Patent Document

TECHNICAL FIELD 
     This invention relates to a tool which defines a basket cavity for removing a discrete object from the body of a human or animal patient, said tool having an elongate shaft having a tool head at a distal end thereof, said tool head having a radially compact disposition and a radially spread disposition for embracing said object. 
     BACKGROUND ART 
     The present applicant manufactures a device for catching, fixing and removing foreign objects form the body of a human patient. These foreign objects can include stones, fragments and concrements in the medical fields of urology and gastro-enterology. In the present device, both ends of a number of individual wires are held together by a ring. Normally, the wires have a circular cross-section. One of these rings forms the distal end of a shaft and the other ring is spaced distally axially from the first ring. When the individual wires are all bowed radially outwardly and are distributed at regular intervals around the circumference of the axis, then these wires form longitudinal strands of an envelope defining a cavity centered on the long axis of the shaft. The wires are resilient and are given an outwardly bowed symmetrically or helically twisted shape so as to define a basket cavity radially inwardly of the envelope defined by the wires. The number of wires is usually in a range of from two to six. The entire device is placed within a sheath. For catching the foreign object, the distal end of the shaft and basket assembly is advanced out of the distal end of the sheath, allowing the resilience of the wires to form the basket by outward bowing. Once the foreign object is fished into the basket, then the shaft can be withdrawn proximally, to a greater or lesser extent, in order that the distal end of the sheath should squeeze down the diameter of the basket so that the basket wires grip the foreign object in the reduced diameter basket cavity immediately adjacent the distal end of the sleeve. Then the shaft and sleeve can together be withdrawn in the proximal direction to carry the foreign object in the basket out of the body. 
     In endoscopic surgery, a small diameter of the sheath is desirable. Currently the devices on the market have a sheath diameter falling within a range of outside diameters from 0.63 to 1.83 mm, which corresponds to a range of 1.9 to 5.5 French (1 French=⅓ mm). 
     One disadvantage of the presently marketed devices is that soldered, welded or glued joints are used to fix the individual wires to the rings and to the shaft. These connections represent a potential failure risk and, in any event, their ultimate strength has to be ascertained by extensive examination and testing. 
     Apart from this, the jointing of the wires at the rings defines the greatest outer diameter of the shaft element of the device, which therefore determines the inner diameter of the sheath and therefore indirectly determines the outer diameter of the sheath, setting a limit on the minimization of the outer sheath diameter. 
     Furthermore, the envelope of wires determines a characteristic mesh size of the basket and this mesh size has to be suitable both for fishing an object into the basket and then for retaining it within the basket until it has been removed from the body. Whereas a small mesh helps retention and removal, it does not help in the process of fishing the foreign object into the basket. A compromise mesh size has to be adopted. 
     EP-A-818 180 discloses an endoscope accessory in the form of a tube with a slitted distal end portion. The slits can be deformed radially outwardly to define a plurality of openings, by pulling from the proximal end of the tube on a pull wire  13  connected at its distal end to the distal end of the slitted portion. The disclosure of EP-A-737 450 is, in these respects, similar and U.S. Pat. No. 4,807,627. 
     EP-A-512 729 discloses an endoscopic surgical instrument which includes a tube having a slitted portion at its distal end. In a relaxed disposition of the wall portions between the slits, they are spaced apart from one another to form a basket. The slitted tube is itself co-axially within an outer tube having a distal end, and the basket can be closed down by drawing the basket, beginning at its proximal end, proximally into the outer tube, past the distal end of the outer tube. The slitted tube is made of a polyurethane material and the basket is formed by the application of steam heating to the slitted end. 
     DE-A-197 22 429 discloses a Nitinol tube, slitted at its distal end, for use as a basket to gather stones from bodily cavities. It is said to differ from previous such baskets in that the strands of the basket are unitary with the tube. 
     WO 94/18888 is another disclosure of a stone-gathering basket made from a plurality of Nitinol wires. The wires are arranged around the circumference of the basket in pairs and given a helical twist, which is said to increase the number of points of contact between the basket and entrapped calculi and to require of the physician no more dexterity than the prior art baskets, having a smaller number of contact points, required. 
     WO 96/23446 discloses a stone-gathering basket in which a distal half of the basket envelope exhibits a greater number of basket strands than the proximal half of the basket envelope. Each lengthwise strand in the proximal half of the baskets splits at half distance over the basket envelope into a plurality of strands which help to define the proximal half of the basket envelope. At the distal end of the basket is a cap to which all of the filaments defining the basket envelope are welded. 
     WO 99/16365 discloses a stone-gathering basket defined by a plurality of legs and with discussion what cross-sectional shapes of the legs are useful, and what surface topography on the inward facing surface of each leg. 
     WO 99/48429 is another disclosure of a stone gathering basket made unitary from a tube with longitudinal slits at its distal end, the basket being relaxed in its expanded configuration and of a material which can be a nickel titanium shape memory alloy such as Nitinol. 
     SUMMARY OF THE INVENTION 
     The present invention aims to mitigate some or all of the above-mentioned difficulties and, in any event, aims to improve present technology. 
     According to one aspect of the present invention, there is provided a medical device as described above, for removing a foreign object from the body of a human or an animal patient, which is characterized in that:
         1. the shaft and tool head are formed from a single length of a tubing;   2. said tubing is slit lengthwise within a length contained within said tool head and stopping short of a distal end surface of said tube, thereby to form at least three parallel first strands which together define an envelope of said basket cavity; and   3. the tool is provided with a set of second strands, each formed by slitting one of the first strands over a distal portion of said first strand, which distal portion is less than the full length of the first strand.       

     In this way, it can be arranged that the mesh size of the basket structure, of the distal end of the basket, is provided as smaller apertures than are present at the proximal end of the basket. In this way, foreign objects can be fished into the basket at its proximal end, after which they can be retained in the smaller aperture mesh at the distal end of the basket. In one preferred embodiment, the second strands have a length in a range of from 45% to 80% of the length of the first strands. 
     It will be appreciated that, in the tool of the present invention, no joints are required. The basket is instead made from the base tubing of the shaft of the tool. 
     Further, it will be appreciated that the largest diameter of the tool is represented by the basic tubing itself, there being no larger diameter of rings at each end of the basket. 
     Conceivably, a basket could be constructed by slitting each of the second strands over a portion of its length which is less than the full length of the second strand, thereby to define a set of third strands over part of the length of the basket, setting a aperture size in that zone of the length of the basket smaller than would otherwise be the case in the absence of the third strands. For example, the zone of the third strands could be in a “belly portion” of the basket where its diameter is close to its maximum, thereby to achieve an aperture size in this belly portion smaller than an aperture size in a proximal half of the basket envelope, thereby better to retain an object captured in the proximal half of the basket in the smaller mesh size of the distal half of the basket. 
     Conveniently, the tubing is made from nickel titanium shape memory alloy and the strands are formed by a narrow diameter laser beam which cuts through the wall of the tubing. 
     It will be appreciated that, the device being based on a tube, there is the possibility to provide a guide wire or other core wire during use of the tool. For example, one could advance the tool into position along a previously placed guide wire. For laser cutting, one could set within the tubing work piece a core, so that the incident laser beam passes through one wall thickness and into the core, but not beyond the core into the wall thickness of the tubing on the opposite side of the core. In this way, one could slit the tube at 120° intervals around its circumference in order to create three first strands, and then the laser could be used to slit each of the three first strands, along a distal portion of its length, into two second strands, making a total of six second strands distributed at sixty degree intervals around the circumference of the tubing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For better understanding of the present invention, and to show more clearly how the same are recurred into effect, reference will now be made, by way of example, to the accompanying drawings, in which: 
         FIG. 1  is a longitudinal diagrammatic section of a prior art tool for removing a foreign object from the body of a patient; 
         FIG. 2  is a similar section through a first embodiment of a tool in accordance with the present invention, in its compact disposition; 
         FIG. 3  is a section corresponding to  FIG. 2 , and showing the  FIG. 2  tool in spread disposition; 
         FIG. 4  shows a transverse section through line IV-IV in  FIG. 2 ; 
         FIG. 5  is a transverse section through line V-V of  FIG. 2 ; 
         FIG. 6  is a longitudinal diagrammatic section of another embodiment of a tool in accordance with the present invention, in its compact disposition; 
         FIG. 7  is a section corresponding to  FIG. 6 , and showing the  FIG. 6  tool in spread disposition. 
         FIG. 8  is a longitudinal diagrammatic section of yet another embodiment of a tool in accordance with the present invention, in its compact disposition; and 
         FIG. 9  is a section corresponding to  FIG. 8 , and showing the  FIG. 8  tool in spread disposition. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a conventional tool has a shaft  12  with a distal end  14  on which is mounted a first ring  16 . Welded within the open distal end of the ring  16 , side by side, are four nickel titanium shape memory alloys circular section wires  18 . All four distal ends of the wire  18  are welded within an end ring  20  spaced from the distal end  14  to the shaft  12  and itself representing a distal end of the device  10 . Each of the wires  18  is given a bowed shape, as shown in the figure, by thermal treatment as is understood by those skilled in this art. The entire device is telescoped within a sleeve (not shown) having an inner diameter big enough to accommodate the rings  16  and  20 . 
     For catching and removing foreign objects, the distal end of the sleeve is advanced to a desired location within the body and then the shaft  12  is advanced until the basket  18  opens just distally beyond the distal end of the sleeve. Moving the sleeve, the medical practitioner fishes the target object into the cavity  22  within the basket defined by the wires  18 , and the shaft  12  is withdrawn proximally by a distance sufficient for the distal end of the sheath to squeeze the wires  18  onto the foreign object, thereby retaining it within the basket cavity  20 . Then the sheath and shaft are together withdrawn proximally, carrying the object out of the body. 
     The method of use of a tool in accordance with the present invention is similar. However, the manufacture of the tool is quite different, as can be seen from  FIG. 2 . 
       FIG. 2  shows a tool  40  based on a single length of tubing  42  having a lumen  44  which runs its full length. The tube is of Nitinol shape memory alloy. Near the distal end of the tube  42  is provided a plurality of slits, comprising a set of four first slits  46  arranged at ninety degree intervals around the circumference of the tube  42 . Evenly spaced between each pair of first slits  46  are the slits of a set of four second slits  48 , again made by laser.  FIG. 2  shows a core wire  49  which can be placed within the lumen  44 , at the distal zone of the tubing  42 , if it is desired for the incident laser beam to penetrate only one wall thickness of the tubing  42 , and not go beyond the lumen  44  (as would be appropriate if, for example, an arrangement of three first slits  46 , at  120  degree intervals around the circumference of the tubing  42 , were to be specified). The length of the set of first slits  46  corresponds to the desired length of the object-catching basket of the tool  40 . 
     Now referring to  FIG. 3 , the basket of the  FIG. 2  tool can be seen in its spread disposition. Just as Nitinol stents are given a remembered dimension by heat treatment, so the tool of  FIG. 2  is given by heat treatment the basket shape illustrated in  FIG. 3 . Thus, when the tubing  42  is advanced into a surrounding sheath, the strands  50  between adjacent first slits  46 , and the strands  52 , between adjacent first and second slits  46 ,  48 , are squeezed down from the spread disposition of  FIG. 3  into the compact disposition shown in  FIG. 2 . Then, when the distal end of the tubing  42  is advanced distally out of the distal end of the sleeve, the strands  50  and  52  can take up the remembered deployed disposition of  FIG. 3 . 
       FIGS. 3 ,  4  and  5  reveal a valuable technical effect of the present invention, namely, that the mesh size of the basket can be varied, from one end of the basket to the other, allowing foreign objects to be introduced into the basket envelope through the relatively wide aperture zone of the proximal end of the basket, but then more securely retained within the basket at the relatively smaller diameter aperture portions at the distal end of the basket. Note also in  FIG. 3  the presence of a guide wire  54 . The tool could be advanced on such a guide wire, into a desired location, then the guide wire  54  could be withdrawn proximally, to leave the basket cavity empty, and then the foreign object could be fished into the basket. 
       FIG. 6  shows a tool  40 ′ based on a single length of tubing  42 ′ having a lumen  44 ′ that runs its full length. Near the distal end of the tube  42 ′ is provided a plurality of slits, comprising a set of four first slits  46 ′ arranged at ninety degree intervals around the circumference of the tube  42 ′. At a distal end of the first slits  46 ′ and evenly spaced between each pair of first slits  46 ′ are the slits of a set of four second slits  48 ′, again made by laser. At a distal end of the second slits  48 ′ and evenly spaced between each pair of second slits  48 ′ are the slits of a set of eight third slits  58 ′, again made by laser. Other slit affangements are contemplated, such as, for example, three first slits  46 ′ at 120 degree intervals around the circumference of the tubing  42 ′. The length of the set of first slits  46 ′ corresponds to the desired length of the object-catching basket of the tool  40 ′. 
     Refeffing to  FIG. 7 , the basket of the  FIG. 6  tool can be seen in its spread disposition. The basket may be constructed by slitting each of the first strands  50 ′ over a distal portion of its length, which is less than the full length of the first strand, thereby defining a set of second strands  52 ′. These second strands  52 ′ may be further slit over a distal portion of its length which is less than the full length of the second strand, thereby defining a set of third strands  60 ′ over a distal part of the length of the basket, setting an aperture size in that zone of the length of the basket smaller than would otherwise be the case in the absence of the third strands  60 ′. The resulting strands achieve an aperture size smaller at the distal end than at the proximal end of the basket envelope, thereby better to retain an object in the smaller mesh size of the distal half of the basket, yet captured in the larger mesh size of the proximal half of the basket. 
       FIG. 8  shows a tool  40 ″ based on a single length of tubing  42 ″ having a lumen  44 ″ which runs its full length. Near the distal end of the tube  42 ″ is provided a plurality of slits, comprising a set of four first slits  46 ″ affanged at ninety degree intervals around the circumference of the tube  42 ″. Evenly spaced between each pair of first slits  46 ″ are the slits of a set of four second slits  48 ″, again made by laser. Evenly spaced between each pair of second slits  48 ″ are the slits of a set of eight third slits  58 ″, again made by laser. Other slit arrangements are contemplated, such as, for example, three first slits  46 ″ at 120 degree intervals around the circumference of the tubing  42 ″. The length of the set of first slits  46 ″ corresponds to the desired length of the object-catching basket of the tool  40 ″. 
     Referring to  FIG. 9 , the basket of the  FIG. 6  tool can be seen in its spread disposition. In this embodiment, the first strands  50 ″ extend along the a distal region of the tool head, stopping short of a distal end surface of the tubing. Second strands  52 ″ are within a distal portion of the first strand  50 ″, where the length of the second strand  52 ″ is less than a length of the first strand  50 ″. In a spread disposition, the second strand  52 ″ extends from a side of the first strand  50 ″ and is directed distally along its length toward the distal end of the tubing  42 ″. Third strand  60 ″ is within a portion of the second strand  52 ″, where the length of the third strand  60 ″ is less than the length of the second strand  52 ″. In the spread disposition, the third strand  60 ″ extends from a side of the second strand  52 ″ and is directed distally along its length toward the distal end of the tubing  42 ″. The distalmost ends of the first strands  50 ″ and second strands  52 ″ may be secured together at the tip  56 ″. In one embodiment, the zone of the third strands could be in a “belly portion” of the basket where its diameter is close to its maximum, thereby to achieve an aperture size in this belly portion smaller than an aperture size in a proximal half of the basket envelope, thereby better to retain an object captured in the proximal half of the basket in the smaller mesh size of the distal half of the basket. 
     Not immediately evident from the drawings is a further useful technical effect of the present invention. Whereas the distal ring  20  of the prior art device has a relatively significant length, the unslitted distal tip  56  of a device in accordance with present invention could be made relatively much shorter in length. This could improve the performance of the device when it is desired to fish into the basket an object which lies rather close to a tissue wall surface within a cavity or lumen of a body. 
     The cutting by laser of slits within the cylindrical wall surface of a tube of Nitinol shape memory alloy is a technology which is by now relatively well understood by those companies which specialize in the manufacture of self-expanding stents. For such companies, it will be apparent from the above description that the accompanying drawings and specific description given above represents only one example of how the concept of the present invention can be realized. The concept of the invention permits a new combination of stone destruction insitu by lithotripsy. The technique of lithotripsy involves hitting a stone with a probe which is itself struck by a projectile at the proximal end of the lithotripsy probe, to provide a kinetic energy ballistic impact on the stone to fragment the stone. It is envisaged that the device of the present invention would trap the stone and then a lithotripsy probe would be introduced into the proximal end of the tubular shaft and advanced into the basket at the distal end, to attack the stone trapped therein. A suitable probe can be obtained from EMS Electromedical Systems SA, CH-1347, Le Sentier, Switzerland. 
     To such readers, variations and modifications of these specific description above will be evident. The scope of the claims which follow is not to be taken as limited to the specific details of the description given above.

Technology Category: 1