U.S. patent application number 15/267765 was filed with the patent office on 2017-03-09 for electrode array configured to wrap around and stimulate the spinal cord.
The applicant listed for this patent is University of Iowa Research Foundation, University of Virginia Patent Foundation. Invention is credited to Timothy Brennan, Brian Dalm, George T. Gillies, Matthew Howard, Randall S. Nelson, Steven Scott, Robert Shurig, Marcel Utz.
Application Number | 20170065814 15/267765 |
Document ID | / |
Family ID | 46051326 |
Filed Date | 2017-03-09 |
United States Patent
Application |
20170065814 |
Kind Code |
A1 |
Howard; Matthew ; et
al. |
March 9, 2017 |
ELECTRODE ARRAY CONFIGURED TO WRAP AROUND AND STIMULATE THE SPINAL
CORD
Abstract
A method for treating intractable pain via electrical
stimulation of the spinal cord. Remote, non-contact stimulation of
a selected region of spinal cord is achieved by placement of a
transceiver patch directly on the surface of that region of spinal
cord, with said patch optionally being inductively coupled to a
transmitter patch of similar size on either the outer or inner wall
of the dura surrounding that region of the spinal cord. By
inductively exchanging electrical power and signals between said
transmitter and transceiver patches, and by carrying out the
necessary electronic and stimulus signal distribution functions on
the transceiver patch, the targeted dorsal column axons can be
stimulated without the unintended stray stimulation of nearby
dorsal rootlets. Novel configurations of a pliable surface-sheath
and clamp or dentate ligament attachment features which realize
undamaging attachment of the patch to the spinal cord are
described.
Inventors: |
Howard; Matthew; (Iowa City,
IA) ; Brennan; Timothy; (Iowa City, IA) ;
Dalm; Brian; (Coralville, IA) ; Utz; Marcel;
(Charlottesville, VA) ; Gillies; George T.;
(Charlottesville, VA) ; Scott; Steven; (Excelsior,
MN) ; Nelson; Randall S.; (Pine Springs, MN) ;
Shurig; Robert; (Saint Paul, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Iowa Research Foundation
University of Virginia Patent Foundation |
Iowa City
Charlottesville |
IA
VA |
US
US |
|
|
Family ID: |
46051326 |
Appl. No.: |
15/267765 |
Filed: |
September 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14821540 |
Aug 7, 2015 |
9486621 |
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15267765 |
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13885157 |
Jan 6, 2014 |
9364660 |
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PCT/US11/60462 |
Nov 11, 2011 |
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14821540 |
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61412651 |
Nov 11, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/36071 20130101;
A61N 1/375 20130101; Y10T 29/49117 20150115; A61N 1/37205 20130101;
A61N 1/0553 20130101; A61N 1/37518 20170801; A61N 1/372 20130101;
A61N 1/3787 20130101; A61N 1/0558 20130101; A61N 1/37514
20170801 |
International
Class: |
A61N 1/05 20060101
A61N001/05; A61N 1/375 20060101 A61N001/375; A61N 1/378 20060101
A61N001/378; A61N 1/36 20060101 A61N001/36 |
Claims
1. An electrode array configured for delivering electrical
stimulation directly to the spinal cord of a subject from inside
the dura surrounding the spinal cord, wherein the array comprises:
(1) a curved backing having a curvature that is contoured to match
the curvature of the spinal cord; (2) a plurality of electrodes
projecting from inside the curvature of the backing, positioned so
as to directly engage the spinal cord when the curved backing is
conformed to the spinal cord; and (3) one or more flexible
attachment arms configured for wrapping around at least part of the
circumference of the spinal cord inside the dura, thereby securing
the electrodes in contact with the spinal cord; wherein the
electrode array has a sufficiently thin profile and configuration
such that when the array of electrodes is secured in direct contact
with the pial surface of the spinal cord, a CSF filled space is
maintained between the electrode array and the dura.
2. An electrode array configured for delivering electrical
stimulation directly to the spinal cord of a subject from inside
the dura surrounding the spinal cord, wherein the array comprises:
(1) a body configured to lie against the spinal cord inside the
dura; (2) a flexible band having a distal end and a proximal end,
attached through the proximal end to the body; and (3) a plurality
of electrodes; wherein the body and the flexible band combine to
form a substrate with a length that matches the circumference of
the spinal cord and is configured such that the distal end of the
flexible band can be passed around the circumference of the spinal
cord and secured to an opposing edge of the substrate, whereupon
the substrate completely encircles the spinal cord; wherein the
electrodes are distributed along the substrate such that when the
array is secured around the spinal cord inside the dura, the
electrodes surround and are in contact with the spinal cord; and
wherein the electrode array has a sufficiently thin profile and
configuration such that when the array of electrodes is secured in
direct contact with the pial surface of the spinal cord, a CSF
filled space is maintained between the electrode array and the
dura.
3. The electrode array of claim 1, comprising a plurality of
flexible attachment arms projecting from the backing and configured
to wrap around the spinal cord circumferentially in opposite
directions.
4. The electrode array of claim 3, wherein at least some of the
electrodes are positioned inside and along the arms.
5. The electrode array of claim 1, wherein the one or more flexible
attachment arms are sized to only partly encircle the spinal cord,
and have a mechanical compliance such that once conformed to the
spinal cord, the electrode array is secured in position.
6. The electrode array of claim 1, wherein the curved backing is
sufficiently elastic to expand and contract with spinal cord
movement.
7. The electrode array of claim 1, wherein individual electrodes in
the array are flexibly mounted to the backing by a soft resilient
material, thereby allowing each electrode to move relative to the
backing.
8. The electrode array of claim 1, wherein the backing has a
thickness of 0.5 mm or less.
9. The electrode array of claim 1, further comprising penetrating
electrodes projecting from inside the curvature of the backing,
configured to penetrate into the spinal cord, thereby accessing an
internal target subregion within the spinal cord.
10. The electrode array of claim 1, further comprising a signal
receiver disposed along the backing of the array and configured to
receive energy wirelessly from a signal generator located outside
an external surface of the patient's dura.
11. An assembly for treating pain or other neurological condition
in a patient, comprising the electrode array of claim 2, and a
means for securely connecting the distal end of the flexible band
to an opposing edge of the array so that the array stays in
position around the circumference of the spinal cord at a target
location.
12. A system for treating pain or other neurological condition in a
patient, comprising the electrode array of claim 1, and circuitry
that is configured to deliver electrical stimulation to the spinal
cord by way of the electrodes.
13. The system of claim 12, wherein the circuitry comprises a
signal generator suitable for providing energy to the electrode
array from outside the patient's dura, and a conductor extendable
through the patient's dura to convey energy from the generator to
the electrode array.
14. A system for treating pain or other neurological condition in a
patient, comprising the electrode array of claim 2, and circuitry
that is configured to deliver electrical stimulation to the spinal
cord by way of the electrodes.
15. The system of claim 14, wherein the circuitry comprises a
signal generator suitable for providing energy to the electrode
array from outside the patient's dura, and a conductor extendable
through the patient's dura to convey energy from the generator to
the electrode array.
16. A method for preparing a patient for spinal cord stimulation
with the electrode array of claim 1, comprising: implanting the
electrode array inside the dura of the subject such that the
electrodes in the array are placed in direct contact with the pial
surface of the subject's spinal cord at a position from which to
deliver electrical stimuli to a target subregion of the spinal
cord; and securing the electrode array so that it stays in place
against the spinal cord as the spinal cord moves inside the
dura.
17. A method for preparing a patient for spinal cord stimulation
with the electrode array of claim 2, comprising: implanting the
substrate around the patient's spinal cord inside the dura such
that the electrodes contact the spinal cord at a target subregion;
connecting the distal end of the flexible band to an opposing side
of the substrate, thereby completely encircling the spinal cord and
securing the electrode array so that it stays in place against the
spinal cord as the spinal cord moves inside the dura.
18. A method of stimulating the spinal cord of a subject using the
electrode array of claim 1, comprising delivering electrical
stimuli to a target subregion of the spinal cord from the electrode
array secured against the subject's spinal cord inside the
dura.
19. A method of stimulating the spinal cord of a subject using the
electrode array of claim 2, comprising delivering electrical
stimuli to a target subregion of the spinal cord from the electrode
array secured against the subject's spinal cord inside the
dura.
20. The method of claim 18, which is a method of treating spinal
cord injury.
Description
CROSS REFERENCE TO RELATED APPLICATION DATA
[0001] This application is a continuation application of U.S.
patent application Ser. No. 14/821,540, filed on Aug. 7, 2015,
which is continuation application of U.S. patent application Ser.
No. 13/885,157, filed on Jan. 6, 2014, and patented as U.S. Pat.
No. 9,364,660, on Jun. 14, 2016, which is The U.S. National Stage
of International Application PCT/US2011/060462, filed on Nov. 11,
2011, which claims the benefit of U.S. Provisional Application No.
61/412,651, filed Nov. 11, 2010; the full disclosures of which are
incorporated herein by reference in their entirety for all
purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to medical devices
and methods. More particularly, the present invention relates to
electrode structures and systems for delivering electrical pulses
directly to the spinal cord of a patient to block pain and for
other purposes.
[0004] The use of spinal cord stimulation (SCS) to relieve
intractable pain symptoms originated in the 1960's along with
emerging theories of the neural basis of pain perception and the
pathophysiology of chronic pain disorders. Results from
experimental animal studies demonstrated the existence of neural
pathways that originate within the brain and project axons through
the spinal cord that eventually terminate at spinal cord levels
where pain signals from the peripheral nervous system enter the
central nervous system. These pathways are postulated to play a
role in the `top-down` modulation of pain perception. Human SCS
studies were initiated based on the theory that by using electrical
stimulation to artificially activate descending pathways within the
dorsal column of the spinal cord, the processing of pain related
signals below the stimulation site could be attenuated, blocked or
otherwise modulated.
[0005] Although the specific neural mechanisms that underlie the
clinical efficacy of this treatment remain poorly understood, there
is now abundant clinical evidence that SCS is capable of providing
sustained pain relief to select patients with intractable chronic
pain. The most important limitation of this treatment method is
that a high percentage of patients implanted with an SCS system or
device may experience only marginal improvement, or no improvement,
in their pain symptoms. Treatment success rates of 50% or less are
frequently reported with known SCS systems.
[0006] The neural mechanisms that mediate the clinical effects of
SCS are complex and likely involve activation of multiple ascending
and descending neural pathways within the spinal cord. Based on
empiric clinical evidence, a number of treatment concepts have
emerged to guide SCS strategies. In general, electrical stimulation
will evoke sensory perceptions in the painful area of the body in
order for the treatment to be effective. To accomplish this, the
region within the dorsal column of the spinal cord that contains
axons that are functionally related to the painful body area must
be activated. Dorsal column axons are somatotopically organized,
meaning that the axons that are functionally related to a
particular body area are positioned in close proximity to each
other, and there is an orderly anatomical pattern of organization
within the spinal cord for the different groups of axons linked to
different body areas. In the cervical spinal cord, for example,
dorsal column axons functionally linked to the back region may be
relatively close to the midline of the spinal cord, and axons
linked to the arms are positioned relatively more laterally.
[0007] Adverse effects of electrical stimulation can result from
unintended activation of non-targeted neural structures. When the
dorsal nerve rootlets are activated, for example, discomfort can
result. The effectiveness of SCS treatment is generally dependent
on the capacity of the device to selectively activate targeted
axons within a specific sub-region of the dorsal column, without
activating the nearby dorsal rootlets. This concept is incorporated
into researcher's use of the term therapeutic range to describe the
range of stimulus intensities that are above perceptual threshold
(i.e. effectiveness threshold) but below the discomfort threshold,
beyond which stimulation effects are no longer tolerated by the
patient. The ideal SCS device will be capable of efficiently and
safely delivering highly focused electrical stimuli to the targeted
sub-region of the dorsal column without activating nearby
structures. The electrode contact should be positioned as close to
the targeted axons as possible and the resulting volumetric pattern
of tissue activation should tightly conform to the anatomy of the
targeted neural pathway.
[0008] The spinal cord is cylindrically shaped and positioned
centrally within the spinal canal. The spinal canal is lined by a
dural membrane and contains cerebrospinal fluid (CSF) that
surrounds the spinal cord and fills the region between the outside
surface of the spinal cord and the inside surface of the dural
membrane. This CSF-filled space plays a critical role in normal
spinal cord biomechanics and is an important factor that should be
considered when performing spinal surgery. During normal movements,
such as flexion and extension of the body, the spinal cord moves
within the spinal canal, altering its position relative to the
dural lining of the spinal canal. The volume of CSF surrounding the
spinal cord serves as a frictionless buffer during these movements.
In some pathological conditions (e.g. tethered cord syndrome) this
normal motion of the spinal cord is impeded by tissue attachments
bridging the space between the spinal cord and the dural lining,
resulting in dysfunction of the spinal cord. In other pathological
conditions, a tissue barrier forms within the spinal canal (e.g.
following trauma or infection) that disrupts the normal flow of CSF
over the surface of the spinal cord. In this setting CSF may
accumulate within the substance of the spinal cord to form a syrinx
and cause neurological dysfunction.
[0009] The dural lining of the spinal canal should be managed with
particular care during spinal surgery. If a defect is created in
this lining, a CSF fistula may develop which increases the risk of
a wound complication (infection or dehiscence) and may cause the
patient to experience disabling positional headaches. In order to
access the spinal cord itself, the dural membrane should be opened
surgically and this is performed in a manner that allows the
surgeon to achieve a `water-tight` closure at the completion of the
operation. Typically this involves sharply incising the dura over
the dorsal aspect of the spinal canal, a location that is readily
accessible and well visualized during surgery. Later the dura is
re-approximated by suturing together the well defined cut margins
of the fibrous membrane. This closure technique is performed in a
manner that preserves the CSF filled space separating the dura from
the spinal cord, thus preventing mechanical constriction, or
tethering, at the surgical site.
[0010] These anatomical and surgical considerations have impacted
the evolution of a wide range of operative procedures, including
spinal cord stimulator surgery. When the design intent is to
minimize the risk of surgical complications, the optimal strategy
is to entirely avoid opening the dural membrane and place the
implant outside of the dura (extra-dural procedure). If the spinal
cord must be accessed directly (intra-dural procedure) the
operation should be designed in a manner that prevents CSF fistula
formation, mechanical tethering of the spinal cord to the dura, or
physical obstruction of the CSF filled space surrounding the spinal
cord.
[0011] There are limitations in the performance characteristics of
the prior art. One such limitation is the following. Existing SCS
devices deliver electrical stimuli through electrodes placed
outside of the fibrous lining of the spinal canal (dura). This
results in inefficient and poorly localized patterns of spinal cord
activation due to the electrical shunting effect of cerebrospinal
fluid that fills the space separating the dural lining and the
spinal cord. This inability to selectively activate targeted
regions of the spinal cord is thought to be an important
contributing factor to the significant incidence of sub-optimal or
poor treatment outcomes with existing SCS devices. Despite these
limitations large numbers of patients are implanted. The size of
the SCS market attests to the large scope of this public health
problem and the fact that under certain circumstances, electrical
activation of the spinal cord provides pain relief for patients who
have failed all other treatment modalities.
[0012] A further limitation of the prior art arises in the nature
of certain tethered forms of spinal cord stimulators. When SCS
electrodes were first placed in human subjects, most were implanted
on the surface of the dura, but in some instances the dura was
opened and electrodes were placed directly on the surface
(intradural) of the spinal cord (Gildenberg 2006, Long 1977, Long
1998, Shealy et al. 1970). The wires from electrodes placed
directly on the spinal cord passed through the dura, thus
mechanically tethering the electrode to the dura. The electrodes
were constructed of conventional conductive and insulting
materials, were bulky, and had a limited number of contacts through
which stimuli could be delivered. The locations of the contacts
relative to targeted and non-targeted neural structures were
difficult to control and could not be adjusted following the
implantation surgery. Because of these factors, and the increased
risks associated with opening the dura, at the time there was no
obvious therapeutic advantage to the intradural approach. The use
of intradural stimulating electrodes was eventually discontinued
and currently all SCS devices use extradural stimulating
electrodes.
[0013] Still another limitation of the prior art arises in terms of
the treatment efficacy. There are two broad classes of extradural
stimulation electrodes. One type can be placed percutaneously
through a needle into the epidural space. These electrodes have
small cylindrically shaped contacts positioned along the shaft of a
flexible linear electrode array. They are used either for minimally
invasive testing of stimulation effects prior to implantation
surgery, or as the device that is permanently implanted. The other
type of extradural electrode is placed during an open surgical
procedure and consists of a flat array of multiple electrode
contacts positioned over the exposed dural surface. An experienced
practitioner is capable of implanting these extradural electrodes
with a high degree of safety. However, the current SCS devices have
suboptimal treatment efficacy. We hypothesize that this shortcoming
is due in large part to the inability of extradural electrodes to
selectively activate the targeted sub-region of the dorsal column
of the spinal cord. By placing devices outside of the dura because
of safety considerations, an intrinsic disadvantage is incurred in
terms of therapeutic efficacy. The presence of a CSF filled space
between an extradural stimulating electrode and the spinal cord
profoundly degrades the ability of the device to create a volume of
electrical activation that selectively encompasses the targeted
sub-region of the spinal cord. This results from the conductive
properties of CSF. CSF is a far more efficient electrical conductor
than any other tissue in the spine (Holsheimer 1998). When an
electrical stimulus delivered by an extradural electrode traverses
the dura and enters the CSF-filled space between the dura and the
spinal cord, a large fraction of the stimulus is electrically
`shunted` diffusely within this CSF filled space. Researchers
estimate that extradural stimulation results in the spinal cord
receiving less than 10% of the delivered stimulus. The stimulus
effect penetrates the spinal cord to a distance of 0.25 mm or less
and the broad volumetric pattern encompasses both targeted (i.e.
dorsal column) and non-targeted (i.e. dorsal rootlets) neural
structures (He et al. 1994, Holsheimer 1998, Holsheimer 2002,
Holsheimer et al. 2007).
[0014] The clinical importance of these limitations of the prior
art are reflected in the numerous efforts made by device
manufactures to mitigate the problems. These include the
development of spatially distributed multi-contact extradural
arrays and stimulation protocols that enable delivery of electrical
charge distributions over widely variable anatomical patterns. This
strategy allows the physician to adjust the anatomical location of
maximal stimulation on the dural surface, but the presence of CSF
shunting continues to markedly attenuate the stimulation effects
within the spinal cord. Clinicians have also used a strategy of
placing multiple cylindrical electrodes within the extradural space
for the purpose of mechanically reducing the size of the CSF-filled
space and displacing the electrode contacts to a position closer to
the spinal cord (Holsheimer et al. 2007). A device modification
recently introduced by one of the largest manufacturer of SCS
devices seeks to address problems associated with movement of the
spinal cord within the CSF-filled spinal canal that occurs when
patients change position. These positional changes alter the
spatial relationship between an extradural electrical source and
the spinal cord, and the pattern of tissue activation. The new
device senses patient position and automatically adjusts stimulus
parameters for the purpose of achieving stable therapeutic effects.
As with all other SCS design changes introduced to-date, the
addition of a position sensor does not address the fundamental
problem of CSF shunting of the electrical stimulus.
BRIEF SUMMARY OF THE INVENTION
[0015] The present invention addresses a major public health
problem: medically intractable chronic pain. Specifically,
embodiments of the invention provide devices and methods for
providing effective symptomatic relief for patients suffering from
chronic pain syndromes resulting from injury or disease affecting
musculoskeletal, peripheral nerve, and other organ systems of the
body. More specifically, embodiments of the invention provide
surgically implanted devices adapted for electrical stimulation of
tissues of the nervous system. Still more specifically, some
exemplary embodiments of the present invention provide devices and
methods for direct electrical stimulation of the spinal cord,
optionally by wireless inductive coupling of signals from an
electrical signal generator which may be located on the dura
surrounding the spinal cord to an electrode assembly adapted to be
implanted directly on the surface of the spinal cord, thus
obviating the need for wires, leads or other such connections
disposed through the dura. Many embodiments of the spinal cord
stimulation devices described herein may be supported in engagement
with the spinal cord by attaching features of the device to dentate
ligaments extending laterally between the spinal cord and the
surrounding dura, with either wireless or wired coupling to a
signal generator disposed outside the dura. Most embodiments of the
devices and methods of the present invention will electrically
stimulate well defined, circumscribed sub-regions of the spinal
cord with both a degree of spatial precision and a therapeutic
level of electrical intensity that cannot be achieved using
existing spinal cord stimulation (SCS) devices. In specific
embodiments, the electrode assemblies comprise flexible electronic
microcircuitry, optionally with thin-film electrode arrays, at
least the latter of which are configured to be in direct physical
contact with the surface of the spinal cord. The implanted
electrode assemblies may be remotely powered and controlled (with
no physical connections to or through the dural lining of the
spinal canal), or may have a plurality of conductors extending
through the dura, to selectively activate targeted regions of the
spinal cord with extreme precision and the requisite electrical
intensity.
[0016] The devices and methods of the subject invention address the
most important deficiencies of current SCS devices in the prior art
by incorporating the following design features into the device:
[0017] 1) the electrical stimuli are delivered directly to the
spinal cord;
[0018] 2) a dense array of electrode contacts enables delivery of
highly localized, spatio-temporally synchronized (could also
multi-plex, alternating stimuli between various electrode
montages), and positionally selective electrical stimuli to any
targeted sub-region of the spinal cord;
[0019] 3) the device does not mechanically tether or form a
physical connection between the spinal cord and dura that
significantly alters the natural support and flexibility provided
by the dentate ligaments;
[0020] 4) the implantable electrode assembly has an ultra-thin
physical profile that does not obstruct or alter CSF flow patterns
around the spinal cord;
[0021] 5) the contact forces between the device and the spinal cord
are stable and unvarying, and hence patient movement does not
affect these contact properties, which results in optimal
electrical coupling between electrode contacts and spinal cord
tissue;
[0022] 6) the compliant nature of the device materials accommodates
pulsations of the spinal cord without any harmful reactive or
dissipative counter-forces;
[0023] 7) the materials used to construct the device are highly
resistant to electronic or structural failure with break rates that
may be lower than (or similar to) existing devices, optionally
using materials that are already included in stimulation implant
devices or novel proprietary materials;
[0024] 8) the surgical procedure (laminectomy) used to implant the
device is well established and safe, and when performed by skilled
practitioners, the risk of CSF fistula formation with this
procedure will not differ significantly from complication rates
associated with current surgical implantation procedures used to
implant extradural electrode arrays;
[0025] 9) the increased duration of implantation surgery, compared
to current procedure times for surgical implantation of extradural
SCS devices, will not exceed 30 minutes; and
[0026] 10) the manufacturing cost of the new device may (in at
least some embodiments) be less than that for existing devices
(particularly for the `wired` I-Patch).
[0027] The electrode assembly, hereinafter referred to as the
Iowa-Patch (I-Patch) fulfills at least some of these design
criteria, and is composed of advanced flexible electronics
technologies. The electronic elements of the I-Patch are imbedded
in (optionally being between layers of) a flexible polymeric or
elastomeric "patch" or substrate. Electrical stimuli are delivered
via an array of contacts that, when in position, can provide axial
and circumferential coverage directly onto the lateral and/or
dorsal surfaces of the spinal cord. Precisely localized patterns of
spinal cord stimuli are achieved by selectively activating the
preferred combinations of electrode contacts in any desired,
programmable spatio-temporal sequences. In one embodiment, flexible
polymer `arms` of the device are optionally contoured to provide a
continuous, gentle inward "capture" force that insures an optimal
electrical interface between the device contacts and spinal cord
tissue, while avoiding mechanical constriction of the spinal
cord.
[0028] In one embodiment, the dorsal (outer) surface of the I-Patch
contains embedded microcircuitry that implements stimulus delivery
algorithms. Circuit elements may include an RE antenna that
receives power and control commands from an intra- or extradural
device described below, as well as other circuit elements that
generate and route electrical stimuli to the appropriate electrode
contacts. The self-contained I-Patch may have no mechanical or
other physical connection with any other element of the SCS system.
Alternatively, small gauge, flexible conductors may extend between
the dura and the spinal cord along a dentate ligament, to which
said conductors may be affixed, said ligaments being the structures
of the body that support the spinal cord within the dura. Hence,
when the device is in place there is no substantive spinal cord
tethering or disruption of CSF flow dynamics around the spinal
cord. All the device surfaces, with the exception of the electrode
contacts, are either composed of or coated with a biocompatible
insulating material, such as medical grade silicone, and the
finished intradural device is very thin, on the order of (and
typically being) 0.5 mm or less.
[0029] In one embodiment, the I-Patch is inserted surgically by
performing a laminectomy, creating a mid-line dorsal durotomy,
inserting the device onto the spinal cord, and then suturing the
dura closed. Because, after implantation of some embodiments, no
portion of the device penetrates the dura, and the dura is opened
and closed in an optimally controlled manner, the risk of CSF
fistula formation will be low.
[0030] A power and control signal transfer circuit assembly,
constructed within a thin, hermetic encapsulation, is positioned
either in the extradural space (over an exterior surface of the
dura) or on the inside surface of the dural membrane, in either
case overlying the I-Patch implant. This transfer circuit assembly
generates power and command signals that are transmitted across the
CSF filled space surrounding the spinal cord, and are received by
the I-Patch, either wirelessly or along a conductor. The power
and/or signal circuit assembly (or components thereof) may be
incorporated in the main power supply battery and control circuit
assembly in wired embodiments of the I-Patch. The extradural device
is secured in place using sutures and includes flexible electrical
leads that are connected to a power supply battery and control
circuit assembly that is implanted in the subcutaneous tissue of
the patient's abdominal wall. The entire system can be controlled
via wireless commands that employ technologies similar to those
used in standard SCS devices. The flexible microelectronics
materials used are extremely robust and resistant to breakage. Such
circuits have been used extensively in harsh conditions ranging
from deep space (rockets and satellites) to consumer use of folding
hand-held cell phones.
[0031] The I-Patch system specifically targets one aspect of SCS
device performance and value: treatment efficacy. Because of
improvements in the ability to precisely activate targeted
sub-regions of the spinal cord, the I-Patch system will
significantly improve the treatment efficacy when compared to
current devices.
[0032] The I-Patch system can be used for all spinal cord
stimulation applications, including treatment of patients with
Parkinson's disease, Spinal Cord Injury, and Congestive Heart
Failure. While usually employing surface contact electrodes, the
system can also be modified to incorporate penetrating
microelectrodes that emanate from the I-Patch platform and enable
delivery of electrical stimuli to sub-surface neural targets. Such
a system can be used not only in the spinal cord, but also in the
brain and other organ systems.
[0033] One skilled in the art can see that many other embodiments
of means and methods for non-contact spinal cord stimulation
according to the technique of the invention, and other details of
construction and use thereof, constitute non-inventive variations
of the novel and insightful conceptual means, system, and technique
which underlie the present invention.
[0034] Thus, in a first specific aspect of the present invention a
method for treating pain in a patient comprises conformably
positioning an electrode array over a surface of the patient's
spinal cord so that a plurality of individual electrodes in the
array directly contact selected locations on the spinal cord.
Electrical stimulation energy is then delivered in a controlled
spatio-temporal sequence to a targeted sub-region of the spinal
cord to relieve pain without stimulating dorsal nerve rootlets.
Typically, conformably positioning the electrode array comprises
circumscribing a structure of the array around the spinal cord,
with some embodiments circumscribing more than 180.degree. but less
than all (360.degree.) of the spinal cord circumference.
Conveniently, the circumscribing array structure can have an
elastic C-shaped geometry which can be opened and elastically
closed over the spinal cord to hold the electrode array in place
while accommodating spinal cord pulsation and other motions. In
this way, the electrode array structure when implanted to
circumscribe the spinal cord will not substantially obstruct CSF
flow, thus reducing the risk of syrinx formation. Alternative
embodiments may circumscribe less than 180.degree. of the spinal
cord, with the electrodes of the array optionally being disposed
primarily or even entirely over the dorsal surface of the spinal
cord between left and right dentate ligaments.
[0035] In preferred aspects of the method of the present invention,
the individual electrodes will be distributed over at least points
on the dorsal surfaces of the spinal cord, and optionally over the
lateral and ventral surfaces, so that sufficient regions of the
spinal cord surface are contacted to permit selective actuation of
the electrodes and targeted stimulation of a variety of spinal cord
anatomical sites as described in more detail below. As described
above, stimulation of the implanted electrode structure on the
spinal cord will optionally be achieved by wirelessly transmitting
energy to the electrode array from a signal generator disposed
remotely from the array. Usually, the signal generator will be
implanted to lie either directly on the external surface of the
dura or just underneath the internal surface of the dura,
preferably directly over the implanted location of the spinal cord
electrode array. Alternatively, however, the signal generator in
some cases could be more remotely located and provide for
transcutaneous or other remote transmission of power and signal to
the implanted spinal cord electrode array. Embodiments may include
one or more flexible conductors (such as a flex-circuit, conductor
wires, or conductor cables) extending between the array structure
and an implanted generator system, with the conductors traversing
through the dura and often extending along and being affixed to a
dentate ligament.
[0036] In still further aspects of the present invention, an
electrode array adapted to conform to an exterior surface of a
patient's spinal cord comprises a compliant backing having an
interior surface and an exterior surface, where the interior
surface is adapted to lie in contact directly over the exterior
surface of the spinal cord. A plurality of electrodes are formed
over at least a portion of the interior surface, and transceiver
and control circuits are disposed on or immediately beneath the
exterior surface of the compliant backing. The transceiver's
antenna may be adapted to receive power and signals from a remote
signal generator, as described above, while the circuitry will be
able to accept and process power and information signals from the
antenna and convert the resulting currents to nerve stimulating
pulses to be delivered by the electrodes to the spinal cord. The
electrode array may include a C-clamp structure adapted to
resiliently circumscribe at least a portion of the spinal cord,
preferably circumscribing over 180.degree. of the circumference
while not completely enclosing the entire circumference.
[0037] In some preferred embodiments, the electrode circuitry
carried by the electrode array will be adapted to selectively
stimulate individual electrodes in response to the external signals
received by the transceiver's antenna in order to deliver
spatio-temporally selected stimuli to targeted regions of the
spinal cord. Hence, a signal generator or other external circuitry
may be programmed to treat particular conditions by stimulating
targeted regions of the spinal cord, and such targeted stimulation
will be achieved by selectively energizing particular ones of the
individual electrodes which are part of the electrode array.
Preferred anatomical target regions within the spinal cord will be
chosen by the neurosurgeon and consulting neurologists and might
include the thoracic, lumbar and sacral regions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 shows a cross-sectional diagram of selected
anatomical elements of the spinal cord.
[0039] FIG. 1A shows a cross-sectional view of the spinal cord with
specific anatomical locations identified.
[0040] FIG. 2 shows a cross-sectional diagram of the results of
extradural stimulation of the spinal cord.
[0041] FIG. 3 shows an illustration of the principal electronic
subsystems resident on a wireless embodiment of the I-Patch
receiver element or array structure.
[0042] FIG. 4 shows an illustration of the underside of the I-Patch
receiver element of FIG. 3, which would be in contact with the
surface of the spinal cord.
[0043] FIG. 5 shows the deployment of the I-Patch receiver device
on the surface of the spinal cord.
[0044] FIG. 6 shows a lateral view of the relative positions of the
wireless I-Patch transmitter and receiver devices, on the surfaces
of the dura and spinal cord, respectively.
[0045] FIG. 7 shows a cross-sectional view of the relative
positions of the I-Patch transmitter and receiver devices, on the
surfaces of the dura and spinal cord, respectively.
[0046] FIG. 8 shows a schematic representation of the inductive
coupling action taking place between the I-Patch transmitter and
receiver devices.
[0047] FIG. 9 illustrates a I-Patch having penetrating electrodes
for accessing internal target regions within the spinal cord.
[0048] FIGS. 10-13 illustrate a full-circumference pliable
electrode structure and method of implantation, intended to fully
circumscribe the spinal cord to provide access to additional
targeted regions therein.
[0049] FIGS. 14, 15, and 15A illustrate spiral and staggered
electrode patch variations according to the present invention.
[0050] FIGS. 16 and 17 illustrate an insertion device for
implanting the electrode assembly of the present invention on a
spinal cord.
[0051] FIGS. 18 through 21 illustrate an intra-dural relay device
for delivering power and signals to the implanted I-Patch when
implanted on the spinal cord.
[0052] FIGS. 22 and 23 show exemplary schematic diagrams of one
embodiment of the circuitry that might be incorporated onto the
I-Patch implant
[0053] FIG. 24 shows the postulated somatotopic organization of the
dorsal spinal column axons.
[0054] FIGS. 25 and 25A show a perspective view and an axial view
of the anatomical arrangement of the spinal cord tissues, including
the presence of the dentate ligaments which support of the spinal
cord within the spinal canal.
[0055] FIGS. 26 and 26A show a top down or dorsal view of an
alternative embodiment of an I-Patch supported on a dorsal surface
of a spinal cord by fixation to a dentate ligament so as to support
the I-Patch, respectively.
[0056] FIGS. 27 and 27A show a perspective view and a plan view of
yet another alternative embodiment of an I-Patch configured to be
supported by arms that clamp to dentate ligaments on either side of
the spinal cord.
[0057] FIGS. 28-28F illustrate a still further `wired` alternative
embodiment of an I-Patch secured to dentate ligaments, along with
implantation of the device so that a lead extends along (and is
attached to) one of the dentate ligaments and is sealed where it
extends through the dura.
[0058] FIG. 29 schematically illustrates an electrode extending
from an interior surface of a backing or substrate of an array
structure of the I-Patch.
[0059] FIG. 30 schematically illustrates individual electrodes
flexibly mounted to a backing or substrate by a soft resilient
material so as to allow the electrode to float and inhibit sliding
movement of the electrode against a surface of the spinal cord
during pulsation.
DETAILED DESCRIPTION OF THE INVENTION
[0060] FIG. 1 shows a cross-sectional diagram of selected
anatomical elements of the spinal cord. These include the layer of
dura mater 10 that encompasses the spinal cord SC and encloses the
spinal canal, the dorsal nerve rootlets 12, the zone of
cerebrospinal fluid 14 that separates the outer surface of the
spinal cord from the inner surface of the dura, and the axons 16
that would be targeted by spinal cord stimulation
instrumentation.
[0061] FIG. 1A illustrates the complex anatomical arrangement of
the postulated human spinal cord pathways. In the large dorsal
column pathways (f. gracilis, f. cuneatus) activation of large
numbers of axons that are located greater than 0.5 mm deep below
pial surface will likely result in broader somatotopic coverage of
painful areas of the body and an increased magnitude of pain
attenuation effects. Activation of axons within deeply positioned
dorsal mid-line structures (e.g. septomarginal f., posterior proper
f.) may result in complete relief of visceral pain. Pathways
positioned within the lateral and anterior regions of the spinal
cord are not activated by current SCS devices. There are many
potential stimulation targets in these regions, including the
posterior and anterior spinothalamic tracts which conduct pain and
temperature signals to the brain.
[0062] Spinal cord stimulation may also be effective in treating
patients with movement disorders (e.g. Parkinson's Disease). There
are a large number of potential motor and motor-modulation pathways
throughout the human spinal cord that may represent optimal targets
for this novel clinical application, e.g. lateral cerebrospinal f.,
rubrospinal f., tectospinal f., dorsal spinocerebellar f., ventro
spinocerebellar f., all of which are beyond the range of current
SCS devices. The I-Patch system (surface and penetrating electrode
variants) will be capable of selectively activating any spinal cord
pathway, in any location, in a patient with a functionally intact
spinal cord. Stimulation of these sites will likely result in
markedly improved spinal cord stimulation clinical efficacy.
[0063] FIG. 2 shows a cross-sectional diagram of the results of
extradural stimulation of the spinal cord. The standard epidural
stimulating electrode 20 is placed on the outside of the dura, and
the field it produces is attenuated significantly by the presence
of the CSF 14. The resulting field within the spinal cord is very
weak, having little effect on the targeted dorsal column axons, but
instead causing discomfort for the patient via parasitic activation
of the dorsal rootlets 12.
[0064] FIG. 3 shows a conceptual illustration of the principal
electronic subsystems resident on a wireless embodiment of the
I-Patch receiver or array structure element 28. Seen there (on the
left) are the turns of a microfabricated coil 30 that is configured
to serve as an RF receiver that couples inductively to the
counterpart coil on a paired transmitter element, this enabling the
I-Patch to receive power, information, and control signals. Also
shown (on the right) are the circuits 32 constituting the control
elements that regulate the size, timing and distribution of the
stimuli that act on the electrodes 34 (center). Flexible attachment
arms 36 extend from either side of a central body of the I-Patch,
with the attachment arms typically being formed at least in part of
the substrate or backing material on which circuit components 32
are mounted or formed.
[0065] FIG. 4 shows an illustration of the underside of the I-Patch
receiver element, which would be in contact with the surface of the
spinal cord. The electrodes 34 (center) are positioned by the
neurosurgeon over the region of spinal cord to be stimulated. The
underside of the biocompatible I-Patch is in contact with the
surface of the spinal cord, and held to it by the gentle clamping
action of the extension arms 36 shown in the figure.
[0066] FIG. 5 shows the deployment of the I-Patch receiver device
28 on the surface of the spinal cord SC. The extension arms 36 of
the receiver device 28 partially encircle the body of the spinal
cord SC, thus gently clamping the I-Patch to it. The extension arms
are positioned to reside between the dorsal rootlets 12, and not be
in contact with them. Under some circumstances a number of dorsal
rootlets may be sectioned to accommodate placement of the
I-Patch.
[0067] FIG. 6 shows a lateral view of the relative positions of the
I-Patch transmitter 40 and receiver 28 devices, on the surfaces of
the dura 10 and spinal cord SC, respectively. The transmitter 40
and receiver 28 patches are inductively coupled to each other by
electromagnetic fields established through current flows in the
windings on their respective surfaces. The strength of the coupling
can be adjusted by regulation of the strength of the current flow.
In this way, power, information, and control signals can span the
zone of CSF resident between the inside surface of the dura and the
outer surface of the spinal cord.
[0068] FIG. 7 shows a cross-sectional view of the relative
positions of the I-Patch transmitter 40 and receiver 28 devices, on
the surface of the dura 10 and surface S of the spinal cord SC,
respectively. By positioning the very thin I-Patch receiver
directly on the surface S of the spinal cord SC, it is possible to
drive the electrodes such that the stimuli fields penetrate through
the whole treatment zone of interest and are not attenuated by the
CSF. Also, this type of stimulus field concentration insures that
there is no parasitic excitation of the dorsal rootlets, with the
resulting associated pain. To a rough approximation, the
instantaneous electric field, E, within the stimulation zone will
be given by E=.sigma./2.kappa..di-elect cons..sub.0 where .sigma.
is the surface charge density created at the electrode's surface,
.kappa..di-elect cons..sub.0 is the product of the dielectric
constant of the spinal cord substrate and the permittivity of free
space. End effects associated with the geometry of each individual
stimulus electrode will modify this simple model, as will
superposition of the fields due to the simultaneous activation of
one or more neighboring electrodes.
[0069] FIG. 8 shows a schematic representation of the inductive
coupling action taking place between the I-Patch transmitter 40 and
receiver 28 devices. As seen there, the power, information, and
control signals generated by the transmitter device on the dura
side of the system are inductively coupled across the CSF fluid to
the receiver device, where they are operated on by the on-board
controller, and stimuli signals are distributed to the electrodes.
The inductive coupling action is governed by the mutual inductance
between the two sets of windings.
[0070] The optional `wireless` design of the I-Patch system is a
very important design aspect of some embodiments. However,
alternative embodiments employ `wired` versions of I-Patch devices
that are safe and effective, as described below. Embodiments of
these wired devices may have higher rates of mechanical failure and
be associated with increased risks of complications compared to a
wireless I-Patch version, but would function and potentially be
useful for certain applications.
[0071] The I-Patch can deliver electrical stimuli to regions of the
spinal cord that are targeted by current SCS devices. This is
accomplished by positioning electrodes on the pial surface of the
spinal cord. It is highly likely that therapeutic effects can also
be achieved by selectively stimulating circumscribed sub-regions of
the spinal cord positioned deep to the pial surface. In fact, the
spatio-temporally selected electrical stimulation of certain
structures within the central regions of the spinal cord may result
in therapeutic benefits that cannot be achieved with surface
stimulation. A broad range of clinical applications, beyond the
currently targeted chronic pain treatments, will likely be
available via placement of chronic penetrating I-Patch electrodes
(e.g. activation of motor pathways to treat patients with movement
disorders or paralysis).
[0072] The penetrating electrode I-Patch 50 is illustrated in FIG.
9. Multi-contact penetrating electrodes 52 extend from the I-Patch
main assembly 54. The interface between the main assembly and
penetrating electrode shaft may be held rigid (at least during
implantation), allowing the surgeon to insert the penetrating
electrode into the spinal cord by advancing the I-Patch device
toward the dorsal spinal cord surface using the I-Patch Applier.
Once the main assembly is in contact with the surface of the spinal
cord, the flexible I-Patch attachment aims are optionally released
resulting in a stable attachment between the spinal cord and the
electrode assembly. In some embodiments, the electrodes may, after
implantation, be supported relative to each other and the substrate
or backing of the I-Patch with resiliently flexible materials,
thereby allowing the overall array of electrodes to accommodate
pulsation and the like. Suitable resilient flexible support of the
electrodes may be provided using a flexible material spanning
between the electrode and walls of an aperture through the
substrate, with the flexible material optionally comprising a
separate layer bonded to the substrate, material insert molded
within apertures through the substrate, or the like. Electrical
stimuli are delivered through select penetrating electrode contacts
using control circuitry embedded in the I-Patch main assembly. The
geometric contour of electrical stimulation effects surrounding a
given penetrating electrode contact is shaped by the selection of
other I-Patch surface and penetrating electrode contacts that are
incorporated into bi-polar, or multi-polar stimulation
montages.
[0073] Clinical applications that target neural pathways on
ventrally located surface structures of the spinal cord that may be
targeted with a malleable full-circumference I-Patch prototype as
illustrated in FIG. 10.
[0074] In contrast to the I-Patch designs with elastic C-clamps, as
described above, the device 60 of FIG. 10 is fully pliable and has
no `memory` of the curvature of the spinal cord. A dense array of
electrode contacts 62 is imbedded in a flexible band 64 extending
from a body of the device and capable of fully circumscribing the
spinal cord. This flexible band 64 is inserted in the space between
the dura and the spinal cord and gently advanced until the leading
edge is visible on the opposite side of the spinal cord (FIGS. 11
and 12). The leading edge of the electrode band is then crimped,
pinned or otherwise secured to the main assembly of the I-Patch
device (FIG. 13) by a crimping device 66 or the like.
[0075] The pliable band achieves the objective of positioning
electrode contacts in an uninterrupted linear array covering the
entire circumference of the spinal cord. The drawbacks of this
design are that the insertion technique is more difficult and
associated with increased risks compared to the standard I-Patch.
When advancing the electrode band around the circumference of the
spinal cord there will be a small risk of injuring nerve roots or
causing a hemorrhage. Also, the mechanical contact, and thus
electrical coupling, achieved between the electrodes and spinal
cord surface will be less optimal than with the standard I-Patch
prototype. The full-circumference band cannot be attached so
tightly that it impedes spinal cord pulsation; this would result in
injury to the neural tissue. Conversely, a `loose fitting`
circumferential band will not exert the optimal inward forces on
the electrode contact and thus allow spinal fluid to flow between
the electrode contact and the pial surface resulting in sub-optimal
electrical coupling. One potential design variant would involve
having the electrode contacts protrude from the flexible band,
allowing for firm contact between electrodes and the pial surface,
but also gaps between the pial surface and the non-electrode
bearing portions of the flexible arm. These gaps would accommodate
pulsatile spinal cord expansion and contraction.
[0076] Alternative patch designs with reduced spinal cord
compression and improved accommodation of spinal cord pulsations
are illustrated in FIGS. 14 and 15. The devices of FIGS. 14, 15,
and 15A have incomplete ring configuration and elastic properties
that enable the devices to gently expand and contract along with
the spinal cord. The I-Patch variant 70 of FIG. 14 has spiral
attachment arms 72, and the staggered I Patch variant 80 of FIGS.
15 and 15A has staggered arms 82
[0077] The devices of FIGS. 14 and 15 further reduce the degree of
mechanical constriction in a given cross-sectional portion of the
spinal cord. The net effect of gently exerting inward forces on the
device to maintain contact with the spinal cord is achieved by
`staggering` the attachment arms, or by using `spiral` configured
attachment arms.
[0078] An I-Patch applier (IPA) 90 is illustrated in FIGS. 16 and
17. The IPA 90 will preferably enable the surgeon to maintain a
rigid, but reversible attachment to the I-Patch main assembly of
receiver 28. While maintaining a rigid attachment of the I-Patch
with a main assembly of the IPA 90, the surgeon will have the
ability to adjust the position of the I-Patch's pliable attachment
arms in an incremental, precisely controlled, and reversible
manner. After the I-Patch is placed on the surface of the spinal
cord, and the flexible attachment arms are in their final position,
the IPA allows the surgeon to safely and efficiently detach the
I-Patch from the IPA.
[0079] The IPA 90 can be used as a hand-held device, or attached to
an intra-operative mechanical advancer device. The surgeon controls
the position of the IPA by controlling the insertion device rod 92
(FIG. 16). A stabilizing plate 94 is attached to the end of this
rod 92. The plate 94 is contoured to match the curvature of the
I-Patch device 28, which in turn is contoured to match the
curvature of the spinal cord SC. The I-Patch main assembly contains
the transceiver antenna and control circuitry and fits snuggly into
IPA stabilizing plate 94.
[0080] The I-Patch flexible attachment arms 36 extend away from the
main assembly and are contoured to follow the curvature of the
spinal cord surface S. The distal ends of these flexible arms 36
can be reversibly extended during the insertion procedure in order
for the I-Patch to be placed on the spinal cord SC. This function
is achieved by securing a suture through an eyelet 96 positioned at
the termination points of the flexible arms 36. A double strand
suture 98 is then passed through a series of islets 100 until
secured to a suture tension adjustment rod having a knob 102. The
surgeon rotates this rod to adjust the conformation of the
extension arms. When the I-Patch is being inserted onto the spinal
cord, the adjustment rod is rotated into a position that achieves
the desired degree of flexible arm extension. Once the I-Patch is
in the desired position, the surgeon rotates the adjustment rod
until the flexible arms have returned to their pre-formed position,
resulting in uniform, gentle, direct contact of the entire I-Patch
device with the spinal cord surface. The surgeon then disengages
the IPA from the I-Patch by cutting the tension sutures. The cut
sutures are gently removed, followed by removal of the IPA. The
entire insertion procedure should be accomplished in approximately
15 seconds (FIG. 17).
[0081] The I-Patch system will typically include a thin-film
extra-dural device 40 that wirelessly transmits power and command
signals to the spinal cord electrode assembly 28. This extra-dural
device element 40 achieves the following design goals. Optionally,
no physical connection between the power/command relay device and
the spinal cord electrode (i.e. no `tethering`). No physical
obstruction of the CSF surrounding the spinal cord (avoid risk of
syrinx formation). Optionally, no device elements penetrate the
dura in a manner that would result in an increased risk of CSF
fistula formation. The distance, or gap, across which wireless
transmission occurs can be made be as short as possible without
compromising the other device design specifications.
[0082] The extra-dural relay device 40, however, will be exposed to
blood products/plasma serum that always accumulates in the
extra-dural space following surgery. In some instances, these
materials could accumulate in the space between the extra-dural
device and dura, altering the spatial and electromagnetic
relationships between the relay device and the spinal cord implant.
While this will not usually be a concern, under certain
circumstances the electromagnetic coupling between the extra-dural
and spinal cord elements may be affected, as it is highly sensitive
to relative spatial relationships and the dielectric properties of
intervening materials.
[0083] An intra-dural relay device (IDRD) 120 as may be used an
alternative to the extra-dural relay element 40 and may have
superior performance characteristics under certain circumstances.
The IDRD 120 includes a thin film power/command relay device body
122 that is placed on the inner surface of the dura lining the
dorsal aspect of the spinal canal See FIGS. 18 through 21. The
pliable thin film device 122 contours to the curved surface of the
dorsal spinal canal dura and is held in place with sutures 124. It
is placed after the spinal cord electrode array device 28 is
positioned, at the beginning of the dural closure procedure. The
dural closure procedure does not differ significantly from the
standard closure procedure. The risk of CSF leak around the lead
cable emanating from the thin film IDRD is eliminated by using a
simple `washer` clamping method at the lead cable exit site.
Following surgery, the IDRD body 122 will lay flush with the inner
surface of the dura. The IDRD's low profile will not obstruct CSF
flow. The spatial relationship between the IDRD and spinal cord
electrode array will not be altered by the post-operative
accumulation of blood products in the extra-dural space. The
surgical technique for suturing closed the dura will not differ
significantly from that used with the `standard` I-Patch procedure.
Only additional seconds are required to place the `washer` and
crimping device, such as by sliding a dual compression washer 126
along a flexible lead 128 beyond a groove 130 so as to secure the
washer in position by a clamping or washer compression device 140,
with the dura clamped between the washer 126 and a flanged, flat
backstop 132 of IDRD body 122. The IDRD 120 can be secured in
position under the surface of dura 10 within cut dura edges 134
with stay sutures 136 placed at proximal and distal ends of the
IDRD body 122. Dural edges 134 can be approximated by sutures 138,
and washer 126 can then be slid along lead 128 beyond groove 130 so
that the crimp or washer compression device 140 engages the
groove.
[0084] FIGS. 22 and 23 show one embodiment of the electronic
elements that might be on-board the I-Patch spinal cord implant.
FIG. 22 shows the transceiver coils that inductively couple power
and information signals into the circuit. A bridge circuit converts
the ac signals to dc voltage levels, in order to provide power to
the rest of the circuit. A reset signal is generated from the input
pulses via a Schmitt trigger. FIG. 23 shows the other elements of
the control and pulsing circuit. These consist of a
phase-locked-loop that generates a pulse train which is operated on
by a counter, and a 3-bit to 8-line decoder that, with a monostable
multivibrator, converts the counter's wavetrain into signals that
are distributed to selected electrodes. The above-mentioned reset
signals are used to clear the circuit elements at the end of each
pulsing cycle.
[0085] FIG. 24 shows the somatotopical organization of the dorsal
spinal column axons. Embodiments of the devices, systems, and
methods described herein may make use of such organization by
selectively energizing electrodes of the array structure 28 so as
to inhibit focal pain of (or otherwise treat) somototopically
corresponding anatomy of the patient. Axial regions T11, T12, L1,
and L2 are associated with low back signals; L3, L4, and L5 are
associated with leg and foot signals 152; and S1-S4 are associated
with pelvis signals 154; so that stimuli applied to one of these
regions may provide therapeutic effects for pain of the associated
anatomy. Note that limiting lateral transmission of stimuli by
employing direct contact or near field signal transmission from a
discrete electrode of the array to the spinal cord may be
particularly beneficial for treatment of low back pain or the like,
as the axons associated with low back pain may be located in close
proximity to the dorsal root entry zone DREZ, and inhibiting
transmission of spurious or collateral signals to the DREZ may
improve the efficacy and/or decrease deleterious effects of the
therapy.
[0086] FIGS. 25 and 25A show dentate ligament structures that
extend laterally between the spinal cord and surrounding dura. More
specifically, FIG. 25 is a profile-view diagrammatic representation
of the human spinal cord with surrounding meninges. Arachnoid mater
A is closely applied to the thick outer dura 10. An intermediate
leptomeningeal layer IL lies between the arachnoid mater A and the
pia mater. This layer is fenestrated and is attached to the inner
aspect of the arachnoid mater. It is reflected to form the dorsal
septum S. Dentate ligaments 160 are present on either side of the
spinal cord SC. The collagenous core of the dentate ligaments fuses
with subpial collagen medially and at intervals laterally with
dural collagen, as shown on the left side of the diagram. Blood
vessels V within the subarachnoid space are seen along a surface of
the spinal cord SC. As can be seen in the axial section through the
spinal cord of FIG. 25A, dorsal rootlets 162 and ventral rootlets
164 may extend from spinal column SC dorsally and ventrally of
denticulate ligaments 160, with the dentate ligaments generally
attaching the left and right lateral portion of the spinal cord SC
to left and right regions along an internal surface of dura 10.
Additional details regarding these anatomical structures may be
understood, for example, with reference to "The Fine Anatomy of the
Human Spinal Meninges" by David S. Nicholas et al.; J. Neurosurg
69:276-282 (1988); and to "The Denticulate Ligament: Anatomy and
Functional Significance" by R. Shane Tubbs et al.; J. Neurosurg
94:271-275 (2001).
[0087] FIGS. 26 and 26A show yet another alternative embodiment of
an I-Patch 170 having an electrode array 34 supported by a body 172
including a flexible substrate or backing as described above, with
the array here configured to engage a dorsal portion of the spinal
cord SC. Dentate ligament attachment features such as flexible arms
174 extend laterally from left and right sides of body 172, with
the arms optionally comprising the same substrate or backing
material from which the body is formed. These arms or other
features are configured to be attached to left and right dentate
ligaments 160 on either side of the treatment region of the spinal
cord so as to support the array 34 in engagement with the surface
of the spinal cord.
[0088] The dentate ligament provides a thin, but high tensile
strength fibrous attachment that extends from the lateral spinal
canal wall to fuse with and attach to the pia-arachnoid membrane on
the lateral surface of the spinal cord, approximately at the
`equator` of the cord as viewed in cross-section. This location and
geometry is well suited for gently exerting a desirable amount of
downward/inward pressure on the I-Patch, optionally without having
to resort to sutures and without using any `non-targeted` parts of
the spinal cord as points of attachment. The body of
dentate-ligament supported I-Patch device 170 may be largely or
entirely flexible and/or elastic. Electrodes 34 may be arrayed to
provide coverage within the dorsal column of the spinal cord and
may be embedded in a flexible silicone-type, biocompatible
material. The dentate ligament attachment features such as
attachment arms 174 may be more highly elastic, optionally having
no electronic elements contained within them, and may extend
laterally from the electrode-bearing body portion of the device.
These attachment arms can be thin (optionally being thinner than
the substrate adjacent the electrode array), flat, and/or floppy.
The attachment arms may `flair` to a larger width adjacent the ends
opposite the array, and/or may have slightly raised groves or
texture at or near these ends to facilitate clipping, crimping,
and/or adhesively bonding the arms to the dentate ligament.
[0089] During implantation, the dentate ligament supported I-Patch
device 170 may be placed and centered over the exposed dorsal
column of the spinal cord. A small number of rootlets may
optionally be sectioned to create room for the attachment arms (as
may also be done with other I-Patch embodiments). The flared end of
each attachment arm can be draped on the dentate ligaments on
either side of the spinal cord. With the patient in the prone
position the gravitational forces will result in a gentle fit of
the electrode bearing portion of the I-Patch on the dorsal spinal
cord. The amount of downward gravitational force exerted on the
I-Patch will not be large enough to occlude surface blood vessels.
The preferred points of contact will be between an array of
slightly protruding electrode contacts and the pial surface of the
dorsal columns. Microclips 176 or other types of fixation or
crimping devices can be used to secure the attachment arms to the
dentate ligaments. Metal microclips used in a variety of surgeries
(e.g. Weck Clips) may be employed, though non-metallic clips or
other fasteners may have particular advantages, and are used widely
for endoscopic surgical procedures. A relatively broad surface of
attachment is beneficial because of the thin, almost spider web
nature of the dentate ligament. An approximately 3 mm clip may, for
example, be employed. Alternatively, a tissue glue could be used.
With many techniques, there is no requirement for the I-Patch, or
I-Patch attachment arms to be jostled or manipulated into position.
The device is simply draped on the dorsal spinal cord surface and
dentate ligaments, and secured in place. With these embodiments,
the `point of attachment` or `anchor point` of the device may be on
connective tissue rather than spinal cord tissue, limiting the
clinical significance of any damage to the supporting tissue
structure.
[0090] A variety of alternative dentate ligament-supported I-Patch
embodiments may be provided, including embodiment 190 of FIGS. 27
and 27A. In general, these embodiments of the I-Patch should be
highly flexible so as to avoid restricting normal spinal cord
pulsations in-situ. Finn, constant mechanical contact should be
achieved between the electrode surfaces and the pial surface of the
spinal cord. A `one size fits` all design is desirable, whereby a
standard device can accommodate almost the full range of spinal
cord anatomy variants encountered in patients, and/or where a
limited number of sizes (1-5) will span a significant patient
population. The implantation procedure should be simple, safe, fast
and un-complicated. Toward that end, embodiment 190 makes use of
the dentate ligaments 160 to serve as a purchase point for a
malleable I-Patch electrode array. There is a simple clasp 192 at
the end of each malleable or plastically deformable I-Patch
attachment arm 194. In the operating room, the surgeon secures the
ends of each attachment arm 194 to the dentate ligaments 160. These
ligaments are comprised of connective tissue and have no
innervation. They are firmly attached to the lateral margin of the
spinal cord. The highly elastic/malleable I-Patch electrode
assembly 190 is thus secured to the spinal cord surface. Advantages
of this and/or other dentate ligament supported I-Patch variants
may include a relatively simple electrode design. Also, these
embodiments should result in excellent mechanical contact between
electrodes and pial surface, as the dentate ligaments will easily
withstand the chronic forces exerted on them by the I-Patch. The
variability provided through deformable arms may allow a `one size
fits all` (or limited number of sizes) in the device, and the
implantation procedure may be relatively less complicated.
Penetrating electrodes may optionally be employed in place of the
contact electrodes, with the body of many of the dentate ligament
embodiments optionally providing a pial surface platform to which
such electrodes could be mounted.
[0091] FIGS. 28-28F illustrate a still further `wired` alternative
dentate ligament (DL) supported embodiment of an I-Patch 200, along
with implantation of that device so that a lead extends along (and
is attached to) one of the dentate ligaments and is sealed where it
extends through the dura. Wired DL I-Patch 200 has a flexible lead
that extends through dura 10, with the lead preferably extending
along one of the DL attachment arm 174. The lead then optionally
runs laterally and dorsally, hugging the inner surface of the dura
10, optionally using a staple, clip, suture, or stapled bracket 210
to maintain the position of the lead against the dura. The lead 202
may exit the dura 210 along the midline. By placing crimping clips
176 to secure the lead bearing I-Patch attachment arm 174 to the DL
160, a strain relieving function will be achieved. This should
prevent torquing on the I-Patch by the leads and injury to the
spinal cord with spinal cord movement. As shown in FIGS. 28B-28F, a
dura-traversing lead fitting 212 can help inhibit lead migration
and facilitate water-tight dural closure, with the lead optionally
being disposed along a re-approximated mid-line durotomy after
closing most of the incision using standard techniques. A
compression clip 216 can engage fitting 214 to help seal the dural
leaflets to each other around fitting 214, and tissue glue 218 can
also be placed on and around the compression clip to effect
closure.
[0092] FIG. 29 schematically illustrates an electrode extending
from an interior surface of a backing or substrate of an array
structure of the I-Patch. The therapeutic benefit of the I-Patch to
the patient may be enhanced by maximizing the SCS current densities
in the targeted conducting tracts of the spinal cord itself, while
minimizing the current density shunted away by the CSF. This
benefit may be enhanced by engaging the electrodes against the
surface of the spinal cord as shown, with a stand-off column 220
extending between the exposed portion of the electrode 34 and the
underside of the implant substrate body 222. This can support the
implant off the surface S of the spinal cord SC by about 100 .mu.m
to accommodate micropulsations of the spinal cord, as described
above. By insulating the surface of stand-off column 220, it is
possible to minimize the shunting effect of the CSF, as the exposed
portion of the electrode will be in contact only with the pial
surface of the spinal cord, and not with the CSF itself. Gentle
inward pressure causes slight inward "dimpling" of the pial surface
by the electrode. As a result, the un-insulated (active) exposed
surface of the electrode is "sealed" by spinal cord tissue
enveloping the protruding portion of the contact. A small gap
separates the electrically inactive portions of the I-Patch device,
providing space into which the spinal cord tissue may expand and
contract with cardiac pulsation cycles.
[0093] FIG. 30 schematically illustrates individual electrodes 34
flexibly mounted to a backing or substrate 230 by a soft resilient
material 232 so as to allow the electrode to resiliently float or
move radially and/or laterally relative to the substrate by a
distance that is at least as large as the pulsations of the surface
S of spinal column SC. This movement of the individual electrodes
may inhibit sliding engagement of the electrodes against the
surface of the spinal cord during pulsation. In some
implementations of the I-Patch the only parts of the I-Patch device
that directly engage the spinal cord are the electrode contacts.
These may serve as mechanical anchoring points for the device. They
should exert just enough pressure to maintain good electrical
contact with the surface of the spinal cord. The pressure exerted
on the spinal cord by the contacts should be generally even for all
of the contacts. Some embodiments achieve this by having electrodes
protruding slightly from contoured attachments arms. These
contoured attachment arms position all contacts in the desired
position relative to the surface of the spinal cord. Outward and
inward movements of the contacts (e.g. with pulsations and
respirations) are accommodated by movements of the semi-rigid
attachment arms. Unfortunately, this makes significant demands on
the mechanical characteristics of the attachment aims. The arms may
benefit from being contoured to a spinal cord of individual
patients, and they should be constructed of materials that both
hold this contour for a decade or more, yet expand and contract to
accommodate spinal cord expansion/contraction.
[0094] The mobile electrode approach facilitates design and
material performance goals of the attachment arms. Each contact is
mobile and attached to the I-Patch via an elastic/spring-like
interface. The degree to which each contact extends out from the
attachment arm is determined by the distance separating the
attachment arm from the spinal cord surface at each contact
location. The elastic nature of the connection between each contact
and the attachment arm/body cause each contact to independently
protrude out from the device until the desired tissue contact/force
interface is achieved. In this way desirable mechanical interfaces
are achieved between some, most, or all electrode contacts and the
spinal cord, even if the attachment arms/body do not conform
perfectly to the shape of the spinal cord. Also, the elastic
interface allows the contacts to slide in and out with
expansion/contraction of the spinal cord without attachment arm
movement. With mobile contacts, the attachment an is can be more
rigid and will not be required to perfectly follow the contour of
each patient's spinal cord.
[0095] In the embodiment of FIG. 30, electrode bodies 234 extend
through apertures 238 in substrate 230, with the substrate being
pliable and having elasticity appropriate to supporting thin film
circuit components. A soft elastomeric material 236 spans the
apertures from substrate 230 to the electrode bodies, with the
elastomeric material here comprising a sheet of material adhered to
the outer surface of the substrate. In other embodiments, the
electrodes may be supported relative to each other and the
substrate with a soft elastomeric material spanning directly
between the electrode and walls of the aperture (such as by insert
molding the material into the apertures with the electrode bodies
positioned therein). In still further alternative embodiments, the
resilient material may form column 220 or the like. Flexible
conductors (not shown) may extend between the substrate and
electrode bodies within or outside the elastic material with these
conductors optionally being serpentine, having loops, or the like
to accommodate movement of each electrode body relative to the
substrate.
[0096] As can generally be understood from the description and the
parent provisional application, embodiments of the invention
provide an implantable electronic system including and/or
consisting of a signal generator means and a signal transceiver
means. The transceiver means conforms to a surface structure of a
region of spinal cord in a patient. The transceiver means is able
to receive signals wirelessly from said signal generator means, and
to process said signals according to an algorithm. The algorithm is
then able to cause said transceiver means to generate electrical
stimuli according to said algorithm. Said stimuli can be applied by
electrodes of said transceiver means to selected points on the
surface of said spinal cord in said patient.
[0097] Optionally, the transceiver means may include and/or
consists of an electronic circuit, a pliable substrate containing
said electronic circuit, a plurality of contact points that apply
said stimuli from said circuit to said spinal cord, and attachment
arms that hold said pliable substrate in non-damaging contact with
said spinal cord.
[0098] In some embodiments, said generator of said wireless signals
consists of a signal production means and an inductive coupling
means such as a planar coil prepared on the surface of a pliable
substrate. In some embodiments, said planar coil of said signal
generator means is configured and positioned so as to conform to
the inner or outer surface of a region of the dura mater
surrounding the spinal cord. In some embodiments, said planar coil
of said signal generator means deployed on a region of said dura
mater of said spinal cord and said transceiver means deployed on
the actual surface of said region of said spinal cord are
positioned in proximity to each other and separated only by the
thickness of said dura mater itself and/or by the layer of
cerebrospinal fluid filling the gap between said inside surface of
said dura mater and said outer surface of said transceiver means
which is in intimate contact with said region of spinal cord.
[0099] In some embodiments, said planar coil of said signal
generator means communicates inductively with an opposing coil that
is part of said electronic circuit means on said transceiver means
in order to transfer electrical power and electrical control
signals from said generator means to said transceiver means, as in
an electromagnetic transformer. In some embodiments, said
electronic circuit on said transceiver means further consists of
circuit elements that may include an information processing means,
a memory means, a bus means, a signal distribution means and other
means for executing the function of the device according to the
method of the invention. In some embodiments, said information
processing means of said transceiver means is able to execute one
of a plurality of algorithms that are resident either within said
memory means of said transceiver or within said generator, with
said algorithm being chosen in response to the physiological and
anatomical needs of said patient.
[0100] The electrical stimuli produced by said transceiver means in
response to the action of said algorithm means can be applied to
selected points on said region of spinal cord of said patient in
response to the physiological and anatomical needs of said patient.
The electrical stimuli produced by said transceiver means are
generated as desired for the treatment of intractable pain as might
be caused by musculo-skeletal disorders, neoplasms, arthritic
degenerations, neurodegenerative disorders, trauma and/or the
like.
[0101] The circuit of said transceiver may include an assembly of
discrete or integrated analog and digital components. The analog
circuit elements within said transceiver may include active and
passive components. The digital circuit elements within said
transceiver may operate on electronic pulses, analog or digitized
waveforms, dc voltage levels, and/or combinations thereof. The
electronic circuit for said transceiver may incorporate a signal
multiplexer that is able to distribute a plurality of stimulus
signals to a plurality of electrodes in contact with a spinal cord
of a patient. The electronic circuit for said transceiver may
incorporate a phase-locked-loop system for detecting, synthesizing
or processing a plurality of electronic waveforms, pulses and
combinations thereof, for subsequent use in generating and
distributing stimulus signals to a plurality of electrodes in
contact with a spinal cord of a patient. The electronic circuit for
said transceiver may incorporate frequency-shift keying and/or
pulse-width modulation means for detecting, synthesizing or
processing a plurality of electronic waveforms, pulses and
combinations thereof, for subsequent use in generating and
distributing stimulus signals to a plurality of electrodes in
contact with a spinal cord of a patient. The electronic circuit for
said transceiver may contain subcircuits to prevent accidental
delivery of excess voltages to the spinal cord of a patient during
the normal application of stimulus signals. The electronic circuit
for said transceiver may contain ferrite elements to prevent the
propagation within the circuit of parasitic or spurious
radio-frequency signal components. The electronic circuit for said
transceiver means may contain miniature solid-state fuses, fusible
links or other such current interrupters, as well as back-up
circuits, to protect said transceiver and said spinal cord of said
patient from short circuits or other modes of failure. The
electronic circuit for said transceiver may contain capacitive or
inductive energy storage to allow for uninterrupted synthesis and
application of stimulus signals in the event of interruption of the
power transfer process.
[0102] While exemplary embodiments of the devices, systems, and
methods have been described in some detail for clarity of
understanding and by way of example, a variety of changes,
modifications, and adaptations will be obvious to those of skill in
the art. Hence, the scope of the invention is limited solely by the
appended claims.
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