Abstract:
A paddle-type electrode or electrode array is implantable like a percutaneously inserted lead, i.e., without requiring major surgery, and once implanted, expands to provide a platform for many electrode configurations. The electrode array is provided on a flexible, foldable, subcarrier or substrate. Such subcarrier or substrate folds or compresses during implantation, thereby facilitating its insertion using percutaneous implantation techniques and tools. Once implanted, such subcarrier or substrate expands, thereby placing the electrodes in a desired spaced-apart positional relationship, and thus achieving a desired electrode array configuration. A steering stylet may be accommodated in a lumen provided in the subcarrier or substrate. Insertion tools useful with such electrode arrays include a needle with an oblong cross-section, which accommodates the dimensions of the folded array, and also accommodates other electrode arrays that are not necessarily folded.

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 09/239,927, filed Jan. 28, 1999, now U.S. Pat. No. 6,205,361 which in turn claims the benefit of U.S. Provisional Application Ser. No. 60/074,198, filed Feb. 10, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to implantable, expandable, multicontact electrodes and tools used for their placement. In a preferred embodiment, such electrodes comprise deployable, paddle-type, multicontact electrodes useful for spinal stimulation. 
     There are two major types of electrodes used for spinal stimulation: (1) percutaneously implanted in-line electrodes/leads requiring local anesthesia for implant, and (2) paddle-shaped electrodes requiring major surgery for implantation. 
     The first type of electrodes, i.e., the in-line electrodes, comprise thin, rod-type electrodes. Such in-line or rod-type electrodes are easy and less invasive to implant, typically requiring only local anesthesia and the use of a large gauge needle. Disadvantageously, such in-line electrodes are not as stable as paddle leads, and are prone to migration. 
     The second type of electrodes, i.e., the paddle-shaped electrodes, provide a large-area electrode surface to contact the body tissue, much like a miniature ping-pong paddle. Advantageously, such paddle-type electrodes are more effective and stable than in-line electrodes. Moreover, such paddle-type electrodes provide a platform for multiple electrodes in many possible configurations to thereby optimize electrode programming and clinical results. In contrast, the percutaneous in-line electrodes can only combine electrodes in a vertical row. Disadvantageously, however, the paddle-type electrodes require complex major surgery for implantation, along with all the attendant risks associated with major complex surgery. 
     It is thus evident, that there is a need in the art for an electrode which can deliver the maximum advantages of the paddle-type electrodes, but without requiring extensive surgery for implantation. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by combining the advantages of both the paddle-type electrode and the in-line (rod-type) electrode. That is, the present invention provides an implantable electrode or electrode array that may be implanted like a percutaneously inserted lead, i.e., without requiring major surgery, but once inserted, expands to provide a platform for many electrode configurations. 
     In accordance with one important aspect of the invention, an electrode array is provided on a flexible, foldable, subcarrier or substrate. Such subcarrier or substrate is folded, or compressed during implantation, thereby facilitating its insertion using percutaneous implantation techniques and tools of the present invention. Once implanted, such subcarrier or substrate expands, thereby placing the electrodes in a desired spaced-apart positional relationship, and thus achieving a desired electrode array configuration. 
     In accordance with another aspect of the invention, the substrate or subcarrier of the electrode array includes a memory element which causes the electrode array to expand or unfold to a desired configuration after the electrode array has been implanted while in a folded up or compressed state. 
     In accordance with yet another aspect of the invention, the electrode array includes a membrane as an integral part thereof that prevents ingrowth of tissue inside the electrode array, thereby facilitating repositioning, removal, and/or reinsertion of the electrode array, as required. 
     In one embodiment, the invention may be characterized as a system for implanting an expandable electrode array. Such system includes an electrode array and an insertion tool. The electrode array comprises (a) a flexible substrate, (b) a plurality of substantially parallel columns (which may be consider by some to be rows) of spaced-apart electrodes integrally formed on a surface of the flexible substrate, and (c) means for making electrical contact with each electrode in each of the plurality of substantially parallel columns of electrodes. The flexible substrate normally assumes a substantially planar, flat shape, but is configured so that it may be collapsed or folded so as to assume a folded or compressed state. The insertion tool comprises a hollow tube or hollow needle wherein the electrode array may be placed while in its folded or compressed state. 
     In order to implant the electrode array, the hollow tube or needle (with the folded or compressed electrode array therein) is injected into the living tissue of the desired implant site. The folded electrode array is then expelled from the hollow tube and allowed to assume its expanded or unfolded state within the tissue. 
     It is thus a feature of the present invention to provide a foldable, paddle-type electrode which can be implanted using a simple, needle-type tool without major surgical intervention. 
     It is a further feature of the invention to provide a loading tool that assists with the folding and inserting of the paddle-type electrode into an insertion tool. 
     It is yet another feature of the invention to provide a simple method of implanting a foldable, paddle-type electrode that does not require major surgical intervention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
     FIG. 1 shows a planar view of an implantable, foldable, collapsible electrode array made in accordance with one embodiment of the invention; 
     FIG. 1A is a sectional view of the electrode array of FIG. 1 taken along the line  1 A— 1 A of FIG. 1; 
     FIG. 1B is a partial sectional view of the electrode array of FIG. 1 taken along the line  1 B— 1 B of FIG. 1; 
     FIG. 2 illustrates one manner in which the electrode array of FIG. 1 may be implanted using an insertion stylet; 
     FIG. 2A depicts the manner in which the distal tip of the electrode array of FIG. 1 is held by the distal tip of the insertion stylet of FIG. 2 during the implantation process; 
     FIG. 2B is a side schematic diagram that illustrates the manner in which a releasable holding string may be threaded through the insertion stylet in order to hold the distal tip of the electrode array in a desired position within a groove of the insertion stylet during the implantation process; 
     FIG. 3 shows a slitted insertion needle into which the foldable electrode array of FIG.  1  and the insertion stylet of FIG. 2 may be placed; 
     FIG. 3A depicts the manner in which the folded electrode array and insertion stylet fit within the lumen of the needle of FIG. 3; 
     FIG. 4 illustrates an alternative embodiment of an implantable, foldable electrode array made in accordance with the invention; 
     FIG. 4A is a sectional view of the electrode array of FIG. 4 taken through the line  4 A— 4 A in FIG. 4; 
     FIG. 5 shows the manner in which the electrode array of FIG. 4 is folded in order to fit within the lumen of an insertion tool; 
     FIG. 6 illustrates the folded electrode array of FIGS. 4 and 5 inside of the lumen of an insertion tool; 
     FIG. 7A shows an alternative implantable, foldable electrode array, and a manner of folding the array to fit within the lumen of an insertion tool; 
     FIG. 7B shows an alternative implantable, foldable electrode array, and a manner of folding the array to fit within the lumen of an insertion tool; 
     FIG. 7C illustrates the folded electrode array of either FIG. 7A or FIG. 7B inside the lumen of an insertion tool; 
     FIG. 8A shows another alternative implantable, foldable electrode array including a lumen for a stylet, and a manner of folding the array to fit within the lumen of an insertion tool; 
     FIG. 8B illustrates the implantable, foldable electrode array of FIG. 8A, with a stylet inserted in the lumen of the electrode array; 
     FIG. 8C illustrates the folded electrode array of FIG. 8A inside the lumen of an insertion tool; 
     FIG. 8D shows alternative manner of folding the array of FIG. 8A to fit within the lumen of an insertion tool; 
     FIG. 8E illustrates the folded electrode array of FIG. 8D inside the lumen of an insertion tool; 
     FIG. 9A shows yet another alternative implantable electrode array including a lumen for a stylet, and a manner of inserting the array within the lumen of an insertion tool; 
     FIG. 9B illustrates the electrode array of FIG. 9A inside the lumen of an insertion tool; 
     FIG. 10 depicts a loading tool that may be used in conjunction with the insertion tool in order to facilitate the folding and insertion of the electrode array of FIG. 4 into the lumen of an insertion tool; 
     FIG. 11A illustrates a top view of an insertion tool of the present invention; 
     FIG. 11B illustrates a side view of the insertion tool of FIG. 11A; 
     FIG. 12A illustrates a top view of a stylet for use with the insertion tool of FIG. 11A; 
     FIG. 12B illustrates a side view of the stylet of FIG. 12A; 
     FIG. 13 depicts a side view of the stylet of FIGS. 12A and 12B inserted into the insertion tool of FIGS. 11A and 11B; and 
     FIG. 14 depicts a side view of an alternative stylet and insertion tool. 
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
     Referring first to FIGS. 1,  1 A and  1 B, there is shown respectively a planar view of one embodiment of an implantable, foldable, collapsible electrode array  10  made in accordance with the invention, a sectional view of the electrode array  10  taken along the line  1 A— 1 A, and a partial sectional view of the electrode array  10  taken along the line  1 B— 1 B. As can be seen in these figures, the electrode array  10  is made in the form of a paddle having a number of electrode contacts  11  arranged along two substantially parallel columns of a cylindrical edge portion  16  of the electrode array  10 . The electrode contacts  11  are spaced apart from each other, and each is electrically connected to a conductive wire(s)  15  that passes through, or is embedded within, the cylindrical edge portion  16  of the array  10 . 
     The electrode contacts  11  may be made, e.g., from a coiled metal foil or clamped as C-shaped metal preforms. As seen best in FIG. 1B, the wires  15  that are electrically connected to the electrode contacts  11  are typically wound around a shape-memory element  12  that passes through the center of the cylindrical edge portions  16  of the array  10 . 
     As indicated, the memory element  12  is placed in the center of the cylindrical edge portion  16 . This memory element is selected to have a shape that maintains the open, paddle shape of the electrode array  10  as shown in FIG.  1 . The shape-memory element  12  may be made from either metal or from a polymer, such as nylon. The memory element  12  is flexible or resilient, so that it can be folded or bent to another shape, as desired or needed, but in the absence of an external folding or bending force, assumes the open, paddle shape shown in FIG.  1 . 
     The space between the cylindrical edge portions  16  of the paddle array  10  is filled with a thin web or membrane  14  made, e.g., from a suitable flexible non-conductive material such as silicone or other implantable lead materials, as is known in the art. Such membrane advantageously prevents tissue ingrowth within the electrode array  10  after implant, thereby making it possible (when needed) to explant the electrode, or to reposition the electrode with minimal trauma to the patient. 
     At a distal tip  17  of the array  10  of one embodiment of the invention, the thin membrane  14  and the cylindrical edge portions  16  terminate so as to expose the memory shape element  12  at the distal tip, thereby forming an attachment loop  13 . This attachment loop  13  is used during the implant operation of the electrode of one embodiment, as explained more fully below. 
     In one embodiment of the invention, the width of the paddle electrode array  10  of the type shown in FIG. 1, when maintained in its extended or full paddle shape as shown in FIG. 1, is approximately 10 mm, and has a length of about 45 mm. The diameter of the cylindrical edge portions is approximately 1.2 mm, and the thickness of the membrane  14  is about 0.2 mm. 
     The electrode array  10  of one embodiment includes an insertion stylet  20 , as shown in FIG. 2,  2 A and  2 B, which insertion stylet  20  is made from a tube  21  and holding string  22 . A distal tip  23  of the insertion stylet  20  may include a groove or slot  24  into which the memory element  12  may be inserted at the attachment loop  13  of the array  10 . The string  22  is threaded through the tube  21  to the distal tip  23 , where it wraps around (½ turn) the memory element  12 , and is then threaded back through the tube  21 . Thus, the two ends of the string  22 , labeled “A” and “B” in the figures, exit from the proximal end of the tube  21 . The diameter of the tube  21  is typically about the same as the diameter of the cylindrical edge portions  16  of the array  10 , e.g., about 1.2 mm. 
     In order to implant the electrode array  10  with the insertion stylet  20 , both the electrode array  10  and insertion stylet  20  are placed within an insertion tool, such as a needle  30 , as shown in FIGS. 3 and 3A. The needle  30  preferably has a longitudinal slit  32  that opens up one side thereof along its entire length. The needle  30  preferably has a sharp distal tip  33  to facilitate its insertion into living tissue. The needle  30  is hollow, having a lumen  34  (or open channel) in the center thereof. The electrode  10  and insertion stylet  20  are configured (folded or compressed) to fit within this lumen  34 , as illustrated in FIG.  3 A. During this configuration (folding) process, the thin membrane  14  folds against itself so that the two perimeter edge portions  16  of the array  10  and the insertion stylet  20  are all held in close proximity to each other. 
     The needle  30  has approximate dimensions of L 1  by L 2  (e.g., 4.0 mm by 3.0 mm), as shown in FIG. 3A, or preferably smaller, so it is insertable in between vertebral elements. The needle can have a slit, as shown in FIG. 3A, although it is not necessary as seen in additional needle configurations herein. When included, the slit  32  preferably has a width of about 1.2 mm, the width of the cylindrical edge portions  16  of the lead  10 , and also the width of the tube  21  that forms part of the insertion stylet  20 . As described in more detail presently, during needle insertion, a removable core stylet is preferably provided in the lumen of the needle which is removed prior to inserting the electrode array. 
     In order to implant the electrode array, according to one embodiment, the electrode array  10 , guided by insertion stylet  20 , is inserted into needle  30 . The insertion stylet  20  is pushed to eject the electrode array  10  from the lumen  34  of the needle  30  into, e.g., the spinal cord cavity. Once ejected from the lumen of the needle in this manner, the memory element  12  (FIG. 1) deploys the electrode paddle array  10  from its folded position, as shown in FIG. 3A to its substantially flat paddle shape, as shown in FIG.  1 . 
     Once thus deployed, the insertion stylet  20  may be further pushed, and/or the electrode lead  10  may be pulled, so as to manipulate the electrode array within the spinal cord cavity to rest in an optimum or desired position. The needle  30  is then removed from the body, and the electrode lead is released either through the opening at the distal end of the needle or through the slot or slit  32  in the needle. The string  22  is then pulled from either the “A” or “B” end in order to release the electrode array  10  from the insertion stylet  20 . The insertion stylet  20  is then also pulled out of the tissue. 
     An alternative embodiment of a percutaneously implanted lead/electrode array  40  and percutaneous implant tools made in accordance with the present invention are depicted in the remaining figures. In accordance with such alternative embodiment, there are two or more columns  42  of spaced-apart electrode contacts connected together with a thin webbing  44 . In some embodiments, columns  42  and webbing  44  taper into a single lead cable  46 , and in other embodiments, the substrate of columns  42  and/or webbing  44  is continuous for the length of the lead (as best seen in FIG.  7 B). 
     In FIG. 4, an embodiment with three columns,  42   a,    42   b  and  42   c,  is shown. Each column of spaced-apart electrodes comprises a finger substrate made, e.g., from a suitable flexible non-conductive material such as silicone or other implantable lead materials, as is known in the art and discussed in more detail presently. Each finger substrate has a plurality of electrode contacts  48  exposed on the surface hereof. Each electrode contact  48  is, in turn, connected electrically with a wire (not shown) embedded within the column  42  and lead cable  46 , thereby facilitating making electrical connection with each electrode. Any suitable implantable conductive material may be used for the electrode contacts  48 . 
     In one particular embodiment of the electrode array  40 , each electrode contact has a length of about 2 mm, and each finger of the array has an active length (where the active length is the length from the most proximal electrode contact to the most distal electrode contact) of about 10 mm. The webbing  44  has a thickness of about 0.2 mm, and is made, e.g., from a suitable flexible non-conductive material such as silicone or other implantable lead materials, as is known in the art. Each finger has a cross section having a width of about 1.75 mm and a height of about 0.80 mm. The width of the webbing  44  between adjacent fingers is approximately 0.75 mm. 
     In order to implant the electrode array  40 , the array  40  is inserted into an insertion tool  50  as shown in FIGS. 5 and 6. As the array  40  is inserted into the insertion tool  50 , the fingers  42   a,    42   b  and  42   c  (or however many columns or fingers there are) collapse and fold over each other. The fingers or columns  42  may be tapered so that a distal end is somewhat smaller than the proximal end. 
     The electrode contacts  48  on the surface of each finger  42  are preferably offset from the location of electrode contacts of an adjacent finger or column. Such offsetting of the electrode contacts facilitates the folding of one column before the next. The electrode array  40  of FIG. 5 in its folded state is shown within the insertion tool  50  in FIG.  6 . An electrode array  40  of the present embodiment with two columns  42   a  and  42   b  of spaced-apart electrode contacts  48  is shown in FIG.  7 A. An additional alternative configuration of an electrode array  40  of the present embodiment is shown in FIG.  7 B. As mentioned earlier, the substrate of columns  42  and webbing  44  is continuous for the length of the lead of FIG.  7 B. This same configuration, with continuous columns, may be used rather than tapered columns and cable  46  for any of the alternatives described herein. FIG. 7C shows the electrode array of FIG. 7A or FIG. 7B within insertion tool  50 . 
     As array  40  is deployed, it returns to the substantially flat state, as shown in FIGS. 4 and 7B, by virtue of the material(s) and/or formation process(es) used to create array  40 . A preferred formation method is injection molding, although other methods, such as other molding methods, casting, or other known methods may be used. A preferred material(s) has good elastic deformation properties, such that, after temporary deformation, the material returns, or substantially returns, to its original shape. Preferred materials include polyurethane and more preferably silicone or some mixture of polyurethane and silicone, or other non-conductive biocompatible materials with good elastic deformation. Array  40  (e.g., of FIG. 7B) is preferably stiff enough to be deployed from insertion tool  50  into position, e.g., in the spinal cord cavity, by pushing its proximal end, which protrudes from the proximal end of insertion tool  50 . 
     In one alternative, a lumen  52  for a steering stylet  54  may be provided through lead cable  46  and through webbing  44 , as depicted in FIGS. 8A and 8B, or rather than going through webbing  44 , may replace webbing  44 . Electrode array  40  is preferably folded into insertion tool  50  as shown in either FIGS. 8A,  8 B, and  8 C or as in FIGS. 8D and 8E. Insertion tool  50  may be a hollow cylinder or tube that is oblong in cross-section with a width greater than a height (FIGS. 8A,  8 B,  8 C), similar to the needle  30  insertion tool, may be oblong with a height greater than a width (FIGS. 8D,  8 E), or may be circular in cross-section, as in FIG.  7 B. For instance, insertion tool  50  may have a width of approximately 3.0 mm and a height of approximately 1.5 mm. The smaller the dimensions of the insertion tools, the better, as this reduces trauma. However, the height and/or width of insertion tool  50  may be as large as about 10 mm to accommodate an electrode array that is as large as about 10 mm. In addition, insertion tool  50  may have a pointed distal tip as in FIG. 3, or distal tips as shown in FIGS. 11A,  11 B,  13 , and  14 , or may have any other useful distal tip configuration. 
     As shown in FIG. 8C, steering stylet  54  preferably protrudes through the distal end of electrode array  40 . Steering stylet  54  preferably has a slightly bent tip, also shown in FIG. 9C, which aids in driving electrode array  40  into position as the bent tip turns while steering stylet handle  55  is rotated. However, steering stylet  54  may, for instance, be straight, and may not protrude from the end of array  40  if there is no opening  56  at the distal end of lumen  52 . For example, in yet another alternative (not shown), a lumen for a steering stylet may be provided through lead cable  46  and/or if desired through a column  42  of electrode array  40 . Steering stylet  54  is preferably made of a stiff biocompatible material, and more preferably of a biocompatible metal material, such as stainless steel, which is strong enough to guide the insertion process, but flexible enough to allow the steering stylet to be withdrawn from electrode array  40 , even if there is a slight bend at the distal tip of the stylet. 
     In another alternative, the lumen  52  for steering stylet  54  is provided as shown in FIGS. 9A and 9B. The electrode array  40  of this example is advantageously compact enough, with webbing  44  so reduced or removed, to slide within insertion tool  50  without being folded. Of course, folding the electrode array of this example is still an option, in which case it may be preferable to use an insertion tool with a different cross-sectional shape. 
     For some implantations, it may be helpful to employ a loading tool  58 , which may, for instance, be shaped as a funnel as illustrated in FIG.  10 . With such loading tool  58 , which preferably attaches to one end of the insertion tool  50 , the lead cable  46  is first inserted through the loading tool  58  and insertion tool  50 , and as this lead cable  46  is pulled through the insertion tool  50 , the e.g., funnel shape of the loading tool  58  automatically causes the various fingers or columns  42   a,    42   b,    42   c  to collapse and fold over each other as they are pulled into the insertion tool  50 . Other shapes of loading tool  58  are possible, such as a simple tube, a cone, or other useful shape. In one alternative, the insertion tool  50  is also used as the loading tool  58 . 
     As mentioned earlier, the distal tip of insertion tool  50  may be pointed, or may have any other useful configuration. FIGS. 11A and 11B depict an example of an insertion tool  50  useful with the electrode arrays of the current invention. As is known in the art, when an insertion tool  50  (often simply called a needle) is inserted into tissue, a core stylet  60  (FIGS. 12A and 12B) is typically provided within tool  50  to prevent tissue from entering the lumen of the tool (often called ‘coring’). FIG. 13 shows the core stylet  60  of FIGS. 12A and 12B inserted in insertion tool  50  of FIGS. 11A and 11B. Once tool  50  is inserted into position, core stylet  60  is removed so that an electrode array, such as electrode array  10  or electrode array  40 , may be inserted through insertion tool  50 . As is known in the art, a slight upward curve at the distal end of the insertion tool is useful for directing the electrode array as it exits the distal end of insertion tool  50 . Another design of insertion tool  50  and core stylet  60  useful with the electrode arrays of the present invention is shown in FIG.  14 . 
     As described above, it is thus seen that the present invention provides a foldable, paddle-type electrode which can be implanted using a simple, needle-type tool without major surgical intervention. 
     As further described above, it is seen that the invention provides a loading tool that assists with the folding and inserting of the paddle-type electrode into an insertion tool. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.