U.S. patent application number 10/844672 was filed with the patent office on 2004-10-21 for spinal cord stimulation lead with an anode guard.
Invention is credited to Drees, Scott F., Erickson, John H..
Application Number | 20040210291 10/844672 |
Document ID | / |
Family ID | 24549616 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040210291 |
Kind Code |
A1 |
Erickson, John H. ; et
al. |
October 21, 2004 |
Spinal cord stimulation lead with an anode guard
Abstract
The present invention relates to an epidural stimulation lead
having at least one electrode that substantially encircles another
electrode. Operatively, the encircling electrode can be set as an
anode and the encircled electrode can be set as a cathode to
generate an electrical field therebetween. The encircling electrode
functions in this capacity as an anode guard, which among other
things, concentrates the electrical field about the designated
cathode and limits the lateral range of a generated electrical
field.
Inventors: |
Erickson, John H.; (Plano,
TX) ; Drees, Scott F.; (McKinney, TX) |
Correspondence
Address: |
Robert A. McLauchlan
Koestner Bertani LLP
P.O. Box 26780
Austin
TX
78755
US
|
Family ID: |
24549616 |
Appl. No.: |
10/844672 |
Filed: |
May 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10844672 |
May 13, 2004 |
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09635910 |
Aug 10, 2000 |
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6754539 |
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Current U.S.
Class: |
607/117 |
Current CPC
Class: |
A61N 1/0553
20130101 |
Class at
Publication: |
607/117 |
International
Class: |
A61N 001/05 |
Claims
1. A stimulation load comprising: a body having a first surface; a
plurality of terminals; a plurality of electrodes positioned
relative to the first surface of the body; and a plurality of
conductors, wherein a conductor electrically couples one terminal
of the plurality of terminals with at least one electrode, wherein
the plurality of electrodes includes a first electrode and a second
electrode, and wherein the second electrode substantially encircles
at least the first electrode.
2. A stimulation lead in accordance with claim 1, wherein the
plurality of electrodes includes a first electrode array, which
includes the first electrode, and the second electrode
substantially encircles the first electrode array.
3. A stimulation lead in accordance with claim 2, wherein the first
electrode array comprises a plurality of electrodes arranged in at
least two columns.
4. A stimulation lead comprising: a plurality of terminals; a
plurality of electrodes forming at least two electrode arrays; and
a plurality of conductors, wherein a conductor electrically couples
one terminal of the plurality of terminals with at least one
electrode, wherein a first electrode array of the at least two
electrode arrays includes at least a first electrode and a second
electrode, and the first electrode substantially circumscribes at
least the second electrode.
5. A stimulation lead in accordance with claim 4, wherein the first
electrode of the first electrode array substantially circumscribes
a plurality of electrodes, such plurality of electrodes including
the second electrode.
6. A stimulation lead in accordance with claim 4, wherein a second
electrode array of the at least two electrode arrays includes at
least a third electrode and a fourth electrode, and the third
electrode substantially circumscribes at least the fourth
electrode.
7. A stimulation lead in accordance with claim 6, wherein the third
electrode of the second electrode array substantially circumscribes
a plurality of electrodes, such plurality of electrodes including
the fourth electrode.
8-11. Canceled.
12. A stimulation lead comprising: a plurality of terminals; a
plurality of electrodes; and a plurality of conductors, wherein a
conductor electrically couples one terminal of the plurality of
terminals with at least one electrode, wherein the plurality of
electrodes includes first electrode and a second electrode, and
wherein the second electrode substantially encircles at least the
first electrode.
13. A method of placing a stimulation lead in a human patient,
comprising the steps of: providing a stimulation lead, the
stimulation lead having: a body; a plurality of terminals; a
plurality of electrodes positioned relative to the first surface of
the body; and a plurality of conductors, wherein a conductor
electrically couples one terminal of the plurality of terminals
with at least one electrode; surgically accessing a site proximate
to a desired stimulation lead placement site in the patient; and
placing the stimulation lead at the desired stimulation lead
placement site, wherein the plurality of electrodes includes a
first electrode and a second electrode, and wherein the second
electrode substantially encircles at least the first electrode.
14. A method of placing a stimulation lead in a human patient,
comprising the steps of: providing a stimulation lead the
stimulation lead having: a body; a plurality of terminals; a
plurality of electrodes positioned relative to the first surface of
the body; and a plurality of conductors, wherein a conductor
electrically couples one terminal of the plurality of terminals
with at least one electrode; percutaneously accessing a site
proximate to a desired stimulation lead placement site in the
patient; and placing the stimulation lead at the desired
stimulation lead placement site, wherein the plurality of
electrodes includes a first electrode and a second electrode, and
wherein the second electrode substantially encircles at least the
first electrode.
15. An epidural stimulation lead operable to provide a stimulation
pattern from an applied electric field comprising: a body having a
first surface; a plurality of terminals; a plurality of electrodes
positioned relative to the first surface of the body; and a
plurality of conductors, wherein a conductor electrically couples
one terminal of the plurality of terminals with at least one
electrode, wherein the plurality of electrodes includes a first
electrode and a second electrode, and wherein the second electrode
substantially encircles at least the first electrode, forming an
anode guard, and wherein said second electrode is coupled to an
energy source that provides a positive polarity to said second
electrode relative to said first electrode.
16. The epidural stimulation lead of claim 15, wherein the first
electrode comprises an array of electrodes substantially encircled
by the second electrode.
17. The epidural stimulation lead of claim 16, wherein the array of
electrodes comprises said first electrode comprising at least two
columns of electrodes.
18. The epidural stimulation lead of claim 16 wherein said second
electrode comprises an array of electrodes that substantially
encircle said first electrode.
19. A method of providing a stimulation pattern from an applied
electric field with an epidural stimulation lead comprising the
steps of: coupling a plurality of terminals of said lead to an
energy source wherein said lead further comprises: a plurality of
conductors, wherein a conductor electrically couples one terminal
of the plurality of terminals with at least one electrode; and a
plurality of electrodes forming at least two electrode arrays,
wherein a first electrode array of the at least two electrode
arrays includes at least a first electrode and a second electrode;
positively biasing said first electrode relative to said second
electrode, wherein said first electrode substantially circumscribes
said second electrode.
20. The method of claim 19 wherein the first electrode of the first
electrode array substantially circumscribes a plurality of
electrodes, such plurality of electrodes including the second
electrode.
21. The epidural stimulation lead of claim 19, wherein a second
electrode array of the at least two electrode arrays includes at
least a third electrode and a fourth electrode, and the third
electrode substantially circumscribes at least the fourth
electrode.
22. The method of claim 19, wherein the third electrode of the
second electrode array substantially circumscribes a plurality of
electrodes, such plurality of electrodes including the fourth
electrode.
23. An epidural stimulation lead operable to provide patterned
stimulation from an electric field comprising: a plurality of
terminals coupled to an energy source; a plurality of electrodes; a
plurality of conductors, wherein a conductor electrically couples
one terminal of the plurality of terminals with at least one
electrode, wherein the plurality of electrodes includes a first
electrode and a second electrode that substantially encircles said
first electrode forming an anode guard.
24. A method of placing a stimulation lead in a human patient,
comprising the steps of: providing a stimulation lead, the
stimulation lead having: a body; a plurality of terminals; a
plurality of electrodes positioned relative to the first surface of
the body; and a plurality of conductors, wherein a conductor
electrically couples one terminal of the plurality of terminals
with at least one electrode; surgically accessing a site proximate
to a desired stimulation lead placement site in the patient; and
placing the stimulation lead at the desired stimulation lead
placement site, wherein the plurality of electrodes includes a
first electrode and a second electrode, and wherein the second
electrode substantially encircles at least the first electrode.
25. A method of providing a stimulation pattern from an applied
electric field, comprising the steps of: providing an epidural
stimulation lead, the stimulation lead further comprising: a body;
a plurality of terminals; a plurality of electrodes positioned
relative to the first surface of the body; and a plurality of
conductors, wherein a conductor electrically couples one terminal
of the plurality of terminals with at least one electrode;
percutaneously accessing a site proximate to a desired stimulation
lead placement site in the patient; placing the stimulation lead at
the desired stimulation lead placement site, wherein the plurality
of electrodes includes a first electrode and a second electrode,
and coupling said epidural stimulation lead to an energy source
wherein said energy source provides a positive voltage to said
second electrode relative to said first electrode, wherein the
second electrode substantially encircles at least the first
electrode.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an epidural stimulation
lead, and in particular, to an epidural stimulation lead having at
least one electrode suited to serve as an anode guard relative to a
substantially encircled cathode.
BACKGROUND OF THE INVENTION
[0002] Application of specific electrical fields to spinal nerve
roots, spinal cord, and other nerve bundles for the purpose of
chronic pain control has been actively practiced since the 1960s.
While a precise understanding of the interaction between the
applied electrical energy and the nervous tissue is not fully
appreciated, it is known that application of an electrical field to
spinal nervous tissue (i.e., spinal nerve roots and spinal-cord
bundles) can effectively mask certain types of pain transmitted
from regions of the body associated with the stimulated tissue.
More specifically, applying particularized electrical energy to the
spinal cord associated with regions of the body afflicted with
chronic pain can induce paresthesia, or a subjective sensation of
numbness or tingling, in the afflicted bodily regions. This
paresthesia can effectively mask the transmission of non-acute pain
sensations to the brain.
[0003] It is known that each exterior region, or each dermatome, of
the human body is associated with a particular spinal nerve root at
a particular longitudinal spinal position. The head and neck
regions are associated with C2-C8, the back regions extends from
C2-S3, the central diaphragm is associated with spinal nerve roots
between C3 and C5, the upper extremities are correspond to C5 and
T1, the thoracic wall extends from T1 to T11, the peripheral
diaphragm is between T6 and T11, the abdominal wall is associated
with T6-L1, lower extremities are located from L2 to S2, and the
perineum from L4 to S4. By example, to address chronic pain
sensations that commonly focus on the lower back and lower
extremities, a specific energy field can usually be applied to a
region between bony level T8 and T10. As should be understood,
successful pain management and the avoidance of stimulation in
unafflicted regions necessarily requires the applied electric field
to be properly positioned longitudinally along the dorsal
column.
[0004] Positioning of an applied electrical field relative to a
physiological midline is equally important. Nerve fibers extend
between the brain and a nerve root along the same side of the
dorsal column as the peripheral areas the fibers represent. Pain
that is concentrated on only one side of the body is "unilateral"
in nature. To address unilateral pain, electrical energy is applied
to neural structures on the side of a dorsal column that directly
corresponds to a side of the body subject to pain. Pain that is
present on both sides of a patient is "bilateral." Accordingly,
bilateral pain is addressed through either an application of
electrical energy along a patient's physiological midline or an
application of electrical energy that transverses the physiological
midline.
[0005] Pain-managing electrical energy is commonly delivered
through electrodes positioned external to the dura layer
surrounding the spinal cord. The electrodes are carried by two
primary vehicles: a percutaneous catheter and a laminotomy
lead.
[0006] Percutaneous catheters, or percutaneous leads, commonly have
three or more, equally-spaced electrodes, which are placed above
the dura layer through the use of a Touhy-like needle. For
insertion, the Touhy-like needle is passed through the skin,
between desired vertebrae, to open above the dura layer.
[0007] For unilateral pain, percutaneous leads are positioned on a
side of a dorsal column corresponding to the "afflicted" side of
the body, as discussed above, and for bilateral pain, a single
percutaneous lead is positioned along the patient midline (or two
or more leads are positioned on each side of the midline).
[0008] Laminotomy leads have a paddle configuration and typically
possess a plurality of electrodes (for example, two, four, eight,
or sixteen) arranged in one or more columns. An example of a
sixteen-electrode laminotomy lead is shown in FIG. 1.
[0009] Implanted laminotomy leads are commonly transversely
centered over the physiological midline of a patient. In such
position, multiple columns of electrodes are well suited to address
both unilateral and bilateral pain, where electrical energy may be
administered using either column independently (on either side of
the midline) or administered using both columns to create an
electric field which traverses the midline. A multi-column
laminotomy lead enables reliable positioning of a plurality of
electrodes, and in particular, a plurality of electrode columns
that do not readily deviate from an initial implantation
position.
[0010] Laminotomy leads require a surgical procedure for
implantation. The surgical procedure, or partial laminectomy,
requires the resection and removal of certain vertebral tissue to
allow both access to the dura and proper positioning of a
laminotomy lead. The laminotomy lead offers a more stable platform,
which is further capable of being sutured in place, that tends to
migrate less in the operating environment of the human body.
[0011] Percutaneous leads require a less-invasive implantation
method and, with a plurality of leads, provide a user the ability
to create almost any electrode array. Although likely more stable
during use, laminotomy leads do not offer an opportunity for
electrode array variance due to the predetermined structure which
defines their electrode arrays.
[0012] To supply suitable pain-managing electrical energy,
stimulation leads are connected to multi-programmable stimulation
systems, or energy sources (not shown). Typically, such systems
enable each electrode of a connected stimulation lead to be set as
an anode (+), a cathode (-), or in an OFF-state. As is well known,
an electric current "flows" from an anode to a cathode.
Consequently, using the laminotomy lead of FIG. 1 as an example, a
range of very simple to very complex electric fields can be created
by defining different electrodes in various combinations of (+),
(-), and OFF. Of course, in any instance, a functional combination
must include at least one anode and at least one cathode.
[0013] Notwithstanding the range of electric fields that are
possible with conventional stimulation leads, in certain instances
it is necessary to concentrate electrical energy at a particular
point, or over a small region. As an example of such occasion,
assume pain-managing electrical energy is applied at or about T8 to
address only localized lower back pain. At T8, however, spinal
nervous tissue corresponding to the patient's lower extremities
commingles with the specific spinal nervous tissue associated with
the lower back. Moreover, it is common that the lower back-related
spinal nervous tissue is deeply embedded within the combined spinal
nervous tissue. Accordingly, it becomes desirable to focus applied
electrical energy to the targeted nervous tissue to (i) reach the
deeply situated target nervous tissue and (ii) avoid undesirable
stimulation of unafflicted regions.
[0014] Accordingly, a need exists for a stimulation lead that
includes a structural arrangement that facilitates a concentration
of delivered electrical energy at a point, i.e., for a given
electrode, or over a small region, i.e., for a plurality of
electrodes.
SUMMARY OF THE INVENTION
[0015] At least one aspect of the present invention is drawn to a
stimulation lead having a plurality of terminals, a plurality of
electrodes carried by a body, and a plurality of conductors, as a
conductor electrically couples one terminal with a respective
electrode. The plurality of electrodes includes a first electrode
and a second electrode, whereby the second electrode substantially
encircles at least the first electrode.
[0016] An object of the present invention is to provide a
electrical stimulation lead having at least two electrodes. Unlike
known stimulation leads, however, an arrangement of the electrodes
of the stimulation lead should facilitate operatively concentrating
delivered electrical energy at a point, i.e., for a given
electrode, or over a small region, i.e., for a plurality of
electrodes.
[0017] Other objects and advantages of the present invention will
be apparent to those of ordinary skill in the art having reference
to the following specification together with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a plan view of a conventional laminotomy spinal
cord stimulation lead;
[0019] FIG. 2 is a plan view of a laminotomy spinal cord
stimulation lead that illustrates the fundamental principle of
construction of the present invention;
[0020] FIG. 3 is a plan view of a first embodiment of a laminotomy
spinal cord stimulation lead in accordance with the present
invention;
[0021] FIG. 4 is a plan view of a second embodiment of a laminotomy
spinal cord stimulation lead in accordance with the present
invention;
[0022] FIG. 5 is a plan view of a third embodiment of a laminotomy
spinal cord stimulation lead in accordance with the present
invention; and
[0023] FIG. 6 illustrates a percutaneous implantation of the
laminotomy spinal cord stimulation lead of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Various embodiments, including preferred embodiments, will
now be described in detail below with reference to the
drawings.
[0025] In reference to FIG. 1, the illustrated laminotomy lead 10
includes a proximal end 12 and a distal end 14. The proximal end 12
includes a plurality of electrically conductive terminals 18, and
the distal end 14 includes a plurality of electrically conductive
electrodes 20 arranged within a flat, thin paddle-like structure
16. Typically, each terminal 18 is electrically connected to a
single electrode 20 via a conductor 22; however, a terminal 18 can
be connected to two or more electrodes 20.
[0026] Terminals 18 and electrodes 20 are preferably formed of a
non-corrosive, highly conductive material. Examples of such
material include stainless steel, MP35N, platinum, and platinum
alloys. In a preferred embodiment, terminals 18 and electrodes 20
are formed of a platinum-iridium alloy.
[0027] The sheaths 24 and the paddle structure 16 are formed from a
medical grade, substantially inert material, for example,
polyurethane, silicone, or the like. Importantly, such material
must be non-reactive to the environment of the human body, provide
a flexible and durable (i.e., fatigue resistant) exterior structure
for the components of lead 10, and insulate adjacent terminals 18
and/or electrodes 20. Additional structure (e.g., a nylon mesh, a
fiberglass substrate) (not shown) can be internalized within the
paddle structure 16 to increase its overall rigidity and/or to
cause the paddle structure 16 to assume a prescribed
cross-sectional form (e.g., a prescribed arc along a transverse
direction of the paddle structure 16) (not shown).
[0028] The conductors 22 are carried in sheaths 24. In the
illustrated example, each sheath 24 carries eight (8) conductors
22. Given the number of conductors 22 that are typically carried
within each sheath 24, the cross-sectional area of each conductor
20 is restricted. As but one example, for a sheath 24 in accordance
with the present invention, having an outer diameter of
approximately 0.055 inches, each conductor 22 would be
approximately 0.0065 inches in diameter.
[0029] Each conductor 22 is formed of a conductive material that
exhibits desired mechanical properties of low resistance, corrosion
resistance, flexibility, and strength. While conventional stranded
bundles of stainless steel, MP35N , platinum, platinum-iridium
alloy, drawn-brazed silver (DBS) or the like can be used, a
preferred embodiment of the present invention uses conductors 22
formed of multi-strands of drawn-filled tubes (DFT). Each strand is
formed of a low resistance material and is encased in a high
strength material (preferably, metal). A selected number of
"sub-strands" are wound and coated with an insulative material.
With regard to the operating environment of the present invention,
such insulative material protects the individual conductors 22 if
its respective sheath 24 was breached during use. Wire formed of
multi-strands of drawn-filled tubes to form conductors 22, as
discussed here, is available from Temp-Flex Cable, Inc. (City,
State).
[0030] In addition to providing the requisite strength,
flexibility, and resistance to fatigue, conductors 22 formed of
multi-strands of drawn-filled tubes, in accordance with the above
description, provide a low resistance alternative to other
conventional materials. Specifically, a stranded wire, or even a
coiled wire, of approximately 60 cm and formed of MP35N or
stainless steel or the like would have a measured resistance in
excess of 30 ohms. In contrast, for the same length, a wire formed
of multi-strands of drawn-filled tubes could have a resistance less
than 4 ohms. Accordingly, in a preferred embodiment, each conductor
22, having a length equal to or less than 60 cm, has a resistance
of less than 25 ohms. In a more preferred embodiment, each
conductor 20, having a length equal to or less than 60 cm, has a
resistance equal to or less than 10 ohms. In a most preferred
embodiment, each conductor 20, having a length equal to or less
than 60 cm, has a resistance of less than 4 ohms.
[0031] While a number of material and construction options have
been discussed above, it should be noted that neither the materials
selected nor a construction methodology is critical to the present
invention.
[0032] The following discussion is directed to a number of examples
illustrated in FIGS. 2-5. While the examples set forth a variety of
variations of the present invention, it may be readily appreciated
that the present invention could take any of a variety of forms and
include any number of electrodes. Importantly, however, the present
invention is characterized by a first electrode, or a first
electrode array, that substantially encompasses or circumscribes at
least one independently controlled electrode. The first electrode
(or first electrode array) can operatively form an "anode guard"
relative to the substantially surrounded independently controlled
electrode(s). To clarify such structure, the following examples are
provided.
[0033] FIG. 2 illustrates a laminotomy lead 100a featuring the
fundamental principle of construction of the present invention.
Specifically, the paddle structure 16 includes a plurality of
electrodes 20, wherein one electrode 30 substantially surrounds
another electrode 40. For this embodiment, each electrode is
electrically coupled to an independent terminal (not shown), which
is connectable to a programmable energy source, for example, a
pulse generator (not shown). The construction and arrangement of
the terminals (and related conductors, which establish the desired
electrical coupling) are not in themselves unique but are
consistent with that described hereinabove.
[0034] Depending upon a configuration/programmability of the energy
source connected to the laminotomy lead 100a, either the electrode
30 or the electrode 40 could operatively assume a positive polarity
(with the remaining electrode assuming a negative polarity) during
active delivery of electrical energy therefrom. For purposes of
focusing applied electrical energy, however, the electrode 30
assumes a positive polarity, whereby in such a condition the
electrode 30 forms an "anode guard" relative to the encompassed
electrode 40.
[0035] The electrode 30 can be constructed in a manner and from a
material consistent with that used to form electrode 40.
Alternatively, as longitudinal and transverse flexibility of the
paddle structure 16 are desirable, it is preferred that the
electrode(s) 30 be formed so as to not otherwise significantly
impair the inherent flexibility of the paddle structure 16.
Accordingly, the electrode 30 can be constructed using less
material--in a thickness direction--than an electrode 40, formed
from a conductive film/foil applied to the surface of the paddle
structure 16, formed through deposition of a conductive material,
constructed using a coil (FIG. 3), or formed using other like
processes/techniques that are well known in the art.
[0036] An anode guard functions, in part, to laterally limit an
applied electrical field, which assists in reducing extraneous
stimulation of surrounding neural tissue. In this regard, neural
tissue at or immediately about the cathode electrode(s) is
depolarized, while neural tissue relative to the anode guard is
subject to hyperpolarization. Further, an anode guard in accordance
with that illustrated in FIG. 2 focuses an applied electrical field
from practically every direction to any cathode-electrode(s)
positioned therein. Thus, for any given drive signal from a coupled
energy source, the stimulation lead of the present invention can
effect a deeper application of applied energy than stimulation
leads of a conventional nature.
[0037] FIG. 3 illustrates a four-channel (a "channel" represents a
controllable electrical output) laminotomy stimulation lead 100b in
accordance with the present invention. The stimulation lead 100b is
shown having a plurality of electrodes 20, which includes an
electrode 30, formed from a coil, that substantially circumscribes
an electrode array formed of three electrodes 40a, 40b, and
40c.
[0038] Again, while each of the plurality of electrodes 20 could
individually function as a cathode or an anode, or placed in an
OFF-state, it is intended that the electrode 30, as an anode guard,
assume a positive polarity. To this end, the form of an electric
field generated using the electrode 30 is altered/controlled
through setting each of the electrodes 40a, 40b, and 40c as a
cathode, an anode, or in an OFF-state. Such control over the
electrodes 40a, 40b, and 40c enables formation of a focused
electrical field with a single electrode 40 as a cathode or a more
diverse electrical field spread over two or more electrodes 40,
whereas each electrode 40 of such plurality functions as a
cathode.
[0039] Furthermore, to the extent that the benefits of an anode
guard are not required, the electrode 30 may be placed in an
OFF-state. In such operative configuration, the laminotomy lead
100b then functions in a manner consistent with conventional
laminotomy stimulation leads.
[0040] The configuration illustrated in at least FIG. 3 enables the
delivery of electrical energy to targeted nervous tissue with fewer
required electrodes. Moreover, it should be noted that the narrow
transverse dimension of the laminotomy lead 100b enables such
laminotomy lead to be implanted percutaneously, if so desired,
using a special insertion needle 200 that accommodates the greater
dimensions of a laminotomy lead, for example, the laminotomy lead
100b. To this end, implantation of the present invention would be
similar that described hereinabove in the context of percutaneous
catheters.
[0041] FIG. 4 illustrates a laminotomy stimulation lead 100c in
accordance with the present invention. The stimulation lead 100c
includes a plurality of electrodes 20, which includes a first
electrode array having a plurality of electrodes 30a-30d that
substantially surrounds a second electrode array having a plurality
of electrodes 40.
[0042] Similar to the stimulation lead 100b, the second electrode
array of the stimulation lead 100c is formed of a group of
individual electrodes that can respectively be set as an anode, a
cathode, or in an OFF-state. Although the electrodes 40 of the
stimulation lead 100c are shown in two, staggered columns, the
arrangement of the electrodes 40 of the second electrode array is
not critical to the present invention--the electrodes 40 of the
second electrode array may assume any multiple-column
arrangement.
[0043] Unlike the other embodiments illustrated, the anode guard is
constructed of a first electrode array that includes electrodes
30a-30d. In a preferred embodiment, each electrode of the first
electrode array extends for a length substantially equivalent to a
comparable dimension of at least two of electrodes 40 of the second
electrode array. Further, and generally consistent with the
structures of FIGS. 2, 3, and 5, the collection of electrodes
30a-30d form an effectively continuous ring that substantially
extends about the second electrode array.
[0044] Although each of the electrodes 30a-30d may be electrically
independent (i.e., coupled to respective conductors/terminals),
allowing each respective electrode to be an anode, a cathode, or
set to an OFF-state, in consideration of practical space
limitations, it may be advisable to electrically couple two or more
of electrodes 30a-30d. In a simplest form, electrodes 30a-30d are
electrically linked so as to maintain the same electrical state
during operation and minimize the number of conductors necessary to
couple the first electrode array to an energy source.
[0045] Of a final note, depending upon the form/construction of the
electrodes 30a-30d, the segmented nature of the illustrated first
electrode array of this embodiment would improve longitudinal
flexibility of the paddle structure 16. As additional segmentation
of electrodes 30b and 30d would likewise improve transverse
flexibility of the paddle structure 16, such modification is within
the scope of this embodiment of the present invention.
[0046] To maintain a generally uniform electrical field between an
anode guard and one or more cathode-electrodes, the distance
between the one or more cathode-electrodes and the anode guard
should be largely equidistant. Achieving this optimum arrangement
is typically hindered by both a need that the platform structure 16
fit easily within the narrow confines of the human epidural space
and a desire that the provided electrode array(s) span a
significant vertebral range of spinal nervous tissue.
[0047] While a long electrode array substantially surrounded by a
single anode guard electrode (or a composite anode guard) would not
be operatively ineffective, an alternative to such structure is
illustrated by the stimulation lead 100d of FIG. 5. Specifically,
the electrodes 40 can be divided into groups 40a and 40b, and each
electrode group 40a and 40b is encompassed by its own independently
controlled anode guard electrode 30a and 30b.
[0048] While the invention has been described herein relative to a
number of particularized embodiments, it is understood that
modifications of, and alternatives to, these embodiments, such
modifications and alternatives realizing the advantages and
benefits of this invention, will be apparent those of ordinary
skill in the art having reference to this specification and its
drawings. It is contemplated that such modifications and
alternatives are within the scope of this invention as subsequently
claimed herein, and it is intended that the scope of this invention
claimed herein be limited only by the broadest interpretation of
the appended claims to which the inventors are legally
entitled.
* * * * *