Patent Publication Number: US-2019192861-A1

Title: Connector assemblies with novel seal 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. 62/609,915, filed Dec. 22, 2017, 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 connectors utilizing a novel spacer design, as well as methods of making and using the same. 
     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 
     One embodiment is a connector assembly including an elongated connector housing having a first end, a second end, and a length, the connector housing defining a port at the second end of the connector housing, the port configured for receiving a proximal end of a lead or lead extension; a lumen that extends from the port along at least a portion of the length of the connector housing; connector contacts axially spaced-apart and disposed along the lumen such that the connector contacts are each exposed to the lumen, the connector contacts configured for coupling to a proximal end of a lead or lead extension when the proximal end of the lead or lead extension is inserted into the lumen; and non-conductive spacers disposed between adjacent connector contacts. Each of the spacers includes an outer tubular extension, an inner tubular extension, and a connection region coupling the outer tubular extension to the inner tubular extension. The inner tubular extension has a free end and the inner tubular extension is configured and arranged to form a seal against the proximal end of the lead or lead extension when inserted into the lumen. 
     In at least some embodiments, the outer tubular extension is configured and arranged to form a seal against the connector housing. In at least some embodiments, the inner tubular extension forms a ring. In at least some embodiments, the outer tubular extension forms a ring. In at least some embodiments, the inner tubular extension and the outer tubular extension have an equal thickness when a lead or lead extension is not inserted into the lumen. In at least some embodiments, the outer tubular extension has a free end. In at least some embodiments, the inner tubular extension or the outer tubular extension or both the inner and outer tubular extensions have two free ends and the connection region couples an intermediate portion of the outer tubular extension to an intermediate portion of the inner tubular extension. 
     In at least some embodiments, the inner tubular extension is configured and arranged to stretch when the proximal end of the lead or lead extension is inserted into the lumen. In at least some embodiments, the connector assembly is configured and arranged so that a one of the connector contacts acts as a stop to stretching of the inner tubular extension of a one of the spacers as the proximal end of the lead or lead extension is inserted into the lumen. 
     In at least some embodiments, the connector assembly is configured and arranged so that a one of the connector contacts acts as a stop to retraction of the inner tubular extension of a one of the spacers as the proximal end of the lead or lead extension is removed into the lumen. In at least some embodiments, the outer tubular extension extends further in an axial direction than the inner tubular extension. In at least some embodiments, the inner tubular extension and the connection region have an equal thickness when a lead or lead extension is not inserted into the lumen. 
     In at least some embodiments, the connection region is curved. In at least some embodiments, at least a portion of the inner tubular extension extends parallel to a longitudinal axis of the lumen. In at least some embodiments, at least a portion of the outer tubular extension extends parallel to a longitudinal axis of the lumen. In at least some embodiments, connector assembly further includes an end stop disposed at an end of the lumen. 
     Another embodiment is an electrical stimulating system including an electrical stimulation lead including a proximal end, a distal end, a plurality of terminals disposed along the proximal end, and a plurality of electrodes disposed along the distal end; and a control module coupleable to the electrical stimulation lead. The control module includes a housing, an electronic subassembly disposed in the housing; and any of the connector assemblies described above, where at least one of the connector contacts is electrically coupled to the electronic subassembly. 
     Yet another embodiment is a lead extension that includes any of the connector assemblies described above disposed on a first end of the lead extension; and terminals disposed along a second end of the lead extension. 
     A further embodiment is a lead assembly that includes a lead and the lead extension described above. Another embodiment is an electrical stimulation system that includes the lead assembly and a control module coupleable to the lead assembly. The control module includes a housing and an electronic subassembly disposed in the housing. In at least some embodiments, the control module includes any of the connector assemblies described above. 
    
    
     
       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 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 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 to couple the lead body to the control module, according to the invention; 
         FIG. 4  is a schematic, cross-sectional view of one embodiment of a connector assembly according to the invention; 
         FIG. 5A  is a schematic, perspective view of a spacer, according to the invention; 
         FIG. 5B  is a schematic, partially cut-away, perspective view of the spacer of  FIG. 5A , according to the invention; 
         FIG. 5C  is a schematic, cross-sectional view of the spacer of  FIG. 5A , according to the invention; 
         FIG. 5D  is a schematic, cross-sectional view of another embodiment of a spacer, according to the invention; 
         FIG. 5E  is a schematic, partially cut-away, perspective view of yet another embodiment of a spacer, according to the invention; 
         FIGS. 6A-6F  are a schematic, cross-sectional views of a portion of a spacer, connector contact, and a lead illustrating one embodiment of interaction between the spacer and the lead during insertion and retraction of the lead from a connector assembly, according to the invention; and 
         FIG. 7  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 connectors utilizing a novel spacer design, as well as methods of making and using the same. 
     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 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 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 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 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 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 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 . 
     It will be understood that the connector assembly described below may be disposed in many different locations including, for example, on lead extensions (see e.g.,  322  of  FIG. 3C ), lead adapters, lead splitters, the connector portion of control modules (see e.g.,  144  of  FIGS. 1-3B ), or the like. In preferred embodiments, the connector assemblies are disposed on the distal ends of lead extensions. 
     A connector assembly in the control module or on a lead extension or other location can include an arrangement of connector contacts separated by spacers (which may also be referred to as seals). The spacers isolate or electrically insulate the connector contacts from each other and may also provide a seal with the lead to further isolate the connector contacts from each other. The spacers provide a sealing force or pressure on the lead body and array of terminals at an end of the lead or lead extension. Providing the seal increases the force for insertion of the lead or lead extension. The insertion force may result in difficulty inserting a lead, user dissatisfaction, or even lead damage due to high columnar loads. Moreover, as the number of electrodes on a lead increases, adding more connector contacts in a connector and terminals on the lead or lead extension will typically increase the insertion force. Therefore, it is desirable to develop spacer configurations with lower insertion force than conventional spacers. 
     A spacer can include an inner tubular extension and an outer tubular extension that are connected along or near one edge of each tubular extension while leaving another edge free to stretch or otherwise deform. In at least some embodiments, this spacer can provide a reliable seal against the lead or lead extension inserted into the connector and may also provide a seal against a housing of the connector. 
       FIG. 4A  shows a schematic, perspective view of a connector assembly  400  having a connector housing  402 , connector contacts  404 , spacers  406  that separate the connector contacts, an optional end stop  408 , and an optional retention block  410 . The connector housing  402  includes apertures  412  exposing the individual connector contacts  404  for attachment of a conductor (e.g., a wire—not shown) to the connector contact. In at least some embodiments, the apertures  412  in a finished connector assembly  400  are filled after or during attachment of the conductors to the connector contacts  404 . 
     The connector housing  402  defines a port  414  that provides access to a connector lumen  416  and the connector contacts  404 . The connector housing  402  can be made of any suitable material or materials. In at least some embodiments, the connector assembly  400  further includes a retention block  410  to fasten the corresponding lead body (or a retention ring on the lead body) of the lead or lead extension to the connector assembly  400  when the lead body is inserted into the connector assembly and prevent undesired detachment of the lead body from the connector assembly or misalignment of the terminals on the lead body with the connector contacts. For example, the retaining element  318  may include an aperture  418  through which a fastener (e.g., a set screw, pin, or the like) may be inserted and secured against an inserted lead body. Other types of retention blocks or retention assemblies can be used including, but not limited to, those described in U.S. Pat. No. 9,440,066; U.S. patent application Ser. Nos. 15/627,016 and 15/641,688; and U.S. Provisional Patent Application Ser. No. 62/464,710, all of which are incorporated herein by reference. 
     The connector contacts  404  may take the form of conductive spring contacts or any other suitable contact arrangement. Examples of connector contacts include, but are not limited to, canted coil contacts available from Bal Seal Engineering, Inc. (Foothill Ranch, Calif.) and contacts described in U.S. Pat. Nos. 7,803,021; 8,682,439; 8,897,876; 9,409,032; 9,604,068; 9,656,093; and 9,770,598; U.S. Patent Application Publications Nos. 2011/0022100; 2016/0228692; and 2016/0296745; U.S. patent application Ser. Nos. 15/627,016 and 15/656,612; and U.S. Provisional Patent Application Ser. No. 62/483,141, all of which are incorporated herein by reference. 
     The connector assembly  400  may include an end stop  408  which, at least in part, modulates insertion of the lead or lead extension into the port  414 . The end stop  408  can be disposed in the lumen  416  of the connector assembly  400 . The end stop  408  can provide one or more surfaces upon which the inserted lead or lead extension contacts, when the lead or lead extension is fully inserted into the port  414 . In some cases, the end stop  408  can provide the proximal-most point of insertion for the lead or lead extension within the connector assembly  400 . 
       FIGS. 5A-5C  illustrate schematic views of one embodiment of a spacer  406 . The spacer  406  can be described as having an outer tubular extension  580 , an inner tubular extension  582 , and a connection region  584  connecting the outer tubular extension  580  to the inner tubular extension  582 . An end  581 ,  583  of each of the outer and inner tubular extensions  580 ,  582  is free. As described below, the free end  583  of the inner tubular extension  582  can be stretched, displaced, or otherwise deformed as the lead is inserted into the connector assembly  400 . In at least some embodiments, the connection region  584  can be viewed as coupling a second end of the inner tubular extension  582  to a second end of the outer tubular extension  580 . 
     In the illustrated embodiments, the inner and outer tubular extensions  582 ,  580  have a circular or ring-like cross-sectional shape, but other forms can also be used including shapes with oval, rectangular, triangular, octagonal, or hexagonal cross-sections or the like. In the illustrated embodiments, the inner and outer tubular extensions  582 ,  580  have at least a portion that extends parallel to a longitudinal axis of the lumen  416  of the connector assembly ( FIG. 4 ), but it will be recognized that other embodiments of the spacer may have an inner tubular extension or an outer tubular extension that is sloped relative to the longitudinal axis of the lumen of the connector assembly or has any other suitable shape. In the illustrated embodiment, the connection region  504  is curved, but in other embodiments, a portion (or all of) the connection region  504  may be straight or have any other suitable shape. 
     The spacer  406  can be made of any suitable flexible, non-conductive material including, but not limited to, silicone, polyurethane, or the like. The material of the spacer  406  is preferably stretchable. In at least some embodiments, the spacer  406  is formed by molding. 
     The inner tubular extension  582  defines a lumen  586  through which a portion of the lead or lead extension extends when the inserted into the connector assembly  400 . The inner diameter of the inner tubular extension  582  is preferably equal to, or slightly smaller (for example, no more than 15%, 10%, or 5% smaller) than, the diameter of the lead or lead extension to be inserted into the connector assembly  400 . In at least some embodiments, the inner tubular extension  582  makes a seal (preferably, a hermetic seal) with the portion of the lead or lead extension inserted into the connector assembly  400 . In at least some embodiments, a ratio of sealing force to insertion force is at least 1.5, 1.6, 1.7, or 1.8. This ratio can be determined using a finite element analysis. 
     Although not wishing to be bound to any particular theory, the following is a description of one method of analyzing the sealing force and the insertion force. In at least some embodiments, the insertion force can be considered the combination of two forces: displacement and friction. Displacement is the force generated by moving the inner tubular extension. As one example of a determination of the displacement force, when the inner tubular extension is bent, the displacement force is proportional to the product of the displacement, the elastic modulus, and the second polar moment of inertia divided by the length of the bending element (e.g., F dis =d*E*I/L). In at least some embodiments, when the flange is stretched, the displacement can be modeled using Hook&#39;s law with the force equal to the product of the stretching distance and a material property, k, (e.g., F=kx). The “stretch” in this case is the portion connecting to the inner and outer tubular extensions, not the circumferential stretch of the inner tubular extension. In at least some embodiments, friction is equal to the product of the normal force and a friction coefficient, μ (e.g., F=μN). In at least some embodiments, the normal force is the sealing force and may be, for example, derived from the radial component of a force related to the circumferential stretching of the inner tubular extension (which may also be calculated using Hook&#39;s law). The friction coefficient depends on the materials of the spacer and the lead, in combination, and other factors such surface texture and possibly lubricity. Calculation of these forces in 360 degrees with multiple interactions between these forces can be complicated and challenging, but may be modeled. 
     In at least some embodiments, the outer diameter of the outer tubular extension  584  is equal to or slightly larger (for example, no more than 15%, 10%, or 5% larger) than, the inner diameter of the connector housing  402  of the connector assembly  400 . In at least some embodiments, the outer tubular extension  584  makes a seal (preferably, a hermetic seal) with the connector housing  402  of the connector assembly  400 . In at least some embodiments, the outer tubular extension  584  makes a seal (preferably, a hermetic seal) with the adjacent connector contacts  404  (or with an adjacent connector contact  404  and the end stop  408  or retention block  410 ) of the connector assembly  400 . 
     In at least some embodiments, the thicknesses of the inner tubular extension  582  and the outer tubular extension  580  are equal or differ by no more than 5%, 10%, or 20%. In at least some embodiments, the thicknesses of the inner tubular extension  582  and the connection region  584  are equal or differ by no more than 5%, 10%, or 20%. In the illustrated embodiments, the outer tubular extension  580  extends further in the axial direction than the inner tubular extension  582  when there is no lead or lead extension in the connector assembly, but it will be recognized that the outer and inner tubular extensions may have the same axial extent, or the inner tubular extension may extend further axially than the outer tubular extension in other embodiments. 
       FIG. 5C  is a cross-sectional view of the spacer  406 .  FIG. 5D  is a cross-sectional view of another embodiment of a spacer  406 ′ that has a smaller axial length than the spacer  406 . 
       FIG. 5E  illustrates yet another embodiment of a spacer  406 ″ with an outer tubular extension  580 , an inner tubular extension  582 , and a connection region  584  connecting the outer tubular extension  580  to the inner tubular extension  582 . In this embodiment, the connection region  584  couples an intermediation region of the outer tubular extension  580  to an intermediate region of the inner tubular extension  582 . The outer tubular extension  580  has two free ends  581   a ,  581   b  and the inner tubular extension  582  has two free ends  583   a ,  583   b  providing a cross-sectional shape similar to the letter “H”. The connection region  584  may couple the outer tubular extension  580  to the inner tubular extension  582  at the center of the respective tubular extension or anywhere along the respective longitudinal lengths of the tubular extensions and may be centered with respect to both the inner and outer tubular extensions or non-centered with respect to one or both of the inner and outer tubular extensions. Moreover, in other embodiments, the connection region  584  may be coupled to different portions of the outer and inner tubular extension, such as, for example, coupled to a center intermediate region of one of the tubular extensions and coupled to an intermediate region that is not centered for the other one of the tubular extensions. The connection region  584  in  FIG. 5E  is illustrated as extending in a straight radial direction, but, in other embodiments, the connection region may be slanted or curved (see, for example,  FIG. 5B ) with respect to the radial direction. 
     In yet other embodiments, the spacer may have a cross-sectional shape similar to the letter “h” with either 1) the outer tubular extension having a single free end (as illustrated in  FIG. 5A ) and the inner tubular extension having two free ends (as illustrated in  FIG. 5E ) or 2) the outer tubular extension having two free ends (as illustrated in  FIG. 5E ) and the inner tubular extension having a single free end (as illustrated in  FIG. 5A ). 
     Any of the embodiments described herein can include one or more radial protuberances  588  extending around a portion of (or the entire) perimeter of the outer surface of the outer tubular extension  580 , as illustrated in  FIG. 5E . The illustrated embodiment in  FIG. 5E  has two protuberances  588  that extend around the entire perimeter of the outer surface of the outer tubular extension, but it will be recognized that any other number of protuberances (e.g., one, three, four, or more) can be used and that the protuberances may only extend around a portion of the perimeter or may be separated into multiple segments (for example, two, three, four, or more segments) that each extend around only a portion of the perimeter. The protuberances  588  may facilitate forming a seal with the connector housing  402 . 
     Any of the embodiments described herein can include one or more radial protuberances  590  extending around a portion of (or the entire) perimeter of the inner surface of the inner tubular extension  590 , as illustrated in  FIG. 5E . The illustrated embodiment in  FIG. 5E  has two protuberances  590  that extend around the entire perimeter of the inner surface of the outer tubular extension, but it will be recognized that any other number of protuberances (e.g., one, three, four, or more) can be used and that the protuberances may only extend around a portion of the perimeter or may be separated into multiple segments (for example, two, three, four, or more segments) that each extend around only a portion of the perimeter. The protuberances  590  may facilitate forming a seal with the lead or lead extension inserted into the connector assembly  400 . 
     In any of the embodiments, the walls of the inner tubular extension or outer tubular extension may be tapered towards the ends. In any of the embodiments, the inner tubular extension may be shorter in width to be stiffer and further resist buckling. Optionally, radial walls or spokes may be added between the inner and outer tubular extensions to further resist buckling. 
       FIGS. 6A-6F  are cross-sectional views of a portion of a spacer  406 , lead  106 , and contact  404  during the insertion ( FIGS. 6A-6C ) and retraction ( FIGS. 6D-6F ) of the lead  106  into/out of a connector assembly. These  FIGS. 6A-6F  illustrate one embodiment of the alterations to the spacer  406  during the insertion/retraction processes. It will be recognized that other spacers of the invention made of different materials or having different forms may move, stretch, or otherwise deform differently. 
     In  FIG. 6A , the end of the lead  106  makes contact with the spacer  406 . As the lead  106  is pushed past the spacer  406 , the inner tubular extension  582  of the spacer may stretch or deform, as illustrated in  FIG. 6B . As the lead  106  is fully inserted into the connector assembly, the inner tubular extension  582  may be stretched substantially from its original shape, as illustrated in  FIG. 5C . In some embodiments, an adjacent connector contact  404  ( FIG. 4 ) or end stop  408  ( FIG. 4 ) may prevent or reduce further stretching of the inner tubular extension  582 . Preferably, the inner tubular extension  582  makes a seal (more preferably, a hermetic seal) with the lead  106 . 
     As the lead is retracted, the inner tubular extension  582  moves back toward the connector contact  404 , as illustrated in  FIGS. 6D and 6E , and may deform. In at least some embodiments, the connector contact  404  may prevent or hinder the inner tubular extension  582  from rolling backward and inverting. As the end of the lead  106  moves past spacer  406 , the inner tubular extension  582  may return to its original shape, as illustrated in  FIG. 6F , (although, in some embodiments, there may be residual deformation or stretching or other inelastic changes to the spacer shape). 
     In  FIGS. 4, 5A to 5D, and 6A to 6F , the inner tubular extension  582  extends away from the connection region  584  toward the proximal end of the connector assembly  400  where the optional end stop  408  may reside, as illustrated in  FIG. 4 . It will be recognized, however, that in other embodiments, the arrangement of the spacers  406  can be reversed so that the inner tubular extension  582  extends away from the connection region  584  toward the distal end of the connector assembly  400  where the port  414  resides. Such an arrangement may lower the insertion force of the lead (and increasing the seal-to-insertion force ratio) as compared to the arrangement of the spacers illustrated in  FIG. 4 . 
       FIG. 7  is a schematic overview of one embodiment of components of an electrical stimulation system  700  including an electronic subassembly  710  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  712 , an antenna  718 , a receiver  702 , and a processor  704 ) 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  712  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  718  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  712  is a rechargeable battery, the battery may be recharged using the optional antenna  718 , if desired. Power can be provided to the battery for recharging by inductively coupling the battery through the antenna to a recharging unit  716  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  704  is generally included to control the timing and electrical characteristics of the electrical stimulation system. For example, the processor  704  can, if desired, control one or more of the timing, frequency, strength, duration, and waveform of the pulses. In addition, the processor  704  can select which electrodes can be used to provide stimulation, if desired. In some embodiments, the processor  704  selects which electrode(s) are cathodes and which electrode(s) are anodes. In some embodiments, the processor  704  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  708  that, for example, allows modification of pulse characteristics. In the illustrated embodiment, the processor  704  is coupled to a receiver  702  which, in turn, is coupled to the optional antenna  718 . This allows the processor  704  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  718  is capable of receiving signals (e.g., RF signals) from an external telemetry unit  706  which is programmed by the programming unit  708 . The programming unit  708  can be external to, or part of, the telemetry unit  706 . The telemetry unit  706  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  706  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  708  can be any unit that can provide information to the telemetry unit  706  for transmission to the electrical stimulation system  700 . The programming unit  708  can be part of the telemetry unit  706  or can provide signals or information to the telemetry unit  706  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  706 . 
     The signals sent to the processor  704  via the antenna  718  and the receiver  702  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  700  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  718  or receiver  702  and the processor  704  operates as programmed. 
     Optionally, the electrical stimulation system  700  may include a transmitter (not shown) coupled to the processor  704  and the antenna  718  for transmitting signals back to the telemetry unit  706  or another unit capable of receiving the signals. For example, the electrical stimulation system  700  may transmit signals indicating whether the electrical stimulation system  700  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  704  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.