Abstract:
A medical device for use within a body cavity comprising an elongated body portion and a retention module. The retention module comprises a fixation element and a tether connector. The tether connector and fixation element permit the device to move a predetermined distance longitudinally. The tether connector reduces ureteral reflux, and minimizes irritation and patient discomfort. The fixation element and the tether connector further function as a graspable structure for removal of the stent.

Description:
TECHNICAL FIELD 
   This invention generally relates to stents and more particularly to ureteral stents. 
   BACKGROUND INFORMATION 
   Ureteral stents are used to create a pathway for urinary drainage from the kidney to the bladder in patients with ureteral obstruction or injury or to protect the integrity of the ureter in a variety of surgical manipulations. A number of clinical conditions can produce interruption in urine flow including, for example, intrinsic obstruction of the ureter due to tumor growth, stricture or stones, compression of the ureter due to extrinsic tumor growth, stone fragment impactation in the ureter following extracorporeal shock wave lithotripsy (ESWL), and ureteral procedures such as ureteroscopy and endopyelotomy. Stents may be used to treat or avoid obstructions of the ureter (such as ureteral stones or ureteral tumors) that disrupt the flow of urine from the corresponding kidney to the urinary bladder. Serious obstructions of the urinary tract may cause urine to back up into the kidney, threatening renal function. Ureteral stents may also be used after endoscopic inspection of the ureter. 
   Ureteral stents typically are tubular in shape, terminating in two opposing ends: a kidney distal end and a urinary bladder proximal end. One or both of the ends of the stent may be coiled in a pigtail spiral or J-shape to prevent the upward and/or downward migration of the stent in the lumen of the ureter due, to day-to-day physical activity of the patient, for example. A kidney end coil is designed to retain the stent within the renal pelvis and to prevent stent migration down the ureter. The urinary bladder end coil is positioned in the bladder and is designed to prevent stent migration upward toward the kidney. The bladder end-coil is also used to aid in retrieval and removal of the stent. 
   A ureteral stent assists in the flow of urine from the kidney to the urinary bladder. The region known as the ureteral vesical junction is a small area of the ureter that is immediately upstream, relative to normal urine flow, to the urinary bladder. The ureteral vesical junction has greater pain sensation relative to other regions of the ureter wall and kidneys and is a major source of patient discomfort when this region of the ureter is in contact with indwelling ureteral stents. 
   Ureteral stents, particularly the portion positioned in the ureter and proximal to the bladder, may produce adverse effects including hemorrhage, a continual urge to urinate, flank pain accompanying reflux of urine back up the ureter due to retrograde pressure when voiding, and trigone irritation resulting from chronic irritation due to the bladder anchoring features of the stent or resulting from intraoperative trauma inflicted from passage of the device in the ureter. In summary, stents may cause or contribute to significant patient discomfort and serious medical problems. 
   SUMMARY OF THE INVENTION 
   In general, one aspect of the invention described herein relates to a medical device for use within a body tract such as a duct, tube or vessel. In one embodiment of this aspect of the invention, the medical device has an elongated body portion defining a lumen and a proximal portion with a proximal end, a distal portion with a distal end, and a retention module disposed proximal to the proximal end of the elongated body portion. The retention module retains the proximal end of the body portion of the stent in the ureter just distal to the urinary bladder. The retention module further includes a fixation element attached to the elongated body portion by a tether connector. The tether connector reduces ureteral reflux and patient discomfort by permitting the ureteral orifice to contract more completely around the tether connector during voiding (urination) than is possible around the elongated body portion of the stent. The tether connector or the fixation element of the retention module may also be a suitable structure for grasping and removal of the stent from the body. 
   In another embodiment, the fixation element of the retention module is substantially buoyant. In this embodiment, the buoyant fixation element may float on the urine within the bladder thereby minimizing contact of the fixation element with the tri gone of the bladder. In some embodiments, the fixation element of the retention module is of a size and configuration so as to prohibit the passage of said fixation element from the lumen of the urinary bladder into the lumen of the ureter and to allow the endoscopic introduction of the fixation element into the urinary bladder. 
   In other embodiments, the fixation element may be a planar spiral, a substantially helical spiral, or substantially spherical. In the substantially spherical form, the fixation element may have a diameter greater than the diameter of the lumen of the ureter. In another embodiment, the proximal portion of the elongated body portion is substantially more compressible than remaining portions of the elongated body portion. In this embodiment, the proximal portion of the elongated body portion will collapse with pressure exerted on it by adjacent body tissue, by peristaltic motion, or by sphincter contraction, for example. 
   In further embodiments, the retention module may have multiple tether connectors and/or multiple fixation elements to facilitate urinary drainage during conditions of peri-renal or peri-ureteral edema, for example. The tether connector of the retention module may be substantially elastic to provide a strain relief function and to minimize longitudinal movement of the stent in the ureter in the direction of the kidney when there is movement of the kidney relative to the bladder, such as during normal respiration. In different embodiments, the tether connector may be substantially rigid. In other embodiments, the elongated body portion may be substantially rigid to prevent deformation during the insertion of the device through the ureter. In another embodiment, the elongated body portion may define a plurality of openings along its length to further facilitate fluidic communication between the lumen of the body portion and the body tract where the body portion is disposed. 
   A second aspect of the invention describes a method of treating at least partial ureteral obstruction of a patient. The method according to the invention includes the steps of providing a medical device with an elongated body portion defining a lumen and having a proximal end, a distal end, a proximal portion, a distal portion, a retention module attached to the proximal end of the elongated body portion by a tether connector, and inserting the medical device into the patient such that the fixation element is positioned in the bladder of the patient. 
   The foregoing and other objects, features and advantages of the present invention disclosed herein, as well as the invention itself, will be more fully understood from the following description of preferred embodiments and claims, when read together with the accompanying drawings. In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
       FIG. 1A  is a plan view of a ureteral stent according to one embodiment of the invention. 
       FIG. 1B  is a cross-sectional view of the ureteral stent illustrated in  FIG. 1A , taken along the line B—B. 
       FIG. 1C  is a cross-sectional view of the ureteral stent illustrated in  FIG. 1A , taken along the line C—C 
       FIG. 1D  is a cross-sectional view of the ureteral stent illustrated in  FIG. 1A , taken along the line A—A. 
       FIG. 1E  illustrates the ureteral stent with a lumen having an oval cross-section according to one embodiment of the invention. 
       FIG. 1F  illustrates the ureteral stent with a lumen having a polygonal cross-section according to one embodiment of the invention. 
       FIG. 1G  illustrates the ureteral stent with a lumen having a D-shaped cross-section according to one embodiment of the invention. 
       FIG. 1H  illustrates the ureteral stent with a lumen having a crescent-shaped cross-section according to one embodiment of the invention. 
       FIG. 1I  illustrates the ureteral stent with a lumen having a rectangular cross-section according to one embodiment of the invention. 
       FIG. 2  illustrates a clinical application of a ureteral stent according to the invention. 
       FIGS. 3A–3C  illustrate enlarged views of embodiments of the retention module of proximal portion of the stent according to the invention. 
       FIGS. 4A–4C  illustrate various embodiments of the distal portion of the stent according to the invention. 
   

   DESCRIPTION 
   This invention generally concerns a drainage device that, when positioned within a body tract such as a duct, tube, or vessel of a mammal, assists in reducing fluid retention with minimal patient discomfort. For simplicity and for illustrative purposes, the invention is described here in the context of draining urine from the urinary tract such as a kidney, through a ureter, and into the urinary bladder. However, the invention is applicable to any situation that requires drainage of fluid from any site within the body. Application of the invention also applies to body sites in the body other than the urinary tract such as, for example, drainage from the gall bladder, or other biliary structures, to the duodenum. 
   Referring to  FIG. 1A , in general, a medical device according to the invention, for example, a stent  5 , is illustrated. The stent  5  includes an elongated tubular body portion  10 , a retention module  15 , a mid-portion  21 , a proximal portion  18  terminating in a proximal drainage end  35 , and a distal portion  40  terminating in a distal drainage end  50 . The retention module  15  is attached to the proximal drainage end  35  at an attachment site  20  and includes a fixation element  30  and a tether connector  25 . 
   Typically, in a ureteral application, the length of the elongated body portion  10  ranges between about 18 cm to 30 cm, preferably about 18 cm to 20 cm. In one embodiment, the body portion  10  of the ureteral stent  5  includes at least one lumen, such as lumen  12  illustrated, for example, in  FIG. 1D . The elongated body portion  10  has an outside diameter of at least about 1.6 mm to 3.3 mm, preferably 2 mm (or French size 6). The thickness of a wall  17  of the elongated body portion  10  is at least about 0.05 mm to 0.35 mm, preferably about 0.2 mm. The stent  5  may be constructed from biocompatible plastics or polymers including polytetrafluoroethylene (PTFE), silicone polyurethane, polyurethane plastics, polyethylene plastics, and thermoplastics, for example. 
   With continued reference to  FIG. 1A , in one embodiment according to the invention, the elongated body portion  10  of the stent  5  has one or more openings  19  which may be, for example, holes, pores, slits, or apertures, through the wall  17  of the stent  5 . The openings  19  allow fluidic communication between the outer surface of the stent  5  with the lumen  12  defined by the wall  17  of the ureter, for example. The elongated body portion  10  has a cross-sectional area as shown in, for example,  FIG. 1D . 
   In one embodiment according to the invention illustrated in  FIG. 1C , the wall thickness at the proximal portion  18  of the elongated body portion  10  of stent  5  is reduced, i.e., thinner relative to the thickness of the wall  17  of the other portions of the elongated body portion  10 , for example, the mid-portion  21  illustrated in  FIG. 1D . The wall  17  is thinner in the proximal portion  18  for the purpose of making the proximal portion  18  more compressible or collapsible relative to at least the mid portion  21  of the elongated body portion  10 . The collapsible wall  17  is compressible such that the wall  17  of the stent  5  in the proximal portion  18  will collapse with pressure exerted on it by adjacent body tissue, by peristaltic motion, or by sphincter contraction, for example. The collapsible wall  17  in the proximal portion  18  is constructed from one or more biocompatible plastics or polymers including, for example, polytetrafluoroethylene (PTFE), silicone, polyurethane, polyurethane plastics, polyethylene plastics, and thermoplastics and it has a thickness of less than 0.07 mm. 
   Referring to  FIG. 2 , when the proximal portion  18  of the stent  5  is compressible or collapsible, chafing and irritation of the ureter  55  is less than with more rigid stents, thereby increasing the comfort level of the patient. By employing a thinner wall  17  in the proximal portion  18  than in the other portions of the elongated body portion  10 , normal drainage of urine through the stent  5  is facilitated while some resistance to retrograde reflux of urine toward the kidney is maintained. Alternatively, the wall  17  of the stent  5  may be sized and configured with a length sufficient to extend the whole length of the ureter  55  from the renal pelvis  95  through and into the urinary bladder  60 . 
   The wall  17  in the distal region  40  of the elongated body portion  10 , for example, as illustrated in  FIG. 1D . is sufficiently thick to be generally resistant to deformation and crimping. Patency of the ureter  55  is maintained when the stent  5  is placed in the ureter  55  even when the ureter might otherwise be constricted due to enlargement of tissue surrounding the stent  5  or movement of the ureter  55  due to patient movement or peristaltic motions. The wall  17  of the distal region  40  of the elongated body portion  10 , resists collapsing upon radial or lateral pressure by the surrounding body tissue or by longitudinal pressure exerted on the wall  17  during insertion of the stent  5  into the body cavity. These properties resisting crimping are imparted to the stent  5  by varying the thickness of the wall  17  of the stent  5  relative to the rigidity of the material used to manufacture the stent  5 . For example, a wall thickness of 0.05 to 0.35 mm may be used with materials such as silicone, polytetrafluoroethylene (PTFE), polyurethane plastics, and polyethylene plastics. Referring to  FIGS. 1D–1I , for example, the cross-section of the lumen  12  of stent  5 , may be any shape that allows the flow of liquid through the lumen  12  including round, oblong, elliptical, hexagonal, D-shaped, crescent-shaped and rectangular, for example. 
   As shown in  FIG. 2 , the elongated tubular body portion  10  of the stent  5  extends from the renal pelvis  95  of the kidney  90  in the lumen  44  of the ureter  55  to a terminus at the proximal drainage end  35  positioned upstream of the urinary bladder  60 . 
   The retention module  15 , illustrated in  FIGS. 3A–3C , extends from the proximal drainage end  35  of stent  5  through the intramural tunnel  80  of the urinary bladder  60  and through ureteral orifice  70  where the retention module  15  ends in the lumen  66  of the urinary bladder  60 . 
   Referring to  FIG. 3A , the retention module  15  includes at least one fixation element  30  and one or more tether connectors  25 . In one embodiment, illustrated in  FIGS. 3A and 3B , the fixation element  30  is a substantially spherical bead having an outside diameter in the range of 3 to 10 mm, preferably 5 mm. In other embodiments, fixation element  30  may include a variety of other shapes, for example an oval, tear-shaped, or peanut-shaped bead. In one particular embodiment, illustrated in  FIG. 3C , the fixation element  30  of the retention module  15  is a suitable anchor such as, for example, a pigtail shape. Fixation element  30  is not limited to the foregoing and can be any shape that limits the passage of the fixation element  30  through the ureteral orifice  70 . 
   According to one embodiment of the invention, the fixation element  30  of the retention module is manufactured from a polymer that permits fixation element  30  to remain buoyant. Some copolymers that may be used to manufacture fixation elements  30  include, for example, a copolymer such as PERCOFLUX® (Medi-Tech, Inc.), C-FLEX® (Xomed-Trease, Inc.), FLEXIMA™, or a high density polyethylene or PTFE such as TEFLON® (E.I. Du Pont De Nemours and Company, Inc.) that permit fixation element  30  to remain buoyant. In a particular embodiment according to the invention, the fixation element  30  is buoyant relative to the specific gravity of the medium, such as urine, in which the fixation element  30  is suspended. This characteristic permits at least the fixation element  30  of the retention module  15  to remain buoyant in the lumen  66  of the urinary bladder  60  illustrated in  FIG. 2 . Alternatively, the fixation element  30  of retention module  15  is hollow and contains air, another gas, or a substance that adds buoyancy. The buoyancy of the fixation element  30  prevents the fixation element  30  from contacting and irritating the trigone  75  of the urinary bladder  60 , illustrated in  FIG. 2 , thereby minimizing patient discomfort. 
   Referring again to  FIG. 1A , retention module  15  is attached to elongated body portion  10  of stent  5  at attachment site  20  at the proximal drainage end  35  of stent  5 . The tether connector  25  of the retention module  15  has a total length in the range of about 2 to 5 cm, preferably 3 cm, a diameter in the range of about 0.15 to 0.23 mm, preferably 0.2 mm. In one embodiment, the tether connector  25  is made of an elastomeric material, for example, HYTREL® (E.I. Du Pont De Nemours and Company, Inc.), silicone, or a thermoplastic elastomer (TPE), to provide strain relief. Typically the tether connector  25  as illustrated in  FIG. 1B , is cord-like, lacking a lumen. In different embodiments, the tether connector  25  may be substantially elastic and flexible or the tether connector  25  maybe substantially rigid and inflexible. 
   Referring again to  FIG. 3A , the tether connector  25  may be integral with, or detachable from, the elongated body portion  10 . For example, tether connector  25  may be integrally formed as part of the proximal portion  18  of the body portion  10 , the circumference of which is subsequently and substantially removed through an appropriate manufacturing process to yield tether connector  25 . Alternatively, tether connector  25  is attached at attachment site  20  of stent  5  before replacement of the stent  5  in the body cavity. In the latter example, tether connector  25  is reversibly attached to elongated body portion  10  at attachment site  20  by any suitable means, such as, for example, by adhesive, or by mechanical connection. Suitable mechanical connections include, for example, threading and tying tether connector  25  through an opening (not shown) in the wall  17  of body portion  10 , or forming tether connector  25  with a preformed shape such as a hook that connects with an opening or attachment site  20  associated with elongated body portion  10 . 
   Referring again to  FIG. 2 , after the stent  5  is deployed in the body, the tether connector  25  is located within the intramural tunnel  80  of the urinary bladder  60 . In general, the length of the tether connector  25  is in the range of about 2 to 5 cm, preferably 3 cm. In one embodiment, the ends of the tether connector  25  extend proximal and distal to the intramural tunnel  80 . The tether connector  25  allows for anatomical variation among patients by compensating for variations in length of the intramural tunnel  80  from patient to patient. The fixation element  30  and/or the tether connector  25  may be grasped by an operator for easy removal of the stent  5  from its location in the body. The tether connector  25  and fixation element  30  of the retention module  15  permit the stent  5  to freely migrate longitudinally in the lumen  44  of the ureter  55  by a distance determined by the length of the tether connector  25 . By flexibly, yet securely joining the proximal portion  18  of the stent  5  to the fixation element  30  by means of a tether connector  25 , the tether connector  25  provides resistance to upward movement of stent  5  in the direction of the kidney  90  during movement of the kidneys caused by respiration, peristalsis or other voluntary or involuntary activity of the patient. The migration of the stent  5  by a fixed distance that corresponds to the length of the tether connector  25  minimizes the irritation and patient discomfort that can be caused by conventional stent anchoring elements that substantially fix the stent  5  in one position in the ureter  55  and do not permit the stent  5  to migrate with body movements. 
   The tether connector  25 , according to the invention, extends from the proximal end  35  of the stent  5  and has a smaller diameter than the elongated body portion  10 . Because of its small diameter, tether connector  25  minimizes ureteral reflux, (i.e., flow of urine back up the ureter toward the kidney during voiding) because the intramural tunnel  80  of the urinary bladder  60  is collapsed around the small diameter tether connector  25  when the urinary bladder contracts during voiding. Tether connector  25  also minimizes patient discomfort associated with obstructions in the ureteral orifice  70 . The number, size and configuration of fixation elements  30 , as described below, may be customized to accommodate the migration-prevention requirements of the particular stent to be implanted in the patient&#39;s body. 
   In another embodiment of the invention illustrated in  FIG. 3A , the retention module  15  includes a plurality of tether connectors  25  attached to the attachment site  20  of the elongated body portion  10 . The plurality of tether connectors  25  facilitates urinary drainage through the intramural tunnel  80  of the urinary bladder  60 , shown in  FIG. 2  under numerous pathological conditions including, for example, swelling of the tissue in and around intramural tunnel  80  caused by edema induced by trauma during insertion of the stent  5 . The combined action of the plurality of tether connectors  25  permits wicking of urine to the urinary bladder  60  but reduces urine reflux from the urinary bladder  60  retrograde to the ureter  55 . In this embodiment, at least one tether connector  25  is attached to the fixation element  30 . In another embodiment, illustrated, for example, in  FIG. 3B , more than one multiple fixation element  30  may be attached to each of the tether connectors  25 . 
     FIGS. 4A–4C  depict an enlarged view of the various embodiments of distal portion  40 . The stent  5  includes a kidney retention anchor or pigtail  45  at the distal portion  40 . The pigtail  45  is formed by bending the distal portion  40  of the stent  5  into a planar or substantially planar spiral. The pigtail  45  is shown having one of a variety of possible configurations that serve to retain the stent  5  in the renal pelvis  95  of the kidney  90 . In one embodiment, as shown in  FIG. 4A , the pigtail  45  is formed by shaping the distal portion  40  of the stent  5  into a spiral planar coil formed with a multiplicity of turns wound concentrically within the same plane. In another embodiment, as shown in FIG.  4 B, the pigtail  45  is formed by shaping the distal portion  40  of the stent  5  into a helical coil formed with at least one wound turn. In a further embodiment, as shown in  FIG. 4C , the pigtail  45  is formed at the distal portion  40  of the stent  5  with at least one helical coil further comprises a plurality of openings  19  arranged in various patterns. 
   Referring again to  FIG. 2 , according to another embodiment of the invention, stent  5  is deployed by an operator in the ureter  55 , by inserting a relatively rigid wire guide (not shown) into lumen  12  of the stent  5  from the proximal portion  18  of the stent  5  to the distal portion  40  of the stent  5 . If the stent  5  includes a pigtail  45  at the distal portion  40  of the elongated portion  10 , the wire guide straightens out the spiral pigtail  45  prior to insertion of the stent  5  into the patient&#39;s body. The wire guide, together with the stent  5 , is inserted by an operator either endoscopically or transurethrally into the urinary bladder  60 . The stent  5  is advanced through one of the ureteral orifices  70  and along the lumen  44  of the ureter  55  via a pushing action until the distal portion  40  of the stent  5  is proximal to the renal pelvis  95 . The wire guide is then withdrawn from the lumen  12  of the distal portion  40  of the stent  5  either endoscopically or transurethrally wherein the pigtail  45  returns to its former spiral shape within the renal pelvis  95 . The spiral shape of pigtail  45  anchors the distal portion  40  thereby reducing longitudinal migration of the stent  5  away from the kidney  90  in the lumen  44  of the ureter  55 . 
   With the distal portion  40  of the stent  5  in place, the wire guide is withdrawn further from the lumen  12  of the elongated body portion  10  of the stent  5  followed by complete removal of the wire guide from the patient. The retention module  15  remains attached to the proximal drainage end  35  of the body portion  10  via the tether connector  25  at the attachment site  20 . The tether connector  25  extends through the intramural tunnel  80  to the fixation element  30  and terminates in the lumen  66  of the urinary bladder  60 . The stent  5  and the retention module  15  are selected according to the clinical needs of the patient and must be attached to the proximal portion  18  of stent  5  before the insertion of stent  5  into a body cavity. 
   Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the invention is not to be limited to the preceding illustrative description but instead by the spirit and scope of the following claims.