Abstract:
An electrostimulation device (e.g.,  100 ) consists of a single paddle (e.g.,  102 ) and at least one lead (e.g.,  110 ) for connecting the electrostimulation device to a pulse generator. The paddle has at least one electrode (e.g.,  106 ) for providing electrical stimulation. The electrode(s) is provided in an area (A) of the paddle and a ratio of the width of the area to the length of the area is greater than 0.5. The present invention also relates to a paddle (e.g.,  102 ) implantable in a vertebra.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an electrostimulation device, along with associated methods of use and manufacture. A particular, but not exclusive, application of the invention is electrical stimulation of the cervical spinal cord for relief of chronic intractable neuropathic and ischaemic pain. 
       BACKGROUND TO THE INVENTION 
       [0002]    Neuropathic pain begins or is caused by damage or dysfunction to the nervous system and is extremely difficult to manage. People are considered to have chronic pain if their symptoms persist for at least 6 months or if they have symptoms that last longer than expected for tissue healing or resolution of an underlying disease. 
         [0003]    Although the actual number is unknown, a proportion of people with chronic neuropathic pain fail to obtain pain relief from pharmacological therapies despite adequate and reasonable efforts to use them. These people are said to have intractable neuropathic pain and they are the target population for Spinal Cord Stimulation (SCS). 
         [0004]    Similar chronic pain can be due to inadequate blood supply (ischaemia). The above comments apply equally to such ischaemic pain. 
         [0005]    Electrical stimulation of the spinal cord by means of electrodes implanted in the spine has been used since 1967 and has since been acknowledged to be an effective method for providing pain relief in some forms of chronic pain. SCS is a reversible pain therapy which involves the application of low-voltage electrical pulses directly to the spinal cord to manage chronic intractable neuropathic pain of the trunk and limbs. 
         [0006]    Electrodes may be either positioned along a flexible elongate type electrostimulation device, which is inserted through a needle such as a standard 14 gauge Touhy needle, or on a substantially flexible flat paddle type electrostimulation device which requires an open operation for positioning. There is evidence to suggest that a paddle electrostimulation device functions better in certain respects than an elongate electrostimulation device e.g. electrodes on a paddle electrostimulation device face the spinal cord and therefore project the current directly to the cord, while electrodes on an elongate electrostimulation device are wrapped around the lead portion such that only a small proportion of the current is projected at the spinal cord. Furthermore, in some situations it is impossible to feed an elongate electrostimulation device through a needle and up to the required vertebral level due to epidural scar tissue, in this instance a paddle electrostimulation device is the only viable option. 
         [0007]    A paddle electrostimulation device is implanted in the epidural space touching dura mater surrounding the spinal cord. However, placing the electrodes at the correct position along the spinal cord is a pre-requisite for satisfactory function. The commonest cause of failure to maintain pain relief is dislodgement of the electrode array of the electrostimulation device. Paddle electrostimulation devices are more stable than elongate electrostimulation devices but due to their long length, even they are prone to dislodgement when placed in the relatively mobile cervical spine. Short paddle length is a feature of a system designed by the applicant and manufactured by Advanced Neuromodulation Systems Inc, Plano, Tex., USA (Lamitrode 22™. This has proved to be considerably more stable than other systems (Simpson BA, Bassett G, Davies K, Herbert C, Pierri M. Cervical spinal cord stimulation for pain: a report on 41 patients. Neuromodulation 2003; 6: 20-26; and Simpson BA “A new dual bipolar electrode system for spinal cord stimulation” First International Congress of the International Neuromodulation Society, Rome, Italy. 1992 pp 13-17 Monduzzi Editore SpA, Bologna). However the Lamitrode 22™ comprises two separate paddles and requires a complex procedure for its insertion including a laminectomy (the removal of the back of one or more vertebrae). 
         [0008]    There is therefore a need for a less invasive method of maintaining electrical stimulation using a paddle type electrostimulation device placed in the cervical spine. 
       OBJECT OF THE INVENTION 
       [0009]    It is an object of the present invention at least in preferred embodiments to provide a less invasive and more effective apparatus and method for electrical stimulation of the cervical spinal cord which overcomes the problem of dislodgement and thereby maintains pain relief. 
       SUMMARY OF THE INVENTION 
       [0010]    Viewed from a first aspect, the present invention relates to an electrostimulation device consisting of a single paddle and at least one lead for connecting to a pulse generator, a plurality of electrodes for providing electrical stimulation being provided in an area of the paddle; wherein the ratio of the width of said area to the length of said area is greater than 0.5. The length of the area is measured along a longitudinal axis of the paddle and the width of said area along a transverse axis. The at least one lead is typically connected to the bottom of the paddle and the longitudinal axis extends from the top of the paddle to the bottom of the paddle. 
         [0011]    The area in which the electrodes are provided is preferably generally rectangular. In, preferred embodiments, the ratio of the width of the area to the length of the area is between 0.5 and 1.75 inclusive. Most preferably, the ratio is between 0.75 and 1.25 inclusive. The ratio may be approximately 0.75 or 1. 
         [0012]    The applicant has recognised that it is particularly desirable that the paddle does not extend across more than one vertebra. The likelihood of the paddle being moved or dislodged after it has been implanted is thereby reduced. The area over which the electrodes are arranged preferably has a length of less than 25 mm. The length is preferably approximately 21 mm. More preferably, the area has a length of less than 20 mm. The length is preferably approximately 16 mm. 
         [0013]    The area preferably has a width greater than 10 mm and less than 30 mm. More preferably, the area preferably has a width greater than 12 mm and less than 25 mm. The width is preferably approximately 16 mm. 
         [0014]    Viewed from a further aspect, the present invention relates to an electrostimulation device consisting of a single paddle and at least one lead for connecting to a pulse generator, at least one electrode being provided on said paddle for providing electrical stimulation; wherein the paddle has a length of less than 25 mm. The paddle may have a length of less than or equal to 16 mm or 21 mm depending on its intended use. The paddle preferably comprises a plurality of electrodes. Thus, the present invention at least in preferred embodiments provides a short-paddle electrostimulation device having various configurations of electrodes positioned along its length and across its width. 
         [0015]    The electrostimulation device is intended to be implanted in a human or animal body. 
         [0016]    The paddle preferably has a width greater than 12 mm and less than 25 mm. More preferably the paddle has a width of between 14 mm and 18 mm. 
         [0017]    The electrodes provided on the paddles described herein are preferably arranged in three or more columns. The electrodes are preferably arranged in three or more rows. The electrodes are preferably positioned on the paddle such that the various configurations facilitate optimal stimulation of various targets. The electrode configurations are compact allowing the paddle to remain sufficiently short, spanning no more than one vertebra, reducing the risk of dislodgement on movement. In contrast, existing commonly used paddle designs are two or more times the length and therefore cross “motion segments” increasing the risk of dislodgement on movement. 
         [0018]    The electrodes may all be connected to each other by one or more internal wires. Alternatively, each electrode may be provided with a dedicated wire. In a further alternative, the electrodes in the array are provided in two or more groups and the electrodes in each group are connected by internal wires and a dedicated wire is provided for each group of electrodes. These latter arrangements enable the application of current to the electrodes to be controlled, for example to provide 2, 3, 4, 5, 6, or more channels. 
         [0019]    The paddle preferably has between 8 and 16 electrodes in total. The electrodes may be oval and/or circular and preferably each have a width or diameter of between 0.5 mm and 5.0 mm and are preferably each between 2 mm and 5 mm long. 
         [0020]    The at least one lead preferably extends from the bottom of the paddle. The at least one lead is preferably provided with a connector for connecting to a pulse generator. The least one lead may be connected to a pulse generator. 
         [0021]    A preferred embodiment of the present invention provides a paddle which is implantable in a vertebra to provide electrical stimulation of a cervical spinal cord. The length of the paddle is preferably less than the height of the vertebra in which it is to be implanted. 
         [0022]    The paddle is preferably provided with at least one suture hole to allow it to be secured in place. The at least one lead is preferably provided with one or more anchors. 
         [0023]    Suture holes (not shown) may be positioned at various points around the outer edge of the paddle through which to secure the paddle to the dura to further prevent dislodgement. 
         [0024]    A second end of the electrostimulation device preferably remains proximal the incision through which the paddle is implanted into the body. The second end of the electrostimulation device is intended for connection to a power source such as any industry standard fully implantable pulse generator (IPG). A connector may be provided at said second end of the electrostimulation device for connecting the electrostimulation device to the (PG. 
         [0025]    The at least one lead is preferably not bifurcated. Thus, the at least one lead preferably extends from the paddle to the pulse generator without branching. The electrostimulation device preferably consists of either a single lead or two separate leads. A single lead may, for example, be used for an electrostimulation device having 12 or less electrodes; and two separate leads may, for example, be used for an electrostimulation device having 12 or more electrodes. 
         [0026]    An anchor is preferably provided for securing the lead of the electrostimulation device to the fascia at the incision site. The anchor may be in the form of a bead which is threaded over the lead(s) toward the paddle. It will be appreciated that more than one anchor may be provided along the length of the lead for anchoring it in position. 
         [0027]    The electrostimulation device may comprise a single electrode or a plurality of electrodes spaced apart along and/or across the paddle. Each electrode may be made of any suitable conductive material; preferably they are made of platinum iridium. The electrodes may be formed integrally with the paddle or they may be formed as a separate component and attached to the paddle. 
         [0028]    The front face of the paddle is preferably substantially planar. 
         [0029]    The at least one lead may be substantially parallel to or coincident with the front face of the paddle in the region where it joins the paddle. Alternatively, said at least one lead may be inclined at an angle α to the front face of the paddle. The angle α is typically greater than 180°. The angle α is preferably between 225° and 315° and, most preferably, is approximately 270°. 
         [0030]    Viewed from a further aspect, the present invention relates to an electrostimulation device comprising a paddle and at least one lead for connecting to a pulse generator, at least one electrode for providing electrical stimulation being provided in an area of the paddle; the at least one electrode being provided on a front face of the paddle; wherein said at least one lead joins the paddle at an angle α relative to the front face of the paddle. 
         [0031]    The angle α between said at least one lead and the front face of the paddle is preferably greater than 180°. The angle α is preferably between 225° and 315° and, most preferably, is approximately 270°. 
         [0032]    The at least one lead is preferably joined to an edge of the paddle. 
         [0033]    Viewed from a still further aspect, the present invention relates to a paddle implantable in a vertebra, the paddle having at least one electrode for providing electrical stimulation; wherein the length of the paddle is less than or equal to the height of the vertebra. The at least one electrode is preferably suitable for providing electrical stimulation of a cervical spinal cord. 
         [0034]    Viewed from a yet further aspect, the present invention relates to a paddle for providing electrical stimulation, the paddle having a plurality of electrodes; wherein said electrodes are arranged in three or more columns. The columns preferably lie substantially parallel to a longitudinal axis of the paddle. The longitudinal axis extends from the top of the paddle to the bottom of the paddle. 
         [0035]    The electrodes are preferably also arranged over three or more rows. The rows of electrodes preferably extend substantially perpendicular to said longitudinal axis. 
         [0036]    At least one lead is preferably provided for connecting said electrodes to a current generator. The at least one lead is preferably connected to the bottom of the paddle. 
         [0037]    Viewed from a yet further aspect, the present invention relates to a method of implanting a paddle in a vertebra to provide electrical stimulation of a cervical spinal cord, the method comprising the step of selecting a paddle having a length less than or equal to the height of the vertebra in which it is to be implanted. 
         [0038]    The proposed design incorporates the advantage of the applicant&#39;s previous design, the Lamitrode 22™, in a single paddle which requires a much simpler operation for its insertion, including substantially less bone removal. Thus, at least in preferred embodiments the present invention offers a practical, less invasive method of electrical stimulation, particularly in but not limited to, the cervical spinal cord, than other previously suggested methods. 
         [0039]    Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]      FIG. 1  shows the back of an electrostimulation device in accordance with a first embodiment of the present invention; 
           [0041]      FIG. 2  shows the front of the electrostimulation device of  FIG. 1 ; 
           [0042]      FIG. 3  shows a perspective view of the electrostimulation device according to the first embodiment; 
           [0043]      FIG. 4  shows a plan view of an electrostimulation device according to a second embodiment of the present invention; 
           [0044]      FIG. 5A  shows a perspective view of a paddle according to a third embodiment of the present invention; 
           [0045]      FIG. 5B  shows a side view of the paddle according to the third embodiment of the present invention; and 
           [0046]      FIGS. 6 to 10  show alternative electrode configurations on an electrostimulation device. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    An electrostimulation device  100  in accordance with a first embodiment of the present invention is shown in  FIGS. 1 and 2 . The electrostimulation device  100  is implantable in a human or animal body to provide electrical stimulation of the cervical spinal cord. 
         [0048]    The electrostimulation device  100  consists of a single paddle  102 . An electrode array  104  of two or more electrodes  106  is provided in an area A (shaded in  FIG. 2 ) on a front face  108  of the paddle  102 . The electrode array  104  in the present embodiment is made up of sixteen electrodes  106  and, as shown in  FIG. 2 , the electrodes  106  are arranged in four rows and four columns. The columns of electrodes  106  extend substantially parallel to a longitudinal axis X of the paddle  102  and the rows extend substantially parallel to a transverse axis Y. 
         [0049]    The electrodes  106  are oval and may be connected electrically to each other by a series of internal wires (not shown) in the paddle  102 . 
         [0050]    Preferably, however, each electrode  106  or one or more groups of electrodes  106  in the electrode array  104  are provided with dedicated internal wires to enable the application of current to different electrodes  106  in the electrode array  104  to be controlled, for example to allow control over 2, 3, 4, 5, 6 or more channels. The internal wires are connected to first and second leads  110 ,  112  to enable a current to be supplied to the electrode array  104 . The first and second leads  110 ,  112  extend from the bottom of the paddle  102  and may comprise one or more wires. If the first and second leads  110 ,  112  are made up of a plurality of wires, the wires are typically sheathed with a suitable insulating material. 
         [0051]    The first and second leads  110 ,  112  are connected to an implantable pulse generator (not shown). First and second connectors may optionally be provided on the free ends of the first and second leads  110 ,  112  (i.e. the ends remote from the paddle  102 ) to facilitate connection of the electrostimulation device  100  to the implantable pulse generator. 
         [0052]    The electrodes  106  are made of platinum iridium and each have a width of approximately 2 mm and a length of approximately 4 mm. It will be appreciated that the size and shape of the electrodes  106  may be varied for different applications. 
         [0053]    The paddle  102  has a total length of approximately 26 mm and a width of approximately 16 mm. The area A in which the electrode array  104  is provided has a width of approximately 16 mm and a length of approximately 21 mm extending from the distal end thereof. The paddle  102  has a neck portion provided between the area A and the first and second leads  110 ,  112 . The corners of the paddle  108  are radiused. 
         [0054]    As shown in  FIG. 3 , the first and second leads  110 ,  112  are provided with an anchor  114  to help prevent migration of the electrostimulation device  100  after it has been implanted. The anchor  114  is a bead which is threaded over the first and second leads  110 ,  112  and fixed in position. In addition to the anchor  114  (or in place thereof), the paddle  108  may be provided with one or more suture holes (not shown) to allow the paddle  102  to be secured in position. The suture holes would typically be provided around the outer edge of the paddle  102 . 
         [0055]    The electrostimulation device  100  is implantable to provide electrical stimulation of the spinal cord. Since the electrostimulation device  100  is not bifurcated, it can be implanted with relative ease. Its relatively compact design allows the paddle  102  to be implanted with the removal of less bone. Furthermore, the length of the paddle  102  is such that, once implanted, it spans only a single vertebra and the risk of it being dislodged after it has been implanted is reduced. 
         [0056]    An electrostimulation device  200  according to a second embodiment of the present invention is shown in  FIG. 4 . 
         [0057]    The electrostimulation device  200  consists of a single paddle  202  which is shorter than the paddle  102  of the first embodiment. Specifically, the paddle  202  has a length of approximately 16 mm. To accommodate the reduction in size of the paddle  202 , the electrode array  204  consists of twelve electrodes  206  arranged in three rows and four columns. The electrodes  206  are each substantially the same size as those in the first embodiment. 
         [0058]    The reduced length of the electrostimulation device  200  is advantageous since the paddle  202  may be implanted more readily. The likelihood of the paddle  202  being dislodged once it has been implanted is also reduced further. 
         [0059]    A third embodiment of an electrostimulation device  300  in accordance with the present invention is shown in  FIGS. 5A and 5B . 
         [0060]    The paddle  302  is made of a transparent material and the electrodes  306  are visible through the back of the paddle  302 , as shown in  FIG. 5A . 
         [0061]    In the first embodiment of the present invention the first and second leads  110 ,  112  extend away from the paddle  102  in a reference plane substantially coincident with the front face  108  of the paddle  102 . 
         [0062]    However, in the third embodiment, the first and second leads  310 ,  312  are predisposed to join the paddle  302  at an angle α relative to a reference plane substantially coincident with the front face  308  of the paddle  302 . In the present embodiment the angle α is approximately 270°, but it may be between 225° and 315°. Thus, the first and second leads  310 ,  312  are predisposed to extend away from the back of the paddle, as shown in  FIG. 5B . 
         [0063]    The paddle  302  has a cover which biases the first and second leads  310 ,  312  in the desired direction. This arrangement provides two different ways in which the paddle  302  may be implanted. In certain applications this configuration can help to locate the paddle  302  when it is implanted and reduce the tendency of the paddle  302  to be dislodged after it has been implanted. 
         [0064]    A fourth embodiment of an electrostimulation device  400  in accordance with the present invention is shown in  FIG. 6 . 
         [0065]    The electrostimulation device  400  consists of a single lead  410  and a different arrangement of electrodes  406 . The electrodes  406  are a combination of oval electrodes  414  and circular electrodes  416  arranged in three rows. The top and bottom rows of electrodes  406  consist of two oval electrodes  414  on each side of a circular electrode  416 . The central row of electrodes  406  consists of two oval electrodes  414  located inwardly of the oval electrodes  414  in the top and bottom rows. The circular electrodes  416  are located along the longitudinal axis X of the paddle  402 ; and the oval electrodes  414  in the middle row are located along the transverse axis Y of the paddle  402 . 
         [0066]    A fifth embodiment of an electrostimulation device  500  in accordance with the present invention is shown in  FIG. 7 . 
         [0067]    The fifth embodiment is similar to the fourth embodiment but the circular electrodes  516  are moved apart from each other along the longitudinal axis X of the paddle  502 . 
         [0068]    A sixth embodiment of an electrostimulation device  600  in accordance with the present invention is shown in  FIG. 8 . 
         [0069]    The sixth embodiment is similar to the fourth embodiment but the oval electrodes  614  in the middle row are moved apart from each other along the transverse axis Y of the paddle  602 . The oval electrodes  614  are thereby arranged in two columns of three. 
         [0070]    A seventh embodiment of an electrostimulation device  700  in accordance with the present invention is shown in  FIG. 9 . 
         [0071]    The seventh embodiment consists of only oval electrodes  714  arranged in four columns with two oval electrodes  714  in each column. The oval electrodes  714  in adjacent columns are offset from each other. 
         [0072]    An eighth embodiment of an electrostimulation device  800  in accordance with the present invention is shown in  FIG. 10 . 
         [0073]    The eighth embodiment consists of two columns of oval electrodes  814  and a pair of circular electrodes  816 . Rather than being parallel, the columns of oval electrodes  814  define an acute internal angle such that the oval electrodes  814  proximal the single lead  810  are closer together than those distal from the lead  810 . The circular electrodes  816  are arranged along the longitudinal axis X of the paddle  802 . 
         [0074]    The references herein to the top, bottom and sides of the paddle are for reference purposes only and are not intended to be limiting on the scope of the invention. 
         [0075]    The described embodiments of the invention are only examples of how the invention may be implemented. Modifications, variations and changes to the described embodiments will occur to those having appropriate skills and knowledge. These modifications, variations and changes may be made without departure from the spirit and scope of the invention defined in the claims and its equivalents. 
         [0076]    For example, it will be appreciated that any number of electrodes in any number of configurations may be provided along the length and across the width of a paddle with an overall dimension of 16 mm wide and between 21 mm and 26 mm long.