained in a desirable shape. 
     FIG. 7  shows a ureteral stent  8   e  having a plurality of thin wires along the core wire. The ureteral stent  8   e  has a plurality of thin wires  28 . The plurality of wires  28  and the core wire are welded together in a first end  11   e.  Moreover, the plurality of wires  28  and the core wire are welded together in a second end  15   e . When the plurality of wires  28  are straightly extended, they are in line contact with each other. 
   In such a ureteral stent  8   e , when the plurality of wires  28  are bundled, the size is preferred to be 4 frenches or less. A diameter is further preferred to be 1 mm or less. Since the diameter is small, the cross section of the ureter  4  outside the ureteral stent  8   e  is large, and the calculus piece is easy to flow. Moreover, since the urine can flow along each surface of the plurality of wires  28 , even the inside of the ureteral stent  8   e  can be used as the urine path. 
     FIG. 8  shows a ureteral stent  8   f  having a plurality of thin core wires and wirings wrapping the core wires. The ureteral stent  8   f  contains a plurality of wires  30  instead of the core wire  16  shown in  FIG. 3 . The plurality of wires  30  are fixed together in a first end  11   f  and a second end  15   f . Moreover, the ureteral stent  8   f  has a wiring  32  for spirally covering the plurality of wires  30 . Braid-processing covering the bundle of the plurality of wires  30  may be employed instead of the wiring  32 . Such a ureteral stent  8   f  has a strong elastic force, and its inside can be used as a urine path. 
     FIG. 9  shows a ureteral stent  8   g . The ureteral stent  8   g  has a core tube having a flow path therein. The surface of the ureteral stent  8   g  is mesh-processed. The ureteral stent  8   g  has a wire  34  that is made of metal and has the shape of a hollow tube. The wire  34  has a first end  11   g  and a second end  15   g . The wire  34  is covered by a covering wire  36  that is a braid-processed wire. The covering wire  36  is preferred to be made of metal. 
   In the ureteral stent  8   g , its inside is reserved as the urine path. With the covering wire  36 , the urine path is reserved even at a position where the ureteral stent  8   g  and the ureter  4  are in contact. The configuration that the wire  34  is made of the metal provides the effect that the uncomfortable feeling and load when it is placed inside the body is reduced. 
     FIG. 10  shows an example of a ureteral stent, in which both ends do not have the shape of the pig tail. The ureteral stent has a first holding portion  10   h  and a second holding portion  14   h  each of which is connected to an end of the connecting portion  12  including the core wire. The first holding portion  10   h  and the second holding portion  14   h  are spiral-shaped (coil-shaped). A connection point between the first holding portion  10   h  and the connecting portion  12  is assumed to be a first point, and a connection point between the connecting portion  12  and the second holding portion  14   h  is assumed to be a second point. When the external force is not applied, a first relative angle that is an angle between a central line for connecting the first point and the second point and the central axis of the coil shape of the first holding portion  10   h  is approximately 0 degree (namely, parallel). When the external force is not applied, a second relative angle that is an angle between the central line for connecting the first point and the second point and the central axis of the coil shape of the second holding portion  14   h  is approximately 0 degree (namely, parallel). The first end  11 h opposite to the first point of the first holding portion  10   h  is welded and processed for reducing the load on the human body. The second end  15   h  opposite to the second point of the second holding portion  14   h  is welded and processed for reducing the load on the human body. 
     FIG. 11  shows another configuration of the ureteral stent in which both ends do not have the shape of the pig tail. The ureteral stent has a first holding portion  10   i  and a second holding portion  14   i  each of which is connected to an end of the connecting portion  12  including the core wire. The first holding portion  10   i  and the second holding portion  14   i  are spiral-shaped (coil-shaped). A connection point between the first holding portion  10   i  and the connecting portion  12  is assumed to be a first point, and a connection point between the connecting portion  12  and the second holding portion  14   i  is assumed to be a second point. When the external force is not applied, a first relative angle that is an angle between a central line for connecting the first point and the second point and the central axis of the coil shape of the first holding portion  10   i  is approximately 0 degree (namely, vertical). When the external force is not applied, a second relative angle that is an angle between the central line for connecting the first point and the second point and the central axis of the coil shape of the second holding portion  14   i  is approximately 0 degree (namely, parallel). The first end  11   i  opposite to the first point of the first holding portion  10   i  is welded and processed for reducing the load on the human body. The second end  15   i  opposite to the second point of the second holding portion  14   i  is welded and processed for reducing the load on the human body. 
   The ureteral stent shown in  FIG. 10  or  11  is easy to process. Moreover, with the first holding portions  10   h ,  10   i  and the second holding portions  14   h ,  14   i , the ureteral stent is placed inside the ureter, and the load on the human body is reduced for the sake of the elastic force of the coil. The first relative angle and the second relative angle are properly adjusted between 0 and 90 degrees, independently of each other. At least one of the first holding portions  10   h ,  10   i  and the second holding portions  14   h ,  14   i  can be replaced by the shape of the pig tail. In the ureteral stent of  FIGS. 10  or  12 , the configuration of the connecting portion  12  can be replaced by the configuration of the connecting portions  12   a  to  12   g  shown in  FIGS. 3 to 9 . 
   The method of manufacturing the ureteral stent  8   a  shown in  FIG. 3  will be described below.
     (1) A wire rod which is used as the material for core wire  16  is cut to a predetermined length.   (2) The first holding portion  10   a  and second holding portion  14   a  of the core wire  16  are polished with a grindstone and shaved thinly to reduce the cross section.   (3) Covering the core wire by the covering wire  18 .   (4) The first end  11   a  and the second end  15   a  are welded. The welding is carried out, for example, by using gas weld. A thermal treatment that uses plasma ion is also preferable.   (5) The core wire  16  is inserted into a die by which the first end  11   a  and the second end  15   a  are elastically deformed and hold in the shape of pig tail respectively, and their shapes are fixed in a sintering furnace.   (6) The ureteral stent  8   a  having double pig tails is sealed in a pack and shipped after the surface is checked and sterilized.   

   The ureteral stent made through the above mentioned method is hard to cut and kink because the first holding portion  10   a , the second holding portion  14   a  and the connecting portion  12   a  are coupled through the integral core wire  16 .