Abstract:
An adapter system is provided for adapting and connecting a leadless microstimulator to a separate monopolar, bipolar, or tripolar electrode. Advantageously, the microstimulator does not need to be physically modified. The adapter system encloses the microstimulator and electrically connects the microstimulator to the selected, separate electrode via an extension lead or leads. The adapter has two forms: a monopolar adapter having a single opening or a bipolar adapter having two openings. The separate electrode is equipped with at least one extension lead having a connector that can be inserted into the opening of the monopolar adapter or the bipolar adapter and connect to the microstimulator that is placed within the monopolar or bipolar adapter.

Description:
The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/494,443, filed 12 Aug. 2003, which application is herein incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to implantable electrical stimulation systems and, more particularly, relates to lead extension and adapter systems that may be used in conjunction with a leadless, implantable microstimulator. 
   A neurostimulator is a device that provides electrical stimulation to selected nerves in the body. One type of neurostimulator that has been developed in recent years is a tiny microstimulator known as a BION® microstimulator. Various embodiments and features of the BION microstimulator are disclosed, e.g., in U.S. Pat. Nos. 5,324,316; 5,405,367; 6,051,017; and in PCT Publications WO 98/37926; WO 98/43700 and WO 98/43701, each of which patents or publications are incorporated herein by reference. 
   A microstimulator may be implanted via a small incision and/or via endoscopic means. In one preferred embodiment, the microstimulator is leadless, having electrodes fashioned or formed into its case. A “lead” as used herein will refer to an elongate body that includes a conductor and an insulation covering the conductor. The lead can further include an electrode on one end of the lead and a connector on the other end of the lead. The term “electrode” will be used herein as that portion (including insulation portion) of a stimulating lead which contains an electrode contact or electrode contacts for delivering the electrical stimulation to a tissue. 
   A leadless microstimulator must be implanted next to the nerve or tissue that is to be stimulated, since the electrode contacts are placed directly on the microstimulator case. The small size of the microstimulator allows it to be placed through minimally invasive surgery. 
   In other applications, however, it is not possible to implant the microstimulator immediately next to the nerve or tissue to be stimulated. In such instances, a leaded BION microstimulator may be used. Some examples are shown in co-pending U.S. patent application Ser. No. 10/188,465, filed 2 Jul. 2002 and in U.S. patent application Ser. No. 10/178,011, filed 20 Jun. 2002. Both of these patent applications are incorporated herein by reference. 
   In some cases, a leadless microstimulator may need to be used for an application that requires a lead extension. In particular, use of a specific type of electrode may be desired because the electrode type and number of electrode contacts are optimized for a specific application. 
   One type of electrode known in the art is a cuff electrode. A cuff electrode encircles a target nerve fiber or bundle and offers the advantage of being effectively attached to the target fiber or bundle, which prevents the electrode from inadvertently moving away from the desired, target nerve. A variation of the cuff electrode is a semi-cuff electrode that wraps or contacts one side of a target nerve bundle. A semi-cuff electrode may have one or more electrode contacts and operate as a monopolar electrode, a bipolar electrode or as a tripolar electrode, among others. 
   It would be desirable, in certain applications, to use a leadless microstimulator and to connect this microstimulator to a specific type of leaded electrode, for instance, a tripolar, semi-cuff electrode. 
   What is needed, therefore, is a system for adapting a leadless microstimulator so that it may be used with an extension lead that is connected to a selected electrode, such as a tripolar, semi-cuff electrode. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the above and other needs by providing a system that adapts a leadless microstimulator so that it may be used with an electrode having at least one or two extension leads. 
   In one aspect of the invention, there is provided a system for connecting a leadless, microstimulator to an electrode having at least one extension lead. The system includes a monopolar adapter, which has an inner, adapter chamber that is sized to accept placement of the microstimulator within the chamber. The adapter chamber opens to the outside of the monopolar adapter through an opening on one end of the adapter. An indifferent electrode is placed on the other end of the monopolar adapter. The system also includes an extension lead connector, which has a connector contact at the end of the extension lead. The other end of the extension lead is electrically connected to a stimulating electrode which has at least one electrode contact. The extension lead connector has at least one part that is dimensioned to be inserted into the opening of the adapter to thereby seal the adapter opening. With the extension lead connector thus placed into the adapter opening, the connector contact abuts against the microstimulator&#39;s cathode electrode contact. When the microstimulator is placed inside the adapter chamber, the indifferent contact within the adapter chamber abuts the microstimulator indifferent electrode. 
   The adapter chamber is preferably substantially cylindrical. In addition, the exterior profile or shape of the adapter is preferably substantially cylindrical, with exception of the end acting as an indifferent electrode. That end preferably has a smooth profile such as a bullet shape or some other curved shaped. 
   In one embodiment, one or more sealing rings are used to encircle the microstimulator when it is placed into the adapter chamber. The sealing ring or rings can be integrated into the inner wall of the adapter chamber and be made of exactly the same material as the adapter chamber wall. 
   To ensure proper long-term connection between the adapter and the extension lead connector, a connection system is provided. This connection system comprises a circular flange located on the extension lead connector. The monopolar adapter also has a circular recess inside the chamber, near the opening of the adapter which recess has a shape that is complementary to the circular flange. In operation, when the extension lead connector is inserted into the adapter opening, the flange snaps into the circular recess. As a further device to ensure that the extension lead connector cannot be easily pulled out from the adapter opening, the monopolar adapter may also have two sliding rings that slide along the exterior length of the adapter. The monopolar adapter may have a slightly larger exterior diameter (or circumference) at the opening end compared to the mid-portion of the adapter. By sliding the sliding ring towards the adapter opening and over the circular recess, the circular flange residing within the recess is placed under compression, thereby locking and sealing the connector within the opening of the monopolar adapter. 
   The use of this connection system in conjunction with an elastic adapter chamber wall also serves another important purpose. After the microstimulator has been inserted into the adapter chamber, the monopolar adapter is “pulled over” the connector. A “lip” placed at the very end of the adapter opening may be used to grasp the adapter during this step. This process of inserting the connector into the adapter opening stretches the monopolar adapter walls lengthwise so that, when the connector flange snaps into the adapter recess, the chamber walls are stretched slightly and therefore placed under elastic tension. This tension serves an important function because it keeps the microstimulator&#39;s indifferent electrode in compressive contact with the indifferent contact inside the adapter chamber and the microstimulator&#39;s cathode contact in compressive contact with the contact on the extension lead connector. 
   In another embodiment of the present invention, there is provided a system for connecting a leadless microstimulator to an electrode having at least two extension leads. The system includes a bipolar adapter, which has an inner, adapter chamber that is sized to accept placement of the microstimulator therein. The adapter has a first end and a second end. The bipolar adapter has a first opening on the first end and a second opening on the second end. The system also includes at least two extension lead connectors, each having a connector contact at the end. Each extension lead is electrically connected to at least one electrode contact and thus there are at least two electrode contacts in the stimulating electrode. Both extension lead connectors are preferably identical and have at least one part that is dimensioned to be inserted into either the first or second opening of the bipolar adapter. With an extension lead connector placed into one of the adapter openings, the connector contact is in contact with one of the electrode contacts of the microstimulator. 
   The adapter chamber within the bipolar adapter may be substantially cylindrical. In the preferred embodiment the adapter exterior shape can be substantially cylindrical along the length of the adapter from the first end to the second end. 
   The adapter may include at least one sealing ring, which ring is sized to encircle the microstimulator when it is placed in the adapter chamber. The sealing ring can be an integral part of the adapter chamber wall and may be made from the same material as the adapter chamber wall. 
   The adapter chamber can include a circular recess near both the first and second adapter openings. The lead connector of the extension lead can also have a circumferential flange that is complementary in shape to the circular recess and fits in the recess. 
   In one embodiment, the bipolar adapter includes a first and second sliding rings that encircle the exterior of the adapter. The sliding rings, preferably made from biocompatible metal, such as stainless steel or titanium, can slide along the exterior length of the adapter. The adapter may have an outer circumference that is slightly larger near the first and second ends of the adapter compared to the mid-portion of the adapter. When a sliding ring is advanced to the opening end, the ring squeezes and compresses the adapter wall and thereby locks the complementary flange into the circular recess. 
   Similar to the monopolar adapter, the chamber wall of the bipolar adapter will be under elastic tension when both first and second adapter openings have been plugged by lead connecters that are attached to extension leads. The elastic tension places the microstimulator&#39;s anode and cathode contacts in compressive contact with the two connector contacts. 
   It is thus a feature of the present invention to provide an adapter system that uses an existing leadless microstimulator without modifying the microstimulator. Various electrode configurations, including monopolar, bipolar and tripolar electrode configurations may be connected to the leadless microstimulator using the appropriate monopolar or bipolar adapter and one or more extension leads having a complementary connector that is insertable into the one or two openings of the monopolar or bipolar adapter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
       FIG. 1  shows, in accordance with the present invention, an illustration of the lead extension and adapter system which includes a microstimulator, a semi-cuff electrode with two extension leads and connectors, and bipolar and monopolar adapters; 
       FIG. 2  shows, in accordance with the present invention, an illustration of an exemplary leadless microstimulator with two electrode contacts; 
       FIG. 3A  shows, in accordance with the present invention, an illustration of a lead connector that can be attached to an extension lead which, in turn, can be connected to an electrode, such as a tripolar, semi-cuff electrode; 
       FIG. 3B  shows, in accordance with the present invention, the indifferent electrode that is incorporated into a monopolar adapter; 
       FIGS. 4A ,  4 B and  4 C show an exemplary semi-cuff, tripolar electrode having three electrode contacts; 
       FIG. 5  shows, in accordance with the present invention, a monopolar adapter; 
       FIG. 6  shows, in accordance with the present invention, a bipolar adapter; and 
       FIG. 7  shows the bipolar adapter of  FIG. 6  but with the microstimulator placed into the adapter chamber and with a lead connector placed into each of the adapter chamber openings. 
   

   Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
     FIG. 1  shows, in accordance with the present invention, an illustration of an adapter system  9  which illustration includes a microstimulator  300 , a semi-cuff, tripolar electrode  10  with two extension leads  22  and  23  and lead connectors  40  and  45 , connector contacts  59  and  58 , respectively, and a bipolar adapter  100  and monopolar adapter  200 . 
     FIG. 2  shows a microstimulator  300  which has two electrode contacts: an anode (positive) contact  302  and a cathode (negative) contact  304 . End  301  may be part of the anode contact. A non-metallic portion  303  of the microstimulator  300  may be made of a body inert material such as a ceramic. 
     FIG. 3A  shows, in accordance with the present invention, a cross-sectional view of lead connector  40  (identical to lead connector  45 ) that is attached to lead extension  22  (or lead extension  23 ) of the tripolar, semi-cuff electrode  10 . The lead connector  40  has an electrode contact  59 , an end portion  57  that is made of an insulating material, a circular flange  56  that has a diameter which is larger than the diameter of the end portion  57 , a section  55  having a diameter (or circumference) that is approximately the same as the end portion  57 , a stop  54 , and a strain relief/grip  52  for grasping the end connector  40 . A conductor  51  extends through the extension lead  22  and connects to the connector contact  59 . 
     FIG. 3B  shows a partial, cross-sectional view of the indifferent electrode  201  alone. The indifferent electrode  201  has a hollowed out chamber that opens at end  230  and thereby forms part of the adapter chamber  212 . The indifferent electrode also may have a thread portion  220  that has circular teeth, threads or ridges  221  that encircle the thread portion  220 . The adapter body, which preferably is a stretchable insulation material such as silicone or polyurethane, may be stretched over the thread portion  220  to form the complete monopolar adapter. 
     FIGS. 4A ,  4 B and  4 C show various views of the tripolar, semi-cuff electrode  10 .  FIG. 4A  shows a side view of the semi-cuff electrode. The view shows the trough  5  of the semi-cuff electrode wherein the electrode contacts  12 ,  13 , and  14  are exposed. The trough has a depth H and width W. The semi-cuff electrode has a distal tip  16  and a proximal end  20 . The electrode contacts are placed on a substrate of insulation  6  which may be, for instance, silicone or polyurethane.  FIG. 4B  shows a top view of the semi-cuff electrode, showing the three electrode contacts  12 ,  13  and  14  placed in parallel and suture holes  18 . Lead extensions  22  and  23  are also shown.  FIG. 4C  shows a schematic view of the electrical connections between the electrode contacts  12 ,  13 , and  14 . In this example, electrode contacts  12  and  14  are connected via connection  24  and are further connected to conductor  23   a  in lead  23 . Electrode contact  13  is connected to conductor  22   a  in lead  22 . In this tripolar electrode arrangement, electrode contacts  12  and  14  are typically anodic (positive) while electrode contact  13  is the cathode (negative). 
   In order to deliver electrical current to the electrode contacts in the tripolar electrode connector, contacts  58  and  59  (as shown in  FIG. 1 ) must be electrically connected to the microstimulator at its electrode contacts  301  and  304  (as shown in  FIG. 2 ). 
     FIG. 5  shows, in accordance with the present invention, a cross-sectional, side view of the monopolar adapter  200  with the microstimulator inserted into the monopolar adapter chamber  212  and with the lead extension connector  40  inserted. The indifferent, anode contact  201  covers one end of the adapter  200 . There is an opening at the other end of the adapter  200 , into which a lead extension connector  40  or  45  may be interchangeably inserted. 
   If connector  45  is inserted into the adapter opening, only the middle electrode contact  13  in the tripolar electrode  10  will be connected. If the connector  40  is inserted into the adapter opening, then the two outer electrode contacts  12  and  14  in tripolar electrode  10  will be connected. Of course, other combinations of electrode contacts may be selected, based on the various possible connections between the electrode contacts in the tripolar electrode  10 . 
   In operation, a microstimulator  300  is first inserted into the monopolar adapter chamber  212  through the adapter opening such that the anode contact  301  of the microstimulator  300  is abutted against the inside end of the indifferent contact  201  within the adapter chamber  212 . The microstimulator  300  is inserted through sealing rings  207  and  208  inside the monopolar adapter chamber  212 . The sealing rings  207  and  208  can be sized so that a microstimulator  300  can fit easily through each ring. A clearance space between the microstimulator and the chamber wall  212  permits the microstimulator to be easily placed inside chamber  212  without sticking. After the microstimulator is placed in the adapter chamber  212 , a connector  40  (or connector  45 ) may be inserted through the adapter opening. The end  210  of the monopolar adapter  200  may have a slightly larger circumference compared to the adapter mid-portion  203 . The lip  213  at the adapter end allows a clinician to grasp the adapter and pull it towards the connector  40  to snap the circular flange  56  of the connector  40  into the complementary circular recess  211  in the monopolar adapter  200 . The circular lip  213 , placed at the adapter opening, can also be grasped when inserting the microstimulator into the adapter chamber  212 . 
   By pulling the adapter end  210 , the length of the adapter from the adapter opening end to the opposite end is stretched. After the flange  56  is snapped into the complementary recess  211 , the adapter wall, which is preferably an elastic material such as silicone or polyurethane, is under elastic tension and the microstimulator inside the adapter chamber  212  is under compression. As a consequence, the microstimulator&#39;s cathode contact  304  is urged against the connector contact  58 , thereby ensuring good electrical contact. At the same time, the microstimulator&#39;s indifferent contact  302  at end  301  is urged against the adapter&#39;s indifferent electrode  201 , thereby ensuring good electrical contact. 
   After the microstimulator is inserted into the monopolar adapter chamber  212  and the connector  40  is inserted, so that the circular flange  56  fits snugly into the complementary shaped circular recess  211 , a locking feature helps to lock the connector  40  to the adapter  200  and to create a water tight seal. To achieve this seal, a slidable locking (or sliding) ring  204  is advanced towards the adapter opening at the lip  213 . Because the adapter portion between lip  213  and portion  210  has a slightly large outer circumference than the adapter mid-portion  203 , advancing the sliding ring  204  towards the end of the adapter compresses that section of the adapter which is over the recess  211 . The compression thus achieved helps to lock the flange  56  into the adapter recess  211  and form a water-tight seal. Another slidable locking (sliding) ring  202  can be used on the other end of the adapter, which portion also has a slightly larger exterior circumference compared to the mid-portion  203  of the adapter. Advancing the sliding ring towards the adapter end forms a water-tight seal between the silicone or polyurethane insulation portion of the adapter and the indifferent adapter electrode contact  201  over the threaded portion  220 . 
     FIG. 6  shows, in accordance with the present invention, a cross-sectional view of a bipolar adapter  100  having a first adapter opening  108  and a second adapter opening  109  which are located at the first adapter end  101  and the second adapter end  105 , respectively. The bipolar adapter has circular recesses  110  and  111  within adapter chamber  115 , which recesses are complementary in dimension and shape to the circular locking flange  56  on the lead extension  40  (or extension  45 ). The bipolar adapter  100  also includes end lips  106  and  107  which may be used to help grasp the adapter  100  during insertion of the microstimulator  300  into the adapter chamber  115  or when the extension lead connector  40  or  45  is inserted into either the first opening  108  or second opening  109 . In addition, the inside of the bipolar adapter chamber  115  includes sealing rings  112  and  113 . The end portions  101  and  105  of the adapter  100  are slightly larger in circumference than the adapter&#39;s mid-portion  103 . 
     FIG. 7  shows a side, cross-sectional view of the bipolar adapter of  FIG. 6  but with the microstimulator  300  inserted into the adapter chamber and with the extension lead connectors  45  and  40  inserted into the first and second adapter openings. The view also shows sliding ring  102  and sliding ring  104  which serve the same function as with the monopolar adapter. That is, the sliding rings serve to help form a water tight seal between the lead extension connectors  40  and  45  and the adapter body, which is preferably insulative material such as silicone or polyurethane. 
   Referring to  FIGS. 6 and 7 , the bipolar adapter  100  may also have circular end lips  107  and  106  which are circumferentially larger than end portions  101  and  105 , respectively. End lips  107  and  106  may be used to grasp the adapter when the microstimulator  300  is inserted into the adapter chamber through either adapter opening  108  or  109 . In addition, the lips may be used to help grasp the bipolar adapter when the connecter  40  or  45  is inserted into opening  109  or  108 , thereby locking the flange  56  of the connector  40  or  45  into complementary recesses  110  or  111  of the adapter. 
   The circular sealing rings  112  and  113  protrude from the inside wall of the adapter chamber  115 . The sealing ring or rings help center the microstimulator within adapter chamber and also prevent passage of fluid from one end of the adapter chamber to the other end and, thus, help prevent a short between the two microstimulator electrodes  302  and  304 , as shown in  FIG. 7 . 
   The operation of the bipolar adapter is similar to the operation of the monopolar adapter. The microstimulator  300  is first placed into the adapter. Next, connector  40  is placed into opening  108  and connector  45  is placed into opening  109 . After these steps are completed, electrode contacts  12  and  14  of the tripolar electrode  10  ( FIGS. 4A ,  4 B and  4 C) are connected to the microstimulator electrode contact facing adapter opening  109  ( FIG. 6 ) and tripolar electrode contact  13  is connected to the microstimulator electrode contact facing adapter opening  108 . Alternatively, connector  40  can be placed into adapter opening  109  and connector  45  can be placed into adapter opening  108 . After the connectors  40  and  45  have been inserted into the adapter openings  108 ,  109 , the sliding rings,  102  and  104 , which are preferably made from a bio-compatible metal such as stainless steel, can be advanced to their respective ends of the adapter  100  to thereby lock the connectors  40  and  45  into place in their complementary recesses. Because the exterior diameter (or circumference) of the adapter increases slightly towards the adapter ends, sliding either ring towards an adapter end compresses that adapter end and thereby locking the inserted connector  40  or  45 . 
   Thus, in accordance with the present invention, the system of the present invention can include at least one adapter, either monopolar or bipolar. If a monopolar adapter is used, the system includes at least one extension lead with a connector that is to be inserted into the one opening of the monopolar adapter. If a bipolar adapter is used, the system includes at least two extension leads with two connectors for insertion into the two openings in the bipolar adapter. 
   While the example lead extension and adapter system are illustrated as adapting a leadless microstimulator to a tripolar, semi-cuff electrode, the type of electrode is not important. It is emphasized that the adapter system of the present invention does not depend on the particular shape or configuration of the stimulating electrode selected, as the adapter system can accommodate any type of monopolar electrode (one electrode contact), a bipolar electrode (two electrode contacts), a tripolar electrode (three electrode contacts), or an electrode having greater than three electrode contacts. The latter, multi-contact electrode array may be employed as either a monopolar or bipolar electrode, with various optional connections made between the array of electrode contacts. 
   For example, it is possible to use the system with a monopolar electrode having a single extension lead and one lead connector  40 . In such a case, a monopolar adapter  200  ( FIG. 5 ) can be used. The microstimulator  300  is placed into the adapter chamber  212  so that the end  301  of the microstimulator&#39;s indifferent electrode contact  302  is in electrical contact with the indifferent contact  201  of the adapter  200 . The lead connector  40  is inserted into opening  206  to place connector contact  59  in electrical connection with the microstimulator cathode contact  304 . The tripolar electrode  10  can be used in a monopolar configuration. For example, the electrode contact  13  ( FIG. 4C ) may be connected and electrode contacts  12  and  14  disconnected. 
   A bipolar electrode configuration may be achieved using the bipolar adapter  100  and the tripolar electrode  10  in a bipolar configuration mode. For example, electrode  12  may be left unused and connection  24  may be disconnected, converting the tripolar electrode  10  into a true bipolar, semi-cuff electrode. The connections to the bipolar adapter are otherwise identical as previously described. 
   In summary, the present invention utilizes a leadless microstimulator having a cathode and anode electrode contacts integrated on the microstimulator body at either end, wherein the microstimulator is shaped substantially as an elongated cylinder. The present invention provides an adapter system that can be connected to a variety of electrode types via one or two extension leads without any preparatory alterations to the physical design of the leadless microstimulator. 
   While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.