Abstract:
In one embodiment, an assembly for conducting pulses from an implantable pulse generator, comprises: at least one percutaneous lead comprising terminals and at least two groups of electrodes, each group of electrodes possessing an intra-group electrode spacing; a frame member comprising first and second arms, the frame member comprising an inner lumen for removably housing the at least one percutaneous lead, each arm of the first and second arms comprising a plurality of apertures that are spaced according to the intra-group electrode spacing to allow conduction of electrical pulses from the electrodes of the at least one percutaneous lead to tissue of the patient when the lead is positioned within the frame member; and a spring member that is connected to the frame member for maintaining the first and second arms of the frame member at a predetermined distance in the absence of an external force on the spring member.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/230,210, filed Sep. 12, 2011, which is a divisional of U.S. application Ser. No. 11/877,282, filed Oct. 23, 2007, now U.S. Pat. No. 8,019,442, which claims the benefit of U.S. Provisional Application No. 60/862,909, filed Oct. 25, 2006, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present application is generally related to an assembly kit for creating paddle-style lead using one or several percutaneous leads and method of lead implantation. 
         [0003]    Application of electrical fields to spinal nerve roots, spinal cord, and other nerve bundles for the purpose of chronic pain control has been actively practiced for some time. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of an electrical field to spinal nervous tissue (i.e., spinal nerve roots and spinal cord bundles) can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated nerve tissue. Specifically, applying electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce “paresthesia” (a subjective sensation of numbness or tingling) in the afflicted bodily regions. Thereby, paresthesia can effectively mask the transmission of non-acute pain sensations to the brain. 
         [0004]    It is known that each exterior region, or each dermatome, of the human body is associated with a particular longitudinal spinal position. Thus, electrical stimulation of spinal nerve tissue must occur at a specific longitudinal location to effectively treat chronic pain. Additionally, it is important to avoid applying electrical stimulation of nerve tissue associated with regions of the body that are unaffected by chronic pain. Positioning of an applied electrical field relative to a physiological midline is also important. 
         [0005]    Percutaneous leads and laminotomy leads are the two most common types of lead designs that provide conductors that deliver stimulation pulses from an implantable pulse generator (IPG) to distal electrodes adjacent to the nerve tissue. As shown in  FIG. 1A , conventional percutaneous lead  100  includes electrodes  101  that substantially conform to the body of the body portion of the lead. Due to the relatively small profile of percutaneous leads, percutaneous leads are typically positioned above the dura layer through the use of a Touhy-like needle. Specifically, the Touhy-like needle is passed through the skin, between desired vertebrae to open above the dura layer for the insertion of the percutaneous lead. 
         [0006]    As shown in  FIG. 1B , conventional laminotomy or paddle lead  150  has a paddle configuration and typically possesses a plurality of electrodes  151  arranged in multiple columns. Multi-column laminotomy leads enable reliable positioning of a plurality of electrodes. Also, laminotomy leads offer a more stable platform that tends to migrate less after implantation and that is capable of being sutured in place. Laminotomy leads also create a unidirectional electrical field and, hence, can be used in a more electrically efficient manner than conventional percutaneous leads. Due to their dimensions and physical characteristics, conventional laminotomy leads require a surgical procedure for implantation. The surgical procedure (a partial laminectomy) is invasive and requires the resection and removal of certain vertebral bone tissue to allow both access to the dura and proper positioning of a laminotomy lead. 
       BRIEF SUMMARY 
       [0007]    Some representative embodiments are directed to an assembly kit for receiving one or several percutaneous leads. The assembly kit includes a frame member through which the percutaneous leads are threaded. The frame member comprises first and second arms for receiving the percutaneous leads. In each arm, the frame member comprises apertures that correspond to the positions and spacing of the electrodes of the percutaneous leads. During assembly, the percutaneous leads are advanced through the frame member until the electrodes are exposed through the apertures. A spring member is attached to the frame member to provide a mechanical bias to retain the arms with their leads at a desired width when an external compressive force is not applied to the spring member. Also, a thin film member is preferably disposed between the first and second arms to prevent tissue in-growth between the two percutaneous leads after implantation. 
         [0008]    During the implantation process, a suitable hollow-channel insertion tool is inserted within the epidural space of the patient according to one representative embodiment. The distal end with the spring member is inserted into the suitable hollow-channel insertion tool. The shape of the spring member allows the spring member and the arms of the frame member to be inwardly compressed to assume a relatively small profile. The compression of the spring member and the frame member enables the implantation to occur through a relatively small insertion tool thereby reducing the trauma to the patient. The spring member, the frame member, and the lead(s) are advanced into the epidural space through the insertion tool. Accordingly, removal of bone tissue is not required. Upon exiting the insertion tool, the spring member causes the arms of the frame member to be separated by the desired amount of space and thereby cause the electrodes of the stimulation lead(s) to be positioned in a manner similar to a paddle lead. The stimulation leads can then be utilized for spinal cord stimulation and the relative positions of the electrodes will remain fixed. Also, the field applied by the electrodes will be substantially unidirectional. 
         [0009]    The foregoing has outlined rather broadly certain features and/or technical advantages in order that the detailed description that follows may be better understood. Additional features and/or advantages will be described hereinafter which form the subject of the claims. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the appended claims. The novel features, both as to organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIGS. 1A and 1B  depict conventional percutaneous and paddle leads respectively. 
           [0011]      FIG. 2A  depicts a paddle-style assembly kit for percutaneous leads according to one representative embodiment.  FIG. 2B  depicts a disassembled view of a frame member and spring member according to one representative embodiment. 
           [0012]      FIG. 3  depicts a percutaneous lead adapted according to one representative embodiment. 
           [0013]      FIG. 4  depicts a “rear” view of a frame member and spring member according to one representative embodiment. 
           [0014]      FIG. 5  depicts a stimulation system according to one representative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring now to  FIG. 2A , assembly kit  200  is shown according to one representative embodiment. Assembly kit  200  comprises frame member  202  that comprises parallel arms. Frame member  202  is preferably fabricated from a relatively high durometer, biocompatible, biostable polymer. Examples of suitable polymers include polyetheretherketone (PEEK) and polyether-ketone ketone (PEKK). Frame member  202  comprises a set of apertures  204  on each arm of frame member  202  (which are shown collectively as  204   a - 204   f ). Apertures  204  can be formed by ablating through the polymer material using a suitable laser. Although only six apertures are shown in  FIG. 2A  for the sake of clarity, any number of apertures can be provided in frame member  202  to accommodate suitable percutaneous leads  201 . Apertures  204  cause the field from electrodes positioned underneath apertures  204  to be substantially unidirectional. The unidirectional characteristic is advantageous, because it reduces the probability of undesired stimulation in spinal cord stimulation applications. Also, the unidirectional characteristic enables stimulation to occur at a reduced power consumption. 
         [0016]    Assembly kit  200  further comprises spring member  203  that is attached to frame member  202 . Spring member  203  may be permanently attached to frame member  202  during fabrication of these components or may be fabricated as a separate component for attachment by a surgeon. When assembled as shown in  FIG. 2A , frame member  202  and spring member  203  can be collapsed to assume a relatively small profile to enable kit  200  to be inserted through a suitable implantation tool. An example of a surgical tool that can be utilized to implant kit  200  is described in U.S. Patent Application Publication No. 20050288759, entitled “Method and apparatus for implanting an electrical stimulation lead using a flexible introducer,” which is incorporated herein by reference. When kit  200  exits the introducer instrument into the epidural space, spring member  203  is no longer subjected to a compressive force and expands the arms of frame member  202  to the predetermined distance. Hence, electrodes of lead(s)  201  are then positioned within the epidural space in a manner that is similar to an electrode spacing provided by a paddle-style lead. 
         [0017]    One advantage of allowing the surgeon to attach spring member  203  during the implantation procedure is that multiple sets of spring members  203  could be provided with each set having different spring characteristics. The surgeon could select a spring member  203  having a greater spring constant if assembly kit  200  does not sufficiently expand in the epidural space using another spring member  203  due to fibrosis or other tissue obstructions. Additionally, to prevent fibrosis or other tissue in-growth from occurring after implantation, thin membrane  205  is provided between the arms of frame member  202 . Thin membrane  205  can be fabricated from a low durometer, elastic Carbosil material as an example. By utilizing membrane  205 , kit  200  can be more readily explanted if subsequently necessary. 
         [0018]    Spring member  203  is also preferably fabricated from PEEK material which possesses a spring memory characteristic. Other suitable biocompatible, biostable polymers can be employed such as PEKK. If spring member  203  is fabricated as a separate component from frame member  202  as shown in  FIG. 2B , complementary connector structures (not shown) are provided on frame member  202  and spring member  203  to facilitate their coupling. In some alternative embodiments, metal spring elements are provided within spring member  203  to provide or augment the spring characteristic of spring member  203 . However, metal spring elements can cause undesired tissue heating during an MRI procedure due to current induction from the strong time-varying RF fields generated by the MRI system. Accordingly, an all plastic structure is preferred to avoid current induction during an MRI procedure. 
         [0019]    Spring member  203  is also preferably shaped so that when the end of spring member  203  encounters the inner wall of an insertion tool, the contact force tends to “pinch” spring member  203  thereby providing a compressive force to spring member  203 . In response to the compressive force, spring member  203  collapses the arms of frame member  202  thereby allowing kit  200  to assume a profile that allows kit  200  to be advanced through the insertion tool. 
         [0020]    Any suitable percutaneous lead(s)  201  can be employed within kit  200  provided that the electrode spacing of the lead(s)  201  corresponds to the spacing of apertures in frame  202 . In one embodiment, a respective percutaneous lead is inserted within each arm of frame member  202 . An example of a suitable commercially available lead for assembly kit  200  is the Axxess® lead available from Advanced Neuromodulation Systems, Inc. (Plano, Tex.). To retain each percutaneous lead  201  within frame, retention clips  207  are provided. Additionally, retention clips  207  facilitate the removal of frame member  202  from the epidural space when leads  201  are explanted. 
         [0021]    In one embodiment as shown in  FIG. 3 , a single lead is adapted to be threaded through both arms of frame member  202  of an assembly kit. Specifically, first and second groups  301  and  302  of electrodes are disposed on the single lead. Electrode groups  301  and  302  are disposed somewhat in the “middle” of the body of the lead. The intra-group electrode spacing in the lead corresponds to the spacing between adjacent apertures  204  in frame member  202 . Also, the two groups of electrodes are separated on the body of the lead by distance  303  that corresponds to the distance between the two most distal apertures ( 204   c  and  204   f  in the specific embodiment of  FIG. 2 ) including the distance along spring member  203 . The lead as shown in  FIG. 3  also comprises respective groups of terminals  304  and  305  at the proximal and distal ends of the lead. Each terminal of the groups  304  and  305  is electrically coupled to a respective electrode of groups  301  and  302  by a respective conductive wire embedded within the insulative body of the lead. The positioning of the groups  301 ,  302 ,  304 , and  305  of electrodes and terminals enables lead  201  to be looped through kit  200 . The looping of the lead through kit  200  is advantageous for explantation of frame member  202  and spring member  203 . 
         [0022]    Also, to facilitate explantation, the proximal portion of frame member  202  is shaped at locations  206   a  and  206   b  to contact the inner wall of the insertion tool as shown in  FIG. 4 . In an explantation procedure, frame  202 , spring member  203 , and lead  201  are removed from the epidural space of a patient through the same type of surgical tool used for the implantation procedure. Essentially, the surgeon places the tool over the proximal ends of the lead and advances the tool until the epidural space of the patient is accessed. In a preferred embodiment, a strengthening wire member is inserted within an inner lumen of the lead to facilitate the explantation. 
         [0023]    After insertion of the strengthening wire member and positioning of the open channel tool, the surgeon “pulls” on the lead and the strengthening wire member. The pulling force causes the lead, frame member  202 , and spring member  203  to move up to the distal end of the tool. When the proximal end of frame member  202  contacts the inner wall of the tool, the resulting force pushes against locations  206   a  and  206   b  and the force is transferred from the arms of frame member  202  to spring member  203 . The transferred force tends to elongate the frame and spring member  203  thereby compressing spring member  203  and bringing the arms of frame  202  together. Accordingly, the profile of frame  202  is reduced thereby allowing the kit  200  to be received within the open channel of the tool for removal from the epidural space. 
         [0024]    In such a procedure, the benefit of looping the lead within the kit  200  is realized. Specifically, the looping of the lead enables the strengthening wire member to follow the entire perimeter of frame member  202  and spring member  203 . Accordingly, a sufficient amount of force can be readily applied to ensure that spring member  203  is compressed to allow the withdrawal of the kit  200  through the surgical tool. Additionally, it shall be appreciated that explantation procedures according to representative embodiments involve relatively little complexity and do not require overly delicate manipulations. 
         [0025]      FIG. 5  depicts stimulation system  500  according to one representative embodiment. System  500  comprises implantable pulse generator  501 . An example of a commercially available pulse generator that can be used according to some representative embodiments is the Eon® stimulator available from Advanced Neuromodulation Systems, Inc. Pulse generator  501  is electrically coupled to lead  201  which is threaded through assembly kit  200 . Lead  201  can be implanted in a patient without performing a laminectomy using a suitable implantation tool. After implantation in the epidural space of a patient, the positioning of the electrodes as provided by kit  201  allows lead  201  to function in a manner similar to paddle-style leads. 
         [0026]    Although representative embodiments and advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure that processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.