Patent Publication Number: US-2017368334-A1

Title: Spinal cord stimulation system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 14/074,425, filed Nov. 7, 2013, which is a continuation of U.S. patent application Ser. No. 13/193,250, filed on Jul. 28, 2011, now U.S. Pat. No. 8,588,936, which claims priority to U.S. Provisional Patent Application No. 61/368,501, filed on Jul. 28, 2010, and to U.S. Provisional Patent Application No. 61/415,181, filed on Nov. 18, 2010. The disclosures of each of the above-referenced applications are hereby incorporated herein by reference in their entirety. 
    
    
     FIELD 
     This invention relates to a spinal cord stimulation system and, more particularly, to a system for optimizing the stimulation of the spinal cord. 
     BACKGROUND 
     Dorsal column stimulation is an established technology for management of chronic low back and leg pain when other surgical options have failed or are not feasible. Conventional dorsal column stimulation systems treat chronic pain by providing electrical stimulation pulses through an electrode array placed in the epidural space next to a patient&#39;s spinal cord. The stimulation parameter set determines the characteristics of the stimulation pulses provided through the electrode array in conjunction with the electrodes used to provide the stimulation pulses. Typically, the optimal stimulation parameter set for a specific patient can be determined from the response of the patient to various sets of stimulation parameters. 
     A dorsal column stimulation system typically includes an implantable pulse generator (IPG), an electrode array, an electrode lead, and an electrode lead extension. Conventionally, the electrodes are implanted against the outer surface of the dura, which is a membrane that surrounds the spinal cord. In operation, the IPG generates electrical pulses that are delivered, via the implanted electrodes, to the dorsal column and dorsal root fibers within the spinal cord. In one aspect, the electrodes are typically arranged and spaced in a desired pattern to create an electrode array and individual wires within one or more electrode leads are connected with each electrode in the array. The electrode leads exit the spinal column and can be attached to one or more electrode lead extensions, which, in turn, are typically tunneled subcutaneously around the torso of the patient to a subcutaneous pocket where the IPG is implanted. 
     In order for dorsal column stimulation to be effective, the electrodes should be placed in a location such that the electrical stimulation will affect the targeted nerves and cause paresthesia (a feeling of tingling or numbness). The paresthesia perceived by the patient and induced by the stimulation should ideally be located in approximately the same place in the patient&#39;s body as the pain that is the target of treatment. If one or more electrodes in the electrode array are not correctly positioned, it is possible that the patient will receive little or no benefit from an implanted dorsal column stimulation system. Thus, correct electrode placement can mean the difference between effective and ineffective pain therapy. 
     However, precise placement of an electrode relative to the patient&#39;s distribution of pain can be difficult due to anatomic variations among patients and due to the inherent limitations of standard electrode designs. Conventionally, electrodes are made of flexible plastic and are inserted into the epidural space through an opening created by a laminotomy procedure that involves the removal of the posterior aspect of a vertebra, which normally forms the spinal canal and protects the spinal cord. Typically, because the electrode is pushed into position by its tail, the electrode will generally follow the path of least resistance, which often results in suboptimal or undesired placement of the electrode with respect to the stimulation target. It is also known that the patient&#39;s anatomy can cause deflection of the electrode during the electrode insertion process, thereby making midline electrode placement difficult to achieve. Even a perfect midline placement, as judged by flouroscopy, can result in unilateral stimulation rather than bilateral stimulation of the spinal cord. This problem can prevent optimal electrode placement and, consequently, limit the pain relief experienced by the patient. 
     There are several known options for overcoming the problems associated with electrode placement; however, each option has significant limitations. One conventional option is the use of a percutaneous cylindrical electrode. These electrodes are typically introduced through a needle and have an internal (coaxial) guidewire that can be contoured to assist with accurate placement. While percutaneous electrodes are well suited for ambulatory trial purposes, these electrodes are not reliable for long-term uses. Specifically, the round, thin designs of percutaneous electrodes make them vulnerable to migration and pullout. Additionally, percutaneous electrodes have compact electrode contact arrays that limit their stimulation distribution. Further, percutaneous electrodes rapidly consume their batteries as energy is expended radially from the electrode contacts rather being exclusively directed toward the spinal cord. 
     Another conventional option for overcoming the problems associated with electrode placement is the use of paddle-style electrodes, which cover a larger surface area and have an extensive contact array that allows for flexibility with programming stimulation parameters. Paddle-style electrodes are also likely to be relatively stable once post-operative scarring occurs. However, it is difficult to adjust the positioning of paddle-style electrodes without more extensive surgical procedures. Conventionally, an extensive laminectomy can be used to expose the entire site for planned electrode coverage. This requires a larger incision and more muscle manipulation that can add time and morbidity to the procedure. Alternatively, a separate laminotomy superior to a first laminotomy can be utilized (either through the same or a second incision) to visualize and adjust the electrode. This too requires a larger incision and muscle manipulation. 
     Accordingly, there is a need in the pertinent art for systems and methods of dorsal column stimulation that allow for precise, efficient, and stable placement and repositioning of stimulating electrodes while requiring only a single small incision. There is a further need for systems and methods of dorsal column stimulation that allow for precise, efficient, and stable placement and repositioning of stimulating electrodes through restriction of the contouring of the stimulating electrodes during implantation. There is a further need for systems and methods of dorsal column stimulation that allow for precise, efficient, and stable placement and repositioning of stimulating electrodes using through the use of stimulating electrodes that are configured to promote the formation of a desired insertion pathway within the body of the subject. 
     SUMMARY 
     Described herein are methods for optimizing stimulation of the dorsal column of the spinal cord of a subject. The method includes providing a stimulating electrode array and a frame element. In one aspect, the stimulating electrode array has an engagement portion and a peripheral side edge and comprises electrodes. In another aspect, the frame element conforms to a portion of the peripheral side edge of the stimulating electrode array. In an additional aspect, the frame element is formed from a material that is more rigid than the stimulating electrode array. In a further aspect, the method includes selectively coupling the frame element thereto the engagement portion of the stimulating electrode array. In still a further aspect, the method includes inserting the coupled frame element and stimulating electrode array into the body of the subject at a desired position proximate the dorsal column of the subject. In still a further aspect, the method includes disengaging the frame element from the engagement portion of the stimulating electrode array such that the stimulating electrode array remains in the desired position. 
     In exemplary aspects, the stimulating electrode array can be inserted into the body of the subject with the assistance of a steering member having a handle, a housing, and a snare means. In these exemplary aspects, the snare means is positioned within the housing and is selectively extendable and retractable relative to an opening in a distal end of the housing. In a further aspect, the snare means is configured to engage at least a portion of the engagement portion of the stimulating electrode array. 
     Systems of optimizing stimulation of the dorsal column of the spinal cord of a subject are also described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       These and other features of the preferred embodiments of the invention will become more apparent in the detailed description in which reference is made to the appended drawings wherein: 
         FIG. 1  is an image of an engagement portion of an exemplary stimulating electrode array as described herein. 
         FIG. 2  is an image of the housing and snare means of an exemplary steering member as described herein. 
         FIGS. 3-4  are images of an exemplary engagement between the snare means of  FIG. 2  and the engagement portion of  FIG. 1  as described herein.  FIG. 3  is an image depicting a close-up view of the engagement between the snare means of the steering member and the engagement portion of the stimulating electrode array.  FIG. 4  is an image depicting an expanded view of the engagement between the snare means of the steering member and the engagement portion of the stimulating electrode array. 
         FIG. 5  is an image of the handle of an exemplary steering member as described herein. As shown in  FIG. 5 , the handle can include a thumb guide ring for activation of the snare means as described herein. 
         FIGS. 6-8  are images of an exemplary engagement between the snare means of two steering members and the corresponding engagement portions of a stimulating electrode array as described herein.  FIG. 6  is an image depicting a top close-up view of the engagement between the snare means of the two steering members and the corresponding engagement portions of the stimulating electrode array.  FIG. 7  is an image depicting an expanded view of the engagement between the snare means of the two steering members and the corresponding engagement portions of the stimulating electrode array.  FIG. 8  is an image depicting another top close-up view of the engagement between the snare means of the two steering members and the corresponding engagement portions of the stimulating electrode array. 
         FIG. 9  is a perspective view of an exemplary steering member having a telescoping portion as described herein. 
         FIG. 10  is a front perspective view of an exemplary snare means including first and second loops, as described herein. 
         FIG. 11  is a side perspective view of the distal beveled portion of the peripheral side edge of an exemplary stimulating electrode array, as described herein. 
         FIG. 12  is a perspective view of an exemplary frame element that is coupled to a stimulating electrode array, as described herein. 
         FIG. 13  is a side perspective view of the beveled edge of the frame element of  FIG. 12 . 
         FIG. 14  is a close-up view of an exemplary jaw assembly as described herein. 
         FIGS. 15A and 15B  are intraoperative prone fluoroscopic images of an adjustment in the positioning of an exemplary stimulating electrode array as described herein from a right oblique location ( FIG. 15A ) to parallel left paramedian location ( FIG. 15B ). 
     
    
    
     DETAILED DESCRIPTION 
     The present invention can be understood more readily by reference to the following detailed description, examples, drawings, and claims, and their previous and following description. However, before the present devices, systems, and/or methods are disclosed and described, it is to be understood that this invention is not limited to the specific devices, systems, and/or methods disclosed unless otherwise specified, and, as such, can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. 
     The following description of the invention is provided as an enabling teaching of the invention in its best, currently known embodiment. To this end, those skilled in the relevant art will recognize and appreciate that many changes can be made to the various aspects of the invention described herein, while still obtaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be obtained by selecting some of the features of the present invention without utilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations to the present invention are possible and can even be desirable in certain circumstances and are a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not in limitation thereof. 
     As used throughout, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a stimulating electrode” can include two or more such stimulating electrodes unless the context indicates otherwise. 
     Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. 
     As used herein, the terms “optional” or “optionally” mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not. 
     As used herein, a “subject” is an individual and includes, but is not limited to, a mammal (e.g., a human, horse, pig, rabbit, dog, sheep, goat, non-human primate, cow, cat, guinea pig, or rodent), a fish, a bird, a reptile or an amphibian. The term does not denote a particular age or sex. Thus, adult and newborn subjects, as well as fetuses, whether male or female, are intended to be included. A “patient” is a subject afflicted with a disease or disorder. The term “patient” includes human and veterinary subjects. As used herein, the term “subject” can be used interchangeably with the term “patient.” 
     In one embodiment, and with reference to  FIGS. 1-10 , the invention relates to a system  10  for optimizing stimulation of the dorsal column of the spinal cord of the body of a subject. In one aspect, the system  10  comprises a stimulating electrode array  20  comprising a plurality of electrodes  22 . In this aspect, the stimulating electrode array  20  can be a paddle-style electrode array as is conventionally known in the art, such as, for example and without limitation, a two-column octet electrode array (Boston Scientific) and a three-column 5-6-5 electrode array (Medtronic). It is contemplated that the plurality of electrodes  22  can comprise any number of electrodes, including, for example and without limitation, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, and 18 electrodes. In one aspect, the stimulating electrode array has a longitudinal axis. 
     In another aspect, the stimulating electrode array  20  can comprise at least one lead  25 . It is contemplated that each lead  25  of the at least one lead can comprise a conventional lead, including, for example and without limitation, conventional electrical wiring. In an additional aspect, each respective at least one lead  25  can be placed in electrical communication with a respective paired at least one electrode  22  of the electrode array  20 . Optionally, and as exemplarily depicted in  FIG. 5 , the system  10  can comprise a holder  70  for stabilizing the orientation of the stimulating electrode array  20 , including the leads  25 , during implantation. 
     It is contemplated that each lead can be operably coupled in electrical communication with an Implantable Pulse Generator (IPG) or other conventional means for creating electrical pulses, thereby permitting electrical transmission of pulses coupled to the at least one electrode  22  of the stimulating electrode array  20 . It is further contemplated that the IPG or other means for creating electrical pulses can be selectively programmable to stimulate the at least one lead and the electrically coupled at least one electrode  22  in a desired pattern and sequence. It is still further contemplated that the IPG or other means for creating electrical pulses can be selectively programmed through the skin of the subject following implantation. 
     In an additional aspect, as shown in  FIG. 1 , the stimulating electrode array  20  can have a top surface  26 , a bottom surface  27 , and a peripheral side edge  28 . In a further aspect, the stimulating electrode array  20  has at least one engagement portion  24 . In this aspect, each engagement portion  24  is configured for engagement with a surgical tool. It is contemplated that each engagement portion  24  can be, for example and without limitation, a suture knot, a hook, a loop, or other protrusion that is configured for engagement with a surgical tool. It is further contemplated that each engagement portion  24  can be prepared as desired by a surgeon prior to implantation of the stimulating electrode array. Alternatively, the stimulating electrode array  20  can be manufactured with the at least one engagement portion  24  such that the surgeon is not required to prepare the engagement portions. One skilled in the art will appreciate that it is understood that any conventional means for engagement with a conventional surgical tool are contemplated as being within the scope of this disclosure. 
     In one exemplary aspect, the at least one engagement portion  24  can be positioned proximate a distal portion  21  of the stimulating electrode array  20 . In another exemplary aspect, the at least one engagement portion  24  can be positioned proximate a medial portion  23  of the stimulating electrode array  20 . In further exemplary aspects, the at least one engagement portion  24  can be positioned at one or more selected locations along the peripheral side edge  28  of the stimulating electrode array  20 . Alternatively, it is contemplated that the at least one engagement portion  24  can be positioned on the top surface  26  of the stimulating electrode array  20 . However, it is contemplated that the at least one engagement portion  24  can be positioned in any location thereon the stimulating electrode array  20  that is accessible by a medical practitioner, as described herein. 
     Optionally, in an additional aspect, the system  10  can comprise at least one steering member  40 . In this aspect, each steering member  40  can have a longitudinal axis A. In one aspect, each steering member  40  of the at least one steering member can comprise an elongate housing  42 . In this aspect, the housing  42  can have a distal end  44  that defines an opening  46 . In one aspect, the distal end  44  of the housing  42  can comprise a blunt or dulled tip. Optionally, the housing  42  can be inwardly tapered proximate its distal end  44  relative to the longitudinal axis A of the steering member  40 . In an exemplary aspect, the steering member  40  can have a longitudinal length ranging from about 12 inches to about 18 inches. 
     In one aspect, the housing  42  of each steering member  40  of the at least one steering member can comprise conventional, sterilizable, surgical instrument materials. In a further aspect, it is contemplated that the housing  42  can comprise one or more materials that are conventionally used to produce medical implants and surgical instruments, including, for example and without limitation, metal and polymeric materials. In one aspect, at least portions of the housing  42  can comprise a metal that is radio-opaque and, thus, visible through conventional fluoroscopic imaging procedures. For example, and without limitation, the housing  42  can comprise stainless steel. It is also contemplated that at least a portion of the housing  42  can comprise a radio-lucent material, such as, for example and without limitation, corrugated plastic. It is further contemplated that a radio-lucent housing can minimize visibility of the housing during conventional fluoroscopic imaging procedures. In another aspect, at least a portion of the housing  42  can be malleable. In this aspect, it is contemplated that the malleable housing can be readily and selectively contoured to a desired shape. 
     In a further aspect, as shown in  FIG. 2 , each steering member  40  of the at least one steering member can comprise a snare means  50  positioned within the housing  42  that is configured to be movable about and between an extended position and a retracted position relative to the opening  46  of the housing along the longitudinal axis A of the steering member. In this aspect, it is contemplated that, in the extended position, the snare means can extend from the distal end  44  of the housing  42  by a distance ranging from about 3 mm to about 7 mm and more preferably being about 5 mm. In one aspect, the snare means  50  can comprise an elongate member positioned within the housing  42  of the steering member  40 , wherein a retractable portion  54  of the elongate member can be moved about and between the extended position and the retracted position relative to the opening  46  of the housing. In this aspect, the elongate member can comprise, for example and without limitation, a wire, a cable or other flexible material that possesses sufficient strength to function as described herein. 
     In an additional aspect, as depicted in  FIGS. 3-4 , the snare means  50  can be configured to operatively engage at least a portion of an engagement portion  24  of the at least one engagement portion of the stimulating electrode array  20 . It is contemplated that the snare means  50  can comprise a loop, a hook, a threaded shape, or any conventional shape that can be configured to engage an engagement portion  24  of the stimulating electrode array  20 . In one exemplary aspect, each engagement portion  24  of the stimulating electrode array  20  can comprise a guide loop configured to receive the snare means  50  of a corresponding steering member  40 . It is contemplated that combinations of different types of engagement portions can be used within the scope of this disclosure. For example, in an exemplary aspect, it is contemplated that a guide loop can be positioned thereon the medial portion  23  of the stimulating electrode array  20  and another engagement portion  24  can be positioned thereon the distal portion  21  of the stimulating electrode array. In this aspect, it is contemplated that the guide loop and the engagement portion can be axially aligned such that a steering member can be passed through the guide loop and then used to engage the engagement portion on the distal portion of the stimulating electrode array. 
     In another aspect, as depicted in  FIG. 10 , the snare means  50  can comprise a first loop  58   a  and a second loop  58   b.  In this aspect, each engagement portion  24  of the stimulating electrode array  20  can have a longitudinal axis B and can protrude therefrom the stimulating electrode array. It is contemplated that both the first and second loops  58   a,    58   b  of the snare means  50  can be configured to receive an engagement portion  24  of the stimulating electrode array  20 . It is further contemplated that, following receipt of the engagement portion  24  within both the first loop  58   a  and the second loop  58   b  of the snare means  50 , the steering member  40  can be configured to retract the snare means such that the first loop and the second loop of the snare means are pulled in opposing directions relative to the longitudinal axis B of the engagement portion, thereby engaging the engagement portion of the stimulating electrode array  20 . 
     In an additional aspect, and with reference to  FIG. 5 , each steering member  40  of the at least one steering member can comprise a handle  60 . It is contemplated that the snare means  50  can be coupled to the handle  60  of a steering member  40 , and the handle can comprise means for selectively deploying and retracting the snare means such that an engagement portion  24  of the stimulating electrode array  20  is engaged. In an exemplary aspect, the handle  60  can comprise a thumb guide ring  62  that is operatively coupled to the snare means. In another exemplary aspect, it is contemplated that the handle  60  can comprise, for example and without limitation, a conventional spring-loaded plunger mechanism that is moveable axially along the longitudinal axis A of the steering member  40  and is configured to effect movement of the snare means  50  about and between the extended position and the retracted position. In an additional exemplary aspect, it is contemplated that the steering member  40  can be a conventional suture retrieval snare, such as, for example and without limitation, those manufactured by Smith &amp; Nephew, Inc. (Andover, Mass.). It is further contemplated that the operation and design of the steering member  40  can be substantially the same as the suture snares described in U.S. Pat. Nos. 4,779,616, 5,501,692, 5,921,918, the disclosures of which are incorporated by reference in their entirety. It is contemplated that the operative coupling between the snare means  50  and the handle  60  as described herein can permit selective, one-handed activation by a user, such as a surgeon. In one aspect, when the distal end  44  of the housing  42  of a steering member  40  has a blunt tip, it is contemplated that, during movement of the steering member while the snare means  50  of the steering member is positioned in the retracted position, the blunt tip of the housing can be configured to prevent the steering member from engaging and becoming entangled with soft tissue of the epidural space of a subject. 
     In one aspect, it is contemplated that, following engagement between the snare means  50  and an engagement portion  24  of the stimulating electrode array  20 , the snare means can be configured to selectively retain the engagement portion of the stimulating electrode array proximate to, or against, the distal end  44  of the housing  42  of a steering member  40 . In this aspect, it is contemplated that, when the snare means  50  is retracted toward the housing  42 , the engagement portion  24  will remain engaged with the snare means such that the engagement portion is retained proximate to, or abuts, the distal end  44  of the housing. In still a further aspect, a steering member  40  of the at least one steering member can be configured to permit a surgeon to guide the stimulating electrode array  20  to a desired position proximate the dorsal column of the spinal cord of the subject. Optionally, upon positioning of the stimulating electrode array  20  at the desired position, the snare means  50  of a steering member  40  can be configured to release or otherwise disengage the engagement portion  24  of the stimulating electrode array such that the stimulating electrode array remains in the desired position. 
     Alternatively, in an optional aspect, and with reference to  FIG. 14 , rather than having a snare means  50  for engaging the at least one engagement portion  24  of the stimulating electrode array  20 , a steering member  40  of the at least one steering member can comprise a jaw assembly  80  having two opposed jaw elements  82   a,    82   b.  In this aspect, the opposed jaw elements  82   a,    82   b  can be configured to be movable about and between an open position and a closed position. It is contemplated that, in the closed position, the opposed jaw elements  82   a,    82   b  can close such that an engagement portion  24 , such as, for example and without limitation, a conventional 3-0 suture, can be grasped without any slippage. It is contemplated that the opposed jaw elements  82   a,    82   b  can be positioned outside of the housing  42  of a steering member  40  proximate the distal end  44  of the housing. In one aspect, the handle  60  of the steering member  40  can comprise means for selectively opening and closing the jaw assembly  80 . For example, it is contemplated that the means for selectively opening and closing the jaw assembly can comprise an elongate member positioned within the housing  42  and operatively coupled to the opposed jaw elements  82   a,    82   b  such that selective movement of the elongate member corresponds to opening and closing of the jaw assembly  80 . It is further contemplated that the elongate member can be positioned in operative communication with a grip portion of the handle  60  of the steering member  40  such that a user can manipulate the handle using the grip portion to create axial movement of the elongate member along the longitudinal axis A of the steering member, thereby providing selective control of the opening and closing of the jaw assembly  80 . In this aspect, the elongate member can comprise, for example and without limitation, a wire, a cable or other flexible material that possesses sufficient strength to function as described herein. It is contemplated that the operative coupling between the jaw assembly  80  and the handle  60  as described herein can permit selective, one-handed activation by a user, such as a surgeon. In a further aspect, the jaw elements  82   a,    82   b  of the jaw assembly  80  can be spring-loaded. 
     In an additional aspect, the jaw assembly  80  can be configured to operatively engage at least a portion of the stimulating electrode array  20 , such as, for example and without limitation, a portion of the top surface  26 , the bottom surface  27 , or the peripheral side edge  28  of the stimulating electrode array. Optionally, the jaw assembly  80  can be configured to operatively engage an engagement portion  24  of the at least one engagement portion of the stimulating electrode array  20 . 
     In another optional aspect, and as shown in  FIG. 9 , the distal end  44  of the housing  42  of the steering member  40  can have a telescoping portion  48  that is extendable and retractable along the longitudinal axis A of the steering member. In this aspect, the steering member  40  can comprise means for extending and retracting the telescoping portion  48 . In one aspect, it is contemplated that the means for extending and retracting the telescoping portion  48  can comprise an elongate member, such as, for example and without limitation, a cable or a wire, that is operatively coupled to the telescoping portion  48 . In this aspect, the elongate member can be in operative communication with the handle  60  of the steering member  40  such that a user can manipulate the handle to create axial movement of the elongate member along the longitudinal axis A of the steering member  40 , thereby providing selective control of the extension and retraction of the telescoping portion  48  of the steering member. It is contemplated that, following engagement between the steering member  40  and the stimulating electrode array  20 , the telescoping portion  48  of the steering member can be used to more effectively direct the stimulating electrode array to a desired position above an opening created during a laminotomy procedure. 
     In a further aspect, it is contemplated that a steering member  40  of the at least one steering member can be used to pull the stimulating electrode array  20  into position, thereby avoiding the tendency of flexible electrodes to follow the path of least resistance as they are conventionally pushed into place by their tails. It is further contemplated that the steering member  40  can be shaped and sized such that the steering member does not cause undesired dural stimulation during positioning of the stimulating electrode array  20 . In yet another aspect, it is contemplated that the malleable steering member  40  can be contoured or otherwise shaped to accommodate a deep wound and/or to guide the stimulating electrode array  20  from a first position to a second position lateral or cephalad (more superior) to the first position. In this aspect, it is further contemplated that the malleable steering member  40  can have sufficient mechanical strength to permit a surgeon to accurately control movement of the steering member in any direction within the epidural space regardless of operational conditions. 
     In still a further aspect, it is contemplated that the cross-sectional dimensions of the housing  42  of a steering member  40  of the at least one steering member  40  can be reduced or flattened proximate the distal end  44  of the housing. For example, in one aspect, the housing  42  of the steering member  40  can have a cross-sectional diameter ranging from about 1 mm to about 3 mm. In this aspect, it is contemplated that the cross-sectional diameter of the housing  42  can be reduced proximate the distal end  44  of the housing. It is contemplated that reductions in the cross-sectional profile of the distal portions of the housing  42  can decrease the portion of the spinal canal that is occupied by the steering member  40  during positioning of the stimulating electrode array  20 , as described herein. It is further contemplated that the resulting increase in unoccupied space within the spinal canal can facilitate epidural dissection. 
     In one aspect, and as shown in  FIGS. 6-8 , the at least one engagement portion  24  of the stimulating electrode array  20  can comprise two spaced engagement portions. In this aspect, it is contemplated that the stimulating electrode array  20  can have a first engagement portion  24   a  and a second engagement portion  24   b  spaced from the first engagement portion. It is contemplated that the first engagement portion  24   a  can be spaced from the second engagement portion  24   b  along a longitudinal axis C of the stimulating electrode array  20 . It is further contemplated that, as shown in  FIGS. 6-8 , the first engagement portion  24   a  can be spaced from the second engagement portion  24   b  substantially perpendicularly to the longitudinal axis C of the stimulating electrode array. 
     In an exemplary aspect, it is contemplated that a first steering member  40   a  as described herein can be used to engage the first engagement portion  24   a  while a second steering member  40   b  as described herein can be used to engage the second engagement portion  24   b.  As further depicted in  FIGS. 6-8 , the first engagement portion  24   a  and the second engagement portion  24   b  can be positioned thereon selected portions of the peripheral side edge  28  of the stimulating electrode array  20 . In an exemplary aspect, the first and second engagement portions  24   a,    24   b  can be positioned thereon the peripheral side edge  28  of the stimulating electrode array  20  proximate the distal portion  21  of the stimulating electrode array. In one aspect, the snare means of the first steering member  40   a  can be configured to engage the first engagement portion  24   a  of the stimulating electrode array  20  and the snare means of the second steering member  40   b  can be configured to engage the second engagement portion  24   b  of the stimulating electrode array. 
     In another aspect, following engagement between the snare means of the first and second steering members  40   a,    40   b  and the stimulating electrode array  20 , when the snare means are retracted toward the housings of each respective steering member, the snare means of the first steering member  40   a  can be configured to selectively retain the first engagement portion  24   a  against the distal end of the housing of the first steering member and the snare means of the second steering member  40   b  can be configured to selectively retain the second engagement portion  24   b  against the distal end of the housing of the second steering member. In a further aspect, the first and second steering members  40   a,    40   b  can be configured to cooperatively guide the stimulating electrode array  20  to a desired position proximate the dorsal column of the spinal cord of the subject. It is contemplated that the above-described placement of the first and second engagement portions  24   a,    24   b  and the use of two steering members  40   a,    40   b  can improve the accuracy with which the stimulating electrode array is positioned. It is further contemplated that the lateral placement of the first and second engagement portions  24   a,    24   b  can decrease the thickness of the steering member-electrode array assembly during insertion within the spinal canal of the subject. 
     Alternatively, it is contemplated that a steering member  40  as described herein can comprise first and second snare means that are spaced along the longitudinal axis A of the steering member. In an exemplary aspect, the first engagement portion  24   a  can be positioned proximate the distal portion  21  of the stimulating electrode array  20  and the second engagement portion  24   b  can be positioned proximate the medial portion  23  of the stimulating electrode array  20 , and the first snare means can be used to engage the first engagement portion while the second snare means can be used to engage the second engagement portion. Similarly, it is contemplated that a steering member  40  as described herein can comprise first and second jaw assemblies that are spaced along the longitudinal axis A of the steering member, and the first jaw assembly can be used to engage the first engagement portion  24   a  while the second jaw assembly can be used to engage the second engagement portion  24   b.  It is contemplated that the two spaced engagement portions  24   a,    24   b  can permit more stable and/or parallel re-positioning of the stimulating electrode array than is provided by a single engagement portion. 
     Optionally, and with reference to  FIG. 11 , in another exemplary aspect, at least a portion of the peripheral side edge  28  of the stimulating electrode array  20  can comprise a substantially rigid biocompatible and biodegradable material, such as, for example and without limitation, a conventional biodegradable polymer. It is contemplated that the substantially rigid biodegradable material can be at least one of Poly(glycolide), Poly(glocolic acid-co-L-lactic acid), Poly(L-lactide), Poly(L-lactic acid-co-e-caprolactone), Poly(e-caprolactone), Poly(p-dioxanone), and Poly(orthoester). In this aspect, it is contemplated that the substantially rigid biodegradable material can be configured to degrade within the body of the subject at a predetermined rate. It is contemplated that, when the predetermined rate of degradation of the substantially rigid biodegradable material corresponds to the period of time required for complete degradation to occur, the rate of degradation of the substantially rigid biodegradable material can range from about 5 minutes to about 1 day, more preferably ranging from about 10 minutes to about 2 hours, and most preferably ranging from about 30 minutes to about 90 minutes. In an exemplary aspect, when the predetermined rate of degradation of the substantially rigid biodegradable material corresponds to the period of time required for complete degradation to occur, the rate of degradation of the substantially rigid biodegradable material can be about one hour. In another aspect, the substantially rigid biodegradable material can be a bioabsorbable material. In these aspects, it is contemplated that, upon implantation, the stimulating electrode array  20  can be suitably rigid to prevent undesired movement or contouring of the stimulating electrode array as the stimulating electrode array approaches a desired position proximate the dorsal column of the spinal cord of the subject. It is further contemplated that, following degradation of the substantially rigid biodegradable material, the stimulating electrode array  20  can be sufficiently flexible for desired positioning proximate the dorsal column of the spinal cord of the subject. 
     Optionally, in a further aspect, the peripheral side edge  28  of the stimulating electrode array  20  can comprise a distal beveled portion  29 . In this aspect, it is contemplated that the distal beveled portion  29  of the stimulating electrode array can be configured to cut through tissue to thereby form an insertion pathway for passage of the stimulating electrode array. In an exemplary aspect, the portion of the peripheral side edge  28  that comprises the substantially rigid biodegradable material can include the distal beveled portion  29 . In this aspect, it is contemplated that the distal beveled portion  29  of the peripheral side edge  28  can degrade within the body of the subject to thereby avoid undesired injury to the tissue of the patient. 
     Optionally, in a further aspect, and with reference to  FIGS. 12-13 , the system  10  can comprise a frame element  30  configured to conform to at least a portion of the peripheral side edge  28  of the stimulating electrode array  20 . Optionally, the frame element  30  can be configured to conform to the peripheral side edge  28  of the stimulating electrode array within at least the distal portion  21  of the stimulating electrode array. In this aspect, the frame element  30  can comprise at least one snare means  36 , such as described herein with respect to the steering member  40 , for selectively coupling with a corresponding engagement portion  34  of the stimulating electrode array  20 . It is contemplated that the selective coupling between the frame element  30  and the stimulating electrode array  20  can permit precise positioning of the stimulating electrode array within the body of the subject. 
     In another aspect, the frame element  30  can comprise a handle portion  38  configured to permit selective advancement of the coupled frame element  30  and stimulating electrode array  20  within the body of the subject. In a further aspect, the handle portion  38  of the frame element  30  can comprise means for selectively deploying the snare means  36  of the frame element such that the snare means engages a corresponding engagement portion  24  of the stimulating electrode array  20 . It is contemplated that the means for selectively deploying the snare means  36  of the frame element  30  can substantially correspond to the means for selectively deploying the snare means  50  of the steering member  40 , as described herein. For example, it is contemplated that the handle portion  38  of the frame element  30  can be in operative communication with an elongate element, such as, for example and without limitation, a conventional spring-loaded plunger mechanism or other elongate member, that is moveable within the frame element  30  and is configured to effect movement of the snare means  36  about and between an extended position and a retracted position. In an exemplary aspect, the handle portion  38  of the frame element  30  can have a thumb guide ring that is operatively coupled to the snare means  36 . 
     Alternatively, in another optional aspect, rather than having a frame element  30  that is selectively coupled to the stimulating electrode array  20 , the frame element  30  can be integrated into the stimulating electrode array  20 . In this aspect, it is contemplated that the handle portion  38  of the frame element  30  can be selectively attachable to and detachable from the stimulating electrode array  20 . In an exemplary aspect, the handle portion  38  can have a threaded portion that can be operatively received by a corresponding threaded portion defined therein the stimulating electrode array  30 . 
     In another aspect, the frame element  30  can comprise a material that is more rigid than the stimulating electrode array  20  but also sufficiently malleable such that the frame element can be contoured to the shape of an insertion pathway formed by an epidural dissection tool. It is contemplated that the rigidity of the frame element can prevent undesired movement or contouring of the stimulating electrode array as the stimulating electrode array  20  approaches a desired position proximate the dorsal column of the spinal cord of the subject. In exemplary aspects, the frame element  30  can comprise one or more materials that are conventionally used to produce medical implants and surgical instruments, including, for example and without limitation, metal and polymeric materials, such as nitinol. In one aspect, at least portions of the frame element  30  can comprise a metal that is radio-opaque and, thus, visible through conventional fluoroscopic imaging procedures. It is also contemplated that at least a portion of the frame element  30  can comprise a radio-lucent material, such as, for example and without limitation, corrugated plastic. It is further contemplated that a radio-lucent frame element can minimize visibility of the housing during conventional fluoroscopic imaging procedures. In another aspect, at least a portion of the frame element  30  can be malleable. Optionally, the frame element  30  can have a substantially circular cross-section. 
     In an additional aspect, it is contemplated that the frame element  30  can comprise a distal portion  32  having a beveled edge  34 . In this aspect, it is contemplated that the beveled edge  34  of the frame element  30  can be configured to cut through tissue to thereby form an insertion pathway for passage of the stimulating electrode array. In these aspects, it is contemplated that the frame element can effectively serve the purpose of both an epidural dissection tool and an electrode delivery/positioning tool. 
     In use, the systems described herein can be employed in a method for optimizing stimulation of the dorsal column of the spinal cord of a subject. It is contemplated that the method can be incorporated into a standard surgical procedure for accomplishing dorsal column stimulation. In one aspect, the surgical procedure can be a minimally invasive approach that only requires a single, small incision, thereby minimizing the recovery time and post-operative pain for the subject. In one aspect, the method can comprise the initial step of providing a stimulating electrode array as described herein. Optionally, in another aspect, the method can comprise providing at least one steering member as described herein. Alternatively, in another optional aspect, the method can comprise providing a frame element as described herein. 
     In an exemplary aspect, when the at least one steering member is provided, the method can comprise selectively deploying a snare means of the at least one steering member such that the snare means engages a corresponding engagement portion of the stimulating electrode array. Following the step of selectively deploying the snare means, the method can comprise selectively retracting the snare means such that the engagement portion of the stimulating electrode array is retained against the distal end of the housing. Following the step of selectively retracting the snare means, the method can comprise selectively moving the steering member such that the stimulating electrode array is guided to the desired position proximate the dorsal column of the spinal cord of the subject, as described herein. It is contemplated that the steps of selectively deploying the snare means and selectively retracting the snare means can be accomplished by selective operation of the handle of the steering member, as described herein. In another aspect, the method can further comprise releasing or otherwise disengaging the engagement portion of the stimulating electrode array from the snare means such that the stimulating electrode remains in the desired position. In a further aspect, the method can comprise the steps of removing the steering member, internalizing the stimulating electrode array and the IPG or other means for creating electrical pulses, and closing the surgical incision using conventional procedures. 
     In another exemplary aspect, when each steering member comprises a jaw assembly, the method can comprise selectively opening and closing the jaw assembly such that the jaw assembly engages a corresponding engagement portion of the stimulating electrode array. Following the step of selectively opening and closing the jaw assembly, the method can comprise selectively moving the steering member such that the stimulating electrode array is guided to the desired position proximate the dorsal column of the spinal cord of the subject, as described herein. It is contemplated that the steps of selectively opening and closing the jaw assembly can be accomplished by selective operation of the handle of the steering member, as described herein. In another aspect, the method can further comprise releasing or otherwise disengaging the engagement portion of the stimulating electrode array from the jaw assembly such that the stimulating electrode remains in the desired position. In a further aspect, the method can comprise the steps of removing the steering member, internalizing the stimulating electrode array and the IPG or other means for creating electrical pulses, and closing the surgical incision using conventional procedures. 
     In further aspects, when the distal end of the housing of each steering member has a telescoping portion, the methods can further comprise the step of selectively extending the telescoping portion following engagement between the steering member and the stimulating electrode array. 
     In an additional exemplary aspect, when a frame element is provided, the method can comprise selectively coupling the frame element thereto the at least one engagement portion of the stimulating electrode array as described herein. In a further aspect, the method can comprise inserting the coupled frame element and stimulating electrode array into the body of the subject at a desired position proximate the dorsal column of the subject. In another aspect, the method can comprise disengaging the frame element from the at least one engagement portion of the stimulating electrode array such that the stimulating electrode array remains in the desired position. 
     In one aspect, the step of inserting the coupled frame element and stimulating electrode array into the body of the subject can comprise selectively advancing a dissection tool configured to form an insertion pathway having a cross-sectional shape and size corresponding to a cross-sectional shape and size of the coupled frame element and stimulating electrode array. 
     In another aspect, when the frame element comprises a distal portion having a beveled edge, the step of inserting the coupled frame element and stimulating electrode array into the body of the subject can comprise selectively advancing the frame element to form an insertion pathway. It is contemplated that the insertion pathway formed by the frame element can be sized and shaped to receive the coupled frame element and stimulating electrode array and permit removal of the frame element without affecting the position of the stimulating electrode array. 
     In still another exemplary aspect, when a portion of the peripheral side edge of the stimulating electrode array comprises a rigid biodegradable material and has a distal beveled portion, the step of inserting the stimulating electrode array into the body of the subject can comprise selectively advancing the stimulating electrode array to form an insertion pathway. It is contemplated that the insertion pathway formed by the distal beveled portion of the stimulating electrode array can be sized and shaped to receive the stimulating electrode array. 
     It is contemplated that the step of selectively moving the steering member such that the stimulating electrode array is guided to the desired position can comprise monitoring the effectiveness of the stimulating electrode array at a variety of positions until the desired position is identified. In exemplary aspects, it is contemplated that the subject can be aroused from sedation while the stimulating electrode array is placed in an initial position, and the surgeon can conduct a stimulation trial, in which the subject can provide feedback as to the effectiveness of the stimulation that is applied by the stimulating electrode array in the initial position. Depending on the feedback from the subject, the position of the stimulating electrode array can be adjusted as necessary until a stimulation trial indicates that the stimulation provided by the stimulating electrode array at a particular location is satisfactory. It is contemplated that the location at which satisfactory stimulation occurs can correspond to the desired position of the stimulating electrode array. It is further contemplated that a steering member and/or frame element can remain engaged with the stimulating electrode array during trial stimulations such that the position of the stimulating electrode array can be quickly adjusted depending on the feedback received from the subject. Conventional imaging techniques, including fluoroscopy, can be used to confirm that the stimulating electrode array is maintained at the desired position. 
     Except where expressly stated to the contrary, it is contemplated that all elements of the systems disclosed herein can comprise biocompatible materials. 
     As one having ordinary skill in the art will appreciate, depending on the number of electrodes and the variety of stimulation pulses that can be generated within a system as described herein, the number of stimulation groups available presents numerous potential parameter sets that can be used by a surgeon or clinician. Accordingly, the methods described herein can further comprise selecting an effective stimulation parameter set for the subject. It is contemplated that the step of selecting an effective stimulation parameter set can comprise performing stimulation trials as described herein with different stimulation parameter sets until a satisfactory stimulation parameter set is identified. 
     EXAMPLES 
     A subject was placed prone on a radiolucent table and administered conventional sedation and antibiotics. A midline low thoracic incision was planned using surface landmarks and fluoroscopic guidance from an X-ray source. The surgical site was deeply infiltrated with local anesthetic, and a small incision was created over the T10 and T11 spinous processes. The dorsal fascia was incised and the paraspinous muscles were elevated sub-periosteally and retracted. The T10 spinous process was partially resected, and the trailing edge of the lamina was defined. Conventional bone rongeurs and curettes were then used to create a small laminotomy and expose the epidural space. The laminotomy was sized according to the widths of the electrodes of the stimulating electrode array to be implanted. A disposable curved epidural dissector or narrow malleable ribbon retractor was then used to create an initial epidural pathway by which the stimulating electrode array could be positioned within the epidural space. 
     The engagement portion of the stimulating electrode array was then prepared. As depicted in  FIG. 1 , a 3-0 vicryl suture was passed through the plastic at the distal end of the stimulating electrode array, just in front of the first electrode. The suture was passed from the dorsal surface of the electrode through to the ventral surface and then back through to the dorsal surface. Four knots were then tied, and the suture tails were trimmed. The knots served as the fixation point for the steering member. As shown in  FIGS. 2-3 , the snare means were then deployed and used to grasp the suture knot (the engagement portion). Once the snare means was retracted, the stimulating electrode array was securely attached to the steering member. 
     As depicted in  FIG. 4 , the steering member was then used to introduce the stimulating electrode array into the epidural space by pulling (rather than pushing) the electrode array into position. Gentle traction was applied on the lead wires while the steering member was advanced to allow the electrode array to be “shimmied” into position. Fluoroscopy was used to place the stimulating electrode array in the initial location. The subject was then aroused from sedation, and a subjective stimulation trial was conducted. The electrode was adjusted as necessary with fluoroscopic guidance. Once satisfactory stimulation coverage was achieved, the snare means was deployed to release the engagement portion (suture knot) of the stimulating electrode array, and the steering member was gently removed. A final image confirmed that the electrode array had not migrated. The subject was then re-sedated, and internalization of the IPG and leads proceeded in conventional fashion. 
     The described technique was used in patients during both initial electrode placement and in revision of previously placed epidural electrodes. Thirteen patients underwent first-time paddle-style electrode placement after a prior ambulatory trial with percutaneous electrodes. One patient underwent revision of a paddle-style electrode that had been placed several years earlier. In this patient, the epidural space was dissected with a malleable ribbon before placement of the new electrode. Another patient underwent placement of a paddle-style electrode after removal of percutaneous electrodes that had migrated. The time required for electrode placement was substantially reduced, generally being as short as 5 minutes and typically being less than 15 minutes. The intra-procedure discomfort for the patients, as judged subjectively by the patients, was also reduced. Stimulating electrode arrays as described herein were successfully and precisely positioned in both unilateral paramedian or midline positions. Paddle-style electrodes from different manufacturers have been placed, including a two-column octet electrode array (Boston Scientific) and three-column 5-6-5 electrode array (Medtronic). No procedural complications related to the methods described herein have been identified. Images of an exemplary adjustment in the positioning of a stimulating electrode array as described herein are depicted in  FIGS. 15A and 15B . 
     Although several embodiments of the invention have been disclosed in the foregoing specification, it is understood by those skilled in the art that many modifications and other embodiments of the invention will come to mind to which the invention pertains, having the benefit of the teaching presented in the foregoing description and associated drawings. It is thus understood that the invention is not limited to the specific embodiments disclosed hereinabove, and that many modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although specific terms are employed herein, as well as in the claims which follow, they are used only in a generic and descriptive sense, and not for the purposes of limiting the described invention, nor the claims which follow.