Abstract:
A ureteral stent comprising a short renal coil made of a pliable material and a wick portion made of a material having a hydrophilicity or hydrophobicity different from that of the renal coil and extending from a ureteropelvic junction to a bladder so as to assist in the transfer of urine out of a kidney and into the bladder and to improve patient comfort. Due to increased hydrophilicity or hydrophobicity, wick may be significantly smaller in diameter than renal coil, resulting in less reflux of urine into the kidney and further decreasing patient discomfort. The stent may further comprise one or more couplers between the renal coil and wick portion, such as clamps, couplers, sutures, adhesives or receiving ends of the renal coil, and the wick portion may further comprise a sheath surrounding an elastic core to prevent kinking and enhance the ability of the wick portion to move with the patient. A novel method of ureteral stent placement is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is directed to an improved stent, for example a ureteral stent. 
         [0003]    2. Description of the Related Art 
         [0004]    A ureteral stent is used to aid in transfer of urine from one of a patient&#39;s kidneys to the patient&#39;s bladder where obstructions or other conditions may inhibit normal flow, typically by creating a path around a blockage. While the stent is used to allow for free flow of urine, the stent itself should stay in place and not migrate out of or further into the kidney, or out of or further into the bladder. 
         [0005]    In the past, ureteral stents consisted of hollow tubes having spirals or loops at both ends. The spirals caused both ends of the stent to deviate from a generally linear or tubular shape, forming structures that would less easily lead to migration of the stent. In addition, in these stents, urine would flow through the center of the tube, while the walls of the tube prevented obstructions from blocking the flow. These tubes often were designed to be as large as possible allow urine to flow more freely. 
         [0006]    Attempts to modify the traditional tube design have included changing the shape of the ends of the stent in an attempt to even further inhibit migration. 
         [0007]    Other attempts have involved replacing the bladder end of the stent with highly flexible strands or loops so as to reduce the size of the stent in the bladder end in an attempt to decrease the discomfort felt by a patient. In these designs, the stent may resemble a traditional tubular stent starting at the renal end and progressing for a significant distance, e.g., about 12 cm, or such a distance as to start the flexible strands or loops at about the iliac vessels of the patient. This significant distance was employed to further enhance migration of the stent. Stents of this type suffer from the problem that stents of multiple sizes must be created and then a physician must select what size stent to use based on approximations of the patient&#39;s physiology. In addition, even with the reduced size of the strands or loops, significant patient discomfort may result. 
         [0008]    What is needed is a ureteral stent that overcomes the drawbacks described above. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    In one aspect of the invention, a ureteral stent, comprising a renal coil at a renal end; a wick portion coupled to the renal coil and extending from an intersection with the renal coil to a bladder end; wherein the wick portion may be more rigid than the renal coil in a proximate end of the wick portion, proximate the renal coil, decreasing in rigidity or stiffness along the length of the wick portion, and the wick portion has significant hydrophilicity or hydrophobicity as compared to that of the renal coil. The renal coil may have a length from a tapered proximal end to a tapered distal end such that the distal end is located proximate a ureteropelvic junction of a patient when the renal coil is inserted into a kidney of a patient with the aid of a guidewire. In addition, the wick portion further may comprise a core and a sheath, the core comprising a material having an elasticity greater than an elasticity of the sheath. 
         [0010]    The stent may further comprise a coupler joining the renal coil to the wick portion, and the coupler may one or more of: at least one clamp, a receiver in a distal end of said renal coil, sutures and/or an adhesive. The renal coil and wick may also be one continuous member of the same hydrophilic or hydrophobic material. 
         [0011]    In another aspect of the invention, a ureteral stent comprising a renal end and a bladder end; a renal coil at the renal end, the renal coil having a proximal end, a distal end and a length therebetween; a wick portion extending from proximate the distal end to the bladder end, the wick portion comprising a hydrophilic or hydrophobic material; and/or a coupler joining the renal coil to the wick portion; wherein the length of the renal coil is such that when the stent is inserted in a patient, the distal end is located proximate a ureteropelvic junction. In addition, the renal coil may comprise a curved portion having a bottom spaced from the distal end by a distance along the renal coil of between about 0.3 cm and about 1.5 cm. Moreover, the wick portion may have an outside diameter between about 1 Fr. and about 3 Fr. 
         [0012]    These and other features and advantages are evident from the following description of the present invention, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0013]      FIG. 1  is a side view of one embodiment of a ureteral stent. 
           [0014]      FIG. 2  is a sectional view of a wick portion, taken through plane  2 - 2  in  FIG. 1 . 
           [0015]      FIG. 3  is a perspective view of one embodiment of an intersection of portions of a ureteral stent. 
           [0016]      FIG. 4  is a side view of the embodiment of  FIG. 3 . 
           [0017]      FIG. 5  is a perspective view of another embodiment of an intersection of portions of a ureteral stent. 
           [0018]      FIG. 6  is a side view of the embodiment of  FIG. 5 . 
           [0019]      FIG. 7  is a perspective view of yet another embodiment of an intersection of portions of a ureteral stent. 
           [0020]      FIG. 8  is a perspective view of still another embodiment of an intersection of portions of a ureteral stent. 
           [0021]      FIG. 9  is a section view of another embodiment of an intersection of portions of a ureteral stent showing one type of possible coupler. 
           [0022]      FIG. 10  is a section view of yet embodiment of an intersection of portions of a ureteral stent showing another type of possible coupler. 
           [0023]      FIG. 11  is a section view of still another embodiment of an intersection of portions of a ureteral stent showing yet another type of possible coupler. 
           [0024]      FIG. 12  is a schematic showing one possible installation of a ureteral stent in a urinary tract of a patient. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    As seen in  FIG. 1 , a stent such as ureteral stent  10  comprising a renal coil  22  at a renal end  20  and wick portion  32  extending from renal coil  22  to a bladder end  30 . 
         [0026]    Renal coil  22  may comprise a flexible coiled material such as a rubberized or polymerized material. As its name implies, renal coil  22  may be coiled at renal end  20  of stent  10  for locating and maintaining renal end  20  inside kidney  2 , preferably proximate renal pelvis  3 . Renal coil  22  may be spiral shaped or generally J-shaped, or it may have other configurations that will keep renal end  20  from migrating out of kidney  2 . Moreover, renal coil  22  may have a tapered end  23  at the proximal end of stent  10 , which may facilitate insertion of stent  10 . Furthermore, renal coil  22  may have a tapered end  25  for ease of stent  10  removal. 
         [0027]    In addition, renal coil  22  may be a generally tubular material having an outer diameter of between about 3 Fr. and about 10 Fr., preferably between about 5 Fr. and about 7 Fr., and in one embodiment about 6 Fr. A thicker diameter renal coil  22  may prevent movement of coil  22  from kidney  2  into ureter  4  and/or bladder  6 . However, a thicker coil  22  may also provide more discomfort for a patient. 
         [0028]    Renal coil  22  may be generally hollow proximate intersection  26  with wick portion  32  so as to provide an opening or receiver  28   a  for a guide wire  60 . In the embodiment shown in  FIG. 1 , renal coil  22  may be generally hollow along its length, which may make manufacture of renal coil  22  easier as renal coil  22  may be formed from a length of hollow tubing without requiring additional manufacturing steps. Inside diameter may be between about ½ Fr. and about 3 Fr., preferably between about 1 Fr. and about 2 Fr., and in one embodiment about 1½ Fr or about 0.038 inches. 
         [0029]    Renal coil  22  may further comprise a plurality of markings  24  spaced generally equidistantly from one another. Markings  24  may comprise a series of holes axially spaced along a length of renal coil  22 . In addition, a radioopaque mark  27  may be circumferentially placed around a perimeter of coil  22  at the distal end  25  of coil  22 , as seen in  FIG. 1 . Mark  27  may be visible to a physician under X-ray, e.g., when viewed during insertion of stent  10 . In this way, the physician may use mark  27  to determine placement of renal coil  22  within kidney  2 . 
         [0030]    To insert stent  10  in a patient, proximal end  21  of renal coil  22  may be placed over a long guidewire  60  that traverses bladder  6 , ureter  4  and resting in kidney  2 . Guidewire  60  may extend substantially along the length of renal coil  22 , from distal end  25  to proximal end  21 , causing renal coil  22  to take on a generally linear shape. 
         [0031]    A pusher may be placed over the guidewire  60  behind the stent  10 . Pusher may be between about 4 Fr. and about 5 Fr. in diameter and about 100 cm in length, although other dimensions are possible for pusher. In one embodiment, a ureteral catheter having a diameter of about 5 Fr. and a length of about 120 cm may be used as a pusher. 
         [0032]    The Pusher may exert an axial force on distal end  25  of renal coil  22  and may be used to place the distal end  25  of renal coil  22  proximate to ureteropelvic junction  5 . While stent  10  is being inserted, the pusher may be alongside wick  32  from distal end  36  up to the level of ureteropelvic junction  5 . Once an appropriate position for stent  10  is determined, guidewire  60  may be removed first, which may cause renal coil  22  to lose its generally linear shape. As renal coil  22  loses its generally linear shape and forms a loop or pigtail  70 , the pusher also may be removed, which may leave stent  10  in its desired configuration and in its desired location. 
         [0033]    Turning to  FIG. 12 , stent  10  preferably is inserted such that renal coil  22  is located within kidney  2  and/or renal pelvis  3  with intersection  26  proximate ureteropelvic junction  5 . To assist in this placement, physician may rely on mark  27 , as described above. In addition, renal coil  22  may be sized such that enough of coil  22  is within kidney  2  and/or renal pelvis  3  to keep stent  10  from migrating out of kidney  3 . At the same time, renal coil  22  may be sized so as to minimize the amount of renal coil  22  extending beyond ureteropelvic junction  5  and into ureter  4 , which may increase patient comfort. As such, renal coil may be between about 1 cm and about 9 cm long, preferably between about 2 cm and about 8 cm long, still more preferably between about 2 cm and about 5 cm long. 
         [0034]    Renal coil  22  may form a curved portion  70  such as a loop or other structure that causes coil  22  to depart from its generally linear shape moving from distal end  25  to proximal end  21 . Loop  70  may have a bottom  72  that may rest against, abut or otherwise contact kidney  2  to prevent stent  10  from inadvertently migrating out of kidney  2  after stent  10  is installed. Bottom  72  may be spaced from distal end  25  of renal coil  22  by a distance along renal coil  22  of between about 0.2 cm and about 2 cm, preferably between about 0.3 cm and about 1.5 cm, still more preferably between about 0.5 cm and about 1 cm, and in one embodiment, about 0.7 cm. 
         [0035]    Turning back to  FIG. 1 , stent  10  further comprises wick portion  32 . Wick portion  32  may comprise a single strand of material from proximal end  34  to distal end  36 . Wick portion  32  may comprise a relatively slender, relatively hydrophilic or hydrophobic material. As such, small diameter may ease patient discomfort by providing a minimally intrusive medium for conveying urine from kidney  2  to bladder  6 . In addition, hydrophilic or hydrophobic material may facilitate wicking of urine from kidney  2  to bladder  6 , further easing patient discomfort by decreasing surface tension along wick portion  32 . This decreased surface tension may also reduce and/or generally eliminate reflux of urine through ureter  4  back into kidney  2 . 
         [0036]    Wick portion  32  may have a generally constant diameter from proximal end  34  to distal end  36 . However, proximal end  34  may have variations in shape for coupling with renal coil  22 , as will be described in greater detail below. Wick portion  32  may have a diameter of between about ½ Fr. and about 6 Fr., preferably between between about 1 Fr. and about Fr., still more preferably between about 1 Fr. and about 3 Fr., and in one embodiment about 1 Fr. 
         [0037]    In addition to being relatively narrow and hydrophilic or hydrophobic, wick portion  32  may be significantly more rigid or stiff than renal coil  22  at its proximal end  34  and significantly more flexible and less rigid than renal coil  22  proximate its distal end  36 . However, despite its rigidity at its proximal end  34 , wick portion  32  preferably is not so rigid as to cause wick portion  32  to be substantially columnar since stent  10  requires flexibility to move along curves of ureter  4  and to move with patient as patient moves, i.e., to negotiate tortuosity of the ureter  4 . Wick portion  32  may have a core  33  and a sheath  35 , the core  33  comprising an elastic material that resists deformation. This may decrease trauma to a patient since elastic material may inhibit plastic deformations of wick portion  32 , which deformations may press along wall of ureter  4  and/or inhibit flow of urine into bladder  6 . In one example, wick portion  32  may be made of a material such as GLIDEWIRE, manufactured by Terumo Corporation. Acceptable properties of wick portion may be described in U.S. Pat. No. 4,876,126 to Takemura, et al. and U.S. Pat. No. 4,925,445 to Sakamoto, et al., the contents of which are both incorporated herein by reference. In another embodiment, wick  32  may also be made of polymer or other soft material with or without sheath and inner core. 
         [0038]    Decreased diameter and increased hydrophilicity or hydrophobicity contribute to decreasing patient discomfort and more than offset any increase in discomfort that may be experienced due to increased rigidity. In addition, increased rigidity and/or hydrophilicity or hydrophobicity allow renal coil  22  to be shorter than otherwise may be necessary because rigidity and/or hydrophilicity or hydrophobicity prevent wick portion  32  from migrating upward into kidney  2 . 
         [0039]    Renal coil  22  and wick portion  32  may meet at intersection  26 . As seen in  FIGS. 3-6 , renal coil  22  and wick portion  32  may be joined at intersection  26  in a number of ways. For example, as seen in the embodiment of  FIG. 3 , renal coil  122  may comprise a plurality of tapered openings or receivers  128  at a tapered distal end  125 . One receiver  128  may be sized and positioned to accommodate a proximal end  134  of wick portion  132  while a second receiver  28   a  may be sized and positioned to accommodate a guide wire  160  for installing stent  110 . Since wick portion  132  may be approximately the same size as guide wire  160 , receivers  128 ,  128   a  may be approximately equally sized and similarly tapered. However, receiver  128  may be slightly smaller than receiver  128   a  in order to allow for an interference fit between renal coil  122  and wick portion  132 . Conversely, receiver  128   a  may be slightly larger than receiver  128  so as to prevent an interference fit between guide wire  160  and receiver  128   a,  thereby allowing for easier removal of guide wire  160  after installation of stent  110 . 
         [0040]    Receiver  128   a  may be generally coaxial with a remainder of renal coil  122  such that guide wire  160  may exert a substantially axial force on renal coil  122  during installation. In this embodiment, renal coil  122  may be generally hollow along its length. This may allow guide wire to extend substantially along a length of renal coil  122  during installation. As such, renal coil  122  may be generally straight during installation, facilitating transport through ureter  4  and reducing patient discomfort. 
         [0041]    In another embodiment, receiver  128   a  may have a predetermined depth from distal end  125  to a closed end of receiver  128   a  at a point along length of renal coil  122 . This configuration may result in less of renal coil  122  being elongated or straightened prior to insertion of stent  110 . However, this configuration also provides a surface against which guide wire  160  may push, which may make installation of stent easier for the physician. 
         [0042]    In yet another embodiment, shown in  FIGS. 5 and 6 , receiver  228  for wick portion  232  may be generally coaxial with renal coil  222 , while receiver  228   a  may be offset. In this embodiment, receiver  228   a  may extend along a length of renal coil  222 . However, receiver  228   a  may have a predetermined length substantially smaller than the length of renal coil  222 . In addition, in this embodiment, receiver  228  for wick  232  may have a closed end a predetermined distance from distal end  223 , and receiver  228   a  for guidewire  260  may continue above closed end of receiver  228  and extend toward proximal end  221  of renal coil  222 . One example of the path of receiver  228   a,  which reflects the path glidewire  260  may take, is represented by the dashed lines in  FIG. 6 . 
         [0043]    In this case, external surface of receiver  228   a  may taper at its closed end  229 . This taper may have several benefits. First, it may create a transition in thickness of renal coil  222  instead of a step-type increase. As outer surface tapers, this may allow renal coil  222  to move more freely and comfortably through ureter  4 , for example, by providing a ramp surface that may slide along ureter wall if renal coil  222  were to contact ureter wall. Second, taper may form a thicker wall opposite from opening of receiver  228   a,  which may inhibit guidewire  260  from piercing renal coil  222  or may direct non-axial forces applied by guidewire  260  toward renal coil  222  instead of away from it, which may further aid in insertion of stent  10 . 
         [0044]    Turning to  FIG. 7 , another possible connection between renal coil  22  and wick portion  32  is shown. (In these embodiments, as in the preceding ones, similar parts have similar reference numerals but varying  100 s prefixes.) In the embodiment of  FIG. 7 , proximal end  334  of wick portion  332  may be flattened or otherwise deformed, e.g., by compressing proximal end  334  to form a segment of the perimeter of a cylinder. This segment may have a radius of curvature approximating that of the outside diameter of renal coil  322  such that proximal end  334  of wick portion  332  and distal end  325  of renal coil  322  substantially interface with one another. Alternatively, as seen in  FIG. 1 , proximal end  34  of wick portion  32  may be unmodified and may simply abut distal end  25  of renal coil. As a further possibility, proximal end  34  may be tapered at its tip to provide a ramp surface for sliding along wall of ureter  4  during installation, which may reduce patient discomfort. 
         [0045]    To assist in coupling of renal coil  22  and wick portion  32 , stent  10  may further comprise a coupler  440 , as shown in  FIG. 8 . Coupler  440  may comprise one or more bands or clamps  442 . Clamp  442  may be sized such that an interference fit is formed when renal coil  422  and wick portion  432  are placed within clamp  442 . As seen in  FIG. 9 , clamp  542  may entirely surround renal coil  522 . Alternatively, as seen in  FIG. 10 , clamp  642  may surround a portion of renal coil  622  and have a pair of spaced apart arms  644  defining a gap in between them. Interior surface  46  of clamp  42  may be generally curvilinear, or, as seen in  FIG. 11 , interior surface  746  may have a depression  748  for accommodating wick portion  732 . Clamp  42  may be formed of a biologically acceptable material, including metal such as titanium, nickel, steel or surgical stainless steel or a plastic material such as polyethylene or polypropylene. Moreover, clamps  42  may be radioopaque to aid in placement of stent  10 . 
         [0046]    Alternatively, or in addition, coupler  40  may comprise one or more sutures  50 . Preferably, sutures encircle renal coil  22  and wick portion  32  a plurality of times to maintain alignment of intersection  26  between wick portion  32  and renal coil. 
         [0047]    Moreover, as another alternative or addition to the couplers  40  described above, wick portion  32  may be affixed to renal coil  22  at intersection  26  using an adhesive or bonding agent. For example, adhesive may be one or more of epoxy, phenolic, thermoplastic, acrylic, cyanoacrylate, urethane, silicone and/or polyolefin. 
         [0048]    Renal coil  22  and wick portion  32  preferably overlap at intersection  26 . Overlapping intersection  26  may be minimized to reduce the width of stent  10  at intersection  26  since a narrower stent  10  may be less noticeable and more comfortable to a patient. Overlap may be between about ½ cm and about 4 cm, preferably between about 1 cm and about 3 cm, still more preferably between about 1.5 cm and about 2.5 cm, and in one embodiment, about 2 cm. 
         [0049]    Since renal coil  22  may be sized so as to terminate proximate ureteropelvic junction  5 , stent  10  may be modified for patients with different length ureters  4  by adjusting length of wick portion  32 . As such, different length stents  10  may be manufactured so that a physician has the option, e.g., of choosing a small, medium or large stent  10 . Alternatively, a longer stent  10  may be manufactured, which physician may be able to customize to an individual patient by trimming distal end  36  of wick portion  32 . This may allow for greater customization of stent  10 , further increasing comfort and/or decreasing trauma to a patient. 
         [0050]    While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific exemplary embodiment and method herein. The invention should therefore not be limited by the above described embodiment and method, but by all embodiments and methods within the scope and spirit of the invention as claimed.