Patent Publication Number: US-2021187284-A1

Title: Implantable lead with flexible paddle electrode array

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 16/370,522, filed Mar. 29, 2019, which is a continuation of U.S. patent application Ser. No. 15/628,426, filed Jun. 20, 2017 (now U.S. Pat. No. 10,245,427), which is a continuation of U.S. patent application Ser. No. 15/151,397, filed May 10, 2016 (now U.S. Pat. No. 9,682,228), which is a division of U.S. patent application Ser. No. 14/479,066, filed Sep. 5, 2014 (now U.S. Pat. No. 9,358,384). 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to medical apparatus and methods. More specifically, the present disclosure relates to neurostimulation methods and systems, and more particularly to paddle leads. 
     BACKGROUND OF THE INVENTION 
     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 applied electrical energy and the neural tissue is not understood, 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 regions of 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. 
     Each exterior region, or each dermatome, of the human body is associated with a particular spinal nerve root at a particular longitudinal spinal position. The head and neck regions are associated with C2-C8, the back regions extend from C2-S3, the central diaphragm is associated with spinal nerve roots between C3 and C5, the upper extremities correspond to C5 and T1, the thoracic wall extends from T1 to T11, the peripheral diaphragm is between T6 and T11, the abdominal wall is associated with T6-L1, lower extremities are located from L2 to S2, and the perineum from L4 to S4. In conventional neurostimulation, when a patient experiences pain in one of these regions, a neurostimulation lead is implanted adjacent to the spinal cord at the corresponding spinal position. For example, to address chronic pain sensations that commonly focus on the lower back and lower extremities using conventional techniques, a specific energy field is typically applied to a region between vertebrae levels T8 and T12. The specific energy field often stimulates a number of nerve fibers and structures of the spinal cord. By applying energy in this manner, the patient commonly experiences paresthesia over a relatively wide region of the patient&#39;s body from the lower back to the lower extremities. 
     Positioning of an applied electrical field relative to a physiological midline is also important. Nerve fibers extend between the brain and a nerve root along the same side of the dorsal column that the peripheral areas the fibers represent. Pain that is concentrated on only one side of the body is “unilateral” in nature. To address unilateral pain, electrical energy is applied to neural structures on the side of a dorsal column that directly corresponds to a side of the body subject to pain. Pain that is present on both sides of a patient is “bilateral”. Accordingly, bilateral pain is addressed through application of electrical energy along both sides of the column and/or along a patient&#39;s physiological midline. 
     Implantable leads have conductors extending there through that place distal electrodes of the lead in electrical communication with implantable pulse generators (IPGs) from which the implantable leads distally extend. The distal electrodes of the leads are positioned adjacent to pertinent nerves such that the electrodes deliver stimulation pulses to the nerves, those stimulation pulses originating from the IPGs and transmitted to the distal electrodes via the conductors of the leads. 
     To supply suitable pain-managing electrical energy, multi-programmable IPGs enable a pattern of electrical pulses to be varied across the electrodes of a lead. Specifically, such systems enable electrodes of a connected stimulation lead to be set as an anode (+), as a cathode (−), or to a high-impedance state (OFF). As is well known, negatively charged ions and free electrons flow away from a cathode toward an anode. Consequently, a range of very simple to very complex electrical fields can be created by defining different electrodes in various combinations of (+), (−), and OFF. Of course, in any instance, a functional combination must include at least one anode and at least one cathode (although in some cases, the “can” of the IPG can function as an anode). 
     Percutaneous leads and paddle leads are the two most common types of lead designs that provide conductors to deliver stimulation pulses from an implantable pulse generator (IPG) to distal electrodes adjacent to the pertinent nerve tissue. Example commercially available leads include the QUATTRODE™, OCTRODE™, LAMITRODE™, TRIPOLE™, EXCLAIM™, and PENTA™ stimulation leads from St. Jude Medical, Inc. 
     A conventional percutaneous lead includes electrodes that substantially conform to the body 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. 
     A conventional laminotomy or paddle lead has a paddle configuration and typically possesses a plurality of electrodes (commonly, eight, or sixteen) arranged in columns. Due to their dimensions and physical characteristics, conventional paddle leads may require a surgical procedure (a partial laminectomy) for implantation. Multi-column paddle leads enable more reliable positioning of a plurality of electrodes as compared to percutaneous leads. Also, paddle leads offer a more stable platform that tends to migrate less after implantation. Paddle leads are capable of being sutured in place. Paddle leads also create a uni-directional electrical field and, hence, can be used in a more electrically efficient manner than at least some known percutaneous leads. 
     Conventional laminotomy or paddle leads may be configured to employ paddle electrode arrays having a plurality of electrodes, which may be in the form of rectangular planar electrodes. Although a staggered electrode arrangement can provide superior electrode coverage as compared to that of a non-staggered electrode arrangement, a paddle electrode array with a staggered electrode arrangement will have reduced flexibility as compared to a similar paddle electrode array with a non-staggered electrode arrangement. The more rigid the paddle electrode array, the more likely the paddle electrode array can result in trauma to the epidural space in which it is implanted. 
     Accordingly, there is a need in the art for a paddle electrode array offering improved electrode coverage while still offering appropriate flexibility. 
     SUMMARY 
     A neurostimulation system is disclosed herein. In one embodiment, the neurostimulation system includes an implantable pulse generator and an implantable therapy lead configured to be electrically coupled to the implantable pulse generator. The implantable therapy lead includes a flexible paddle electrode array with flexible electrodes. Each flexible electrode has a segmented configuration having first and second electrode segments and a flexible bridge or living hinge joining together the first and second electrode segments. 
     In one embodiment, the flexible paddle electrode array also includes nonflexible electrodes that do not extend across flex lines of the flexible paddle electrode array. The flex lines extend generally perpendicular to the longitudinal length of the flexible paddle electrode array to pass through the flexible bridges. The flex lines are locations along the length of the flexible paddle electrode array where the array can flex. Because the nonflexible electrodes do not extend across the flex lines, and the flexible bridges of the flexible electrodes are aligned with the flex lines such that the bridges can act as living hinges to allow the electrode segments of the flexible electrodes to flex relative to each other at their respective living hinges, the flexible paddle electrode array can flex or bend along the various flex lines. 
     Another neurostimulation system is disclosed herein. In one embodiment, the neurostimulation system includes an implantable pulse generator and an implantable therapy lead configured to be electrically coupled to the implantable pulse generator. The implantable therapy lead includes a flexible paddle electrode array that has a row of laterally aligned flexible electrodes and a row of laterally aligned nonflexible electrodes. The row of laterally aligned flexible electrodes at least partially contributes to the formation of a flex line in the flexible paddle electrode. The row of laterally aligned nonflexible electrodes is longitudinally offset from the row of laterally aligned flexible electrodes such the flex line does not extend across the row of laterally aligned nonflexible electrodes. 
     In one embodiment, a flexible electrode of the flexible electrodes may include a first electrode segment and a second electrode segment spaced-apart from the first electrode segment. The flex line passes between the spaced-apart first and second electrode segments. 
     The flexible electrode of the flexible electrodes may further include a flexible living hinge joining the spaced-apart first and second electrode segments. The flex line passes through the flexible living hinge. The flexible living hinge may include a V-shape or U-shape. 
     The flexible electrode may be of an integrated construction such that at least one of the first electrode segment, the second electrode segment or the flexible living hinge are separate pieces joined together during manufacturing of the flexible electrode. The joining together during manufacturing of the flexible electrode may include at least one of welding or crimping. 
     Alternatively, the flexible electrode may be of a unitary and continuous construction such that the first electrode segment, the second electrode segment and the flexible living hinge are formed from a single material piece during manufacturing of the flexible electrode. The forming during manufacturing of the flexible electrode may include at least one of stamping or laser cutting. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic diagram of the spinal cord and the nerve roots in relation to the vertebral spinal canal. 
         FIG. 1B  is a schematic diagram of a neurostimulation system including a paddle lead extending from an implantable pulse generator in communication with a wireless programmer. 
         FIG. 1C  is a schematic diagram of the paddle lead of  FIG. 1B , wherein the paddle lead has a flexible paddle electrode array. 
         FIG. 2  is an isometric view of the flexile paddle electrode array of the paddle lead of  FIG. 1C , as viewed from a patient contact side of the flexile paddle electrode array. 
         FIG. 3  is an isometric view of the flexile paddle electrode array of  FIG. 2 , except as viewed from an electrically insulated side of the flexile paddle electrode array opposite the patient contact side illustrated in  FIG. 2 . 
         FIG. 4A  is an isometric view of an outer or patient contact side of a nonflexible electrode of the flexible paddle electrode array of  FIG. 2 . 
         FIG. 4B  is an isometric view of an inner side of the nonflexible electrode of  FIG. 4A , the inner side being opposite the patient contact side. 
         FIG. 4C  is a side elevation view of the nonflexible electrode of  FIG. 4A . 
         FIG. 5A  is an isometric view of an outer or patient contact side of a flexible electrode of the flexible paddle electrode array of  FIG. 2 . 
         FIG. 5B  is an isometric view of an inner side of the flexible electrode of  FIG. 5A , the inner side being opposite the patient contact side  62 . 
         FIG. 5C  is a side elevation view of the flexible electrode of  FIG. 5A . 
         FIG. 6  is an enlarged view of a region of  FIG. 3 . 
         FIGS. 7A and 7B  are plan views of a shortened coverage electrode array and an elongated electrode array, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     Neurostimulation systems  5  and methods are disclosed herein. In addition to an implantable pulse generator (IPG)  310 , the neurostimulation system  5  also includes an implantable therapy lead  10  that is capable of being coupled to the IPG  310 . As discussed in detail below, in one embodiment, the lead  10  includes a flexible paddle electrode array  11  that includes nonflexible electrodes  36  and flexible electrodes  38 . Each flexible electrode  38  includes first and second electrode segments  68 A,  68 B and a living hinge  70  that joins together the electrode segments  68 A,  68 B to allow the electrode segments  68 A,  68 B to flex or articulate relative to each other about the living hinge  70 , but still remain in solid contact with patient tissue. 
     The nonflexible electrodes  36  are grouped into rows of laterally aligned nonflexible electrodes  36  on the flexible paddle electrode array  11 . Similarly, the flexible electrodes  38  are grouped into rows of laterally aligned flexible electrodes  38  on the flexible paddle electrode array  11 . The even longitudinal spacing of the rows of laterally aligned nonflexible electrodes  36  is offset or staggered from the even longitudinal spacing of the rows of laterally aligned flexible electrodes  38 . Further, the living hinges  70  of each row of laterally aligned flexible electrodes  38  are aligned along a flex or hinge line  100  of the flexible paddle array  11 . Since no portion of a nonflexible electrode  36  extends across these flex or hinge lines  100 , the flexible paddle electrode array  11  has transverse lines of reduced rigidity or stiffness at these flex or hinge lines  100 , thereby allowing the flexible paddle electrode array  11  to flex or deflect along its length at these hinge lines  100 . Because of the living hinges  70 , the staggered arrangement of the rows of the nonflexible and flexible electrodes, and the flex or hinge lines  100 , the flexible paddle electrode array  11  is able to flex along its length, but be sufficiently rigid to maintain the nonflexible and flexible electrodes in adequate contact with patient tissue. 
     a. Definitions 
     Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. For purposes of the present disclosure, the following terms are defined below. 
     As used herein, the use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one”, but it is also consistent with the meaning of “one or more,” “at least one”, and “one or more than one”. Still further, the terms “having”, “including”, “containing” and “comprising” are interchangeable and one of skill in the art is cognizant that these terms are open-ended terms. Some embodiments may consist of or consist essentially of one or more elements, method steps, and/or methods of the disclosure. It is contemplated that any method or composition described herein can be implemented with respect to any other method or composition described herein. 
     As used herein, the use of the term “dorsal column” refers to conducting pathways in the spinal cord that are located in the dorsal portion of the spinal cord between the posterior horns, and which includes afferent somatosensory neurons. The dorsal column is also known as the posterior funiculus. 
     As used herein, “spinal cord,” “spinal nervous tissue associated with a vertebral segment,” “nervous tissue associated with a vertebral segment” or “spinal cord associated with a vertebral segment or level” includes any spinal nervous tissue associated with a vertebral level or segment. Those of skill in the art are aware that the spinal cord and tissue associated therewith are associated with cervical, thoracic and lumbar vertebrae. As used herein, C1 refers to cervical vertebral segment 1, C2 refers to cervical vertebral segment 2, and so on. T1 refers to thoracic vertebral segment 1, T2 refers to thoracic vertebral segment 2, and so on. L1 refers to lumbar vertebral segment 1, L2 refers to lumbar vertebral segment 2, and so on, unless otherwise specifically noted. In certain cases, spinal cord nerve roots leave the bony spine at a vertebral level different from the vertebral segment with which the root is associated. For example, the T1 nerve root leaves the spinal cord myelum at an area located behind vertebral body T8-T9 but leaves the bony spine between T11 and T12. 
     As used herein the term “chronic pain” refers to a persistent state of pain experienced for a substantial amount of time (e.g., longer than three months). 
     As used herein the term “complex regional pain syndrome” or “CRPS” refers to painful conditions that usually affect the distal part of an upper or lower extremity and are associated with characteristic clinical phenomena. CRPS is divided into two subtypes CRPS Type I and CRPS Type II. Generally, the clinical characteristics of Type I are the same as seen in Type II. The central difference between Type I and Type II is that Type II typically occurs following a sensory nerve injury whereas Type I occurs in the absence of any known nerve injury. 
     b. Organization of Nervous System 
     The nervous system includes two general components, the central nervous system, which is composed of the brain and the spinal cord, and the peripheral nervous system, which is composed of ganglia or dorsal root ganglia and the peripheral nerves that lie outside the brain and the spinal cord. Those of skill in the art will appreciate that the components of the nervous system may be linguistically separated and categorized, but functionally they are interconnected and interactive. 
     The central nervous system includes the brain and spinal cord, which together function as the principal integrator of sensory input and motor output. In general terms, the brain consists of the cerebrum (cerebral hemispheres and the diencephalons), the brainstem (midbrain, pons, and medulla), and the cerebellum. The spinal cord is organized into segments, for example, there are eight cervical (C1-C8), 12 thoracic (T1-T12), five lumbar (L1-L5), five sacral (S1-S5), and one cocygeal (Co1) spinal segments. In adults, the spinal cord typically ends at the level of the L1 or L2 vertebral bones. As shown in  FIG. 1A , which is a schematic diagram of the spinal cord and the nerve roots in relation to the vertebral spinal canal, the nerve roots travel downward to reach their exit points at the appropriate levels. Left and right sensory and motor nerve roots arise from each segment of the spinal cord except for the C1 and Co1 segments, which have no sensory roots. Associated sensory and motor nerve roots fuse to form a single mixed spinal nerve for each segment. The mixed spinal nerves further fuse and intermingle peripherally to form plexuses and nerve branches. 
     The peripheral nervous system is divided into the autonomic system (parasympathetic and sympathetic), the somatic system, and the enteric system. The term peripheral nerve is intended to include both motor and sensory neurons and neuronal bundles of the autonomic system, the somatic system, and the enteric system that reside outside of the spinal cord and the brain. Peripheral nerve ganglia and nerves located outside of the brain and spinal cord are also described by the term peripheral nerve. 
     c. Overview of Neurostimulation System 
       FIG. 1B  is a schematic diagram of a neurostimulation system  5  including a paddle lead  10 , an implantable pulse generator (IPG)  310 , and a programmer  320 . The paddle lead  10  extends from the IPG  310 . The programmer  320  is in wireless communication with the IPG  310 . An example of a commercially available IPG  310  is the Eon™ Rechargeable IPG from St. Jude Medical, Inc. (Plano, Tex.), although any suitable IPG, such as RF powered devices, could be alternatively employed. 
       FIG. 1C  is a schematic diagram of the paddle lead  10  employed in the system  5  of  FIG. 1B , according to one embodiment. The paddle lead  10  includes a proximal end  14  and a distal end  16 . The proximal end  14  includes a connector end or assembly  18  with a plurality of electrically conductive terminals  22 . The distal end  16  includes a flexible paddle electrode array  11  that includes a plurality of nonflexible electrodes  36  and flexible electrodes  38  arranged within a substantially flat and thin paddle style structure  17 . The electrodes  36 ,  38  are mutually separated by the electrically insulative material of the paddle  17 . Further details regarding the flexible paddle electrode array  11  and its construction are given below. 
     A lead body  12  of the lead  10  extends between the flexible paddle electrode array  11  and the connector end  18 . Conductors  24 , which are embedded within respective insulative sheaths  15  of the insulative lead body  12 , electrically connect the electrodes  36 ,  38  to the terminals  22 . 
     The terminals  22  are preferably formed of a non-corrosive, highly conductive material. Examples of such material include stainless steel, MP35N, platinum, and platinum alloys. In one embodiment, the terminals  22  are formed of a platinum-iridium alloy. 
     Each conductor  24  is formed of a conductive material that exhibits desired mechanical properties of low resistance, corrosion resistance, flexibility, and strength. While conventional stranded bundles of stainless steel, MP35N, platinum, platinum-iridium alloy, drawn-brazed silver (DBS) or the like can be used, one embodiment uses conductors  24  formed of multi-strands of drawn-filled tubes (DFT). Each strand is formed of a low resistance material and is encased in a high strength material (preferably, metal). 
     A selected number of “sub-strands” may be wound and coated with an insulative material. With regard to the operating environment of representative embodiments, such insulative material protects an individual conductor if its respective sheath is breached during use. 
     In addition to providing the requisite strength, flexibility, and resistance to fatigue, conductors  24  formed of multi-strands of drawn-filled tubes, in accordance with the above description, provide a low resistance alternative to other materials. Specifically, a stranded wire, or even a coiled wire, of approximately 60 cm and formed of MP35N or stainless steel or the like may have a measured resistance in excess of 30 ohms. In contrast, for the same length, a wire formed of multi-strands of drawn-filled tubes could have a resistance less than 4 ohms. 
     In the embodiment shown in  FIG. 1C , the flexible paddle electrode array  11  includes five columns and four rows of electrodes  36 ,  38  arranged in a grid configuration, for a total of twenty electrodes  36 ,  38 . As can be understood from  FIG. 1C  and as discussed in greater detail below, those columns may be three columns of non-flexible electrodes  36  and two columns of flexible electrodes  38 , wherein the columns of non-flexible electrodes  36  are staggered more distally relative to the flexible electrodes  38 . 
     Alternative numbers of columns and rows may be employed. For example, in some embodiments, thirty-two or more electrodes are distributed into multiple rows and multiple columns. Also, every row need not contain the same number of columns. For example, a number of rows can include a “tri-pole” design having three columns of electrodes while additional rows can include five or more columns of electrodes to enable a greater amount of electrical field resolution. Regardless of the number of columns and rows employed for the flexible paddle electrode array  11 , as long as the non-flexible electrodes  36  and flexible electrodes  38  are arranged such that the flexible paddle electrode array  11  has transverse lines of reduced rigidity or stiffness at flex or hinge lines  100  discussed in detail below, the flexible paddle electrode array  11  will be able to flex or deflect along its length at those hinge lines  100 , while maintaining the electrodes  36 ,  38  in adequate contact with the patient tissue. 
     The multiple columns of electrodes  36 ,  38  enable lateral control of the applied electrical field to stimulate the exact lateral position of the pertinent nerve fiber(s), as described herein. Specifically, it may be desirable to selectively stimulate a given dorsal column fiber that is associated with an afflicted region of the patient&#39;s body without affecting other regions of the patient&#39;s body. The multiple columns of electrodes according to representative embodiments provide sufficient resolution to relatively finely control the stimulation of one or several specific fibers, as described herein. Additionally, the multiple columns provide a degree of positional tolerance during the surgical placement of the flexible paddle electrode array  11  within the epidural space, as any one of the columns may be used to stimulate the pertinent nerve fiber(s). Also, if the flexible paddle electrode array  11  is displaced relative to the pertinent nerve fibers subsequent to implantation (e.g., due to lead migration), the stimulation pattern applied by a pulse generator can be shifted between columns to compensate for the displacement. 
     The multiple rows of electrodes  36 ,  38  enable multiple pain locations to be treated with a single implanted lead. Specifically, a first row can be used to treat a first pain complaint (e.g., pain in the lower extremities) and a second row can be used to treat a second pain location (e.g., post-laminectomy pain in the back). Furthermore, by separating the first and second rows by one or more “buffer” rows of high-impedance electrodes, the stimulation in the first and second rows may occur on a substantially independent basis. Specifically, anodes in the second row will have relatively minimal effect on the field distribution generated by cathodes in the first row. 
     In some embodiments, the flexible paddle electrode array  11  can be implanted within a patient such that electrodes  36 ,  38  are positioned within the cervical or thoracic spinal levels. After implantation, an electrode combination on a first row of electrodes can be determined that is effective for a first pain location with minimal effects on other regions of the body. The first pain location can be addressed by stimulating a specific dorsal column fiber due to the relatively fine electrical field resolution achievable by the multiple columns. Then, another electrode combination on a second row of electrodes can be determined for a second pain location with minimal effects on other regions of the body. The second pain location could be addressed by stimulating another dorsal column fiber as an example. After the determination of the appropriate electrodes for stimulation, a patient&#39;s IPG  310 , which is depicted in  FIG. 1C , can be programmed to deliver pulses using the first and second rows according to the determined electrode combinations. 
     When determining the appropriate electrode configurations, the selection of electrodes to function as anodes can often facilitate isolation of the applied electrical field to desired fibers and other neural structures. Specifically, the selection of an electrode to function as an anode at a position adjacent to another electrode functioning as a cathode causes the resulting electron/ion flow to be limited to tissues immediately surrounding the two electrodes. By alternating through a plurality of anode/cathode combinations it is possible to improve resolution in the stimulation of dorsal column fibers. Also, it is possible to confine the applied electrical field to or away from a periphery of the flexible paddle electrode array  11 . 
     The operation of anodes can also be used to hyperpolarize neural tissue. Depending on the anode amplitude and the proximity to the pertinent neural tissue, the hyperpolarization can be used to prevent selected neural tissue from propagating action potentials. The hyperpolarization can also be used to prevent an adjacent cathode from initiating propagation of an action potential beginning at the selected neural tissue. 
     Multiple columns of electrodes  36 ,  38  also enable lateral “steering” of the electrical field using a single channel pulse generator. A single channel pulse generator refers to a pulse generator that provides an equal magnitude pulse to each active electrode at a given time. Specifically, each electrode is either “active” (i.e., it is coupled to the pulse generator output during pulse generation by a suitable gate or switch) or “inactive” (i.e., the gate or switch does not couple the electrode to the pulse generator output). Each “active” electrode experiences the same amplitude; only the polarity varies depending upon whether electrode is set as a cathode or anode as defined by positions of respective gates and/or switches. The steering of the electrical field occurs by selecting appropriate states for each of electrodes  36 ,  38 . 
     The conductors  24  are carried in sheaths  15 . In some embodiments, each sheath  15  carries eight conductors  24 . With only two sheaths with eight conductors each, there would only be sixteen conductors. To accommodate the lower number of conductors than electrodes  36 ,  38 , multiple electrodes may be coupled to the same conductor (and, hence, to a common terminal  22 ). 
     In some embodiments, other electrode designs can be employed to minimize the number of conductors  24  required to support the various electrodes  36 ,  38 . For example, a relatively large number of electrodes (e.g., thirty-two, sixty-four, and greater) could be utilized on the flexible paddle electrode array  11 . The electrodes could be coupled to one or several electrical gates (e.g., as deposited on a flex circuit). The electrical gates can be controllably configured to couple each electrode to a conductor carrying cathode pulses, to couple each electrode to an anode termination, or to maintain each electrode at a high impedance state. The electrical gates could be controlled using a main controller, such as a logic circuit, on the flexible paddle electrode array  11  that is coupled to a data line conductor  24 . The data line conductor communicates signals from the IPG  310  that identify the desired electrode states, and the main controller responds to the signals by setting the states of the electrical gates as appropriate. 
     In another embodiment, a cathode conductor line  24  and an anode conductor line  24  are provided in one or several lead bodies  12  along with a plurality of optical fibers. The optical fibers are used to carry optical control signals that control the electrode states. Specifically, the flexible paddle electrode array  11  includes photodetectors (e.g., photodiodes) that gate connections to the anode conductor line and the cathode conductor line. The use of optical fibers to carry optical control signals may be advantageous, because the diameter of optical fibers suitable for such functionality is smaller than electrical conductors  24 . Therefore, a larger number of electrodes (as compared to using a separate electrical conductor  24  for each electrode) can be independently controlled while maintaining the lead body diameters at an acceptable size. 
     The sheaths  15  and the paddle support structure  17  of the flexible paddle electrode array  11  are preferably formed from a medical grade, substantially inert material, for example, polyurethane, silicone, or the like. Importantly, such material should be non-reactive to the environment of the human body, provide a flexible and durable (i.e., fatigue resistant) exterior structure for the components of the paddle lead  10 , and insulate adjacent terminals  22  and/or electrodes  36 ,  38 . 
     The flexible paddle electrode array  11  may be fabricated to possess a substantially flat profile. Alternatively, the flexible paddle electrode array  11  may have an arcuate or bowed profile. In some embodiments, a wing structure or other type of stabilization structure extends along one or both longitudinal sides of the paddle structure  17 . Such stabilization structures may be formed for the purpose of retaining the flexible paddle electrode array  11  within the central portion of the epidural space. In some embodiments, one or more electrodes  36 ,  38  may be disposed on the stabilization structures. Regardless of whether the flexible paddle electrode array  11  has a substantially flat profile or an arcuate profile or is equipped with one or more stabilization structures, as long as the non-flexible electrodes  36  and flexible electrodes  38  are arranged such that the flexible paddle electrode array  11  has transverse lines of reduced rigidity or stiffness at flex or hinge lines  100  discussed in detail below, the flexible paddle electrode array  11  will be able to flex or deflect along its length at those hinge lines  100 , while maintaining the electrodes  36 ,  38  in adequate contact with the patient tissue. 
     As can be understood from  FIGS. 1B and 1C , the paddle lead  10  is coupled to the IPG  310  by the lead connector assembly  18  of the paddle lead  10  being received in the header ports  311  of the IPG  310 . Each header port  311  electrically couples the respective terminals  22  to a switch matrix (not shown) within the IPG  310 . 
     The switch matrix selectively connects the pulse generating circuitry (not shown) of the IPG  310  to the terminals  22  of the paddle lead  10 , and, hence to electrodes  36 ,  38 . A sealed portion  312  of the IPG  310  contains pulse generating circuitry, communication circuitry, control circuitry, and a battery (not shown) within an enclosure to protect the components after implantation within a patient. The control circuitry may include a microprocessor, one or more application specific integrated circuits (ASICs), and/or any suitable circuitry for controlling the pulse generating circuitry. The control circuitry controls the pulse generating circuitry to apply electrical pulses to the patient via the electrodes  36 ,  38  of the flexible paddle electrode array  11  according to multiple pulse parameters (e.g., pulse amplitude, pulse width, pulse frequency, etc.). The electrodes  36 ,  38  are set to function as cathodes or anodes or set to a high-impedance state for a given pulse according to the couplings provided by the switch matrix. The electrode states may be changed between pulses. 
     When the paddle lead  10  is initially implanted within the patient, a determination of the set(s) of pulse parameters and the electrode configuration(s) that may effectively treat the patient&#39;s condition is made. The determination or programming typically occurs through a physician&#39;s interaction with configuration software  321  executed on the programmer device  320 , as indicated in  FIG. 1B . The configuration software  321  steps the physician through a number of parameters and electrode configurations based on a trolling algorithm. In some embodiments, the electrode configurations are stepped through by laterally “steering” the electrical field by moving the anodes and/or cathodes along a row of the paddle. The patient provides feedback to the physician regarding the perceived stimulation that occurs in response the pulse parameters and electrode configuration(s). The physician may effect changes to the parameters and electrode configuration(s) until optimal pulse parameters and electrode configuration(s) are determined. The final pulse parameters and configurations are stored within the IPG  310  for subsequent use. The pulse parameters and configurations are used by the IPG  310  to control the electrical stimulation provided to the patient via the paddle lead  10 . Although single channel IPGs have been described according to some embodiments, multiple current or voltage source IPGs could alternatively be employed. 
     d. Flexible Paddle Electrode Array 
       FIG. 2  is an isometric view of the flexile paddle electrode array  11  of the lead of  FIG. 1C , as viewed from a patient contact side  30  of the array  11 .  FIG. 3  is an isometric view of the array  11  of  FIG. 2 , except as viewed from an electrically insulated side  32  of the array  11  opposite the patient contact side  30  illustrated in  FIG. 2 . As shown in  FIGS. 2 and 3 , the paddle electrode array  11  includes a planar flexible substrate  34 , non-flexible electrodes  36 , flexible electrodes  38 , and an enclosure  40 . The planar flexible substrate  34  and enclosure  40  can be said to form a substantially flat and thin paddle style structure  17 . The nonflexible electrodes  36  and flexible electrodes  38  are arranged within the paddle style structure  17 . The electrodes  36 ,  38  are mutually separated by the electrically insulative material of the paddle  17 . 
     The planar flexible substrate  34  may be formed of polyether ether ketone (PEEK), Fiberglass, or Liquid Crystal Polymer. The substrate  34  may have a thickness of between approximately 0.007″ and approximately 0.1″, a width of between approximately 0.37″ and approximately 0.5″, and a length of between approximately 0.7″ and approximately 2.0″. The substrate  34  includes a patient contact side  44  and an electrically insulated side  46  opposite the patient contact side  44 . These sides  44 ,  46  of the substrate  34  respectively correspond to the patient contact side  30  and the electrically insulated side  32  of the array  11 . 
     As illustrated in  FIGS. 2 and 3 , longitudinally extending long slots  42  extend through the thickness of the substrate  34  to daylight at the patient contact side  44  and opposite electrically insulated side  46  of the substrate  34 . The long slots  42  run parallel to a longitudinal axis of the flexible paddle electrode array  11 . The long slots  42  have a length of between approximately 0.20″ and approximately 0.30″ and a width of between approximately 0.025″ and approximately 0.38″. 
     Similarly, as can be understood from  FIG. 3 , longitudinally extending short slots  48  extend through the thickness of the substrate  34  to daylight at the patient contact side  44  and opposite electrically insulated side  46  of the substrate  34 , although, as can be understood from  FIGS. 2 and 3 , the short slots  48  are hidden by the electrodes  36 ,  38  on the patient contact side  44  of the substrate  40 . The short slots  48  run parallel to the longitudinal axis of the flexible paddle electrode array  11 . The short slots  48  have a length of between approximately 0.05″ and approximately 0.10″ and a width of between approximately 0.015″ and approximately 0.025″. 
     Except as noted below, the enclosure  40  extends coextensively about the entirety of all surfaces of the substrate  34  and the electrodes  36 ,  38  supported on the substrate  34 . The exception to this statement is the planar faces  50  of the electrodes  36 ,  38  on the patient contact side  30  of the paddle  11 . These electrode faces  50  extend through the enclosure  40  to be exposed for making electrical contact with patient tissue, as can be understood from  FIG. 2 . 
     As can be understood from  FIGS. 1C-3 , the paddle electrode array  11  extends from the lead body  11 . The enclosure  40  may be a continuous or generally continuous extension of one or more insulation layers of the jacket of the lead body  12 . The jacket of the lead body  12  and the enclosure  40  may be in the form of one or more insulation layers. Such insulation layers may be fabricated of silicone rubber, polyurethane, silicone rubber—polyurethane—copolymer (SPC), polytetrafluoroethylene (“PTFE”), and/or other suitable polymers. The lead body  12  and electrode array  11  include many internal components, including electrical conductors  24  extending through the lead body  12  and electrode array  11  from the electrical contacts  22  of the lead connector assembly  18  to the electrodes  36 ,  38  supported on the electrode array  11 . The insulation layers of the lead body  12  and enclosure  40  isolate these internal components of the lead body  12  and paddle array  11  from each other and the surrounding environment. 
     The patient contact side  30  includes exposed electrode faces  50  that are configured to contact patient tissue and administer electrical energy to the patient tissue and/or sense electrical signals from the patient tissue. The electrically insulated side  32  of the array  11  is opposite from the patient contact side  30  and has a continuous and unbroken layer of the enclosure  40  extending over it such that no electrical contact can be established with the electrodes  36 ,  38  by patient tissue coming into contact with the electrically insulated side  32 . 
     For a discussion regarding the nonflexible electrodes  36  employed in the electrode array  11 , reference is made to  FIGS. 4A-4C .  FIG. 4A  is an isometric view of an outer or patient contact side  52  of a nonflexible electrode  36  of the flexible paddle electrode array  11  of  FIG. 2 .  FIG. 4B  is an isometric view of an inner side  54  of the nonflexible electrode  36  of  FIG. 4A , the inner side  54  being opposite the patient contact side  52 .  FIG. 4C  is a side elevation view of the nonflexible electrode  36  of  FIG. 4A . 
     As shown in  FIGS. 4A-4C , the patient contact side  52  of the nonflexible electrode  36  includes a planar face  50 , and the inner side  54  of the nonflexible electrode  36  includes another planar face  56  opposite the planar face  50  of the patient contact side  52 . As illustrated in  FIG. 2 , the planar face  50  of the patient contact side  52  is not covered by the enclosure  40  and, as a result, serves as the exposed surface  50  of the electrode  36  through which the electrode  36  administers and/or senses electrical signals. As can be understood from  FIGS. 2, 3 and 6 , which is an enlarged area of  FIG. 3 , the planar face  56  of the inner side  54  abuts against the patient contact side  44  of the substrate  34  in generally planar surface contact. While a short slot  48  may open underneath the planar face  56  of the inner side  54 , the enclosure  40  extends over the entirety of the electrically insulated side  46  of the substrate  34 . As a result, the planar face  56  of the inner side  54  is electrically isolated and does not serve as a surface through which the electrode  36  may administer and/or sense electrical signals. 
     As indicated in  FIGS. 4A-4C , the nonflexible electrode  36  includes a single continuous rectangular body  58  that includes the two planar surfaces  50 ,  56 . At the opposite ends of the body  58  are folded over tabs  59 . As can be understood from  FIGS. 2 and 3 , these tabs  59  may be employed for welding or otherwise affixing the electrode  36  to the substrate  34  and the respective electrical conductors  24  that extend from the contacts  22  of the lead connector assembly  18  and through the body  12  and array  11  to the electrode  36 . 
     For a discussion regarding the flexible electrodes  38  employed in the electrode array  11 , reference is made to  FIGS. 5A-5C .  FIG. 5A  is an isometric view of an outer or patient contact side  62  of a flexible electrode  38  of the flexible paddle electrode array  11  of  FIG. 2 .  FIG. 5B  is an isometric view of an inner side  64  of the flexible electrode  38  of  FIG. 5A , the inner side  64  being opposite the patient contact side  62 .  FIG. 5C  is a side elevation view of the flexible electrode  38  of  FIG. 5A . 
     As indicated in  FIGS. 5A-5C , the flexible electrode  38  includes a discontinuous or segmented rectangular body  68  having a first rectangular body segment  68 A joined via a flexible bridge  70  to a second rectangular body segment  68 B. Each body segment  68 A,  68 B includes a respective pair of planar surfaces  60 A,  68 A and  69 B,  68 B. 
     As illustrated in  FIG. 5C , the flexible bridge  70  is V-shaped or U-shaped and protrudes outwardly from the inner side  64  of the electrode  38 . As shown in  FIGS. 5A-5C , the U-shaped flexible bridge  70  is approximately the same thickness as the body segments  68 A,  68 B, but has a width that is approximately half as wide or less than the width of the body segments  68 A,  68 B. The U-shaped flexible bridge  70  has arcuate or curved transitions between itself and the adjoining body segments  68 A,  68 B. Further the U-shaped flexible bridge  70  has an arcuate or curved transition at its extreme apex, which projects outwardly from the inner side  64  of the electrode  38  a distance that slightly exceeds that of the tabs  69 . 
     Folded over tabs  69  are at the opposite ends of the segmented body  68 . As can be understood from  FIGS. 2, 3 and 6 , these tabs  69  may be employed for welding or otherwise affixing the electrode  38  to the substrate  34  and the respective electrical conductors  24  that extend from the contacts  22  of the lead connector assembly  18  and through the body  12  and array  11  to the electrode  38 . 
     As shown in  FIGS. 5A-5C , the patient contact side  62  of the flexible electrode  38  includes planar faces  60 A,  60 B. Each such face  60 A,  60 B is part of a respective rectangular body segment  68 A,  68 B. Similarly, the inner side  64  of the flexible electrode  38  includes planar faces  66 A,  66 B opposite the planar faces  60 A,  60 B of the patient contact side  62 . Each such face  66 A,  66 B is part of a respective rectangular body segment  68 A,  68 B. 
     As illustrated in  FIG. 2 , the planar faces  60 A,  60 B of the patient contact side  62  are not covered by the enclosure  40  and, as a result, serve as the exposed surfaces  60 A,  60 B of the flexible electrode  38  through which the flexible electrode  38  administers and/or senses electrical signals. As can be understood from  FIGS. 2, 3 and 6 , the planar faces  66 A,  66 B of the inner side  64  abut against the patient contact side  44  of the substrate  34  in generally planar surface contact. While a short slot  48  opens underneath the planar faces  66 A,  66 B of the inner side  64 , and while the flexible bridge  70  extends through the short slot  48 , the enclosure  40  extends over the entirety of the electrically insulated side  46  of the substrate  34 . As a result, the planar faces  66 A,  66 B of the inner side  64  and the flexible bridge  70  are electrically isolated and do not serve as surfaces through which the electrode  38  may administer and/or sense electrical signals. 
     As can be understood from  FIGS. 2, 4A-4C, and 5A-5C , in one embodiment, each nonflexible electrode  36  has an overall length of between approximately 0.18″ and approximately 0.28″, and an overall width of between approximately 0.026″ and approximately 0.042″. Each flexible electrode  38  has an overall length of between approximately 0.26″ and approximately 0.29″, and an overall width of between approximately 0.026″ and approximately 0.042″. 
     Each electrode segment  68 A,  68 B has an overall length of between approximately 0.11″ and approximately 0.12″. Each flexible electrode  38  also has a gap distance over which the bridge  70  extends between immediately adjacent ends of the segments  68 A,  68 B that is between approximately 0.02″ and approximately 0.03″. 
     End-to-end spacing between immediately adjacent electrodes in the same column is between approximately 0.08″ and approximately 0.2″. Side-to-side spacing between immediately adjacent electrode columns is between approximately 0.02″ and approximately 0.04″. 
     The electrodes  36 ,  38  are formed of an electrically conductive and biocompatible material. Examples of such candidate electrode materials include stainless steel, MP35N, platinum, and platinum alloys. In one embodiment, the electrodes  36 ,  38  are formed of a platinum-iridium alloy. 
     As can be understood from  FIGS. 1C-6 , the implantable therapy lead  10  includes a flexible paddle electrode array  11  with flexible electrodes  38 . Each flexible electrode  38  has a segmented configuration having first and second electrode segments  68 A,  68 B and a flexible bridge or living hinge  70  joining together the first and second electrode segments  68 A,  68 B. As noted above, the flexible bridge  70  may be V-shaped or U-shaped and have a width that is less than a width of the first electrode segment  68 A or the second electrode segment  68 B. 
     In one embodiment, the flexible electrode  38  is of an integrated construction such that the electrode segments  68 A,  68 B and the living hinge  70  are manufactured of one or more individual pieces that are joined together via, for example, welding or crimping. In another embodiment, the flexible electrode  38  is of a unitary and continuous construction such that the electrode segments  68 A,  68 B and the living hinge  70  are formed from a single piece of material via stamping, laser cutting or other methods. As a result, the flexible electrode  38  have a unitary construction such that the segments  68 A,  68 B and the living hinge  70  are not individual components that are joined together during the manufacturing process, but are of a single, unitary and continuous piece of material to form a flexible electrode  38  of a continuous and unitary construction. 
     Regardless of how the flexible electrode  38  is manufactured and regardless of whether it is of an integrate construction or an integral construction, the living hinge  70  allows the flexible electrode  38  to flex along the hinge  70  while still being a one-piece electrode  38 . Accordingly, the flexible electrode  38  only requires a single feeder electrical conductor contact and does not require a jumper wire between the two electrode segments  68 A,  68 B. 
     The flexible paddle electrode array  11  also includes a substrate  34  on which the flexible electrodes  38  are supported. The substrate  34  includes a short slot  48  that extends through the thickness of the substrate  34 , and the flexible bridge  70  is located in the short slot  70 , as shown in  FIG. 6 . 
     As illustrated in  FIGS. 2-3 , the flexible paddle electrode array  11  also includes nonflexible electrodes  36  that do not extend across flex lines  100  of the flexible paddle electrode array  11 . The flex lines  100  extend generally perpendicular to the longitudinal length of the array  11  to pass through the flexible bridges  70 . In other words, the flex lines  100  extend laterally across the array  11  to pass through the flexible bridges  70 . 
     The flex lines  100  may be considered lines of reduced stiffness or rigidity in the flexible paddle electrode array  11  on account of the reduced stiffness or rigidity provided by the laterally aligned living hinges  70 . The flex lines  100  are locations along the length of the flexible paddle electrode array  11  where the flexible paddle electrode array  11  can flex. Because the nonflexible electrodes  36  do not extend across the flex lines  100 , and the flexible bridges  70  of the flexible electrodes  38  are aligned with the flex lines  100  such that the bridges  70  can act as living hinges  70  to allow the electrode segments  68 A,  68 B (see  FIGS. 5A-5C ) of the flexible electrodes  38  to flex relative to each other at their respective living hinges  70 , the flexible paddle electrode array  11  can flex or bend along the various flex lines  100 . Thus, as can be understood from  FIGS. 2 and 3 , the flexible electrodes  38  allow for staggered rows of electrodes on the flexible paddle electrode array without increasing stiffness between the rows of electrodes. 
     As indicated in  FIGS. 2 and 3 , the flexible electrodes  38  are part of a plurality of flexible electrodes  38  evenly spaced along at least one column line (i.e., longitudinally extending line) that is generally parallel with a longitudinal axis of the flexible paddle electrode array  11 . Similarly, the nonflexible electrodes  36  are part of a plurality of nonflexible electrodes  36  evenly spaced along at least another column line (i.e., longitudinally extending line) that is generally parallel with the longitudinal axis of the flexible paddle electrode array  11 . 
     These column lines of flexible electrodes  38  and nonflexible electrodes  36  are laterally offset from each other. In one embodiment, there may be two column lines of flexible electrodes  38  and three column lines of nonflexible electrodes  36 . The column lines of flexible electrodes  38  and nonflexible electrodes  36  are arranged in an alternating configuration running laterally across the flexible paddle electrode array  11 . The flexible electrodes  38  are evenly spaced apart from each other, as is also the case with the nonflexible electrodes  36 . The flexible electrodes  38  are staggered along a length of the flexible paddle electrode array  11  relative to the nonflexible electrodes  36 . In one embodiment, each of the two column lines of flexible electrodes  38  includes four flexible electrodes  38 , and each of the three column lines of nonflexible electrodes  36  includes four nonflexible electrodes  36 . Such an embodiment can also be said to have four row lines (i.e., transversely extending lines) of two flexible electrodes  38  that are laterally or transversely space apart from each other, and four row lines (i.e., transversely extending lines) of three nonflexible electrodes  36  that are laterally or transversely spaced apart from each other, as can be understood from  FIG. 2 . 
     The flexible paddle electrode array  11  and its components can be configured as depicted in  FIGS. 1C-6  and dimensioned as discussed above. In other embodiments, the array  11  and its components may have other arrangements. For example, as illustrated in  FIG. 7A , in one embodiment, the flexible paddle electrode array  11  may employ an electrode array that is shortened or longitudinally compressed. The paddle structure  17  can be curved or flat. The electrode array may extend over a longitudinal length of approximately 37 mm and, as a result, be substantially short of the full length of the underlying paddle structure  17 . The paddle structure  17  may have a width of approximately 9.5 mm and the array width may be approximately 9 mm. Electrode column spacing and electrode row spacing may be approximately 1 mm and approximately 5 mm, respectively. The electrodes  36 ,  38  may be approximately 4 mm long by approximately 1 mm wide. The nonflexible electrodes  36  may be longitudinally staggered relative to the flexible electrodes  38  with stagger overlap of approximately 0.5 mm. 
     In another embodiment, as depicted in  FIG. 7B , the flexible paddle electrode array  11  may employ an electrode array that is elongated or longitudinally extended. The paddle structure  17  can be curved or flat. The electrode array may extend over a longitudinal length of approximately 45 mm and, as a result, extend nearly the full length of the underlying paddle structure  17 . The paddle structure  17  may have a width of approximately 9.5 mm and the array width may be approximately 9 mm. Electrode column spacing and electrode row spacing may be approximately 1 mm and approximately 4.5 mm, respectively. The electrodes  36 ,  38  may be approximately 6.5 mm long by approximately 1 mm wide. The nonflexible electrodes  36  may be longitudinally staggered relative to the flexible electrodes  38  with stagger overlap of approximately 1 mm.