referring now to fig2 a , assembly kit 200 is shown according to one representative embodiment . assembly kit 200 comprises frame member 202 that comprises parallel arms . frame member 202 is preferably fabricated from a relatively high durometer , biocompatible , biostable polymer . examples of suitable polymers include polyetheretherketone ( peek ) and polyether - ketone ketone ( pekk ). frame member 202 comprises a set of apertures 204 on each arm of frame member 202 ( which are shown collectively as 204 a - 204 f ). apertures 204 can be formed by ablating through the polymer material using a suitable laser . although only six apertures are shown in fig2 a for the sake of clarity , any number of apertures can be provided in frame member 202 to accommodate suitable percutaneous leads 201 . apertures 204 cause the field from electrodes positioned underneath apertures 204 to be substantially unidirectional . the unidirectional characteristic is advantageous , because it reduces the probability of undesired stimulation in spinal cord stimulation applications . also , the unidirectional characteristic enables stimulation to occur at a reduced power consumption . assembly kit 200 further comprises spring member 203 that is attached to frame member 202 . spring member 203 may be permanently attached to frame member 202 during fabrication of these components or may be fabricated as a separate component for attachment by a surgeon . when assembled as shown in fig2 a , frame member 202 and spring member 203 can be collapsed to assume a relatively small profile to enable kit 200 to be inserted through a suitable implantation tool . an example of a surgical tool that can be utilized to implant kit 200 is described in u . s . patent application publication no . 20050288759 , entitled “ method and apparatus for implanting an electrical stimulation lead using a flexible introducer ,” which is incorporated herein by reference . when kit 200 exits the introducer instrument into the epidural space , spring member 203 is no longer subjected to a compressive force and expands the arms of frame member 202 to the predetermined distance . hence , electrodes of lead ( s ) 201 are then positioned within the epidural space in a manner that is similar to an electrode spacing provided by a paddle - style lead . one advantage of allowing the surgeon to attach spring member 203 during the implantation procedure is that multiple sets of spring members 203 could be provided with each set having different spring characteristics . the surgeon could select a spring member 203 having a greater spring constant if assembly kit 200 does not sufficiently expand in the epidural space using another spring member 203 due to fibrosis or other tissue obstructions . additionally , to prevent fibrosis or other tissue in - growth from occurring after implantation , thin membrane 205 is provided between the arms of frame member 202 . thin membrane 205 can be fabricated from a low durometer , elastic carbosil material as an example . by utilizing membrane 205 , kit 200 can be more readily explanted if subsequently necessary . spring member 203 is also preferably fabricated from peek material which possesses a spring memory characteristic . other suitable biocompatible , biostable polymers can be employed such as pekk . if spring member 203 is fabricated as a separate component from frame member 202 as shown in fig2 b , complementary connector structures ( not shown ) are provided on frame member 202 and spring member 203 to facilitate their coupling . in some alternative embodiments , metal spring elements are provided within spring member 203 to provide or augment the spring characteristic of spring member 203 . however , metal spring elements can cause undesired tissue heating during an mri procedure due to current induction from the strong time - varying rf fields generated by the mri system . accordingly , an all plastic structure is preferred to avoid current induction during an mri procedure . spring member 203 is also preferably shaped so that when the end of spring member 203 encounters the inner wall of an insertion tool , the contact force tends to “ pinch ” spring member 203 thereby providing a compressive force to spring member 203 . in response to the compressive force , spring member 203 collapses the arms of frame member 202 thereby allowing kit 200 to assume a profile that allows kit 200 to be advanced through the insertion tool . any suitable percutaneous lead ( s ) 201 can be employed within kit 200 provided that the electrode spacing of the lead ( s ) 201 corresponds to the spacing of apertures in frame 202 . in one embodiment , a respective percutaneous lead is inserted within each arm of frame member 202 . an example of a suitable commercially available lead for assembly kit 200 is the axxess ® lead available from advanced neuromodulation systems , inc . ( plano , tex .). to retain each percutaneous lead 201 within frame , retention clips 207 are provided . additionally , retention clips 207 facilitate the removal of frame member 202 from the epidural space when leads 201 are explanted . in one embodiment as shown in fig3 , a single lead is adapted to be threaded through both arms of frame member 202 of an assembly kit . specifically , first and second groups 301 and 302 of electrodes are disposed on the single lead . electrode groups 301 and 302 are disposed somewhat in the “ middle ” of the body of the lead . the intra - group electrode spacing in the lead corresponds to the spacing between adjacent apertures 204 in frame member 202 . also , the two groups of electrodes are separated on the body of the lead by distance 303 that corresponds to the distance between the two most distal apertures ( 204 c and 204 f in the specific embodiment of fig2 ) including the distance along spring member 203 . the lead as shown in fig3 also comprises respective groups of terminals 304 and 305 at the proximal and distal ends of the lead . each terminal of the groups 304 and 305 is electrically coupled to a respective electrode of groups 301 and 302 by a respective conductive wire embedded within the insulative body of the lead . the positioning of the groups 301 , 302 , 304 , and 305 of electrodes and terminals enables lead 201 to be looped through kit 200 . the looping of the lead through kit 200 is advantageous for explantation of frame member 202 and spring member 203 . also , to facilitate explantation , the proximal portion of frame member 202 is shaped at locations 206 a and 206 b to contact the inner wall of the insertion tool as shown in fig4 . in an explantation procedure , frame 202 , spring member 203 , and lead 201 are removed from the epidural space of a patient through the same type of surgical tool used for the implantation procedure . essentially , the surgeon places the tool over the proximal ends of the lead and advances the tool until the epidural space of the patient is accessed . in a preferred embodiment , a strengthening wire member is inserted within an inner lumen of the lead to facilitate the explantation . after insertion of the strengthening wire member and positioning of the open channel tool , the surgeon “ pulls ” on the lead and the strengthening wire member . the pulling force causes the lead , frame member 202 , and spring member 203 to move up to the distal end of the tool . when the proximal end of frame member 202 contacts the inner wall of the tool , the resulting force pushes against locations 206 a and 206 b and the force is transferred from the arms of frame member 202 to spring member 203 . the transferred force tends to elongate the frame and spring member 203 thereby compressing spring member 203 and bringing the arms of frame 202 together . accordingly , the profile of frame 202 is reduced thereby allowing the kit 200 to be received within the open channel of the tool for removal from the epidural space . in such a procedure , the benefit of looping the lead within the kit 200 is realized . specifically , the looping of the lead enables the strengthening wire member to follow the entire perimeter of frame member 202 and spring member 203 . accordingly , a sufficient amount of force can be readily applied to ensure that spring member 203 is compressed to allow the withdrawal of the kit 200 through the surgical tool . additionally , it shall be appreciated that explantation procedures according to representative embodiments involve relatively little complexity and do not require overly delicate manipulations . fig5 depicts stimulation system 500 according to one representative embodiment . system 500 comprises implantable pulse generator 501 . an example of a commercially available pulse generator that can be used according to some representative embodiments is the eon ® stimulator available from advanced neuromodulation systems , inc . pulse generator 501 is electrically coupled to lead 201 which is threaded through assembly kit 200 . lead 201 can be implanted in a patient without performing a laminectomy using a suitable implantation tool . after implantation in the epidural space of a patient , the positioning of the electrodes as provided by kit 201 allows lead 201 to function in a manner similar to paddle - style leads . although representative embodiments and advantages have been described in detail , it should be understood that various changes , substitutions and alterations can be made herein without departing from the spirit and scope of the appended claims . moreover , the scope of the present application is not intended to be limited to the particular embodiments of the process , machine , manufacture , composition of matter , means , methods and steps described in the specification . as one of ordinary skill in the art will readily appreciate from the disclosure that processes , machines , manufacture , compositions of matter , means , methods , or steps , presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized . accordingly , the appended claims are intended to include within their scope such processes , machines , manufacture , compositions of matter , means , methods , or steps .
in one embodiment , an assembly for conducting pulses from an implantable pulse generator , comprises : at least one percutaneous lead comprising terminals and at least two groups of electrodes , each group of electrodes possessing an intra - group electrode spacing ; a frame member comprising first and second arms , the frame member comprising an inner lumen for removably housing the at least one percutaneous lead , each arm of the first and second arms comprising a plurality of apertures that are spaced according to the intra - group electrode spacing to allow conduction of electrical pulses from the electrodes of the at least one percutaneous lead to tissue of the patient when the lead is positioned within the frame member ; and a spring member that is connected to the frame member for maintaining the first and second arms of the frame member at a predetermined distance in the absence of an external force on the spring member .