Abstract:
An electrode system includes an implantable flexible electrode, especially an epidural electrode, having at least one distal electrical contact ( 12 ). The electrode includes a subcutaneously implantable port ( 26 ), a probe that can be introduced into the port ( 26 ) forms part of the electrode system with at least one probe contact ( 53 ), and at least one electrical contact element ( 56 ) connected to the distal contact ( 12 ) is arranged in the port ( 26 ) in order to generate an electrical connection with the probe contact ( 53 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an electrode system comprising an implantable, flexible electrode, particularly an epidural electrode, comprising at least one distal electrical contact. According to a further development, the electrode is arranged in an implantable, flexible catheter, particularly an epidural catheter. 
     Generally, such a catheter has at least one channel which, for example, is used to administrate drugs via the catheter. Sometimes, however, an electrode without a channel is also called a catheter, for example, a stimulation catheter. Such catheters with a distal electrical contact which do not comprise a channel and therefore are not a catheter in its actual sense, are subsequently called electrodes. 
     Catheters are known technical medical products which are manufactured for various intended purposes of usage in diagnostics or therapy. For example, epidural catheters are known which can be inserted by a physician into the epidural space in the region of the spinal canal so as to be able to inject pain-killing drugs, for example. Such a method is particularly applied in treatment of chronic pain. The catheter can remain in the body for a time period of 1 to 30 days, for example, and the injection of the drugs can be effected through external or implanted pumps. 
     Instead of catheters also electrodes are used in therapy of chronic pain. For example, electrodes for implantation are known which are connected to a pulse generator for permanent stimulation of the spinal cord or the nerves. 
     Moreover, special needles are known which are connected to a generator of pulsed high frequency. Such special needles and high frequency generators are used to trigger the release of pain-inhibiting substances in the spinal cord by selectively stimulating nerves, thereby effecting a pain treatment. However, usage of these special needles is frequently limited due to anatomical reasons or is avoided because of the risk of injury at introducing the special needles. 
     From EP 1 181 947 A2, an epidural catheter is known having at least three electrodes arranged in line. The electrodes serve to electrically stimulate nerves or the spinal cord. A channel for administration of drugs can be provided, so that, in addition to the electrical stimulation of the spinal cord or the spinal nerves, an injection of pain-killing drugs is possible. 
     A further implantable epidural catheter is known from DE 203 08 422 U1. This catheter is, for example, suitable for applying pulsed high frequency for stimulation of nerves. Furthermore, a syringe or a drug pump can be connected. The catheter comprises a fixation member which can serve to fasten the catheter at a point of entry into a body and through which electrical leads and a hose line of the catheter are led. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electrode system of the kind mentioned Initially, comprising a catheter or an electrode, the system offering a more flexible application of the system. 
     According to the invention, this object is achieved by providing an electrode system of the kind mentioned initially, wherein the electrode comprises a port which is subcutaneously implantable, wherein a probe comprising at least one probe contact is introduceable into the port and forms a part of the electrode system, and wherein at least one electrical contact element for establishing an electrical connection to the probe contact is arranged in the port, said electrical contact element being connected to the distal contact. According to a further development, the electrode is arranged in an implantable, flexible catheter, particularly an epidural catheter. In this case, an access opening of the catheter is arranged in the port. 
     After inserting the electrode or the catheter, the electrode/catheter can be completely implanted, including the port, beneath the skin near to the point of entry into the body. Being concealed below the skin, the catheter is less cumbersome for the patient. Moreover, the risk of infection and the risk of complications are reduced. Thus, the electrode system according to the invention allows, for example, after an ambulatory stimulation treatment of a patient to leave the electrode or the catheter inside the body of the patient and to dismiss the patient to go home until a new stimulation will be necessary after, for example, some days or weeks. Then, for example, a probe in the form of a needle can be introduced into the port in order to apply a stimulation current again. Thus, the electrode system according to the invention has distinct advantages regarding its application as compared to a conventional implantable electrode. 
     In an especially preferred embodiment, the electrical contact element and the probe contact are adapted to transmit radio frequency. Thus, a stimulation with high frequency pulses can take place. 
     The electrode system comprising the catheter is an advancement which also opens up an increased range of application as compared to a conventional implantable catheter or stimulation catheter. When, for example, the catheter is inserted as an epidural catheter into the area of the spinal canal, in addition to the stimulation of the spinal cord or the spinal nerves by, for example, a pulsed high frequency current, according to requirements an injection of a pain-killing drug via the port and the access opening of the catheter can take place. The implantable port can, for example, comprise a septum which is reachable from external with an injection needle. 
     Optionally, between the port and the catheter, a drug pump can be provided being also implantable. Thereby, an evenly distributed dispensing of drugs is achievable over a longer time period. 
     Optionally, an injection chamber for the catheter is arranged at the port. Thereby, the injection of drugs into the port is facilitated, and the injection chamber can also serve as a reservoir chamber for an implantable drug pump. 
     Further advantageous details of the invention are indicated in the dependent claims. 
     Preferably, the probe comprises a coupling member, and the port of the electrode or of the catheter comprises a coupling device for the coupling member. These, for example, constitute means for mechanically anchoring the probe at the port. This can, for example, be a mechanical mounting or locking mechanism, e.g. a snap fastener. In particular, a secure contact can be established between the probe contact and the electrical contact element by the coupling device and the coupling member. When the probe is held at the port, this also facilitates the application of pulses for stimulation of nerves, for example. 
     Preferably, a threaded shoulder constitutes the coupling member of the probe. Preferably, a threaded member constitutes the coupling device. For example, a probe can be screwed into the latter with the threaded shoulder. 
     According to a preferred embodiment of the electrode or the catheter, the port comprises a septum for being punctured it with a needle. For example, the needle constitutes the probe. Alternatively, the needle accommodates the probe, and the probe can be pushed forward out of the needle. Then, the electrical contact element is arranged within the port such that an electrical connection can be established to at least one probe contact of the probe. Furthermore, in the case of the coupling device, for example, the coupling device is also arranged in relation to the septum in such a manner that the probe can be coupled to the coupling device. A septum has the advantage that the interior space of the port is insulated and sealed against the surroundings both with and without a needle penetrating the septum. 
     Preferably, a guide member is provided at the port, which guide member guides the probe to the electrical contact element and, if applicable, to the coupling device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments will be described below with reference to the drawings, wherein: 
         FIG. 1  is a schematic view of an epidural catheter having an implantable port and of a needle which accommodates a probe: 
         FIG. 2  is a schematic longitudinal sectional view of the tip of the epidural catheter; and 
         FIG. 3  is a schematic, perspective view of the port, into which the probe has been introduced. 
     
    
    
     For reasons of clarity, the drawings are not drawn to scale. 
     DETAILED DESCRIPTION 
     The epidural catheter  10  shown in  FIG. 1  comprises, in its distal region, an electrical contact  12 , which forms a cap encasing the end of the catheter  10 . The contact  12  is drawn with hatching. A lateral aperture  16  of a hose line  18  of the catheter is arranged next to the contact  12 . The edge of the electrical contact  12  is flush with a sheathing  20  of the catheter  10  made of silicone rubber. The outer diameter of the sheathing  20  is 1.33 mm, corresponding to a specification of 4 French. In the longitudinal direction of the catheter  10 , the contact  12  extends to a length approximately corresponding to the outer diameter of the sheathing  20 . 
     At the proximal end of the catheter  10 , the catheter is seamlessly connected to a flat casing  22 . The upper wall of the casing  22  comprises a bulge in which a port  26  is formed, the upper wall of the port  26  being formed by a pricking septum  28 . Via the pricking septum  28 , the port  26  is accessible from external by an injection needle, for example. The pricking septum  28  is made in a known manner such that its wall is sufficiently dense and elastic so as to provide a reliable sealing again, after an injection needle previously inserted through the septum has been retracted. 
     Inside the catheter  10 , an electrical lead  29  for the electrical contact  12  runs inside the sheathing  20  parallel to the hose line  18  and is, like the hose line  18 , indicated with dashed lines. The configuration of the catheter  10  will be further explained below with reference to  FIG. 2 . 
     In a known manner, an aseptic guide wire (not shown) is arranged inside the hose line, which guide wire serves to shift the catheter  10  to the desired position in the spinal canal and is then retracted. An introduction aperture for the guide wire is sealed before the casing  22  is implanted. The guide wire is slightly bendable in the region of its leading end. 
     The probe  30  shown in  FIG. 1  is accommodated within a needle  32  and is slideably guided therein. At its rear end, it is connected to an adapter  34  on which a connector  36  for a syringe or a drug pump and an electrical connector  38  are arranged. The electrical connector  38  is adapted to be directly or via an adapter (now shown) connected to a pulse generator  40 , which generates a pulsed high frequency current. The pulse generator  40  can, for example, be the device N50 of the company Stryker How Medica, the device RFG-3C+ of the company Radionics or the device Neurotherm of the company RDG Medical. 
       FIG. 2  shows the tip of the catheter  10  as a longitudinal sectional view. The electrical lead  29  runs parallel to the hose line  18 , said lead  29  being internally soldered to the electrical contact  12 . The electrical lead  29  comprises an insulation  44  and runs within a thickened region of the wall of the sheathing  20 . The hose line  18  is formed by an additional internal tubular layer  46  inside the sheathing  20 . The sheathing  20  encloses the tube formed by the internal layer  46  as well as the insulation  44 . The internal layer  46  is isolated from the contact  12  by the sheathing  20 . At least at the aperture  16 , which penetrates the layer  46  and the sheathing  20 , the internal layer  46  is tightly connected to the sheathing  20 . However, the internal layer  46  can also be a part of a sheathing of the catheter constituted of two or more layers. 
     The tube formed by the inner layer  46  ends on the other side of the aperture  16 . It can, however, also extend into the cap formed by the distal contact  12 , as indicated by chain dotted lines. 
     Alternatively to or additionally to the cap-shaped electrical contact  12 , however, there can also be provided an annular contact  48  near the lateral aperture  16 , as is indicated by dashed lines. Then, an aperture at the end of the catheter  10  can be provided alternatively to the lateral aperture  16 . 
     In  FIG. 3 , the pricking septum  28  has been punctured by the needle  32 , and the probe  30  has been introduced into the port  26  through the needle  32 . The lower region of the probe  30  is shown in section. 
     At its lower end, the probe  30  comprises a threaded shoulder  50  which is screwed into a socket being formed inside the casing  22  and having a threaded member  51  and a counterpiece  52 . 
     In the region of the threaded shoulder  50 , the probe  30  comprises an electrically conducting region which forms a probe contact  53  drawn with hatching and which, for example, extends over the height of two thread turns. Above and below the probe contact, the outer wall of the probe comprises an insulating sheathing  54 . 
     The threaded shoulder  50  with the probe contact  53  is retained between the threaded member  51  and the counterpiece  52 , the latter comprising an electrical contact element  56 . The electrical contact element  56  extends over a limited height region of the counterpiece  52  and lies approximately at a height at which the probe contact  53  is situated when the probe  30  is screwed into the socket against a stop. In this manner, an electrical connection between the probe contact  53  and the electrical contact element  56  being connected to the electrical lead  29  is established. At the same time, the probe  30  is mechanically coupled to the casing  22  of the port  26 . Here, the threaded shoulder  50  constitutes a coupling member of the probe  30 , and the socket with the threaded member  51  and the counterpiece  52  constitutes a coupling device of the port  26 . 
     Below the pricking septum  28 , there is arranged a cone  58  at the port  26 , which cone forms a guide member for the probe  30  and thus facilitates the placing of the threaded shoulder  50  in the port  26 . Then, by rotating the probe  30  in the needle  32 , the threaded shoulder  50  is screwed into the socket with the threaded member  51 . 
     The probe contact  53  is connected to the electrical connector  38  of the adapter  34 . Thereby, an electrical connection is established between the pulse generator  40  and the electrical contact  12  of the catheter  10 . The contact  12 , the lead  29 , the electrical contact element  56 , the probe contact  53 , and the probe  30  with the adapter  34  are adapted both for applying pulses for a test stimulation of nerves or the spinal cord having, for example, a voltage in the range of 0-12 V, a frequency in the range of 50 to 150 Hz, and a pulse width in the range of 150 to 400 microseconds, as well as for applying pulsed high frequency having, for example, a voltage in the range of 20 to 30 V and a pulsed frequency of, for example, 50 kHz or 500 kHz and a pulse width of 20 milliseconds. The numerical values given are only examples to illustrate the range of application of the catheter. 
     Thus, using high frequency pulses with an epidural catheter, for example, by stimulating the nerves inside the spinal canal, in many cases a treatment or stimulation of nerve tissue with special needles in front of the spinal column or in dangerous regions can be avoided and also those nerves can be treated with high frequency pulses which otherwise would not have been accessible for this treatment. 
     An access duct  60  runs inside the probe  30 , said duct  60  being open at its bottom end and being connected to the connector  36  of the adapter  34  at its upper end. The bottom end of the access duct  60  is arranged in front of an access opening  62  of a connecting member  64  of the port  26 , when the threaded shoulder  50  is screwed to the threaded member  51 . Via the connecting member  64 , the access opening  62  is connected to the hose line  18  of the catheter  10  and thus to the aperture  16 . 
     The wall of the access duct  60  comprises an insulation layer  66  which is connected to the insulation sheathing  54  at the bottom end of the probe  30 , so that the access duct  60  is electrically isolated from the probe contact  53  and its lead to the electrical connector  38 . In the example shown, the probe  30  is that far screwed into the socket with the screwed member  51  that the probe  30  is tightly attached to the connecting member  64 . Thereby, the probe contact  53  and the electrical contact element  56  are sealed against the access duct  60  and the access opening  62  of the catheter  10 , so that a liquid being situated in the access duct  60  and the hose line  18  does not get in contact with the probe contact  53 . Optionally, the sealing can be effected, for example, also at the outer circumference of the threaded shoulder  50  below the electrical contact element  56 . 
     After the implanting of the catheter  10 , the probe  30  and the catheter  10  allow, at a later, further treatment of the patient, to get along with introducing the needle  32  with the probe  30  into the port  26  without requiring further surgery. Moreover, due to the proximity of the contact  12  to the distal aperture  16  of the catheter  10 , the advantage results that during insertion of the catheter  10 , the location of the catheter can be checked with a test stimulation with reduced voltage and frequency. Another advantage is that the x-ray contrast of the contact is sufficiently high to allow a positioning of the catheter with x-ray monitoring without application of a contrast agent. A further advantage is that the same area can be treated with drugs as well as with electrical stimulation without having to alter the location of the catheter. Thus, for example, a drug can be injected into the catheter  10  via the connector  36 . 
     Optionally, a sealing of the connection between the access duct  60  and the hose line  18  by the connecting member  64  or by the socket with the threaded member  51  can be dispensed with, for example, because the inside of the port  26  is in any case always sealed against the body of the patient by the pricking septum  28 , and because a contact of the liquid to the electrical contact element  56  can be acceptable as the case may be. 
     By leaving out the hose line  18 , the lateral aperture  16  and the connecting member  64  from the described catheter  10 , an embodiment of an epidural electrode according to the invention is obtained. An embodiment of the probe adapted thereto results, for example, by leaving out the access duct  60  and the connector  36  at the adapter  34 . 
     The described embodiments of the electrode, the catheter and the probes are to illustrate a possible arrangement and contacting of the probe contact  53  and the electrical contact element  56  as well as a possible connection between an access duct  60  and the hose line  18  and shall present one possibility of the realization of the port. 
     It is understood that the electrode system according to the Invention can also have a configuration which differs hereof. For example, at least one further electrical contact can be provided next to the electrical contact  12 , and the electrical contacts can be connected to separate probe contacts via separate contact elements, said probe contacts being, for example, arranged at different heights. Then, the counterpiece  52  can be extended correspondingly. Further electrical connections can be provided, for example, for a temperature sensor arranged in the distal region of the catheter, the connection leads of which being arranged within the catheter. 
     Also, the realization of the coupling member of the probe  30  and of the coupling device of the catheter  10  as a threaded shoulder  50  and a threaded member  51  with counterpiece  52  is merely one possible embodiment. Thus, for example, a click-in-fastener or other mechanical anchoring is also possible.