Abstract:
An apparatus for compressing a coiled stent having at least one protrusion, such as an enlarged coil disposed at the end of the stent, has a mandrel insertable into a lumen of the stent for holding the stent by friction and a coil compressor coupled to the mandrel. The mandrel is rotatable on an axis relative to the coil compressor and the coil compressor has a tab extending therefrom towards the mandrel. A stent is placed on the mandrel with the enlarged coil extending toward the coil compressor. The tab presses the enlarged coil inwardly toward the lumen of the stent when the mandrel is rotated relative to the coil compressor.

Description:
FIELD OF THE INVENTION 
     The present invention relates to apparatus used for compressing a coiled stent and more particularly, for compressing a specific end portion of a stent prior to insertion either into an insertion apparatus or directly within the body. 
     BACKGROUND OF THE INVENTION 
     Lower urinary tract symptoms (LUTS), common among older men, include a variety of disorders that can lead to urinary retention and complications resulting from retention. Some of the conditions falling under a LUTS diagnosis include an enlarged prostate, BPH, and bladder outlet obstruction. 
     The constriction of the urethra due to prostatic enlargement can be treated by the implantation of a prostatic urethral stent. The stent serves to hold the prostatic urethra open to allow urination. This is typically an interim solution used before or after corrective treatment, e.g., a stent may be implanted after radiation treatments, thermal therapy or cryosurgery to keep the urethra open while post-treatment edema subsides. In some instances, a stent may be implanted as a primary treatment. 
     Generally, urethral stents are tubular in shape and may be in the form of a solid tube, coiled wire, ribbon or mesh, or formed from braided filaments. Coiled stents may be designed to have at least a portion thereof with outer diameter equal to or larger than the average urethral lumen diameter, such that when expanded, the stent frictionally engages the urethra into which it has been inserted. The larger diameter coils of such stents need to be radially compressed prior to insertion into a stent delivery system, e.g., a catheter sheath, or within the urethra. After being positioned in the urethra, urethral stents are radially expanded into their final shape, typically by thermal or mechanical means, or, in the case of self-expanding stents, allowed to elastically expand when a sheath or other restraining means is removed. 
     Brenneman et al. (U.S. Pat. No. 5,160,341) disclose a device including a retractable sheath surrounding a rotatable rod journaled in a stationary tubular bushing. One end of the stent is mounted on the rod while the other end of the stent is fixed to the bushing so that relative rotation of the rod and bushing compresses the entire stent by coiling it more tightly. After insertion within the body, the rod and bushing are then rotated in the opposite direction to uncoil the stent to its original diameter. A shearing sleeve with a shearing edge is advanced between the rod and bushing to sever the stent from its attachment to the bushing and the rod. 
     In the above device, both ends of the stent are used to engage the urethra and the diameter along the entire stent length is reduced. Reduction of stent diameter results in a concomitant increase in length in the reduced region. Reduction of stent diameter along the entire stent length will therefore result in significant length increases upon diameter reduction, sizing, bunching, and consequent placement issues within the anatomy. In some coil stent designs, only an end portion of the stent has a varying diameter. It is undesirable, particularly with polymer stents, to expose a stent to unnecessary forces due to risk of plastic deformation or creep. There are also risks associated with introducing a shearing sleeve with shearing edge within the urethra e.g. breakage, contamination and/or injury. In addition, the cut ends of the stent are sharp and pose a risk of penetrating the urethra. 
     Yachia et al. (U.S. Pat. No. 5,246,445) disclose stents with non-uniform windings such that one or more coils along the length of the stent bulge out circumferentially. An apparatus is disclosed which fixes either end of the stent and through torquing action, radially compresses the bulges. Here again, the entire length of the stent is reduced by rotating the ends of the helical spiral in opposite directions. A small hook, ring, or ball is provided at each end of the stent for grasping it. These features diminish uninterrupted flow capacity through the stent and increase the complexity of manufacture. Counter-rotation is required to release the stent. 
     Limon (U.S. Pat. No. 5,476,505) discloses a stent delivery system including a catheter formed from coaxially arranged inner and outer flexible shafts, the distal ends of which have slots or apertures to engage the ends of a coiled stent. The entire length of the stent is effected by inducing tighter coiling. The device is counter-rotated to expand and release the stent. 
     It would therefore be desirable to be able to radially compress selected regions of a coiled stent without compressing the entire stent. Such a device can be used to facilitate placement of the stent either within a secondary insertion tool or directly within the body. 
     SUMMARY OF THE INVENTION 
     The limitations of prior art apparatus for compressing stents are overcome by the present invention which includes an apparatus for compressing a coiled stent having at least one protrusion. The apparatus has a mandrel insertable into a lumen of the stent for holding the stent and a coil compressor coupled to the mandrel. The mandrel is rotatable on an axis relative to the coil compressor and the coil compressor has a tab extending therefrom towards the mandrel. The tab presses the protrusion of the stent inwardly toward the lumen of the stent when the mandrel is rotated relative to the coil compressor. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The novel features of the present invention will be more readily apparent upon reading the following description in conjunction with the drawings in which like elements in different figures are identified by the same reference numeral and wherein: 
         FIG. 1  is an exploded view of a stent reducer in accordance with an embodiment of the present invention; 
         FIG. 2  is an exploded view of a latch assembly of the stent reducer of  FIG. 1 ; 
         FIG. 3  is a perspective view of the latch assembly of  FIG. 2 ; 
         FIG. 4  is a partially exploded view of the latch assembly and mandrel knob of the stent reducer of  FIGS. 1-3 ; 
         FIG. 5  is a perspective view of the stent reducer of  FIGS. 1-4 ; 
         FIG. 6  is a perspective view of the stent reducer device of  FIGS. 1-5  with a stent on the mandrel; 
         FIG. 7  is a partial cross-sectional view of the stent reducer of  FIGS. 1-6  taken along section line VII-VII looking in the direction of the arrows and with a stent on the mandrel prior to reduction of the distal stent diameter; 
         FIG. 8  is a cross-sectional view like  FIG. 7 , but after reduction of the distal stent diameter; 
         FIG. 9  is a cross-sectional view like  FIG. 8  as the stent is being loaded into a sheath; and 
         FIG. 10  is a cross-sectional view of the stent loaded into the sheath. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 through 9  show a stent reducer  10  for use in radially compressing selected larger diameter, radially-expanded coils  86  (See  FIG. 6 ) of a coiled stent  80  without radially compressing the entire stent along its length. Stent  80  has a generally cylindrical coil shape, such as the stent described in U.S. patent application Ser. No. 10/602,338, entitled “Biodegradable stent”, assigned to Ethicon Incorporated, filed Jun. 24, 2003, and incorporated herein by reference. 
     The stent  80  has a distal end  84  and a proximal end  82 . Note that “proximal” and “distal” are reversed from the directionality of the stent reducer  10 , because the convention applied to the stent  80  is relative to the bladder of the patient in which the stent  80  is placed. The diameter of the distal end  84  is greater than the remainder of the stent  80  due to radially expanded coil  86 . While more than one complete turn of the coiled stent  80  is enlarged in  FIG. 6 , less than or greater than one complete turn of the stent  80  may be enlarged. 
     As shown in  FIG. 1 , stent reducer  10  has a mandrel  20  with a tapering distal end  22  which facilitates the insertion of the mandrel  20  into the lumen  81  (See  FIG. 6 ) of the coiled stent  80 , a proximal end  24  and a stent fixation zone  26 . The diameter of the stent fixation zone  26  is the same as, or slightly larger than, the inner diameter of at least some portion of the stent  80 , so that an interference fit is established between stent  80  and stent fixation zone  26  when the mandrel  20  is inserted into the stent  80 . Preferably, the stent  80  can be rotated on the mandrel manually with minimal resistance. Since the stent  80  has a spiral shape, manual rotation of the stent  80  on the mandrel  20  can serve to advance the stent  80  over the mandrel  20  in threaded fashion. The surface of the stent fixation zone  26  may be textured to enhance the interference fit/thread-like interaction established between the stent  80  and stent fixation zone  26 . The mandrel  20  may be one-piece or in a plurality of modular sections to accommodate various stent  80  sizes. The modular sections can be connected by conventional means, e.g., threads, snap-fit coupling, etc. A latch assembly  30  for compressing protrusions in the stent  80 , such as expanded coils  86 , slips over the proximal end  24  of the mandrel  20 , as does mandrel knob  60 . 
       FIG. 2  shows an exploded view of latch assembly  30 , which includes latch knob  40  and latch collar  50 . The latch knob  40  has a grip portion  42 , a hub portion  44  with a slot  45 , and a post portion  46  with a relief  47 . The latch knob  40  has an axial cannulation  41  into which the post  64  of mandrel knob  60  inserts and which also allows the mandrel  20  to extend through the latch knob  40 . The latch knob  40  has ball plunger detents  49  on its proximal end (see  FIG. 4 ). Latch collar  50  has a flange  52  against which the fingers of a user may press to control the position thereof. A pin  57  extends through hole  58  after the latch collar  50  is slidably and coaxially slipped onto the hub portion  44 , the end of the pin  57  being accommodated in slot  45  and retaining the latch collar  50  on the latch knob  40  while permitting relative movement to the extent of the length of the slot  45 . The latch collar  50  has a stepped internal bore  59  having internal dimensions approximating the external dimensions of the hub and post portions  44 ,  46  of the latch knob  40 . A sleeve  54  extends from the flange  52  and has a distal tab  56  for contacting and compressing the stent  80 . 
     As shown in  FIG. 3 , when assembled to form latch assembly  30 , tab  56  overhangs relief  47 . The length of slot  45  limits the range of axial motion of latch knob  40  in the distal direction to the point where tab  56  at least partially overhangs relief  47 . 
       FIG. 4  shows mandrel knob  60 , which has a grip portion  62  with a mandrel bore  65  for receiving proximal end  24  of mandrel  20  therein. The mandrel  20  is retained by a set screw (not shown) inserted into a threaded bore  66  and bearing upon the proximal end  24  thereof. A ball plunger  68  or similar spring-tape resilient member (not shown) is received within mating bore  69 . Detents  49  are provided on a proximal surface  43  of latch knob  40  and receive the ball plunger  68  therein to control the axial rotation of mandrel knob  60  and mandrel  20  relative to the latch knob  40 .  FIG. 4  shows the latch knob  40  withdrawn to a proximal position wherein the tab  56  is retracted from relief  47 . 
       FIG. 5  shows the fully assembled stent reducer  10 . The diameter of stent fixation zone  26  is approximately the same as the diameter of post portion  46 . This prevents latch assembly  30  from sliding off of the mandrel  20 . 
       FIG. 6  shows a stent  80  in position on the mandrel  20  of stent reducer  10  prior to compression of radially expanded coils  86  on the distal end  84  of the stent  80 . 
       FIG. 7 through 10  show cross-sectional views of the stent reducer  10  and how it is used to reduce the diameter of the enlarged coils  86  at the distal end  84  of the stent  80 , and load the stent  80  into a sheath  90 . In  FIG. 7 , the mandrel  20  is inserted into the lumen of stent  80 . The enlarged coils  86  of stent  80  distal end  84  are of a larger diameter than the remainder of the stent  80  and extend beyond the stent fixation zone  26  in the proximal direction. The latch collar  50  is positioned proximally on the latch knob  40  such that the tab  56  is retracted to a position removed from relief  47 . 
       FIG. 8  shows the reduced distal end  84  of the stent  80  resulting from pushing the latch collar  50  forward, such that the tab  56  extends over an outer surface of the enlarged coil  86 , capturing it between the tab  56  and the relief  47 . 
     The user then grasps the mandrel knob  60  and the latch knob  40  and axially rotates the mandrel knob  60  relative to the latch knob  40  to reduce the diameter of the distal end  84  of stent  80 . The ball plunger  68  and ball plunger detents  49  ( FIG. 4 ) provide controlled relative rotation defining discrete tightening steps to avoid overrotation of stent  80 . Once the outer diameter of the enlarged coils  86  are reduced, the stent  80  may be inserted into the sheath  90 . When the stent  80  is fully inserted into sheath  90  i.e., beyond sheath proximal end  92 , the user pulls the latch collar  50  proximally, releasing its hold on the enlarged coils  86  and permitting them to expand with the sheath exerting a frictional grip thereon. The mandrel  20  is then removed from the stent lumen  81 , leaving the stent  80  disposed (loaded) in the sheath  90 .  FIG. 10  shows a stent  80  in a sheath  90  after removal of the mandrel  20 .