Abstract:
An insertion needle facilitates the implantation of an electrode array carried on a flexible, foldable or compressible, subcarrier or substrate. Such subcarrier or substrate folds or compresses during implantation, thereby facilitating its insertion using the insertion needle. 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. The insertion needle has a lumen with a non-circular cross-sectional shape, e.g., having a width greater than its height, to facilitate sliding the folded or compressed paddle-type electrode array therein, and further includes a longitudinal slit.

Description:
This application is a Divisional of U.S. application Ser. No. 09/778,267, filed Feb. 7, 2001, to be issued as U.S. Pat. No. 6,415,187; which is a Continuation of U.S. application Ser. No. 09/239,927, filed Jan. 28, 1999, now U.S. Pat. No. 6,205,361, which claims the benefit of U.S. Provisional Application Serial No. 60/074,198, filed Feb. 10, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to implantable, expandable, multicontact electrodes. 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. 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 parallel columns 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 parallel columns of electrodes. The flexible substrate normally assumes a 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 A—A of FIG. 1; 
     FIG. 1B is a partial sectional view of the electrode array of FIG. 1 taken along the line B—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 A—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 the insertion tool; and 
     FIG. 7 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 the 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 A—A, and a partial sectional view of the electrode array  10  taken along the line B—B. As can be seen in these figures, the electrode array  10  is made in the form of a silicone paddle having a number of electrode contacts  11  arranged along 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 silicone web or membrane  14 . 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 , 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 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  includes an insertion tool  20 , as shown in FIGS. 2,  2 A and  2 B. This insertion tool  20  may also be referred to as an insertion stylet  20 . 
     In one embodiment, the insertion tool  20  is made from a tube  21  and holding string  22 . A distal tip  23  of the insertion tool  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 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 a needle  30 , as shown in FIGS. 3 and 3A. The needle  30  has a longitudinal slit  32  that opens up one side thereof along its entire length. The needle  30  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 tool  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 tool  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.  3 A. The slit  32  has a width of about 1.2 mm, the width of the cylindrical edge portions of the lead  10 , and also the width of the tube  21  that forms part of the insertion tool  21 . 
     In order to implant the electrode array, the needle  30  with electrode array  10  and insertion tool  20  inside, is inserted into the spinal cord cavity. The insertion tool  20  is then pushed so as to eject the electrode array  10  from the lumen  34  of the needle  30  into 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 flat paddle shape, as shown in FIG.  1 . 
     Once thus deployed, the insertion tool  20  may be further pushed, and/or the electrode lead 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 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 tool  20 . The insertion tool  20  is then also pulled out of the tissue. 
     An alternative embodiment of a percutaneously implanted expandable lead/electrode array  40  made in accordance with the present invention is depicted in FIGS. 4,  4 A,  5 ,  6  and  7 . In accordance with such alternative embodiment, there are two or more rows  42  of spaced-apart electrode contacts connected together with a thin webbing  44  and tapering into a single lead  46 . In FIG. 4, three such rows,  42   a ,  42   b  and  42   c , are shown. Each row 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. Each finger substrate has a plurality of electrode contacts  48  exposed on the surface thereof. Each electrode contact  48  is, in turn, connected electrically with a wire (not shown) embedded within the row  42  and lead  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. As seen in FIG. 4A, the webbing  44  has a thickness of about 0.2 mm. 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 implant tool  50 , the fingers  42   a ,  42   b  and  42   c  (or however many rows or fingers there are) collapse and fold over each other. The fingers or rows  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 row. Such offsetting of the electrode contacts facilitates the folding of one row before the next. The electrode array  40  in its folded state is shown within the insertion tool  50  in FIG.  6 . 
     For some implantations, it may be helpful to employ a funnel loading attachment tool  52  as illustrated in FIG.  7 . With such loading tool  52 , which attaches to one end of the insertion tool  50 , the lead cable  46  is first inserted through the funnel tool  52  and insertion tool  50 , and as this lead  46  is pulled through the tool  50 , the funnel shape of the loading tool  52  automatically causes the various fingers or rows  42   a ,  42   b ,  42   c  to collapse and fold over each other as they are pulled into the insertion tool  50 . 
     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.