Patent Publication Number: US-2018028820-A1

Title: Biased ball-spring contacts for electrical stimulation systems and methods of making and using same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 62/368,610, filed Jul. 29, 2016, which is incorporated herein by reference. 
    
    
     FIELD 
     The present invention is directed to the area of implantable electrical stimulation systems and methods of making and using the systems. The present invention is also directed to implantable electrical stimulation leads having biased ball-spring type contacts and connect assemblies, as well as methods of making and using the contacts, contact assemblies, and the electrical stimulation systems. 
     BACKGROUND 
     Implantable electrical stimulation systems have proven therapeutic in a variety of diseases and disorders. For example, spinal cord stimulation systems have been used as a therapeutic modality for the treatment of chronic pain syndromes. Peripheral nerve stimulation has been used to treat chronic pain syndrome and incontinence, with a number of other applications under investigation. Functional electrical stimulation systems have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients. Stimulation of the brain, such as deep brain stimulation, can be used to treat a variety of diseases or disorders. 
     Stimulators have been developed to provide therapy for a variety of treatments. A stimulator can include a control module (with a pulse generator), one or more leads, and an array of stimulator electrodes on each lead. The stimulator electrodes are in contact with or near the nerves, muscles, or other tissue to be stimulated. The pulse generator in the control module generates electrical pulses that are delivered by the electrodes to body tissue. 
     BRIEF SUMMARY 
     In one embodiment, a connector assembly includes an elongated connector housing having a first end, an opposing second end, and a longitudinal axis. The connector assembly further includes a port defined at the first end of the connector housing. The port is configured and arranged for receiving a proximal end of a lead or lead extension, wherein the proximal end of the lead or the lead extension includes a plurality of terminals electrically insulated from one another. The connector assembly further includes a lumen defined in the connector housing, and the lumen extends from the port along the longitudinal axis of the connector housing. Lastly, the connector assembly includes a plurality of contacts disposed in the elongated connector housing and electrically insulated from one another. At least one of the plurality of contacts is configured and arranged to couple to at least one of the plurality of terminals when the proximal end of the lead or lead extension is received within the lumen of the connector housing. Each of the plurality of contacts includes a contact ring and a plurality of ball-spring assemblies distributed around the contact ring. Each ball-spring assembly includes a housing coupled to the contract ring, a biasing member disposed within the ball-spring housing, and a conductive ball disposed at least partially within the ball-spring housing. The ball-spring housing defines an opening that is smaller than a diameter of the ball and the biasing member urges the ball towards the opening so that, absent a force countering the biasing member, a portion of the ball extends out of the opening in the ball-spring housing. 
     Another embodiment is an electrical contact for a lead assembly that includes a contact ring and a plurality of ball-spring assemblies distributed around the contact ring. Each ball-spring assembly includes a housing coupled to the contract ring, a biasing member disposed within the ball-spring housing, and a conductive ball disposed at least partially within the ball-spring housing. The ball-spring housing defines an opening that is smaller than a diameter of the ball and the biasing member urges the ball towards the opening so that, absent a force countering the biasing member, a portion of the ball extends out of the opening in the ball-spring housing. 
     In at least some embodiments, the ball-spring housing is a cylindrical body. In at least some embodiments, a fillet adjoins the ball-spring housing and an inner surface of the contact ring. In at least some embodiments, the ball is free to rotate within the ball-spring housing. 
     In at least some embodiments, each biasing member is a spring such as, but not limited to a helical compression spring or a conical compression spring. In at least some embodiments, the conductive ball is metallic. Optionally, the conductive ball is made from a conductive polymer or some other, non-metallic conductive material. 
     In at least some embodiments, the ball is free to translate within the housing. Additionally or alternatively, the biasing member is configured to move in a radial direction with respect to the longitudinal axis of the elongated connector housing. In at least some embodiments, the biasing member is further disposed between the ball and an inner surface of the contact ring. 
     Yet another embodiment is lead assembly that includes a lead or a lead extension having a proximal end and a distal end, wherein the proximal end of the lead or the lead extension includes a plurality of terminals electrically insulated from one another. The lead assembly also includes any of the connector assemblies described above. 
     A further embodiment is an electrical stimulating system includes any of the lead assemblies described above and a control module coupled to the lead assembly. 
     The control module includes a housing, and an electronic subassembly disposed in the housing. In at least some embodiments, the connector assembly is part of the control module. In at least some embodiments, the lead assembly includes the lead and the electrical stimulation system further includes a lead extension coupleable to the control module and the lead, where the connector assembly is part of the lead extension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
       For a better understanding of the present invention, reference will be made to the following Detailed Description, which is to be read in association with the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of one embodiment of an electrical stimulation system that includes a paddle body coupled to a control module via lead bodies, according to the invention; 
         FIG. 2  is a schematic view of another embodiment of an electrical stimulation system that includes a percutaneous lead body coupled to a control module via a lead body, according to the invention; 
         FIG. 3A  is a schematic view of one embodiment of a plurality of connector assemblies disposed in the control module of  FIG. 1 , the connector assemblies configured and arranged to receive the proximal portions of the lead bodies of  FIG. 1 , according to the invention; 
         FIG. 3B  is a schematic view of one embodiment of a connector assembly disposed in the control module of  FIG. 2 , the connector assembly configured and arranged to receive the proximal portion of one of the lead body of  FIG. 2 , according to the invention; 
         FIG. 3C  is a schematic view of one embodiment of a proximal portion of the lead body of  FIG. 2 , a lead extension, and the control module of  FIG. 2 , the lead extension configured and arranged to couple the lead body to the control module, according to the invention; 
         FIG. 4A  is a schematic, perspective view of a contact with ball-spring assemblies for a lead or a lead extension according to at least some embodiments of the present invention; 
         FIG. 4B  is a close-up view, cross-sectional view of the contact of  FIG. 4A ; 
         FIG. 5  is a close-up view, cross-sectional view of the contact of  FIG. 4A  with a terminal concentrically disposed within ball-spring assemblies of the contact according to at least some embodiments of the present invention; 
         FIG. 6  is a schematic, perspective view of a contact with ball-spring assemblies showing an insertion or withdrawal direction for a lead or a lead extension according to at least some embodiments of the present invention; 
         FIG. 7  is a schematic, side-elevational view of a contact with ball-spring assemblies having conical springs according to at least some embodiments of the present invention; 
         FIG. 8  is a schematic, perspective view of a contact assembly with a plurality of ball-spring assemblies electrically insulated from each other according to at least some embodiments of the present invention; and 
         FIG. 9  is a schematic overview of one embodiment of components of a stimulation system, including an electronic subassembly disposed within a control module, according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to the area of implantable electrical stimulation systems and methods of making and using the systems. The present invention is also directed to implantable electrical stimulation leads having biased ball-spring type contacts and connect assemblies, as well as methods of making and using the contacts, contact assemblies, and the electrical stimulation systems. 
     Suitable implantable electrical stimulation systems include, but are not limited to, a least one lead with one or more electrodes disposed along a distal end of the lead and one or more terminals disposed along the one or more proximal ends of the lead. Leads include, for example, percutaneous leads, paddle leads, and cuff leads. Examples of electrical stimulation systems with leads are found in, for example, U.S. Pat. Nos. 6,181,969; 6,295,944; 6,391,985; 6,516,227; 6,609,029; 6,609,032; 6,741,892; 7,244,150; 7,450,997; 7,672,734;7,761,165; 7,783,359; 7,792,590; 7,809,446; 7,949,395; 7,974,706; 8,831,742; 8,688,235; 6,175,710; 6,224,450; 6,271,094; 6,295,944; 6,364,278; and 6,391,985; U.S. Patent Applications Publication Nos. 2007/0150036; 2009/0187222; 2009/0276021; 2010/0076535; 2010/0268298; 2011/0004267; 2011/0078900; 2011/0130817; 2011/0130818; 2011/0238129; 2011/0313500; 2012/0016378; 2012/0046710; 2012/0071949; 2012/0165911; 2012/0197375; 2012/0203316; 2012/0203320; 2012/0203321; 2012/0316615; 2013/0105071; 2011/0005069; 2010/0268298; 2011/0130817; 2011/0130818; 2011/0078900; 2011/0238129; 2011/0313500; 2012/0016378; 2012/0046710; 2012/0165911; 2012/0197375; 2012/0203316; 2012/0203320; and 2012/0203321, all of which are incorporated by reference in their entireties. 
     Examples of connectors, connector contacts and connector assemblies for electrical stimulation systems with leads are found in, for example, U.S. Pat. Nos. 8,849,396; 7,244,150; 8,600,507; 8,897,876; 8,682,439; U.S. Patent Applications Publication Nos. 2012/0053646; 2014/0148885; 2015/0209575; 2016/0059019; and U.S. Patent Provisional Patent Application Nos. 62/193,472; 62/216,594; 62/259,463; and 62/278,667, all of which are incorporated by reference in their entireties. 
       FIG. 1  illustrates schematically one embodiment of an electrical stimulation system  100 . The electrical stimulation system includes a control module (e.g., a stimulator or pulse generator)  102  and a lead  103 . The lead  103  including a paddle body  104  and one or more lead bodies  106  coupling the control module  102  to the paddle body  104 . The paddle body  104  and the one or more lead bodies  106  form the lead  103 . The paddle body  104  typically includes a plurality of electrodes  134  that form an array of electrodes  133 . The control module  102  typically includes an electronic subassembly  110  and an optional power source  120  disposed in a sealed housing  114 . In  FIG. 1 , two lead bodies  106  are shown coupled to the control module  102 . 
     The control module  102  typically includes one or more connector assemblies  144  into which the proximal end of the one or more lead bodies  106  can be plugged to make an electrical connection via connector contacts (e.g.,  316  in  FIG. 3A ) disposed in the connector assembly  144  and terminals (e.g.,  310  in  FIG. 3A ) on each of the one or more lead bodies  106 . The connector contacts are coupled to the electronic subassembly  110  and the terminals are coupled to the electrodes  134 . In  FIG. 1 , two connector assemblies  144  are shown. 
     The one or more connector assemblies  144  may be disposed in a header  150 . The header  150  provides a protective covering over the one or more connector assemblies  144 . The header  150  may be formed using any suitable process including, for example, casting, molding (including injection molding), and the like. In addition, one or more lead extensions  324  (see  FIG. 3C ) can be disposed between the one or more lead bodies  106  and the control module  102  to extend the distance between the one or more lead bodies  106  and the control module  102 . 
     It will be understood that the electrical stimulation system can include more, fewer, or different components and can have a variety of different configurations including those configurations disclosed in the electrical stimulation system references cited herein. For example, instead of a paddle body  104 , the electrodes  134  can be disposed in an array at or near the distal end of a lead body  106 ′ forming a percutaneous lead  103 , as illustrated in  FIG. 2 . The percutaneous lead may be isodiametric along the length of the lead body  106 ″. The lead body  106 ′ can be coupled with a control module  102 ′ with a single connector assembly  144 . 
     The electrical stimulation system or components of the electrical stimulation system, including one or more of the lead bodies  106 , the control module  102 , and, in the case of a paddle lead, the paddle body  104 , are typically implanted into the body of a patient. The electrical stimulation system can be used for a variety of applications including, but not limited to, spinal cord stimulation, brain stimulation, neural stimulation, muscle activation via stimulation of nerves innervating muscle, and the like. 
     The electrodes  134  can be formed using any conductive, biocompatible material. Examples of suitable materials include metals, alloys, conductive polymers, conductive carbon, and the like, as well as combinations thereof. In at least some embodiments, one or more of the electrodes  134  are formed from one or more of: platinum, platinum iridium, palladium, titanium, or rhenium. 
     The number of electrodes  134  in the array of electrodes  133  may vary. For example, there can be two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, or more electrodes  134 . As will be recognized, other numbers of electrodes  134  may also be used. In  FIG. 1 , sixteen electrodes  134  are shown. The electrodes  134  can be formed in any suitable shape including, for example, round, oval, triangular, rectangular, pentagonal, hexagonal, heptagonal, octagonal, or the like. 
     The electrodes of the paddle body  104  or one or more lead bodies  106  are typically disposed in, or separated by, a non-conductive, biocompatible material including, for example, silicone, polyurethane, and the like or combinations thereof. The paddle body  104  and one or more lead bodies  106  may be formed in the desired shape by any process including, for example, molding (including injection molding), casting, and the like. Electrodes and connecting wires can be disposed onto or within a paddle body either prior to or subsequent to a molding or casting process. The non-conductive material typically extends from the distal end of the lead  103  to the proximal end of each of the one or more lead bodies  106 . The non-conductive, biocompatible material of the paddle body  104  and the one or more lead bodies  106  may be the same or different. The paddle body  104  and the one or more lead bodies  106  may be a unitary structure or can be formed as two separate structures that are permanently or detachably coupled together. 
     Terminals (e.g.,  310  in  FIG. 3A ) are typically disposed at the proximal end of the one or more lead bodies  106  for connection to corresponding conductive contacts (e.g.,  316  in  FIG. 3A ) in connector assemblies (e.g.,  144  in  FIG. 1 ) disposed on, for example, the control module  102  (or to other devices, such as conductive contacts on a lead extension, an operating room cable, a splitter, an adaptor, or the like). 
     Conductive wires (not shown) extend from the terminals (e.g.,  310  in  FIG. 3A ) to the electrodes  134 . Typically, one or more electrodes  134  are electrically coupled to a terminal (e.g.,  310  in  FIG. 3A ). In some embodiments, each terminal (e.g.,  310  in  FIG. 3A ) is only coupled to one electrode  134 . 
     The conductive wires may be embedded in the non-conductive material of the lead or can be disposed in one or more lumens (not shown) extending along the lead. In some embodiments, there is an individual lumen for each conductive wire. In other embodiments, two or more conductive wires may extend through a lumen. There may also be one or more lumens (not shown) that open at, or near, the proximal end of the lead, for example, for inserting a stylet rod to facilitate placement of the lead within a body of a patient. Additionally, there may also be one or more lumens (not shown) that open at, or near, the distal end of the lead, for example, for infusion of drugs or medication into the site of implantation of the paddle body  104 . The one or more lumens may, optionally, be flushed continually, or on a regular basis, with saline, epidural fluid, or the like. The one or more lumens can be permanently or removably sealable at the distal end. 
     As discussed above, the one or more lead bodies  106  may be coupled to the one or more connector assemblies  144  disposed on the control module  102 . The control module  102  can include any suitable number of connector assemblies  144  including, for example, two three, four, five, six, seven, eight, or more connector assemblies  144 . It will be understood that other numbers of connector assemblies  144  may be used instead. In  FIG. 1 , each of the two lead bodies  106  includes eight terminals that are shown coupled with eight conductive contacts disposed in a different one of two different connector assemblies  144 . 
       FIG. 3A  is a schematic side view of one embodiment of a plurality of connector assemblies  144  disposed on the control module  102 . In at least some embodiments, the control module  102  includes two connector assemblies  144 . In at least some embodiments, the control module  102  includes four connector assemblies  144 . In  FIG. 3A , proximal ends  306  of the plurality of lead bodies  106  are shown configured and arranged for insertion to the control module  102 .  FIG. 3B  is a schematic side view of one embodiment of a single connector assembly  144  disposed on the control module  102 ′. In  FIG. 3B , the proximal end  306  of the single lead body  106 ′ is shown configured and arranged for insertion to the control module  102 ′. 
     In  FIGS. 3A and 3B , the one or more connector assemblies  144  are disposed in the header  150 . In at least some embodiments, the header  150  defines one or more ports  304  into which the proximal end(s)  306  of the one or more lead bodies  106 / 106 ′ with terminals  310  can be inserted, as shown by directional arrows  312 , in order to gain access to the connector contacts disposed in the one or more connector assemblies  144 . 
     The one or more connector assemblies  144  each include a connector housing  314  and a plurality of connector contacts  316  disposed therein. Typically, the connector housing  314  defines a port (not shown) that provides access to the plurality of connector contacts  316 . In at least some embodiments, one or more of the connector assemblies  144  further includes a retaining element  318  configured and arranged to fasten the corresponding lead body  106 / 106 ′ to the connector assembly  144  when the lead body  106 / 106 ′ is inserted into the connector assembly  144  to prevent undesired detachment of the lead body  106 / 106 ′ from the connector assembly  144 . For example, the retaining element  318  may include an aperture  320  through which a fastener (e.g., a set screw, pin, or the like) may be inserted and secured against an inserted lead body  106 / 106 ′. 
     When the one or more lead bodies  106 / 106 ′ are inserted into the one or more ports  304 , the connector contacts  316  can be aligned with the terminals  310  disposed on the one or more lead bodies  106 / 106 ′ to electrically couple the control module  102  to the electrodes ( 134  of  FIG. 1 ) disposed at a distal end of the one or more lead bodies  106 . Examples of connector assemblies in control modules are found in, for example, U.S. Pat. Nos. 7,244,150 and 8,224,450, which are incorporated by reference. 
     In at least some embodiments, the electrical stimulation system includes one or more lead extensions. The one or more lead bodies  106 / 106 ′ can be coupled to one or more lead extensions which, in turn, are coupled to the control module  102 / 102 ′. In  FIG. 3C , a lead extension connector assembly  322  is disposed on a lead extension  324 . The lead extension connector assembly  322  is shown disposed at a distal end  326  of the lead extension  324 . The lead extension connector assembly  322  includes a contact housing  328 . The contact housing  328  defines at least one port  330  into which a proximal end  306  of the lead body  106 ′ with terminals  310  can be inserted, as shown by directional arrow  338 . The lead extension connector assembly  322  also includes a plurality of connector contacts  340 . When the lead body  106 ′ is inserted into the port  330 , the connector contacts  340  disposed in the contact housing  328  can be aligned with the terminals  310  on the lead body  106  to electrically couple the lead extension  324  to the electrodes ( 134  of  FIG. 1 ) disposed at a distal end (not shown) of the lead body  106 ′. 
     The proximal end of a lead extension can be similarly configured and arranged as a proximal end of a lead body. The lead extension  324  may include a plurality of conductive wires (not shown) that electrically couple the connector contacts  340  to terminal on a proximal end  348  of the lead extension  324 . The conductive wires disposed in the lead extension  324  can be electrically coupled to a plurality of terminals (not shown) disposed on the proximal end  348  of the lead extension  324 . In at least some embodiments, the proximal end  348  of the lead extension  324  is configured and arranged for insertion into a lead extension connector assembly disposed in another lead extension. In other embodiments (as shown in  FIG. 3C ), the proximal end  348  of the lead extension  324  is configured and arranged for insertion into the connector assembly  144  disposed on the control module  102 ′. 
     It will be understood that the control modules  102 / 102 ′ can receive either lead bodies  106 / 106 ′ or lead extensions  324 . It will also be understood that the electrical stimulation system  100  can include a plurality of lead extensions  224 . For example, each of the lead bodies  106  shown in  FIGS. 1 and 3A  can, alternatively, be coupled to a different lead extension  224  which, in turn, are each coupled to different ports of a two-port control module, such as the control module  102  of  FIGS. 1 and 3A . 
     In at least some conventional electrical stimulation systems, coupling a neuromodulation lead to a lead extension or coupling a lead or lead extension to an implantable pulse generator (IPG) header is accomplished using canted coil spring contacts within the IPG header. An alternative contact assembly, described below, includes a plurality of contact rings with ball-spring assemblies. Such an arrangement may reduce an insertion force of a proximal end portion of a lead or lead extension during insertion into or withdrawal from a mating component such as an IPG header, a connector on a lead extension or any other connector. Biasing members, which may take the form of springs, urge spherical balls into contact with the lead or lead extension to keep the lead or lead extension concentrically aligned with the contact, reduce the frictional forces on the lead or lead extension (e.g., reduce the drag), and thus lower or reduce the insertion or withdrawal force of the lead or lead extension vis-à-vis the mating component. 
       FIGS. 4A and 4B  show schematic, perspective views of a contact  400  having a contact ring  402  with an inner surface  404  and an outer surface  406 . A plurality of ball-spring assemblies  408  project or extend from the inner surface  404 . Each ball-spring assembly  408  includes a ball-spring housing  410 , a ball  412  and a biasing member  414  ( FIG. 4B ). The ball-spring housing  410  can be attached to the inner surface  404  of the contact ring  402  by a variety of techniques such as, but not limited to, welding or bonding. In at least one embodiment, the ball-spring housing  410  can be attached to the inner surface  404  of the contact ring  402  by a metal molding technique. In the illustrated embodiment, the ball-spring housing  410  is welded to the inner surface  404  of the contact ring  402 , which generates a fillet  416 . The ball-spring housing  410  may take the form of a cylindrical body, but it is appreciated that other shapes are possible. The ball  414  may take the form of a spherically shaped ball that made be made from a conductive material such as, but not limited to, a metallic or other conductive material like a conductive polymer. It is appreciated that the ball, the biasing member and the contact ring are made from one or more conductive materials to form a conductive path with the lead terminal. 
     In a preferred embodiment, at least three ball-spring assemblies  408  advantageously provide at least three points of contact for a lead or a lead extension (hereinafter lead) during insertion or withdrawal of the lead from the contact  400 . The three ball-spring assemblies  408  permit the lead to be concentrically located relative to the contact ring  402 . Additionally or alternatively, the frictional forces on the lead during insertion or withdrawal depend, at least in part, on the spring constant (e.g., spring force) of the biasing member. Using at least three ball-spring assemblies  408  supports the lead concentrically during insertion and withdrawal. Alternatively, more than three ball-spring assemblies  408  may be disposed on the contact ring  402 . 
     Referring to  FIG. 4B , the ball-spring housing  408  includes a wall  418  and a stop  420 . The wall  418  extending from the inner surface  404  of the contact ring  402  and is preferably a continuous, cylindrical member. The stop  420  is integrally formed with or coupled to the wall  418 . The stop  420  defines an opening (located where the ball  412  is seated in  FIG. 4B ). The opening, in turn, is smaller than a diameter of the ball  412 , which in turn prevents the ball from being pushed out of or otherwise falling out of the ball-spring housing  410 . In at least some embodiments, the bore sized of the ball-spring housing  410  in cooperation with the narrow opening permits the ball  412  to rotate and move freely within the ball-spring housing  410 , wherein the movement of the ball includes translation of the ball  412  in a radial direction relative to a longitudinal axis of the contact ring  402  or relative to the longitudinal axis of the elongated connector housing, which is coincident to the longitudinal axis of the contact ring  402 . However, the radial translation of the ball  412  is constrained by cooperation of the stop  420  and the biasing member  414 . 
     In at least some embodiment, the biasing member  414  takes the form of a helical compression spring. As noted above, the spring constant may be adjustable or modified prior to assembly, which in turn would require either more or less force to move the ball  412  outward toward the inner surface  404  of the contact ring  402  during insertion, withdrawal, or both of the lead or lead extension. The biasing member  414  is disposed within the ball-spring housing  410 , and more specifically disposed between the ball  412  and the inner surface  404  of the contact ring  402 . 
       FIG. 5  shows a schematic, cross-sectional view of the contact  400  with a terminal  422  concentrically disposed within the contact  400 . The terminal  422  may take the form of terminals  310  in  FIG. 3C . 
       FIG. 6  shows a schematic, perspective view of the contact  400 . The arrow  426  indicates the insertion or withdrawal direction of the lead or lead extension vis-à-vis the contact  400 . Even if the lead or lead extension is not directly aligned with the contact  400 , the ball-spring assemblies  408  may operate to concentrically align or position the lead or lead extension during insertion or withdrawal. 
       FIG. 7  shows a schematic, cross-sectional view of another contact  500  that includes the same features, aspects and components as the contact  400  except that the biasing members  514  disposed within the ball-spring assemblies  508  take the form of conical springs, as compared to helical springs. In at least some embodiments, the biasing members  514  may take other types of springs such as, but not limited to, hourglass and barrel-shaped springs or various types of flat springs. Any of the springs described herein may advantageously provide a low solid height with lateral stability or resistance to surging. In at least some embodiments, conical springs can be selected or designed so that each coil nests wholly or partly into an adjacent coil. The solid height can be as low as one wire diameter. Additionally or alternatively, the spring constant or spring rate for conical springs generally increases with deflection because the number of active coils decreases progressively as the spring approaches solid. Although by varying the pitch, conical springs can be designed to have a uniform rate. 
     In at least some other embodiments, the biasing member may take the form of a compressible or viscous fluid or some other type of device capable of urging and maintaining the ball radially inward relative to the contact ring. 
       FIG. 8  shows a schematic, perspective view of a connector assembly  600 . In at least some embodiments, the connector assembly  600  includes a plurality of contacts  602  that are electrically insulated from one another with a silicon material  604 . By way of example, the contacts may be disposed in, or separated by, a non-conductive, biocompatible material such as, for example, silicone, polyurethane, polyetheretherketone (“PEEK”), epoxy, and the like or combinations thereof. The contacts themselves can be formed using any conductive, biocompatible material. Examples of suitable materials include metals, alloys, conductive polymers, conductive carbon, and the like, as well as combinations thereof. In at least some embodiments, one or more of the contacts are formed from one or more of: platinum, platinum iridium, palladium, palladium rhodium, or titanium. 
       FIG. 9  is a schematic overview of one embodiment of components of an electrical stimulation system  800  including an electronic subassembly  810  disposed within a control module. It will be understood that the electrical stimulation system can include more, fewer, or different components and can have a variety of different configurations including those configurations disclosed in the stimulator references cited herein. 
     Some of the components (for example, a power source  812 , an antenna  818 , a receiver  802 , and a processor  804 ) of the electrical stimulation system can be positioned on one or more circuit boards or similar carriers within a sealed housing of an implantable pulse generator, if desired. Any power source  812  can be used including, for example, a battery such as a primary battery or a rechargeable battery. Examples of other power sources include super capacitors, nuclear or atomic batteries, mechanical resonators, infrared collectors, thermally-powered energy sources, flexural powered energy sources, bioenergy power sources, fuel cells, bioelectric cells, osmotic pressure pumps, and the like including the power sources described in U.S. Pat. No. 7,437,193, incorporated herein by reference. 
     As another alternative, power can be supplied by an external power source through inductive coupling via the optional antenna  818  or a secondary antenna. The external power source can be in a device that is mounted on the skin of the user or in a unit that is provided near the user on a permanent or periodic basis. 
     If the power source  812  is a rechargeable battery, the battery may be recharged using the optional antenna  818 , if desired. Power can be provided to the battery for recharging by inductively coupling the battery through the antenna to a recharging unit  816  external to the user. Examples of such arrangements can be found in the references identified above. 
     In one embodiment, electrical current is emitted by the electrodes  134  on the paddle or lead body to stimulate nerve fibers, muscle fibers, or other body tissues near the electrical stimulation system. The processor  804  is generally included to control the timing and electrical characteristics of the electrical stimulation system. For example, the processor  804  can, if desired, control one or more of the timing, frequency, strength, duration, and waveform of the pulses. In addition, the processor  804  can select which electrodes can be used to provide stimulation, if desired. In some embodiments, the processor  804  selects which electrode(s) are cathodes and which electrode(s) are anodes. In some embodiments, the processor  804  is used to identify which electrodes provide the most useful stimulation of the desired tissue. 
     Any processor can be used and can be as simple as an electronic device that, for example, produces pulses at a regular interval or the processor can be capable of receiving and interpreting instructions from an external programming unit  808  that, for example, allows modification of pulse characteristics. In the illustrated embodiment, the processor  804  is coupled to a receiver  802  which, in turn, is coupled to the optional antenna  818 . This allows the processor  804  to receive instructions from an external source to, for example, direct the pulse characteristics and the selection of electrodes, if desired. 
     In one embodiment, the antenna  818  is capable of receiving signals (e.g., RF signals) from an external telemetry unit  806  which is programmed by the programming unit  808 . The programming unit  808  can be external to, or part of, the telemetry unit  806 . The telemetry unit  806  can be a device that is worn on the skin of the user or can be carried by the user and can have a form similar to a pager, cellular phone, or remote control, if desired. As another alternative, the telemetry unit  806  may not be worn or carried by the user but may only be available at a home station or at a clinician&#39;s office. The programming unit  808  can be any unit that can provide information to the telemetry unit  806  for transmission to the electrical stimulation system  800 . The programming unit  808  can be part of the telemetry unit  806  or can provide signals or information to the telemetry unit  806  via a wireless or wired connection. One example of a suitable programming unit is a computer operated by the user or clinician to send signals to the telemetry unit  806 . 
     The signals sent to the processor  804  via the antenna  818  and the receiver  802  can be used to modify or otherwise direct the operation of the electrical stimulation system. For example, the signals may be used to modify the pulses of the electrical stimulation system such as modifying one or more of pulse duration, pulse frequency, pulse waveform, and pulse strength. The signals may also direct the electrical stimulation system  800  to cease operation, to start operation, to start charging the battery, or to stop charging the battery. In other embodiments, the stimulation system does not include the antenna  818  or receiver  802  and the processor  804  operates as programmed. 
     Optionally, the electrical stimulation system  800  may include a transmitter (not shown) coupled to the processor  804  and the antenna  818  for transmitting signals back to the telemetry unit  806  or another unit capable of receiving the signals. For example, the electrical stimulation system  800  may transmit signals indicating whether the electrical stimulation system  800  is operating properly or not or indicating when the battery needs to be charged or the level of charge remaining in the battery. The processor  804  may also be capable of transmitting information about the pulse characteristics so that a user or clinician can determine or verify the characteristics. 
     The above specification provides a description of the structure, manufacture, and use of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended.