Adjustable simulation device and method of using same

A device and method for stimulating neural tissue in a patient comprising: providing a lead having opposed first and second ends defining a longitudinal axis therebetween wherein the lead having at least one electrode provided thereon for delivering electrical stimulation; implanting the lead adjacent the neural tissue; applying electrical signals to the at least one electrode to provide electrical stimulation to the neural tissue; closing all incisions made to implant the lead so that the lead is completely implanted in the patient; and adjusting, at any time after the step of closing all the incisions, the position of the lead so that it moves in a direction substantially perpendicular to the longitudinal axis of the lead.

BACKGROUND OF THE INTENTION

This invention relates to a medical device and method for electrically stimulating tissue. More particularly, the invention is directed to a medical device and method for electrically stimulating the spinal cord and motor cortex.

Stimulating the spinal cord for the purpose of controlling pain was first implemented based upon the gate control theory of pain. Simply stated, the gate control theory is based on the premise that activation of large-diameter afferent nerve fibers causes an inhibition of activity in small-diameter nerve fibers. Since small-diameter fibers are involved in the perception of pain their inhibition leads to a consequent inhibition in the perception of pain. As an alternative to the gate control theory some researchers propose that, rather than a physiological gating mechanism, the activation of action potentials in the dorsal columns of the spinal cord leads to a functional blocking of signals in the collaterals of the dorsal columns which, when activated, add to the perception of pain. Under either theory the objectives and principles of spinal cord stimulation for pain control remain the same.

Pain inhibition by activation of large-diameter fibers is directly related to the area or segment of the spinal cord being stimulated. For example, to inhibit pain occurring in the foot, stimulation must activate the large-diameter fibers carrying sensory information from the foot to the spinal cord and higher brain centers. The objective of spinal cord stimulation is to induce sensory paresthesia in such a way that it broadly covers the area in which the patient feels pain. Thus, the proper location of the stimulation electrode is critical to successful pain control.

It is well known that various areas of the body are associated with the dorsal roots of nerve fibers at various spinal segments. Since the dorsal columns receive additional nerve fibers at each spinal segment, the relative position of the nerve fibers from a particular area in the periphery change from the lower spinal segments to the cervical segments. For effective pain control the electrode must be placed adjacent to the spinal column rostral to the dorsal root associated with the painful area.

It is equally well known that stimulation of the dorsal columns at different points medial to lateral will evoke paresthesia perceived as coming from different locations of the body. Additionally, the sensory fibers in the dorsal columns travel to the medulla on the same side of the cord as the peripheral area which they represent. Pain on the right side of the body is treated by placing the electrode to the right of the midline. Pain on the left side of the body is treated by placing the electrode to the left side of the midline. Bilateral pain is treated by placing the electrode on the midline or by placing electrodes on both sides of the midline. Thus, successful pain control through spinal cord stimulation depends on proper positioning of the stimulating electrode both in the longitudinal or rostral-caudal direction and in the lateral to medial direction.

Typically, implantable spinal cord stimulating leads contain multiple electrodes. Two basic styles are available. One style is the percutaneously inserted lead which is introduced through a Touhy needle. The implanting physician places the electrode in an appropriate location using fluoroscopic visualization. The procedure is done under a local anesthetic. Proper electrode placement is tested using a trial stimulation screening technique to assure that paresthesia is perceived in the affected area. An example of this type of lead is disclosed in U.S. Pat. No. 4,379,462 issued to Borkan. That lead has at least three in-line electrodes equally spaced along the distal end of the lead and is designed to be inserted so that the electrodes lie in-line along the spinal cord. Although different pairs of electrodes may be selected so that the area of stimulation may be moved longitudinally along the midline of the spinal cord, there is no provision for stimulating laterally to either or both sides of the midline unless the lead is inserted to one side of midline. In that case once the lead is placed there is no ability to stimulate other than unilaterally on the side of the midline to which the lead is placed. Should the patient later develop the need for bilateral stimulation the physician generally has three options. The physician may reposition the existing lead, implant an additional lead, or remove and replace the existing lead. Percutaneously inserted leads of this type provide focused stimulation patterns and are generally suited for unilateral pain problems. If the pain is bilateral it is often necessary to implant two leads, one on each side of the midline of the spinal cord. The leads may be connected to one pulse generator or to two pulse generators. The use of two leads can cause problems since it is difficult to maintain the relative positions of the leads with respect to one another, both in the longitudinal and lateral directions. Migration of one or both of the leads may result in a loss of paresthesia at the affected location.

The second basic spinal cord stimulation lead type are those surgically implanted through a laminotomy. An example of this type of lead is the RESUME® lead manufactured by Medtronic, Inc. of Minneapolis, Minn., the assignee of the present invention. This lead has four in-line electrodes located on an elongate paddle at the distal end of the lead. The lead is normally implanted so that the electrodes lie over the midline of the spinal cord. Because leads of this type are surgically implanted, the size of the electrodes may be made larger than those of the percutaneously implanted leads. Various electrode combinations may be selected so that the area of stimulation may be moved along the midline of the spinal cord. The lead provides a broader stimulation pattern more suitable for midline and bilateral pain problems than the percutaneously inserted lead. Since it is surgically implanted it can be sutured to prevent dislodgement and reduce lead migration. In situations where longitudinal placement of the lead over the midline of the spinal cord has not been effective to produce bilateral paresthesia this lead has been placed at an angle with respect to the midline. Once the lead has been inserted at an angle across the spinal cord it is possible, by selection of appropriate electrodes, to stimulate unilaterally on either side of the spinal cord or bilaterally across the spinal cord. However, it is no longer possible to change the stimulation pattern longitudinally along the midline. Additionally, although unilateral stimulation on either side may be provided, the stimulation areas are asymmetric or at different dorsal root levels with respect to the dorsal column. Further, since it is very difficult to maintain the precise angled placement of the lead, any migration of the lead may result in a loss of paresthesia at the affected location.

Another example of a surgically implanted lead is disclosed in U.S. Pat. No. 3,724,467 issued to Avery et al. In one embodiment the lead consists of a flat body portion at the distal end of the lead with electrodes grouped on either side of the longitudinal axis of the lead. The lead is meant to be implanted within the dura and is used for use bilateral stimulation of the spinal cord. In another embodiment the electrodes are mounted on one side of the longitudinal axis of the lead and are meant to provide stimulation to only one side of the spinal cord. In neither embodiment is there any provision for altering the stimulation pattern other than by changing the location of the lead. Thus, once this lead has been implanted there is no way to change the area of stimulation to correct for any loss of paresthesia.

In addition to the problem of lead migration as noted above it is often desirable to effect a change in the area of stimulation in order to vary the effects of paresthesia as the needs of the patient change. The problem of lead migration and the ability to effectively vary the area of stimulation both longitudinally and laterally are areas in which prior art leads have been unable to adequately address. For example, percutaneously inserted leads are difficult to anchor and have a tendency to become dislodged. Even if the initial placement is accurate, lead migration can occur which can adversely affect paresthesia. Additionally, the area in which the patient is experiencing pain can move. Percutaneous leads provide only limited means to change the area of stimulation if the lead migrates or if the needs of the patient change. This is a significant problem with respect to percutaneous leads since the electrodes must be made small enough to fit through a Touhy needle. The area of stimulation is consequently small and even a slight movement of the lead, especially laterally, can adversely affect paresthesia.

Surgically implanted leads are less affected by the problem of lead migration because the electrodes are usually larger and the lead may be stabilized by sutures. However, in instances where lead migration does occur prior art leads have allowed for changes in stimulation only longitudinally along the axis of the lead. There is no mechanism to effect a change of stimulation laterally. The same limitations apply when the needs of the patient change and it becomes desirable to alter the paresthesia.

Thus, it would be desirable to have an electrode lead that includes a position adjustment mechanism where the position of the electrode lead could be adjusted in situ after the electrode lead has been implanted into the patient.

SUMMARY OF THE INVENTION

A device and method for stimulating a spinal cord in a patient comprising: providing a lead having opposed first and second ends defining a longitudinal axis therebetween wherein the lead has at least one electrode provided thereon for delivering electrical stimulation; implanting the lead adjacent the dorsal side of a spinal cord such that the longitudinal axis of the lead is oriented substantially parallel to the midline of the spinal cord; applying electrical signals to the at least one electrode to provide electrical stimulation to the spinal cord; closing all incisions made to implant the lead so that the lead is completely implanted in the patient; and adjusting, at any time after the step of closing all the incisions, the position of the lead in situ so that it moves in a direction substantially perpendicular to the midline of the spinal cord.

A device and method for stimulating neural tissue in a patient comprising: providing a providing a lead having opposed first and second ends defining a longitudinal axis therebetween wherein the lead having at least one electrode provided thereon for delivering electrical stimulation; implanting the lead adjacent the neural tissue; applying electrical signals to the at least one electrode to provide electrical stimulation to the neural tissue; closing all incisions made to implant the lead so that the lead is completely implanted in the patient; and adjusting, at any time after the step of closing all the incisions, the position of the lead so that it moves in a direction substantially perpendicular to the longitudinal axis of the lead.

DETAILED DESCRIPTION OF THE INVENTION

In the description that follows, like parts are indicated throughout the specification and drawings with the same reference numerals, respectively. The figures are not drawn to scale and the proportions of certain parts have been exaggerated for convenience of illustration.

FIGS. 1A and 1Billustrate one embodiment of an adjustable stimulation device100according to the present invention. Device100comprises a housing base105extending along a plane106, a pair of tongue members110provided on base105, a stimulation lead assembly115slidably mounted to tongue members110, a position control mechanism120to adjust the position of stimulation lead115within base105, and a housing cover125releasably secured to housing base105to enclose the components provided therein.

FIGS. 2A and 2Bare top and cross-sectional side views, respectively, of lead assembly115. Lead assembly115includes an insulated cable portion205connected at its proximal end to a flat connector210and at its distal end to lead body215. Lead body215is an elongated body having a top portion220, a bottom portion225, a first end230, and a second end235. Lead body215includes an axis AA that extends longitudinally along the length of lead body215between first end230and second end235. Although lead body215has a generally rectangular shape, lead body215may be configured in any conceivable shape.

A plurality of electrodes240are provided along the top portion220of lead body215to deliver electrical stimulation to targeted tissue. Although four electrodes are illustrated in the figures, it is obvious that more than four electrodes or less than four electrodes (e.g., one electrode) may be utilized. As best seen inFIG. 2B, lead body215is comprised of a molded silicone rubber portion245surrounding a mesh portion250made of DACRON®, a polyester material made by E. I. du Pont de Nemours & Co. Electrodes240are embedded within rubber portion245and may protrude slightly above the surface of lead body215in order to enhance their tissue stimulation effectiveness. As best shown inFIG. 2A, the shape and arrangement of electrodes240on lead body215are illustrated. Although electrodes240are circular in shape and arranged in a columnar fashion along lead body215, it is obvious that electrodes240may take the form of other shapes such as oval, square, rectangular and may be arranged in any pattern such as a linear array or staggered array.

The insulated cable portion205of lead assembly215has a single lumen that encloses a plurality of conductors255. Each conductor255interconnects an electrode240located on lead body215with respective stainless steel pins or terminals260that are molded into flat connector210. Conductors255are welded to the distal ends of electrodes240, respectively, and are crimped at ferrules (not shown) which provide strain relief The insulated cable portion205and flat connector210are made of a physiologically inert material such as silicone rubber or polyethylene. Conductors255are made of an appropriate electrically conductive material such as stranded stainless steel and are separately insulated with an appropriate insulating material. Preferably, they are coated with polytetrafluoroethylene (PTFE).

As stated above, lead assembly115is slidably mounted to a pair of tongue members110that may guide the movement of lead assembly115relative to housing base105. As shown inFIGS. 3A and 3Bwhere housing cover125is not shown to better illustrate the underlying components, tongue members110extend laterally along a portion of the width of base105substantially perpendicular to axis AA. Tongue members110may include any male-type structure that extends laterally along a portion of the width of base105. Although the preferred male-type structure is a tongue member, other male-type structures are within the scope of the present invention such as a tab, rail, or track. Preferably, tongue members110have a T-shaped profile; however, the profile of tongue members110may take the form of any shape. Although tongue members110or any other male-type structure may be separate parts that are attached to base105, it is possible that base105and tongue members110may be one integral part or component. If tongue members110are separate parts, they may be attached to base105by screws, rivets, or snaps. It is also possible to utilize one tongue member or three or more tongue members and still be within the scope of the present invention.

Bottom portion225of lead body215is provided with cooperating structures that engage tongue members110to permit lead body215to move along tongue members110in a direction perpendicular to axis AA along a plane109that extends parallel to the plane106of the base105. In one embodiment, the cooperating structure is a T-shaped groove defined by a pair of guide shoes305that are projected from bottom portion225of lead body215to support lead assembly115on tongue members110as shown inFIG. 3B. Each guide shoe305includes a first portion310, which is substantially perpendicular to bottom portion225, and a second portion315that extends from first portion310in a direction towards the second end235of lead body215. Preferably, second portion315is substantially parallel to bottom portion225of lead body215to form the T-shaped groove. Further, guide shoe305includes a third portion320, which is substantially perpendicular to bottom portion225, and a fourth portion325that extends from third portion320in a direction towards the first end230of lead body215. Preferably, fourth portion325is substantially parallel to bottom portion225of lead body215to form the T-shaped groove.

Although guide shoes305may be separate parts that are attached to bottom portion225of lead body215, it is preferred that guide shoes305and lead body215are one integral part. If guide shoes305are separate parts, they may be attached to lead body215by screws, rivets, or snaps. Although the preferred shape of the groove defined by guide shoes305is T-shaped, the grooves defined by guide shoes305may take the form of any shape so long as the cooperating structure (i.e., the groove) permits sliding movement of lead body215along tongue members110perpendicular to axis A and captures tongue members110such that lead body215is constrained from moving in a direction parallel to axis AA.

Alternatively, the cooperating structure may include a female-type structure disposed in bottom portion225of lead body215that extends laterally along the width of lead body215. Although the preferred female-type structure defines a groove or channel, other female-type structures are within the scope of the present invention such as a slot or notch. Preferably, the groove or channel has a T-shaped profile; however, the groove or channel may have a simple rectangular profile or any other shape.

Alternatively, the forms of the structure disposed in or extending from lead body215and the cooperating structure disposed on or extending from base105may be reversed such that the tongue member or male-type structure may be provided on or extending from lead body215and the groove or female-type cooperating structure may be providing in or extending from base105.

Although the illustrated embodiment depicts a tongue and groove sliding assembly, other sliding assemblies contemplated within the present invention include a roller/track assembly, other male/female slides, rack and pinion, and other sliding assemblies known in the art. Also, the addition of ball bearings to the slide assembly may prove helpful in minimizing friction.

As stated above, adjustable stimulation device100includes a position control mechanism120to adjust the position of lead assembly115relative to base105. Position control mechanism120is capable of moving lead assembly115in the directions indicated by arrows A (seeFIG. 1) which is substantially perpendicular to axis AA and along the plane109extending parallel to the plane106of the housing base105, thereby adjusting the position of lead assembly115relative to housing base105.

In one embodiment, as shown inFIGS. 3A and 3B, position control mechanism120includes a rack gear330having teeth335disposed thereon and a pinion gear340having teeth345disposed thereon. Rack gear330is coupled to lead body215such that movement of rack gear330forces movement of lead body215. Pinion gear340includes a hexagonal shaped head350and is rotatably mounted to shaft353that is coupled to base105. The teeth335of rack gear330engage and mesh with the teeth345of pinion gear340such that rotational movement of pinion gear340causes rack gear330to move laterally in the directions indicated by arrows B. Although gear rack330may be a separate part that is attached to lead body215, it is possible that gear rack330and lead body215may be one integral part. If gear rack330is a separate part, it may be attached to lead body215by screws, rivets, or snaps.

Pinion gear340may be rotated by inserting a rigid tool (not shown), having a hexagonal socket, around the hexagonal shaped head350of pinion gear340and rotating the tool either clockwise or counter-clockwise to move rack gear330in either lateral direction. Rack gear330includes stops355to prevent excessive movement of rack gear330. Alternatively, pinion gear340may be rotated by a small motor implanted in device100which runs on an electrical battery or transmitted and received radio frequency signals. Small 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. Other devices that are capable of rotating pinion gear340include magnetic or electromagnetic devices. Such electromechanical (i.e. motors), electromagnetic, and magnetic devices may be operated and controlled by external sources via RF signals or other telemetric systems.

As stated above, housing cover125engages housing base105and encloses the components provided therebetween. As shown inFIGS. 4A and 4B, housing cover125includes a top wall405and side walls410,415,420, and425. Top wall405of housing cover125includes a grid430comprised of a plurality of electrically conductive panels435surrounded by electrically insulated frames440wherein each frame440prevents electrical continuity between adjacent panels435. For example, when only one panel (see panel P inFIG. 4A) is electrically active, the adjacent panels (see panels P1-P8) are electrically inactive because the frame surrounding panel P prevents the electrical current from traveling to the adjacent panels.

Each electrically conductive panel435includes a top surface445and a bottom surface450. When housing cover125is engaged with housing base105, the bottom surface450of at least a portion of panels435(seeFIG. 5Awhere panels435are shaded) come into contact or at least close enough proximity with the top surface of electrodes240(collectively referred to as “electrical contact”) such that when electrodes240are electrically active, the panels435that are in electrical contact with electrodes240are electrically active. Accordingly, when lead body215is moved to a new position (e.g., when pinion gear340is rotated clockwise, rack gear330moves in the direction indicated by arrow C), only the panels435that are in electrical contact with electrodes240remain electrically active (seeFIG. 5Bwhere panels435are shaded), while panels435that are no longer in electrical contact with electrodes240return to being electrically inactive.

Further, housing cover125includes an opening to permit the head350of pinion gear340to protrude through the top wall405to permit an operator to access and rotate the head350of pinion gear340with a tool without having to access the internal components of device100. Alternatively, housing cover125may include an access panel or other closeable-type opening to permit access to pinion gear340if the head does not protrude through the top wall405.

The housing base105and cover125are constructed of any material such as a physiologically inert plastic. Panels435are constructed of any electrically conductive material such as platinum-iridium, stainless steel, or titanium. The electrically insulated frames440are constructed of a material similar to the housing components or any other insulating material such as silicone rubber or polyethylene.

Although housing base105and housing cover125may be separate part or components, it is possible that housing base105and housing cover125may be of unitary construction.

Although the invention will be described herein with reference to spinal cord stimulation (SCS) procedures, Cortical Surface Stimulation, and or Deep Brain Stimulation (DBS) it will be recognized that the invention finds utility in applications other than SCS procedures, including other applications such as Peripheral Nerve or Ganglia Stimulation, Intra-Spinal Stimulation, Sacral Root Stimulation, or Intraventricular Cerebral Stimulation. In addition, the invention finds applicability to SCS procedures where the lead is placed in the intrathecal or subdural space. The present invention may also be utilized to provide stimulation of various muscles of the body such as the cardiac muscle.

FIG. 6is a cross-sectional view of spinal cord600at spinal bone level T-6 having device100implanted therein in accordance with one embodiment of the present invention. Spinal cord600generally includes white matter605, grey matter610, and a surrounding dural sack615.FIG. 6shows the average width, height and spacing of tissue components at vertebral bone level T6. The dashed lines in these figures indicate distances of one standard deviation from the mean. See J. Holsheimer et al., “MR Assessment of the Normal Position of the Spinal Cord in the Spinal Cannal,” Am. J. Neuroradiology, Vol. 15, pp. 951-959 (1994).

As shown, device100is implanted in the epidural space outside of dural sack615, but may alternatively be implanted in the intrathecal spinal space or subcortically beneath dural sack615. In this embodiment, device100has a curved shape to match the shape of dural sack615. The curvature may be matched to each spinal level or may be a general shape to approximately match all levels of spinal cord. Alternatively, device100may be flat such that it “grips” the vertebral bone on its dorsal edges and is less prone to migration or rotation. Device100has a dorsal side620away from spinal cord600and a ventral side625facing spinal cord600.

As shown inFIG. 7, device100is adapted to be implanted in a human patient along the dorsal side of the spinal column700. A detailed description of the method of stimulate the spinal cord is described in a chapter entitled “Spinal Cord Stimulation for Pain Relief” in the text “Neurosurgery” by Giancarlo Barolet and Ashwini Sharan, edited by Wilkins and Rengacharey, Edition 3, (2003), which is hereby incorporated by reference in its entirety herein. Device100is first implanted such that the longitudinal axis AA of lead body215is oriented substantially parallel to the midline of said spinal cord. This aligns electrodes240on lead assembly115substantially parallel to the midline of spinal cord600. Each electrode is independently selectable so that a variety of stimulation patterns may be selected by providing stimulation signals to two or more of electrodes240. The stimulation signals or pulses are provided by an external pulse generator during an initial screening procedure to determine a correct lead placement and electrode combination that will adequately supply paresthesia to the desired location. During the screening process, various electrode combinations are tested until the right combination is achieved.

After the screening process has been completed and device100is properly anchored in place, device100is connected to an implanted pulse generator710by a lead extension715as shown inFIG. 7. Lead extension715has a flat connector720at its distal end which connects to flat connector210and has a plug-in connector725at its proximal end which connects to pulse generator710. Pulse generator710may be a fully implanted system such as the “ITREL II” pulse generator available from Medtronic. Inc. or may employ a partially implanted radio-frequency system such as the “XTREL” system also available from Medtronic, Inc.

In use, device100is designed to be implanted in the epidural space after the dura has been exposed by a partial laminectomy. Although the invention will be described primarily in connection with its implantation in the epidural space along the dorsal column for use in stimulating the spinal cord as a method of treating pain, it should be noted that the electrode may be used for any spinal cord stimulation application such as stimulation to induce motor function or to inhibit spasticity. When used for such other applications, device100may be implanted laterally or on the ventral side of the spinal column. Device100is also suitable for use in applications other than spinal cord stimulation such as stimulation of peripheral nerves.

Once the stimulation system including device100has been implanted and all the incisions made to implant device100have been closed so that said lead is completely implanted in said patient, device100provides the flexibility to make modifications to the area of paresthesia should the needs of the patient change or should there be any lead migration. This may be accomplished using an adjustment procedure described herein. First, the surgeon identifies the exact location of the hexegonal shaped head350of pinion gear340using CT or MRI equipment. Once the surgeon identifies the location of the hexegonal shaped head350of pinion gear340, the surgeon makes in opening in the back of the patient to access the the hexegonal shaped head350of pinion gear340. Once the hexegonal shaped head350of pinion gear340is accessible, the surgeon passes a rigid tool (not shown) having a hexagonal-shaped socket through the patient's skin and engages hexegonal shaped head350of pinion gear340. The surgeon may then rotate the pinion gear340clockwise or counterclockwise using tool to actuate rack330back and forth thereby causing lead body215(and electrodes240provided thereon) to move in a direction substantially perpendicular to the midline of the spinal cord600. Advantageously, electrodes240may be repositioned relative to the spinal cord600such that the targeted neural tissue is stimulated with optimal efficacy. Thus, device100provides a substantial amount of flexibility in achieving a stimulation pattern which is moveable laterally along the spinal column and which is effective in supplying paresthesia even if the area of pain changes or there is migration of the lead.

FIGS. 8A and 8Billustrate another embodiment of an adjustable stimulation device800according to the present invention. Adjustable stimulation device800includes a similar base105, tongue members110, and position control mechanism120as shown and described above. Lead assembly815is also similar to lead assembly115as shown and described and includes a lead body820and a plurality of electrodes824disposed thereon., except that the width of lead body820may be larger.

In this embodiment, housing cover825also engages housing base105and encloses the components provided therebetween. As shown inFIGS. 8A and 8B, housing cover825includes a top wall830having a top surface832and bottom surface834, and side walls835,840,845, and850. Housing cover825includes an aperture855in top wall830to expose a portion of lead body820and electrodes824to tissue. When housing cover825is engaged with housing base105, the bottom surface834of at least a portion of top wall830overlaps at least a portion of the perimeter of lead body820and comes into contact with the top surface of lead body820to thereby prevent fluid or tissue from entering device800. Although the bottom surface834of top wall830comes into contact with the top surface of lead body820, the friction between the two surfaces is low enough to permit lead body820to move relative to top wall830of housing cover825, but large enough to prevent fluid or tissue from entering device800. Preferably, the width (w) of aperture830is large enough so that lead body820(and electrodes824) can move laterally as indicated by arrows D with respect to base105. Optionally, electrodes824may protrude slightly above the surface of top wall830in order to enhance their tissue stimulation effectiveness.

Device800is implanted and operates in a similar fashion as device100shown and described above. Once the stimulation system including device800has been implanted, device800provides the flexibility to make modifications to the area of paresthesia should the needs of the patient change or should there be any lead migration. This may be accomplished using an adjustment procedure similar to the procedure described above.

Further, housing cover825includes an opening to permit the head350of pinion gear340to protrude through the top wall830to permit an operator to access and rotate the head350of pinion gear340with a tool without having to access the internal components of device800. Alternatively, housing cover825may include an access panel or other closeable-type opening to permit access to pinion gear340if the head does not protrude through the top wall830.

FIGS. 9A,9B, and9C illustrate another embodiment of an adjustable stimulation device900according to the present invention. Device900comprises a housing base905and a plurality of rollers910provided on base905. Rollers910extend parallel to the surface of base905defining axis BB. A continuous belt915or other tensile member is provided in rolling engagement with the outside diameter of rollers910. A stimulation lead assembly920is coupled to belt915such that movement of belt915causes lead assembly920to move. Lead assembly920is similar to lead assembly215described above and includes a lead body922and a plurality of electrodes924disposed thereon.

A position control mechanism925is provided to adjust the position of stimulation lead920within base905. Position control mechanism925includes a first bevel gear930that is coupled to and shares the same axis as one of the rollers910. Position control mechanism925further includes a second bevel gear935having an axis of rotation in a different plane oriented ninety degrees from axis BB of first bevel gear930. Second bevel gear935includes a hexagonal shaped head940and is rotatably mounted to shaft945that is coupled to base905. The teeth of first bevel gear930engage and mesh with the teeth of second bevel gear935such that rotational movement of first bevel gear930as indicated by arrows E causes second bevel gear935to rotate in a plane perpendicular to rotation of first bevel gear930thereby causing roller910and belt915(and lead body922) to move in the directions indicated by arrows F.

Second bevel gear935may be rotated by inserting a rigid tool (not shown), having a hexagonal socket, around the hexagonal shaped head938of second bevel gear935and rotating the tool either clockwise or counter-clockwise to rotate first bevel gear930thereby moving belt915in either lateral direction. Alternatively, second bevel gear935may be rotated by a small motor implanted in device900which runs on an electrical battery or transmitted and received radio frequency signals. Small 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. Other devices that are capable of rotating pinion gear340include magnetic or electromagnetic devices. Such electromechanical (i.e. motors), electromagnetic, and magnetic devices may be operated and controlled by external sources via RF signals or other telemetric systems.

In this embodiment, a housing cover950is provided to mate with housing base905and enclose the components provided therebetween. As shown inFIGS. 9A,9B, and9C, housing cover950includes a top wall955having a top surface960and bottom surface965. Housing cover950includes an aperture970in top wall955to expose a portion of lead body922and electrodes924to tissue. When housing cover950is engaged with housing base905, the bottom surface965of at least a portion of top wall955overlaps at least a portion of the perimeter of lead body922and comes into contact with the top surface of lead body922to thereby prevent fluid or tissue from entering device900. Although the bottom surface965of top wall955comes into contact with the top surface of lead body922, the friction between the two surfaces is low enough to permit lead body922to move relative to top wall955of housing cover950, but large enough to prevent fluid or tissue from entering device900. Preferably, the width (w) of aperture970is large enough so that lead body922(and electrodes924) can move laterally as indicated by arrows G with respect to base905. Optionally, electrodes924may protrude slightly above the surface of top wall830in order to enhance their tissue stimulation effectiveness.

Further, housing cover950includes an opening to permit the head940of second bevel gear935to protrude through the top wall955to permit an operator to access and rotate the head940of second bevel gear935with a tool without having to access the internal components of device900. Alternatively, housing cover950may include an access panel or other closeable-type opening to permit access to second bevel gear935if the head does not protrude through the top wall955.

Device900is implanted and operates in a similar fashion as device100shown and described above. Once the stimulation system including device900has been implanted, device900provides the flexibility to make modifications to the area of paresthesia should the needs of the patient change or should there be any lead migration. This may be accomplished using an adjustment procedure similar to the procedure described above.

FIGS. 10A and 10Billustrate yet another embodiment of an adjustable stimulation device1000according to the present invention. Device1000comprises the same components as device900shown and described above, but includes a housing cover1025different from housing cover950of device900. Stimulation lead assembly1020is similar to lead assembly915described above and includes a lead body1022and a plurality of electrodes1024disposed thereon.

As stated above, housing cover1025engages housing base1005and encloses the components provided therebetween. As shown inFIGS. 10A and 10B, housing cover1025includes a top wall1030and side walls1035,1040,1045, and1050. Top wall1030of housing cover1025includes a grid1055comprised of a plurality of electrically conductive panels1060surrounded by electrically insulated frames1065wherein each frame1065prevents electrical continuity between adjacent panels1060. The relationship between the electrically conductive panels1060and electrodes1024disposed on lead body1022is similar to the electrically conductive panels435and electrodes240disposed on lead body215described above for device100.

Further, housing cover1025includes an opening to permit the head940of second bevel gear935to protrude through the top wall1030to permit an operator to access and rotate the head940of second bevel gear935with a tool without having to access the internal components of device1000. Alternatively, housing cover1025may include an access panel or other closeable-type opening to permit access to second bevel gear935if the head does not protrude through the top wall1030.

Device1000is implanted and operates in a similar fashion as device100shown and described above. Once the stimulation system including device900has been implanted, device900provides the flexibility to make modifications to the area of paresthesia should the needs of the patient change or should there be any lead migration. This may be accomplished using an adjustment procedure similar to the procedure described above.

As stated above, the position control mechanisms may be actuated by electromechanical, electromagnetic, or magnetic devices that may be operated and controlled by external sources via RF signals or other telemetric systems. Further, the individual electrodes on the lead may be adjusted post-operatively by turning them on/off, adjusting the voltage, adjusting the frequency, and adjusting other electrical signal parameters through the use of telemetry, RF signals, or other systems known in the art. Also, if chemical stimulation is also provided, the ports may be opened or closed or the amount of drug being delivered may be adjusted post-operatively through the use of telemetry, RF signals, or other systems known in the art. Systems for communicating with implantable medical devices are disclosed, for example, in U.S. Application Serial No. 2002/0082665 entitled System And Method Of Communicating Between An Implantable Medical Device And A Remote Computer System Or Health Care Provider and U.S. Application Serial No. 2001/0012955 entitled Method And Apparatus For Communicating With An Implantable Medical Device, and U.S. Pat. No. 6,201,993 entitled Medical Device Telemetry Receiver Having Improved Noise Discrimination, and are incorporated by reference in their entireties herein for their teachings.

The system may optionally include one or more sensors to provide closed-loop feedback control of the treatment therapy and/or electrode positioning. One or more sensors are attached to or implanted into a portion of a patient's body suitable for detecting a physical and/or chemical symptom or an important related symptom of the body.

The present invention may also be implemented alone or in combination with a drug delivery system to provide chemical stimulation utilizing a drug, pharmaceutical, or therapeutic agent. In this embodiment, a pump and catheter is provided either alone or in combination with the signal generator and the electrode. The pump may be implanted below the skin of a patient and has a port into which a hypodermic needle can be inserted through the skin to inject a quantity of a liquid agent, such as a drug, pharmaceutical, or therapeutic agent. The liquid agent is delivered from pump through a catheter port into a catheter. The catheter is positioned to deliver the liquid agent to a predetermined region of the brain.

Optionally, the present invention may incorporate a closed-loop feedback system to provide automatic adjustment of the electrical and/or chemical stimulation therapy. The system may incorporate a sensor to provide feedback to provide enhanced results. Sensor can be used with a closed loop feedback system in order to automatically determine the level of electrical and/or chemical stimulation necessary to provide the desired treatment. Sensor may be implanted into a portion of a patient's body suitable for detecting symptoms of the disorder being treated. Sensor is adapted to sense an attribute of the symptom to be controlled or an important related symptom. Sensors suitable for this purpose may include, for example, those disclosed in U.S. Pat. No. 5,711,316, which is incorporated herein by reference in its entirety. In cases where the attribute of the symptom is the electrical activity of the brain, stimulating electrodes may be intermittently used to record electrical activity. Alternatively, one or more electrodes implanted within the brain may serve as a sensor or a recording electrode. When necessary, these sensing or recording electrodes may deliver stimulation therapy to the predetermined region of the brain. The output of an external feedback sensor may communicate with the implanted pulse generator through a telemetry down-link.

The operator preferably may also selectively adjust the energy, amplitude or pulse parameters delivered to each electrode. The selective control over each electrode may be achieved by employing a programmer which is coupled via a conductor to a telemetry antenna. The programmer is capable of sending signals via the telemetry antenna to control the electrical signal delivered to the electrodes and to control the actuator system. The system permits attending medical personnel to select the various pulse output options after implant using telemetry communications. While the preferred system employs fully implanted elements, systems employing partially implanted generators and radio-frequency coupling may also be used in the practice of the present invention. Advantageously, the present invention allows the locus of excitation to be selectively adjusted and/or steered to precisely target portions of the brain to achieve the desired treatment therapy. The steering may be accomplished in the manner described in U.S. Pat. No. 5,713,922 which is incorporated herein by reference in its entirety.

Furthermore, it is understood that one ordinarily skilled in the art can appreciate the ability to select and power individual electrodes independently from other electrodes in order to stimulate the desired target region and to obtain desired directional properties. Specifically, this ability to control the energizing of electrodes enables a physician to focus (i.e. direct) an electrical field around the chosen powered electrode thus pinpointing the stimulation area. Additionally, the shape of the electric field will vary corresponding to the power applied, the number and arrangement of electrodes, and particular shapes and sizes chosen for the electrodes. Also, each electrode may be selectively powered as an anode, cathode or neither.

From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a neurological stimulation lead for spinal cord stimulation has been disclosed. Although several particular embodiments of the invention have been disclosed herein in detail, this has been done for the purpose of illustration only, and is not intended to be limiting with respect to the scope of the appended claims, which follow. In particular, it is contemplated by the inventors that various substitutions, alterations and modifications may be made to the embodiments of the invention without departing from the spirit and scope of the invention as defined by the claims. For instance, the choice of materials or variations in the shape of the lead body or electrodes or electrode array are believed to be a matter of routine for a person of ordinary skill in the art with knowledge of the embodiments disclosed herein. Likewise, although the embodiments disclosed relate primarily to spinal cord stimulation for treatment of pain, the stimulation lead disclosed herein could be used for other applications such as nerve stimulation for control of motor function.