Abstract:
An implantable lead is provided with at least one extendable member to position therapy delivery elements, which may be electrodes or drug delivery ports, after the lead has been inserted into the body. The lead may formed as a resilient element which is contained in a retainer tube that may be removed to permit the lead to deploy. Alternatively, a non-resilient lead may be provided with a slotted retainer tube. A series of mechanical linkages for expanding and retracting the lead within the human body may be actuated with various mechanisms. A control system may be provided for closed-loop feedback control of the position of the extendable members. The invention also includes a method for expanding an implantable lead in situ.

Description:
RELATED APPLICATIONS 
     This is a divisional of U.S. patent application Ser. No. 10/767,244, filed Jan. 27, 2004, pending, which was a continuation of U.S. patent application Ser. No. 10/158,521, filed May 30, 2002, which is a divisional application of U.S. patent application Ser. No. 09/862,104 filed May 21, 2001, now U.S. Pat. No. 6,442,435 which is a continuation of U.S. patent application Ser. No. 09/584,572 filed May 31, 2000, now U.S. Pat. No. 6,292,702, which is a divisional of U.S. patent application Ser. No. 09/070,136 filed Apr. 30, 1998, now U.S. Pat. No. 6,161,047 for which priority is claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to implantable leads for delivering therapy, in the form of electrical stimulation or drugs, to the human body. Specifically, this invention relates to implantable leads that may be expanded, retracted or adjusted after implantation in the human body. This invention also relates to mechanisms for accomplishing such expansion, retraction or adjustment of such leads in situ. Further, this invention relates to control systems for controlling such expansion, retraction or adjustment of such an implanted lead. 
     Recent efforts in the medical field have focused on the delivery of therapy in the form of electrical stimulation or drugs to precise locations within the human body. Therapy originates from an implanted source device, which may be an electrical pulse generator, in the case of electrical therapy, or a drug pump, in the case of drug therapy. Therapy is applied through one or more implanted leads that communicate with the source device and include one or more therapy delivery sites for delivering therapy to precise locations within the body. In drug therapy systems, delivery sites take the form of one or more catheters. In electrical therapy systems, they take the form of one or more electrodes wired to the source device. In Spinal Cord Simulation (SCS) techniques, for example, electrical stimulation is provided to precise locations near the human spinal cord through a lead that is usually deployed in the epidural space of the spinal cord. Such techniques have proven effective in treating or managing disease and acute and chronic pain conditions. 
     Percutaneous leads are small diameter leads that may be inserted into the human body usually by passing through a Tuohy (non-coring) needle which includes a central lumen through which the lead is guided. Percutaneous leads are advantageous because they may be inserted into the body with a minimum of trauma to surrounding tissue. On the other hand the types of lead structure, including the electrodes or drug-delivery catheters, that may be incorporated into percutaneous leads is limited because the lead diameter or cross-section must be small enough to permit the lead to pass through the Tuohy needle. 
     Recently, the use of “paddle” leads, like Model 3586 Resume® Lead or Model 3982 SyrnMix® Lead of Medtronic, Inc., which offer improved therapy control over percutaneous leads, have become popular among clinicians. Paddle leads include a generally two dimensional set of electrodes on one side for providing electrical therapy to excitable tissue of the body. Through selective programmed polarity (i.e., negative cathode, positive anode or off) of particular electrodes, electric current can be “steered” toward or away from particular to tissue within the spinal cord or other body areas. Such techniques are described by Holsheimer and Struijk, Stereotact Funct Neurosurg, vol. 56, 199: pp 234-249; Holsheimer and Wesselink, Neurosurgery, vol. 41, 1997: pp 654-660; and Holsheimer, Neurosurgery, vol. 40, 1997: pp 990-999, the subject matter of which is incorporated herein by reference. This feature permits adjustment of the recruitment areas after the lead has been positioned in  15  the body and therefore provides a level of adjustment for non-perfect lead placement. Such techniques are disclosed in U.S. Pat. Nos. 5,643,330, 5,058,584 and 5,417,719, the subject matter of which is incorporated herein by reference. Additionally, the value of a transverse tripole group of electrodes has been demonstrated for spinal cord stimulation, as described by Struijk and Holsheimer, Med &amp; Biol Engng &amp; Comput, July, 1996: pp 273-276; Holsheimer, 20 Neurosurgery, vol. 40, 1997: pp 990-999; Holsheimer et al., Neurosurgery, vol. 20, 1998. This approach allows shielding of lateral nervous tissue with anodes, like the dorsal roots and steering of fields in the middle under a central cathode by use of two simultaneous electrical pulses of different amplitudes. 
     One disadvantage recognized in known paddle leads is that their installation, repositioning and removal necessitates laminectomies, which are major back surgeries involving removal of part of the vertebral bone. Laminectomies are required because paddle leads have a relatively large transverse extent compared to percutaneous leads. Thus, implantation, repositioning and removal require a rather large passage through the vertebral bone. 
     Another disadvantage with paddle leads is that optimal positioning is often difficult during implant. For example, the transverse tripole leads described above work optimally if the central cathode is positioned coincident with the physiological midline of the spinal cord. Such placement is difficult since the doctor cannot see the spinal cord thru the dura during implant. Moreover, lead shifting may occur subsequent to implant, thereby affecting the efficacy of the therapy delivered from the lead. 
     Yet another disadvantage recognized with paddle leads is that the lead position may change merely with patient movement. For example, when a patient lies down, the spacing between an epidural lead and the spinal cord decreases to a large extent, so that it is often is necessary to lower the amplitude of the stimulation by half. It is reasonable to assume that steering effects of a tripole lead might also be affected if the CSF width changes dramatically, or if due to patient twisting or activity, the orientation between the lead and spinal cord changes. 
     While the prior art has attempted to provide deformable leads, which may provide improved insertion characteristics or enhanced stability once inside the body, they have not succeeded in providing a device which remedies the aforementioned problems. For example, U.S. Pat. No. 4,285,347 to Hess discloses an implantable electrode lead having a distal end portion with a laterally extending stabilizer, preferably in the form of curved loops. Similarly, and U.S. Pat. No. 4,519,403 to Dickhudt discloses an inflatable lead for enhanced contact of the electrode with the dura of the spinal cord. U.S. Pat. No. 5,121,754 to Mullett discloses a device to allow electrodes to move to more lateral positions after insertion, when a stiffening guidewire used during insertion is removed. In Mullett&#39;s device, only one electrode can be found at any particular longitudinal location, since only gentle curves of the lead were designed, and the curves are not adjustable after implant of the lead. Similar problems apply to the device disclosed by O&#39;Neill in U.S. Pat. No. 4,154,247. 
     Patent Cooperation Treaty (PCT) Publication No. WO 93/04734 to Galley discloses a lead tip that has four spans that will bulge into four different directions when a confining outer catheter is drawn proximally back over the lead body. The publication describes one electrode on the middle of each span. In situ in the epidural space, these four electrodes will form a square or rectangular cross-sectional shape. Two of them might be pressed into the dura (at lateral positions) and the other two would be dorsal, against the vertebral bone. Only the electrodes nearest the spinal cord would be useful for programming. While this could give two electrodes at the same longitudinal position, their medial to lateral locations are difficult to control, and their ability to spread apart depends on the relative stresses in the spans and tissue-like adhesions that may be present. Other malecot-type lead tips have been proposed for positioning of electrodes in the heart (U.S. Pat. No. 4,699,147, Chilson and Smith, 1985; U.S. Pat. No. 5,010,894, Edhag, 1989) or anchoring of lead bodies (U.S. Pat. No. 4,419,819, Dickhudt and Paulson, 1982; U.S. Pat. No. 5,344,439, Otten, 1992) or positioning of ablation electrodes (Desai, U.S. Pat. Nos. 5,215,103, 5,397,339 and 5,365,926). While the aforementioned prior art devices provide various configurations for compact insertion or lead stabilization after implant, they do not offer the advantages and improved efficacy recognized with respect to paddle lead configurations. 
     It would therefore be desirable to provide a lead structure for stimulation of excitable tissue surfaces which combines the advantages offered by percutaneous leads with respect to minimized trauma during insertion, repositioning and removal with the advantages offered by paddle-type leads with respect to improved efficacy, ability to provide electrodes in places lateral to the axis of the lead and tailoring of treatment. 
     It would also be desirable to provide a lead structure which permits adjustment of the lead dimensions and therefore the delivery site location in situ for enhanced control of the therapy being applied to the excitable body tissues. 
     It would be further desirable to provide a paddle lead which is capable of automatically adjusting its width or delivery site spacing automatically in response to patient factors such as body position or activity or in response to a parameter such as muscle contraction or action to potentials, which may be characteristic of the stimulation or therapy being applied. 
     SUMMARY OF THE INVENTION 
     The invention combines the advantages of percutaneous leads with those of paddle leads. In a preferred embodiment, the invention provides a lead structure including a central core portion and at least one flexible, semi-flexible or semi-rigid transversely extending span which may be positioned in a compact position during insertion in which it is wound around or otherwise disposed in close proximity to the central core portion. Each span may also be deployed or shifted to a position in which it extends outward from the central core portion in a transverse direction. Each span has disposed on one surface a number of therapy delivery elements, in the form of electrodes or catheter ports, for delivering therapy in the respective form of electrical or drug therapy to the body. In the compact insertion position, the lead may be easily inserted within a catheter or Tuohy needle. Once the lead has been positioned at the appropriate place in the body, the span or spans may be deployed from the compact position to the extended position in which the therapy delivery elements are positioned in a fashion similar to a paddle lead. The flexibility of the spans also permits the lead to be retracted back to the compact position in the event that the lead must be removed from the body. 
     In a preferred embodiment, the invention provides a lead which includes a central core portion and at least one flexible paddle extending therefrom and which may be coiled around the core portion when the lead is to be compacted for insertion. As the lead is inserted through a catheter or Tuohy needle, the spans are kept in the compact position by lead rotation in a direction opposite their direction of winding around the central core. Also according to the invention, the spans are deployed by rotating the central core portion in the same direction in which the spans are coiled around the central core portion. Because of the flexibility of the spans, they are caused to move outward, away from the central core as the lead is uncoiled. In another embodiment of the invention, the spans can be formed of a resilient material in which resilient forces develop when the lead is configured in its compact position. The lead is maintained in its compacted form while inside of the insertion tool, i.e. Tuohy needle. The resilient forces cause the spans to extend outward once the lead exits the end of the insertion tool. 
     An outer concentric retainer tube may be provided in combination with the lead, the outer retainer tube acting to retain the lead in its compact position during insertion. The retainer tube may be provided with a pair of notches on its distal end to aid in the retraction of the lead after deployment. Specifically, the notches are disposed on the distal end of the retainer tube in such a manner that the spans will engage the notches when the central core portion is rotated and pulled toward a proximal end of the retainer tube. The notches retain the spans in position as the central core rotates, thus causing the spans to coil around the central core portion and assume a compact position. 
     The present invention also provides a lead which may be compacted in a different manner than described above. The lead is comprised of a series of therapy delivery elements which are attached to a thin backing sheet which permits the sheets to be disposed one on top of the other in the compact insertion position and then to expand to a generally planar orientation once the lead is inserted to the appropriate position in the body. 
     The following are exemplary advantages of adjustable leads constructed according to the preferred embodiments of the invention: 
     1. The spacing of the sites can be matched to important dimensions of the tissue affected, e.g., the width of the Cerebro-Spinal Fluid (CSF) between the dura and the spinal cord. 
     2. As the dimensions of the lead tip are changed, the locations of the sites relative to the tissue affected may be advantageously altered. For example, as a paddle&#39;s width is increased the paddle will move toward the spinal cord in the semicircular dorsal part of the epidural space. 
     3. In cases where the bones or fluid compartments have large widths (e.g., CSF depth at spinal level T7 or T8) or are too wide in a particular patient, the paddle width can be increased appropriately to ensure effective therapy. 
     4. Changes in paddle width and the accompanying medial and lateral movement of the sites can have a beneficial effect on the therapy. For example, the ability to stimulate only the medial dorsal columns versus the more lateral dorsal roots may provide enhanced therapeutic results. 
     5. As the patient ages, their pathological condition changes, their degree of fibrosis or scar tissue changes, or the effects of the therapy change, adjustments of the paddle dimension(s) might restore or maintain the benefit. 
     6. If the paddle&#39;s dimension(s) can be changed after implant, it may be possible to optimize the benefits and minimize undesirable side effects. 
     7. By changing the paddle&#39;s dimension(s), it may be possible to avoid surgery to replace or reposition the lead. 
     8. By changing the paddle&#39;s dimension(s), it may be possible to position the sites optimally relative to important physiological locations, e.g., the physiological midline of nervous tissue, or receptors responsive to the drugs being delivered. 
     9. It may be possible to minimize the use of energy by optimizing efficiency of therapy delivery through adjustment of paddle width. 
     10. There may be minimal insertion trauma and operating room time and resources needed if it is possible to place a lead with percutaneous techniques, and then expand it in situ. 
     11. Repositioning of a paddle lead can be done without laminectomy. Removal is also made quicker and less traumatic. 
     12. With closed loop feedback control of the paddle&#39;s dimension(s), optimal therapy can be maintained with less interference with the patient&#39;s lifestyle. 
     Another preferred embodiment allows automatic changes in at least one dimension of a paddle lead. Such a system would measure an effect of the stimulation, e.g., a compound action potential caused by stimulation/drugs, a muscle contraction, the direction of gravity, increased activity of the patient, relative motion of vertebral bones, or other effects. Measurement techniques for compound action potentials are disclosed in U.S. Pat. No. 5,702,429 the subject matter of which is incorporated herein by reference. Such a recorded signal should be altered if the lead paddle dimension that is controlled is changed. Then, after filtering, amplifying, integrating and comparing the recorded signal to a previous stored signal, the parts of the lead that control the dimension in question will be moved or activated, causing a change In said dimension, which will restore the effect measured to its original value. This constitutes closed loop feedback control, and can enable to patient to be less affected by changes in the therapy caused by his/her position, activity, etc. Of course there should be governors on the dimensional changes allowed, so that if the measured parameter is very greatly changed, neither the device nor the patient will undergo damage or trauma. The described embodiments show preferred techniques to expand a lead in directions transverse to the main axis of the lead body. The invention also contemplates devices for expanding the lead in a direction substantially parallel to the lead axis. 
     Other advantages novel features, and the further scope of applicability of the present invention will be set forth in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings which are incorporated into and form a part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating a preferred embodiment of the invention and are not to be construed as limiting the invention. In the drawings, in which like numbers refer to like parts throughout: 
         FIG. 1  is a plan view of a lead according to the present invention being inserted through a Tuohy needle near the dura of a human spine; 
         FIGS. 2A-2D  are isometric views of a lead according to the present invention in a compact insertion position: 
         FIG. 2E  is an isometric view of the lead of  FIG. 2A  in an expanded or deployed position; 
         FIG. 3  is an isometric view of a lead according to another embodiment of the invention; 
         FIG. 4A  is an isometric view of a lead and retainer tube according to yet another embodiment of the invention; 
         FIG. 4B  is an isometric view of a lead retainer tube according to the present invention; 
         FIG. 4C  is an isometric view of a lead and retainer tube according to the present invention; 
         FIG. 5A  is an isometric view of a lead and expansion mechanism according to another embodiment of the present invention; 
         FIG. 5B  is a top view of the lead of  FIG. 5A  in a compact position; 
         FIG. 6A  is a cross section of a lead according to another embodiment of the invention; 
         FIG. 6B  is a front view of an expansion mechanism according to a preferred embodiment of the present invention; 
         FIG. 7  is a front view of an expansion mechanism according to another preferred to embodiment of the present invention; 
         FIGS. 8A and 8B  are front views of an expandable lead according to another preferred embodiment of the invention; 
         FIG. 8C  is a front view of the expandable lead of  FIGS. 8A and 8B  with an alternative embodiment for the actuating mechanism; 
         FIGS. 9A and 9B  are side and front views, respectively, of another preferred embodiment of the present invention; 
         FIGS. 10A and 10B  are front views of another preferred embodiment of the present invention; 
         FIGS. 11A and 11B  depict yet another preferred embodiment of the present invention; 
         FIG. 12A  is a front view of an adjustment mechanism according to a preferred embodiment of the invention; 
         FIG. 12B  is a front view of an adjustment mechanism according to another preferred embodiment of the invention; 
         FIG. 12C  is a front view of an adjustment mechanism according to yet another preferred embodiment of the invention; and 
         FIG. 12D  is a front view of an adjustment mechanism according to still another preferred embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a lead according to a preferred embodiment of the invention being utilized in an SCS implementation. In accordance with known techniques, a Tuohy needle  14  is positioned near the dura  12  of spine  10 . Lead body  20  is inserted through the lumen of s Tuohy needle  14  and positioned near the dura  12 . A proximal end (not shown) of lead body  20  is connected to a source device (not shown) which may be a pulse generator, in the case of electrical stimulation, or a drug pump in the case of drug therapy. Although the invention will be described herein with reference to SCS procedures and the embodiments described in relation to electrical therapy, it will be recognized that the invention finds utility in applications to other than SCS procedures, including other applications such as Peripheral Nervous System (PNS) Stimulation, Sacral Root Stimulation, Cortical Surface Stimulation or Intravecular Cerebral Stimulation. In addition, the invention finds applicability to SCS procedures where the lead is placed in the intrathecal (subdural) space. The invention also finds utility to drug therapy where electrical components are replaced with conduits and catheters for conducting is drug material to the therapy site. In this case, especially, the lead may be placed in the intrathecal space. 
       FIGS. 2A  thru  2 D illustrate a lead according to a preferred embodiment of the present invention. Lead  20  is provided with a distal tip  30  that may be compacted for insertion  20  and unfolded after it has been positioned appropriately within the body. Distal tip  30  includes a central portion  32  which has at least one span  34  depending therefrom. Span  34  is comprised of a flexible, insulative material, such as polyurethane or silicone rubber. The term “flexible” as used herein refers to both resilient and non-resilient materials. Central portion  32  may have a generally semi-circular cross-section as shown, or may be flat. A central passage  33  may run axially along the inside of lead  20 . A centering stylet  25  is provided through central passage  33  and extends in a distal direction through central portion  32  for engaging a part of the body, such as adhesions in the epidural space, to stabilize lead tip  30  as it is deployed. Affixed to a surface of spans  34  and to the central portion  32  is a series of other therapy delivery elements in the form of electrodes  36 A-E. In accordance with the invention, lead  20  may be configured into a compact insertion position shown in  FIG. 2A . As shown in  FIG. 2B , spans  34  are coiled around central portion  32  such that the lateral extent of lead tip  30  is no larger than the lumen of Tuohy needle  14 . 
     Once in position within the epidural space, lead tip  30  may be deployed out of the Tuohy needle  14 , as shown in  FIG. 2C .  FIG. 2D  shows the view from the side opposite the side illustrated in  FIG. 2C . In the embodiment described in which the spans are flaccid or to semirigid, deployment of lead tip  30  may be implemented by rotating the lead body  20  in a counterclockwise direction once lead tip  30  is beyond the end of the Tuohy needle in a desired position. As spans  34  encounter dura or dorsal bone of spinal canal, they can uncoil to assume a generally planar shape in which electrodes  36 A-E are disposed on one side of the lead facing the dura, as shown in  FIG. 2E . As shown in phantom in  FIG. 2D , electrodes  36 A-E communicate electrically with the source device (not shown) via conductor paths  39  and  41 . Conductor paths  39  and  41  may be comprised of a flexible electrical conductor or thin wires which are embedded or molded within lead  20 . 
     In the case of drug therapy, the electrodes  36 A-E illustrated in  FIGS. 2C-E  would be replaced by ports which act as therapy delivery elements to convey drug to the body. Similarly, conductor paths  39  and  41  would be replaced by conduits formed in the interior of lead  20  for conveying drug from the source device. Stylet  25  may be left permanently in the epidural space or may be withdrawn from the lead  20  after the lead tip  30  is uncoiled. In the case of a drug delivery device, stylet  25  might remain as a catheter at some preferred distance. 
       FIG. 3  illustrates another embodiment of the invention in which lead  20  is provided with a pair of guide pins  40  which are affixed to a more proximal removable sheath  41  that surrounds lead body  20 . Alternatively, guide pins may be formed integrally on Tuohy needle (not shown). Guide pins  40  act to guide spans  34  outward as the lead body  20  is rotated in a counterclockwise and to guide spans  34  to coil around central portion as lead body  20  is rotated in a clockwise direction. Guide pins  40  may be comprised of a rigid, material and may be extended or retracted from sheath  41  or Tuohy needle  14 . After spans  34  are deployed, sheath  41  may be removed. 
       FIG. 4A  illustrates another embodiment of the invention in which spans  34  are formed as resilient or elastic elements. The term “resilient” as used herein refers a tendency to return to an undeformed state once spans  34  are no longer compressed to lay beside central part  32 . In accordance with this embodiment of the invention, a retainer tube  50  is provided to retain lead tip  30  in its compacted position until deployment is desired. Retainer tube  50  includes an inner passage which is sufficient to accommodate the diameter or lateral extent of lead body  20  and its compact shape-changing tip  30 . The outer diameter of retainer tube  50  is small enough that retainer tube  50  may also be inserted through the lumen of Tuohy needle  14  ( FIG. 1 ). Alternatively, tube  50  may replace the Tuohy needle. Spans  34  are formed in such a manner that they have a tendency to undertake a position in which they are extended from central portion  32 . Thus, in the compact insertion position illustrated in  FIG. 4A , resilient forces are present in spans  34  to urge them outward into their extended, uncoiled position. The resiliency of spans  34  may derive from the polymeric material used to construct spans  34  or from resilient elements like wires (not shown) which are incorporated into the interior or onto the exterior surface of spans  34 . Referring to  FIGS. 4B and 4C , in accordance with yet another preferred embodiment of the invention, a notch  60  is provided in a distal end  52  of retainer tube  50  to facilitate retraction of a deployed lead. Preferably, one notch is provided for each span  34  provided on lead tip  30 . In operation, retainer tube  50  is inserted around a proximal end (not shown) of lead body  20  and pushed towards lead tip  30  a sufficient distance until retainer tube  50  encounters lead tip  30 . 
     Lead body  20  is then pulled in a proximal direction and simultaneously rotated, in a direction which may be clockwise or counterclockwise, until lower edges  37  of spans  34  slide into notches  60 . Under continued rotation of lead tip  30  and lead, notches  60  function to guide spans  34  into their coiled, compacted position. Once compacted, lead  20  may be retracted further into retainer tube  50 . Compacted lead  20  and retainer tube  50  may then be repositioned to a higher or lower point along the spinal cord or may be removed from the body. 
       FIGS. 5A and 5B  illustrate an expandable lead tip  130  according to another embodiment of the invention. Referring to  FIG. 5B , lead tip  130  is comprised of a series of electrodes  136 A-E which are fastened to a flexible insulative backing sheet or span  140 . The central portion of lead tip  130  is comprised of middle electrode  136 C. Span  140  may be constructed of polyurethane or DACRON-reinforced silicone rubber. Electrodes  136 A-E are in electrical communication with source device (not shown) via a series of conductors  139  incorporated into or onto span  140 . Electrodes  136 A-E are embedded in span  140  or fastened by adhesive or other known means. Ends  142  of span  140  are provided with eyelets  144  for fastening to an expanding mechanism which will be described below. This aspect of the invention provides a lead tip  130  which may assume a compacted position, in which electrodes  136 A-E are stacked one on top of the other such that the thickness of lead tip  130  may be reduced to a dimension that is slightly larger than the collective thicknesses of electrodes  136 A-E. 
     Referring to  FIG. 5A , lead tip  130  may be expanded with the use of an expansion mechanism  150  according to one aspect of the invention. Expansion mechanism  150  comprises a series of struts  152  which are pivotally linked to one another such that points A and B may be caused to move towards and away from one another in order to compact or expand lead tip  130 , respectively. A first linkage  156  is pivotally connected to struts  152 A and  152 B. A second link  158  is pivotally connected to links  152 C and  152 D. First and second links  156  and  158  extend to a proximal end of lead body  20  where they can be individually actuated by a clinician. By moving first link  156  with respect to second link  158 , points A and B are caused to move toward or away from one another, thereby contracting or expanding lead tip  130 . By using rigid struts and linkages, sufficient forces can be applied so that a space may be created for the expanded size of lead tip  130 . Introductory Sheath  170  may be removed after lead tip  30  is expanded. Or, as another embodiment, it might remain in the position shown, and a locking mechanism to keep links  156  &amp;  158  at a constant position might be able to compress sheath  170  over the two links. A tether  188  sets a limit on the separation of points A and B, and guarantees that electrodes are evenly spaced when the length of tether  188  equals the length of span  140 . 
       FIGS. 6A and 6B  illustrate another embodiment of the invention.  FIG. 6A  is a cross-section of a lead tip  230  according to a preferred embodiment of the invention which comprises a single span  234  incorporating a series of conductors  236 A-F therein.  FIG. 6B  illustrates a plan view of a mechanism  250  suitable for deploying lead tip  230  or a stack of electrodes as shown in  FIG. 5B . Mechanism  250  comprises a pair of links  252 A and  252 B pivotally connected to one another and each pivotally connected to a respective actuator link  258 A and  258 B. Through relative movement of actuator links  258 A and  258 B, point A is caused to move toward or away from link  258 A, thereby causing contraction or expansion of lead tip  230  or  130 . One eyelet  144  on span  234  is attached to point A, and the other eyelet may slide on link  258 A. With this embodiment, since the lead tip is pulled in one direction, mechanism  250  in its initial, collapsed position should be positioned toward one side, for example, over the dorsal roots on one side of the spinal cord. In the expanded position, point A would advance to the opposite dorsal roots. Once again, a way to lock point A at a certain expanded position is to have an anchor along sheath  170  that compresses and holds sheath  170  against links  258 A and  258 B. Like mechanism  150 , by using rigid struts and linkages, a space can be created for lead tip  230 . 
       FIG. 7  illustrates an expansion mechanism according to another preferred embodiment of the invention. Lead tip  130  may be expanded with the use of mechanism  350 , comprised of struts  311 ,  310 ,  321 , and  320 . Linkage  330  is pivotally connected to the end of struts  320 ,  321 . Linkage  340  is pivotally connected to one end of struts  320 ,  321 , which in turn have their respective other ends pivotally connected to the center of struts  320 ,  321 . In the embodiment illustrated, strut  320  connects struts  310  and  340  as illustrated and strut  321  connects struts  311  and  321  as illustrated. As linkages  330  and  340  are moved relative to each other by a clinician, tips  360  will move together or apart. Eyelets  144  of lead tip  130  ( FIG. 5B ) can be connected to tips  360 . moved relative to each other by a clinician, tips  360  will move together or apart. Eyelets  144  of lead tip  130  ( FIG. 513 ) can be connected to tips  360 . 
       FIGS. 8A and 8B  illustrate an expandable lead according to another preferred embodiment of the present invention. The lead comprises a flexible outer coaxial accessory tube  802  which is mounted over the distal end of lead body  801 . A stop  806  is affixed to the distal end of lead body  801  to prevent movement of the upper end  830  of accessory tube  802  relative to lead body  801 . The lower end  832  of accessory tube  802  is adapted to slide with respect to lead body  801 . Accessory tube  802  includes a central slot  805  forming two flexible leaf portions  820  and  822 . A recess  824  is provided in each leaf portion  820  to form a bending joint therein. The lower end  832  may be moved upward, thereby causing leaf portions  820  to bend and deploy outward from the lead body  801 . To actuate the mechanism an actuator  807  is slid over the axial tube  801  by the clinician. While holding onto the axial tube  801 , the clinician pushes the actuator  807  against the accessory tube which causes the slot  805  to separate and the lead to open as illustrated in  FIG. 8B . A series of ratchet rings  811 .  812  and  813  are formed in lead body  801  to prevent downward movement of lower end  832  of accessory tube  802  to thereby retain the leaf portions  820  in their outward, deployed position. These ratchet rings will also allow and hold different amounts of lateral expansion to be chosen by the clinician. A rigid barrel electrode  803  is mounted on each leaf portion  820  of the accessory tube  802 . In the expanded position of accessory tube  802 , central electrodes  808 ,  809  and  810  are exposed. Central electrodes  808 ,  809  and  810  and barrel electrodes  803  communicate electrically with the source device (not shown) through electrical conductors (not shown) within the lead body. 
       FIG. 8C  illustrates an expandable lead according to another preferred embodiment of the present invention. This embodiment is the same as that illustrated in  FIGS. 8A and 8B  except that a screw actuator is provided for precise adjustment of the outward deployment of leaf portions  820 . The axial lead body  801  has a threaded portion  811  formed therein. A threaded drive nut  812  is mounted on the threaded portion of the lead body  811 . The drive nut has multiple indented holes  812   a  to receive an actuation driver similar to  813 . The drive nut is interlocked by pins ( 813   a ) on an actuation driver  813  and rotated by the driver. This screw apparatus allows finer adjustment of the expansion and also adjustment of the expansion after implantation of the lead device. 
       FIGS. 9A and 9B  illustrate another embodiment of the invention. Mechanism  450  can have a central element  410  that may contain an electrode or catheter port  405 . It may house progressively smaller mobile telescoping parts  420 ,  430 ,  440  that can be pushed outward toward one or more directions. Each mobile part is provided with a shoulder  422  to limit its outward movement and to recruit an adjacent mobile part. A tab  424  is provided to limit inward movements. For an expansion in one plane, element  410  may have inside it one or more mechanisms  150  ( FIG. 5A ),  250  ( FIG. 6B ) or  350  ( FIG. 7 ). Alternatively there might be single, curved linkage passing along lead  20  and attached to the final electrode or catheter port site  445 . As this linkage is moved by a clinician, site  445  will move outward or inward, and intermediated sites will follow if the movement of each site relative to the next site is limited. 
       FIGS. 10A and 10B  illustrate another embodiment of the invention. In  FIG. 10A , the lead  20  is in a compacted position, with elastic and resilient transverse spans  500  bent to remain inside the lumen of Tuohy needle  14 . Spans  500  are adapted to bend to a position substantially parallel to the axis of lead  20  in the compact position. Once the lead is pushed beyond the needle, spans  500  will move by their resiliency to their natural position, as shown in  FIG. 10B . Those of ordinary skill will note that the grouping of central electrode or catheter port  510  and the two nearest side electrodes or ports  520  form a tripole/triport arrangement transverse to the longitudinal direction of the lead  20 . The clinician may have to place and manipulate a mechanism like  150 ,  250  or  350  prior to placement of this lead to create a space. Alternatively, a metal material like NITINOL may be placed inside span  500  and treated so that its position after removal of the confinement of needle  14  will be perpendicular to the lead axis. 
       FIGS. 11A and 11B  illustrate another embodiment of the invention. In  FIG. 11A , the lead  20  is in a compacted position with elastic and resilient spans  600  bent to remain inside the lumen of Tuohy needle  14 . There is a central electrode or catheter port  610 . The lateral electrodes/ports  620  are on members that will remain parallel to the lead axis due to pivot points  630  and equal length spans  600  above and below. 
     In  FIG. 11B , the lead tip is beyond the introducing needle. The spans  600  resume their normal, unstressed positions perpendicular to the lead body axis. Lateral electrodes/ports  620  are on either side of central electrode/port  610 . Removal may be accomplished by pulling on the lead body with sufficient force to bend the spans  600  back along the lead body, or by pushing another catheter or needle over lead  20  It is recommended that there be a thin, inert and flexible film (not shown) over the space between spans to help removal by preventing tissue in growth. One embodiment of the invention is to lock linkages as shown in  FIGS. 5-7  into a fixed orientation by using a compressive sleeve to squeeze the lead body  20  inward against the linkages. This sleeve may be an anchor to superficial (subcutaneous) tissue. To make a change, minor surgery can be done to cut down to this anchor, loosen or remove it, adjust the positions of the linkages, replace the anchor/compressive sleeve, and resutured the wound. Obviously, the clinician and patient need to believe that the benefits of such a procedure out weigh the discomfort and risks. 
       FIGS. 12A through 12D  illustrate mechanisms that may be used to operate the linkages illustrated and described with respect to  FIGS. 5A ,  6 B,  7  and  9  in accordance with preferred embodiments of the invention.  FIG. 12A  illustrates an embodiment of the invention that allows chronic adjustment of the relative positions of two actuating members  710  and  720 . A rigid needle  775  with a sharp hexagonal tip  785  is passed through the skin and engages a hexagonal receptacle (possibly via reduction gears)  790  that is capable of turning a circular component  760  inside of a container  750  beneath the patient skin. On end of this container  750  attaches to the lead body  20 , which contains the two actuating members  710  and  720  and wires/catheters  730  that go to the distal tip of the lead  20 . Another end of the container  750  connects to a lead  721  that conveys the wires/catheters  730  to a source device (not shown). Actuating members  710  and  720  are connected to the rotating component  760  are connected to the rotating component  760  by pivot points  770  and  780 . As the needle  775  is rotated, the linkages  710  and  720  will move relative to each other. This device  750  should be large enough to be palpated under the skin, and the rotating component  760  should be large enough so that limited rotation of approximately 60° causes sufficient movement of the linkages. 
       FIG. 12B  illustrates another preferred embodiment of a linkage actuating mechanism according to a preferred embodiment of the invention. This embodiment allows chronic adjustment of the position of one linkage  810  relative to the lead body  20  using a rack gear and pinion gear arrangement. This embodiment may be used with a two-actuating member configuration as described with respect to  FIG. 12A , where one actuating member is fixed with respect to lead body  20 . As in the embodiment described above with respect to  FIG. 12A , a rigid needle (not shown) with a hex-head sharp tip is passed through the patient&#39;s skin and engages a hexagonal receptacle  865  that drives an internal gear  860  of subcutaneous container  850 . As gear  860  turns possibly with the aid of reducing gears, it will, move the actuating member  810  back or forth, which has gear teeth  840  formed on its proximal end. A stop  870  prevents excessive movement of actuating member  810 . A wire/catheter group  830  passes from lead  20  through the container to another lead  821  from the source device. Alternatively, the source device could be on the back side of the container  850 . It will be recognized by those of ordinary skill that there could be a number of gears to inside container  850  to change the direction of movement of the actuating member  810 , for example, to a rotary direction. 
       FIG. 12C  illustrates another preferred embodiment of a linkage actuating mechanism according to a preferred embodiment of the invention. This embodiment allows is chronic adjustment of the position of linkage  910  relative to the lead body  20 . Again, this embodiment may be used with two linkage configurations where on linkage is fixed with respect to the lead body  20 . This embodiment utilizes a hydraulic cylinder arrangement to actuate linkage  910 . In this case a noncoring hypodermic syringe needle (not shown) is passed through the patient&#39;s skin and through a compressed rubber septum  960  provided on the side of container  950 . Fluid may be added or withdrawn from beneath the septum, which is connected to a syringe  940 . The moveable plug of this syringe  920  is connected to the moveable linkage  910 . Again, the wires/catheters  930  from the proximal tip of lead  20  pass through container  950  and on to the source device. Alternatively, the source device could be on the back side of container  950 , although, for drug delivery there would need to be another system on the front of container  950  for refilling the drug. 
       FIG. 12D  illustrates an actuating mechanism according to a preferred embodiment of the present invention that allows chronic adjustment of the degree of rotation of linkage  1010  relative to lead body  20 . A rigid needle with a hex-head sharp tip can be inserted into a hexagonal receptacle  1070  in container  1050 . Rotation of this needle device rotates gear  1020  which causes rotation of gear  1040  attached to linkage  1010 . There may be restrictions on the movement of gear  1020  to prevent excessive rotation. 
     The embodiments shown in  FIGS. 12A-D  demonstrate devices to actuate linkages that pass to the distal tip of the lead and cause changes in one or more dimensions of the lead paddle. As described, these involve transmission of force or energy through the skin by means to of a needle that passes through the skin. The same effects can be achieved by having a small motor implanted into the container parts shown, or into the power source itself (not shown) which runs on an electrical battery or transmitted and received radio frequency signal, such as the motor provided in the totally implantable, programmable drug device called SynchroMed®, manufactured by Medtronic, Inc. of Minneapolis, Minn. Smaller motors may be acceptable, especially if a sequence of gears may be used to provide mechanical advantage. If such motors are used, there should be a mechanical circuit breaker to prevent excess motion of the linkages. 
     Very similar techniques would allow expansion of a lead in a direction parallel to the lead body. For example, telescoping elements with electrodes could move parallel to the axis of the lead body (parallel to the spinal cord), similar to the way a car antenna can be extended and retracted. By attaching electrodes and catheter ports to the axial linkages of  FIGS. 5 through 8 , or attaching eyelets  144  of compacted groups of electrodes/ports such as items  130  or  230 , it is possible to extend or compact said groups of electrodes in an axial direction. This is a valuable feature if one wishes to match the axial spacing of electrodes/ports to important dimensions of the structure to be stimulated/affected. For example, Holsheimer (Neurosurgery, vol. 40, 1997: pp 990-999) has shown that there may be preferred longitudinal spacing of electrodes based upon the recruitment factors in spinal cord tissue, and also critically dependent upon the width of the CSF (cerebrospinal fluid) layer between the spinal cord dorsal surface and the dura mater. Therefore, we wish to include the ability to increase or decrease the longitudinal spacing between electrodes/ports by these inventions, and to be able to make a change in said spacing after initial implant of a complete therapeutic system. 
     Those skilled in the art will recognize that the preferred embodiments may be altered or amended without departing from the true spirit and scope of the invention, as defined in the accompanying claims.