U.S. patent application number 11/027227 was filed with the patent office on 2005-06-02 for methods for implanting a spinal cord stimulator.
Invention is credited to Kuzma, Janusz A., Mann, Carla M., McGivern, James P., Whitehurst, Todd K..
Application Number | 20050119713 11/027227 |
Document ID | / |
Family ID | 34278057 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050119713 |
Kind Code |
A1 |
Whitehurst, Todd K. ; et
al. |
June 2, 2005 |
Methods for implanting a spinal cord stimulator
Abstract
Methods for implanting spinal cord stimulators are provided,
including implanting at least one electrode in an anterolateral
area of the spine. Stimulation provided by the stimulator(s) may be
used to treat patients with chronic pain. The stimulator(s) use a
power source/storage device, such as a rechargeable battery.
Periodic recharging of such a power source/storage device is
accomplished, for example, by inductive coupling with an external
applience. The stimulators provide means of stimulating a nerve(s)
or other tissue when desired, without the need for external
appliances during the stimulation session. When necessary, external
appliances are used for the transmission of data to and/or from the
stimulator(s) and for the transmission of power, if necessary. In a
preferred embodiment, the system is capable of open- and
closed-loop operation. In closed-loop operation, at least one
implant includes at least one sensor, and the sensed condition is
used to adjust stimulation parameters.
Inventors: |
Whitehurst, Todd K.; (Santa
Clarita, CA) ; McGivern, James P.; (Stevenson Ranch,
CA) ; Mann, Carla M.; (Beverly Hills, CA) ;
Kuzma, Janusz A.; (Parker, CO) |
Correspondence
Address: |
ADVANCED BIONICS CORPORATION
25129 RYE CANYON ROAD
VALENCIA
CA
91355
US
|
Family ID: |
34278057 |
Appl. No.: |
11/027227 |
Filed: |
December 30, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11027227 |
Dec 30, 2004 |
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09929597 |
Aug 13, 2001 |
|
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6871099 |
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60226333 |
Aug 18, 2000 |
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Current U.S.
Class: |
607/46 ;
607/72 |
Current CPC
Class: |
A61N 1/36071 20130101;
A61N 1/36062 20170801 |
Class at
Publication: |
607/046 ;
607/072 |
International
Class: |
A61N 001/18 |
Claims
1-24. (canceled)
25. A method for implanting a spinal cord stimulator, comprising:
providing at least one stimulator having at least two electrodes;
implanting the at least one stimulator in, on or near an
anterolateral area of the spinal cord; providing operating power to
the at least one stimulator; providing stimulation parameters to
the at least one stimulator; generating stimulation pulses in
accordance with the stimulation parameters; and delivering the
stimulation pulses to nerves and tissue of the anterolateral area
of the spinal cord via the at least two electrodes; wherein the
stimulator has a size and shape suitable for placement in, on or
near the anterolateral area of the spinal cord.
26. The method of claim 25 wherein the stimulation pulses are
delivered at greater than about 100 Hz.
27. The method of claim 25 further comprising implanting the at
least one stimulator in position to deliver the stimulation pulses
to at least one nerve fiber of C5, C6, C7, C8, and T1 to treat
chronic pain located in one or both arms.
28. The method of claim 25 further comprising implanting the at
least one stimulator in position to deliver the stimulation pulses
to at least one nerve fibers of L1-L5, S1, and S2 to treat chronic
pain located in one or both legs.
29. The method of claim 25 further comprising implanting the at
least one stimulator in position to deliver the stimulation pulses
to at least one nerve fibers of T10, T11, T12, L1-L5, and S1-S5 to
treat chronic pain located in the pelvic region.
30. The method of claim 25 further comprising implanting the at
least one stimulator in position to deliver the stimulation pulses
to at least one nerve fibers of T1-T2, L1-L5, and S1 to treat
chronic pain located in the back.
31. The method of claim 25 further comprising implanting the at
least one stimulator in position to deliver the stimulation pulses
to at least one nerve fibers of C2, C3, C4, and C5 to treat chronic
pain located in the cervical region.
32. The method of claim 25 further comprising implanting the at
least one stimulator in position to deliver the stimulation pulses
to at least one nerve fibers of C1-C8 to treat chronic pain located
in the head/neck region.
33. The method of claim 25 further comprising: providing at least
one sensor; using the at least one sensor to sense at least one
physical condition; and determining the stimulation parameters
based upon the at least one sensed condition.
34. The method of claim 25 wherein providing stimulation parameters
comprises receiving the stimulation parameters from at least one
external appliance.
35. The method of claim 25 wherein providing operating power
comprises receiving the operating power from at least one external
appliance.
36. The method of claim 25 further comprising providing and
implanting more than one stimulator.
37. A method for treating a patient with chronic pain, comprising:
providing at least one stimulator having at least two electrodes;
implanting at least one electrode in, on or near an anterolateral
area of the spinal cord; providing operating power to the at least
one stimulator; providing stimulation parameters to the at least
one stimulator; generating stimulation pulses in accordance with
the stimulation parameters; and delivering the stimulation pulses
to nerves and tissue of the anterolateral area of the spinal cord
via the at least two electrodes; wherein the stimulator has at
least one electrode suitable for placement in, on or near the
anterolateral area of the spinal cord.
38. The method of claim 37 wherein the body of the stimulator is no
more than 150 mm from the tissue to be stimulated.
39. The method of claim 37 wherein one of the at least two
electrodes is a case electrode.
40. The method of claim 37 wherein at least one of the at least two
electrodes is positioned on an implantable lead electrically
connected to the body of the stimulator.
41. The method of claim 40 wherein the implantable lead is up to
150 mm long.
42. The method of claim 37 wherein the stimulation parameters are
determined using at least one external appliance.
43. The method of claim 37 wherein providing operating power to the
at least one stimulator comprises receiving power from at least one
external appliance.
44. The method of claim 43 wherein providing power to the at least
one stimulator further comprises storing the power received from
the at least one external appliance.
Description
[0001] The present application is a continuation of U.S. patent
application Ser. No. 09/929,597, filed Aug. 13, 2001, now allowed,
which application claims the benefit of U.S. Provisional Patent
Application Ser. No. 60/226,333, filed Aug. 18, 2000. These
applications are incorporated herein by reference in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to implantable
stimulator systems, and more particularly relates to an implantable
stimulator system utilizing one or more implantable
microstimulators for treating chronic pain.
BACKGROUND OF THE INVENTION
[0003] Chronic pain is usually a multidimensional phenomenon
involving complex physiological and emotional interactions. For
instance, one type of chronic pain, complex regional pain syndrome
(CRPS)--which includes the disorder formerly referred to as reflex
sympathetic dystrophy (RSD)--most often occurs after an injury,
such as a bone fracture. The pain is considered "complex regional"
since it is located in one region of the body (such as an arm or
leg), yet can spread to additional areas. Since CRPS typically
affects the sympathetic nervous system, which in turn affects all
tissue levels (skin, bone, etc.), many symptoms may occur. Pain is
the main symptom. Other symptoms vary, but can include loss of
function, temperature changes, swelling, sensitivity to touch, and
skin changes.
[0004] Another type of chronic pain, failed back surgery syndrome
(FBSS), refers to patients who have undergone one or more surgical
procedures and continue to experience pain. Included in this
condition are recurring disc herniation, epidural scarring, and
injured nerve roots.
[0005] Arachnoiditis, a disease that occurs when the membrane in
direct contact with the spinal fluid becomes inflamed, causes
chronic pain by pressing on the nerves. It is unclear what causes
this condition.
[0006] Yet another cause of chronic pain is inflammation and
degeneration of peripheral nerves, called neuropathy. This
condition is a common complication of diabetes, affecting 60%-70%
of diabetics. Pain in the lower limbs is a common symptom.
[0007] An estimated 10% of gynecological visits involve a complaint
of chronic pelvic pain. In approximately one-third of patients with
chronic pelvic pain, no identifiable cause is ever found, even with
procedures as invasive as exploratory laparotomy. Such patients are
treated symptomatically for their pain.
[0008] A multitude of other diseases and conditions cause chronic
pain, including postherpetic neuralgia and fibromyalgia syndrome.
Neurostimulation of spinal nerves, nerve roots, and the spinal cord
has been demonstrated to provide symptomatic treatment in patients
with intractable chronic pain.
[0009] Many other examples of chronic pain exist, as chronic pain
may occur in any area of the body. For many sufferers, no cause is
ever found. Thus, many types of chronic pain are treated
symptomatically. For instance, many people suffer from chronic
headaches/migraine and/or facial pain. As with other types of
chronic pain, if the underlying cause is found, the cause may or
may not be treatable. Alternatively, treatment may be only to
relieve the pain.
[0010] All of the devices currently available for producing
therapeutic stimulation have drawbacks. Many are large devices that
must apply stimulation transcutaneously. For instance,
transcutaneous electrical nerve stimulation (TENS) is used to
modulate the stimulus transmissions by which pain is felt by
applying low-voltage electrical stimulation to large peripheral
nerve fibers via electrodes placed on the skin. TENS devices can
produce significant discomfort and can only be used
intermittently.
[0011] Other devices require that a needle electrode(s) be inserted
through the skin during stimulation sessions. These devices may
only be used acutely, and may cause significant discomfort.
[0012] Implantable, chronic stimulation devices are available, but
these currently require a significant surgical procedure for
implantation. Surgically implanted stimulators, such as spinal cord
stimulators, have been described in the art. These spinal cord
stimulators have different forms, but are usually comprised of an
implantable control module to which is connected a series of leads
that must be routed to nerve bundles in the spinal cord, to nerve
roots and/or spinal nerves emanating from the spinal cord, or to
peripheral nerves. The implantable devices are relatively large and
expensive. In addition, they require significant surgical
procedures for placement of electrodes, leads, and processing
units. These devices may also require an external apparatus that
needs to be strapped or otherwise affixed to the skin. Drawbacks,
such as size (of internal and/or external components), discomfort,
inconvenience, complex surgical procedures, and/or only acute or
intermittent use has generally confined their use to patients with
severe symptoms and the capacity to finance the surgery.
[0013] There are a number of theories regarding how stimulation
therapies such as TENS machines and spinal cord stimulators may
inhibit or relieve pain. The most common theory--gate theory or
gate control theory--suggests that stimulation of fast conducting
nerves that travel to the spinal cord produces signals that "beat"
slower pain-carrying nerve signals and, therefore, override/prevent
the message of pain from reaching the spinal cord. Thus, the
stimulation closes the "gate" of entry to the spinal cord. It is
believed that small diameter nerve fibers carry the relatively
slower-traveling pain signals, while large diameter fibers carry
signals of e.g., touch that travel more quickly to the brain.
[0014] Spinal cord stimulation (also called dorsal column
stimulation) is best suited for back and lower extremity pain
related to adhesive arachnoiditis, FBSS, causalgia, phantom limb
and stump pain, and ischemic pain. Spinal cord stimulation is
thought to relieve pain through the gate control theory described
above. Thus, applying a direct physical or electrical stimulus to
the larger diameter nerve fibers of the spinal cord should, in
effect, block pain signals from traveling to the patient's brain.
In 1967, Shealy and coworkers first utilized this concept,
proposing to place stimulating electrodes over the dorsal columns
of the spinal cord. (See Shealy C. N., Mortimer J. T., Reswick, J.
B., "Electrical Inhibition of Pain by Stimulation of the Dorsal
Column", in Anesthesia and Analgesia, 1967, volume 46, pages
489-491.) Since then, improvements in hardware and patient
selection have improved results with this procedure.
[0015] The gate control theory has always been controversial, as
there are certain conditions such as hyperalgesia, which it does
not fully explain. The relief of pain by electrical stimulation of
a peripheral nerve, or even of the spinal cord, may be due to a
frequency-related conduction block which acts on primary afferent
branch points where dorsal column fibers and dorsal horn
collaterals diverge. Spinal cord stimulation patients tend to show
a preference for a minimum pulse repetition rate of 25 Hz.
[0016] Stimulation may also involve direct inhibition of an
abnormally firing or damaged nerve. A damaged nerve may be
sensitive to slight mechanical stimuli (motion) and/or
noradrenaline (a chemical utilized by the sympathetic nervous
system), which in turn results in abnormal firing of the nerve's
pain fibers. It is theorized that stimulation relieves this pain by
directly inhibiting the electrical firing occurring at the damaged
nerve ends.
[0017] Stimulation is also thought to control pain by triggering
the release of endorphins. Endorphins are considered to be the
body's own pain-killing chemicals. By binding to opioid receptors
in the brain, endorphins have a potent analgesic effect.
[0018] Recently, an alternative to 1) TENS, 2) percutaneous
stimulation, and 3) bulky implantable stimulation assemblies has
been introduced. Small, implantable microstimulators have been
introduced that can be injected into soft tissues through a cannula
or needle. What is needed is a way to effectively use such small,
fully implantable, chronic neurostimulators for the purpose of
treating chronic pain.
BRIEF SUMMARY OF THE INVENTION
[0019] The invention disclosed and claimed herein addresses the
above and other needs and provides means and systems for
chronically stimulating a nerve root(s), spinal nerve(s), and/or
spinal cord with a miniature implantable neurostimulator(s) that
can be implanted via a minimal surgical procedure.
[0020] The nerve roots lie within the spinal column, and the spinal
nerves exit the spinal column at the intervertebral foramen. To
treat chronic pain, a miniature implantable electrical stimulator,
such as a stimulator similar to a Bionic Neuron (also referred to
as a BION.TM. microstimulator) may be implanted via a minimal
surgical procedure (e.g., injection or small incision) in the
spinal column, preferably adjacent to a dorsal root, for
stimulation of a nerve root(s), and/or lateral to the
intervertebral foramen for stimulation of a spinal nerve(s).
Additionally or alternatively, a BION stimulator may be implanted
in or on the spinal cord to stimulate, e.g., the dorsal column or
the spinothalamic tract. A single microstimulator may be implanted,
or two or more microstimulators may be implanted to achieve greater
stimulation of one or more nerve roots, spinal nerves, and/or areas
of the spinal cord. For instance, one or more microstimulator(s)
may be implanted adjacent to the dorsal root of the third and/or
fourth lumbar nerve (i.e., L3 and/or L4), and/or lateral to the
intervertebral foramen of the third and/or fourth lumbar nerve.
[0021] Stimulation and control parameters of the implanted
microstimulator are preferably adjusted to levels that are safe and
efficacious with minimal patient discomfort. Different stimulation
parameters generally have different effects on neural tissue, and
parameters are thus chosen to target specific neural populations
and to exclude others. For example, large diameter nerve fibers
(e.g., A-.alpha. and/or A-.beta. fibers) respond to relatively
lower current density stimulation compared with small diameter
nerve fibers (e.g., A-.delta. and/or C fibers).
[0022] According to one embodiment of the invention, chronic pain
may be treated with stimulation to decrease excitement of targeted
nerve roots, spinal nerves, and/or areas of the spinal cord;
high-frequency electrical stimulation of such nerve fibers is
likely to produce such inhibition. According to another embodiment
of the invention, the stimulation can increase excitement of
targeted nerve roots, spinal nerves, and/or areas of the spinal
cord; low-frequency electrical stimulation of such nerve fibers is
likely to produce such excitement.
[0023] The neurostimulator also includes a means of stimulating a
nerve either intermittently or continuously. Specific stimulation
parameters may provide therapeutic advantages for various forms of
pain.
[0024] The microstimulator used with the present invention
preferably possesses one or more of the following properties:
[0025] at least two electrodes for applying stimulating current to
surrounding tissue;
[0026] electronic and/or mechanical components encapsulated in a
hermetic package made from biocompatible material(s);
[0027] an electrical coil or other means of receiving energy and/or
information inside the package, which receives power and/or data by
inductive or radio-frequency (RF) coupling to a transmitting coil
placed outside the body, thus avoiding the need for electrical
leads to connect devices to a central implanted or external
controller;
[0028] means for receiving and/or transmitting signals via
telemetry;
[0029] means for receiving and/or storing electrical power within
the microstimulator; and
[0030] a form factor making the microstimulator implantable via a
minimal surgical procedure.
[0031] A microstimulator may operate independently, or in a
coordinated manner with other implanted devices, or with external
devices. In addition, a microstimulator may incorporate means for
sensing pain, which it may then use to control stimulation
parameters in a closed loop manner. According to one embodiment of
the invention, the sensing and stimulating means are incorporated
into a single microstimulator. According to another embodiment of
the invention, a sensing means communicates sensed information to
at least one microstimulator with stimulating means.
[0032] Thus, the present invention provides a therapy for chronic
pain that utilizes one or more miniature neurostimulators and is
minimally invasive. The simple implant procedure results in minimal
surgical time and possible error, with associated advantages over
known treatments in terms of reduced expense and opportunity for
infection or other complications. Other advantages, inter alia, of
the present invention include the system's monitoring and
programming capabilities, the power source, storage, and transfer
mechanisms, the activation of the device by the patient or
clinician, the system's open and closed-loop capabilities and
closed-loop capabilities coupled with sensing a need for and/or
response to treatment, coordinated use of one or more stimulators,
and the small size of the stimulator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The above and other aspects, features, and advantages of the
present invention will be more apparent from the following more
particular description thereof, presented in conjunction with the
following drawings wherein:
[0034] FIG. 1A illustrates the relation of spinal nerve roots to
vertebrae;
[0035] FIG. 1B illustrates the areas of skin innervated by the
dorsal root axons at the various spinal levels;
[0036] FIG. 2A depicts the nerve pathways in and near the thoracic
part of the spinal cord;
[0037] FIG. 2B illustrates the principal fiber tracts of the spinal
cord;
[0038] FIG. 3 depicts a section through a lumbar vertebra;
[0039] FIG. 4 illustrates an exemplary embodiment of a stimulation
system of the present invention;
[0040] FIG. 5 illustrates preferred external components of the
invention; and
[0041] FIG. 6 depicts a system of implantable devices that
communicate with each other and/or with external
control/programming devices.
[0042] Corresponding reference characters indicate corresponding
components throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0043] The following description is of the best mode presently
contemplated for carrying out the invention. This description is
not to be taken in a limiting sense, but is made merely for the
purpose of describing the general principles of the invention. The
scope of the invention should be determined with reference to the
claims.
[0044] As indicated above, the present invention is directed to
treating chronic pain using one or more small, implantable
neurostimulators, referred to herein as "microstimulators". The
microstimulators of the present invention are preferably similar to
the type referred to as BION.TM. devices. The following documents
describe various features and details associated with the
manufacture, operation, and use of BION implantable
microstimulators, and are all incorporated herein by reference:
1 Application/Patent/ Filing/Publi- Publication No. cation Date
Title U.S. Pat. No. 5,193,539 Issued Implantable Microstimulator
Mar. 16, 1993 U.S. Pat. No. 5,193,540 Issued Structure and Method
of Manufacture of an Implantable Mar. 16, 1993 Microstimulator U.S.
Pat. No. 5,312,439 Issued Implantable Device Having an Electrolytic
Storage May 17, 1994 Electrode U.S. Pat. No. 5,324,316 Issued
Implantable Microstimulator Jun. 28, 1994 U.S. Pat. No. 5,405,367
Issued Structure and Method of Manufacture of an Implantable Apr.
11, 1995 Microstimulator PCT Publication published Battery-Powered
Patient Implantable Device WO 98/37926 Sep. 3, 1998 PCT Publication
published System of Implantable Devices For Monitoring and/or WO
98/43700 Oct 8, 1998 Affecting Body Parameters PCT Publication
published System of Implantable Devices For Monitoring and/or WO
98/43701 Oct 8, 1998 Affecting Body Parameters U.S. Pat. No.
6,051,017 Issued Improved Implantable Microstimulator and Systems
(application. Ser. Apr. 18, 2000 Employing Same No. 09/077,662)
published Micromodular Implants to Provide Electrical Stimulation
September, 1997 of Paralyzed Muscles and Limbs, by Cameron, et al.,
published in IEEE Transactions on Biomedical Engineering, Vol. 44,
No. 9, pages 781-790.
[0045] FIG. 1A illustrates the relation of spinal nerve roots to
vertebrae, and FIG. 1B depicts the areas of skin innervated by the
dorsal root axons at the various spinal levels, known as
dermatomes. FIG. 2A illustrates the nerve pathways in and near the
thoracic portion of the spinal cord, while FIG. 2B illustrates the
principal fiber tracts of the spinal cord. FIG. 3 depicts a section
through a lumbar vertebrae.
[0046] Among the most common complaints of chronic pain is pain in
the limbs. As depicted in FIGS. 1A and 1B, the nerves in and near
the spinal column from vertebra L1 down to the top portion of the
sacrum (i.e., nerves L1, L2, L3, L4, L5, S1 and S2) have the
greatest affect on sensations in the legs. Therefore, for example,
in accordance with the teachings of the present invention,
electrical stimulation at these same levels, L1-L5, S1, and S2, is
provided to relieve leg pain.
[0047] Under normal conditions, pain signals are carried from the
source of the pain through afferent nerve fibers which convey the
impulses toward a nerve center (e.g., the brain or spinal cord). In
the depictions of FIGS. 2A and 2B, the pain signals are carried
toward the spinal cord via nerve fibers 100. The pain signals are
then conducted up an ascending nerve pathway (via the spinothalamic
tract 118 of the anterolateral system) to the brain, which
processes the signals and induces the pain sensation. These pain
signals travel through relatively small diameter nerve fibers
(i.e., A-.delta. and C fibers) that enter the spinal cord at
Lissauer's tract 114, decussate at the ventral commissure 116 over
a distance of one to two spinal segments, then ascend to the brain
within spinothalamic tract 118.
[0048] To treat chronic pain, a microminiature stimulator 150, such
as a BION microstimulator, illustrated, e.g., in FIGS. 2A and 4, is
preferably implanted e.g., adjacent to one or more dorsal (i.e.,
posterior) roots 110 and/or one or more spinal nerves 112. The
nerve roots lie within the spinal column. The spinal nerves exit
the spinal column at the intervertebral foramen 120 (FIG. 3). As
seen in FIG. 2A, the microstimulator is placed on or near a spinal
nerve 112, preferably lateral to intervertebral foramen 120, for
stimulation of a spinal nerve(s).
[0049] Stimulating one or more dorsal nerve roots 110 and/or one or
more spinal nerves 112, which would normally transmit pain
sensations, should cause the pain to be eliminated or moderated.
Additionally or alternatively, stimulation of pain pathways in the
spinal cord, such as along Lissauer's tract 114, the ventral
commissure 116, and/or the spinothalamic tract 118 may be used to
treat chronic pain.
[0050] Based on the gate control theory described earlier,
stimulating fast-conducting, larger diameter nerve fibers will
block, or gate, the slower pain signals from reaching the brain.
The somatic sensory fibers responsible for touch, pressure, and
position sense are carried through relatively large diameter nerve
fibers (i.e., A-.alpha. and/or A-.beta. fibers) that enter the
spinal cord and travel via a dorsal column 120, which is made up of
the cuneate fasciculus 122 and the gracile fasciculus 124. As such,
stimulation may additionally or alternatively be applied to these
fibers as a treatment for chronic pain.
[0051] In accordance with the present invention, a single
microstimulator 150 may be implanted, or two or more
microstimulators may be implanted to achieve greater stimulation of
the targeted tissue, or for a longer period of time. As shown in
FIG. 4, microstimulator device 150 includes a narrow, elongated
capsule 152 containing electronic circuitry 154 connected to
electrodes 156 and 158, which pass through the walls of the capsule
at either end. As detailed in the referenced patent publications,
electrodes 156 and 158 comprise a stimulating electrode (to be
placed close to the nerve) and an indifferent electrode (for
completing the circuit). Other preferred configurations of
microstimulator device 150 are possible, as is evident from the
above-referenced patent publications.
[0052] Advantageously, a preferred implantable microstimulator 150
is sufficiently small to permit its placement near the structures
to be stimulated. (As used herein, "adjacent" and "near" mean as
close as reasonably possible to targeted tissue, including touching
or even being positioned within the tissue, but in general, may be
as far as about 150 mm from the target tissue.) Capsule 152
preferably has a diameter no greater than about 4-5 mm, more
preferably only about 3 mm, and most preferably less than about 3
mm. Capsule length is preferably no greater than about 25-35 mm,
more preferably only about 20-25 mm, and most preferably less than
about 20 mm. The shape of the microstimulator is preferably
determined by the structure of the desired target, the surrounding
area, and the method of insertion. A thin, elongated cylinder with
electrodes at the ends, as shown in FIG. 4, is currently preferred,
but other shapes, such as spheres, disks, or helical structures,
are possible.
[0053] Microstimulator 150 is preferably implanted with a surgical
insertion tool specially designed for the purpose, or is injected
(e.g., via a hypodermic needle). Alternatively, device 150 may be
implanted via conventional surgical methods, or may be inserted
using other endoscopic or laparoscopic techniques. A more
complicated surgical procedure may be required for purposes of
fixing the microstimulator in place.
[0054] The external surfaces of stimulator 150 are advantageously
composed of biocompatible materials. Capsule 152 is preferably made
of glass, ceramic, or other material that provides a hermetic
package that will exclude water vapor but permit passage of
electromagnetic fields used to transmit data and/or power.
Electrodes 156 and 158 are preferably made of a noble or refractory
metal or compound, such as platinum, iridium, tantalum, titanium,
titanium nitride, niobium, or alloys of any of these, in order to
avoid corrosion or electrolysis which could damage the surrounding
tissues and the device.
[0055] In one preferred embodiment of the instant invention,
microstimulator 150 comprises two, leadless electrodes. However,
either or both electrodes 156 and 158 may be located at the ends of
short, flexible leads as described in U.S. patent application Ser.
No. 09/624,130, filed Jul. 24, 2000 (which claims priority to U.S.
Provisional Patent Application No. 60/156,980, filed Oct. 1, 1999),
which is incorporated herein by reference in its entirety. Other
configurations may also permit electrical stimulation to be
directed more locally to specific tissue a short distance from the
surgical fixation of the bulk of the implantable stimulator 150,
while allowing elements of stimulator 150 to be located in a more
surgically convenient site. Such configurations minimize the
distance traversed and the surgical planes crossed by the device
and any lead(s), which herein defines any means to locally direct
the electrical stimulation. In a preferred embodiment, the leads
(i.e., directing means) are no longer than about 150 mm.
[0056] Microstimulator 150 preferably contains electronic circuitry
154 for receiving data and/or power from outside the body by
inductive, radio-frequency (RF), or other electromagnetic coupling.
In a preferred embodiment, electronic circuitry 154 includes an
inductive coil for receiving and transmitting RF data and/or power,
an integrated circuit (IC) chip for decoding and storing
stimulation parameters and generating stimulation pulses (either
intermittent or continuous), and additional discrete electronic
components required to complete the electronic circuit functions,
e.g. capacitor(s), resistor(s), coil(s), and the like.
[0057] In some preferred embodiments, microstimulator 150
advantageously includes a programmable memory 160 for storing a
set(s) of stimulation and control parameters, if required. This
feature allows stimulation and control parameters to be adjusted to
settings that are safe and efficacious with minimal discomfort for
each individual. Specific parameters may provide therapeutic
advantages for various forms and severity of pain. For instance,
some patients may respond favorably to intermittent stimulation,
while others may require continuous stimulation to alleviate their
pain.
[0058] In addition, stimulation parameters are typically chosen to
target specific neural populations and to exclude others. For
example, relatively low frequency neurostimulation (i.e., less than
about 100-150 Hz) may have an excitatory effect on surrounding
neural tissue, whereas relatively high frequency neurostimulation
(i.e., greater than about 100-150 Hz) may have an inhibitory
effect. In addition, large diameter fibers (e.g., A-.alpha. and/or
A-.beta. fibers) respond to relatively lower current density
stimulation compared with small diameter fibers (e.g., A-.delta.
and/or C fibers).
[0059] The preferred implantable stimulator 150 also includes a
power source and/or power storage device 162. Possible power
options, described in more detail below, include but are not
limited to an external power source coupled to stimulator 150 via
an RF link, a self-contained power source utilizing any means of
generation or storage of energy (e.g., a primary battery, a
rechargeable battery such as a lithium ion battery, an electrolytic
capacitor, or a super- or ultra-capacitor), and if the
self-contained power source is replenishable or rechargeable, means
of replenishing or recharging the power source (e.g., an RF link,
an optical link, a thermal link, or other energy-coupling
link).
[0060] According to one embodiment of the invention, a
microstimulator operates independently. According to another
embodiment of the invention, a microstimulator operates in a
coordinated manner with other microstimulator(s), other implanted
device(s), or other device(s) external to the patient's body. For
instance, a microstimulator may control or operate under the
control of another implanted microstimulator(s), other implanted
device(s), or other device(s) external to the patient's body. A
microstimulator may communicate with other implanted
microstimulators, other implanted devices, and/or devices external
to a patient's body via, e.g., an RF link, an ultrasonic link, a
thermal link, or an optical link. Specifically, a microstimulator
may communicate with an external remote control (e.g., patient
and/or physician programmer) that is capable of sending commands
and/or data to a microstimulator and that is preferably capable of
receiving commands and/or data from a microstimulator.
[0061] In order to help determine the strength of electrical
stimulation required to produce the desired therapeutic effect, in
one preferred embodiment, a patient's response to and/or need for
treatment is sensed, such as sensing changes in levels of pain
medication. Thus, when implantable stimulator 150 is implanted, for
example, near a spinal nerve(s) 112, the signals from a sensor
built into microstimulator 150 are used to adjust stimulation
parameters. Alternatively, a "microstimulator" dedicated to sensory
processes may communicate with a microstimulator that provides the
stimulation pulses. As described below, the implant circuitry 154
amplifies and transmits these sensed signals, which may be analog
or digital. Other methods of determining the required stimulation
include a sensor on the hypogastric plexus for sensing increased
sympathetic discharge and other markers of the potential for pain,
as well as other methods mentioned herein, and yet others that will
be evident to those of skill in the art upon review of the present
disclosure. The sensed information is preferably used to control
the electrical and/or control parameters in a closed-loop
manner.
[0062] In operation, as illustrated in FIG. 5, the patient 170
turns the implantable stimulator 150 on and off by use of
controller 180, which is preferably handheld. Implantable
stimulator 150 is operated by controller 180 by any of various
means, including sensing the proximity of a permanent magnet
located in controller 180, or sensing RF transmissions from
controller 180.
[0063] External components of one preferred embodiment for
programming and/or providing power to the implantable stimulator
150 are also illustrated in FIG. 5. When it is required to
communicate with the implanted stimulator 150, the patient 170 is
positioned on or near external appliance 190, which appliance
contains one or more inductive coils 192 or other means of
communication (e.g., RF transmitter and receiver). External
appliance 190 is connected to or is a part of external electronic
circuitry appliance 200 which receives power 202 from a
conventional power source. External appliance 200 contains manual
input means 208, e.g., a keypad, whereby the patient 170 or a
caregiver 212 can request changes in the stimulation parameters
produced during the normal operation of the implantable stimulator
150. In this preferred embodiment, the manual input means 208
includes various electro-mechanical switches and/or visual display
devices that provide the patient and/or caregiver with information
about the status and prior programming of the implantable
stimulator 150.
[0064] Alternatively or additionally, the external electronic
appliance 200 is provided with an electronic interface means 216
for interacting with other computing means 218, such as by a serial
interface cable or infrared link to a personal computer or to a
telephone modem. Such interface means 216 thus permits a clinician
to monitor the status of the implant and prescribe new stimulation
parameters from a remote location.
[0065] The external appliance(s) may advantageously be embedded in
a cushion, mattress cover, or garment. Other possibilities exist,
including a belt or other structure that may be affixed to the
patient's body or clothing.
[0066] Thus, it is seen that in accordance with the present
invention, one or more external appliances are preferably provided
to interact with microstimulator 150 to accomplish one or more of
the following functions:
[0067] Function 1: If necessary, transmit electrical power from the
external electronic appliance 200 via appliance 190 to the
implantable stimulator 150 in order to power the device and/or
recharge the power source/storage device 162. External electronic
appliance 200 may include an automatic algorithm that adjusts
stimulation parameters automatically whenever the implantable
stimulator(s) 150 is/are recharged.
[0068] Function 2: Transmit data from the external appliance 200
via the external appliance 190 to the implantable stimulator 150 in
order to change the operational parameters (e.g., electrical
stimulation parameters) used by stimulator 150.
[0069] Function 3: Transmit sensed data indicating a need for
treatment or in response to stimulation (e.g., impedance, muscle
activity (e.g., EMG), nerve activity (e.g., ENG), electrical
activity of the brain (e.g., EEG), or other activity) from
implantable stimulator 150 to external appliance 200 via external
appliance 190.
[0070] Function 4: Transmit data indicating state of the
implantable stimulator 150 (e.g., battery level, stimulation
settings, etc.) to external appliance 200 via external appliance
190.
[0071] By way of example, a treatment modality for chronic lower
extremity and low back pain is carried out according to the
following sequence of procedures:
[0072] 1. A stimulator 150 is implanted so that its electrodes 156
and 158 are lateral to the intervertebral foramen 120 of vertebra
L3 (for stimulation of spinal nerve 112).
[0073] 2. Using Function 2 described above (i.e., transmitting
data) of external electronic appliance 200 and external appliance
190, implantable stimulator 150 is commanded to produce a series of
electrical stimulation pulses with gradually increasing
amplitude.
[0074] 3. Set stimulator on/off period to an appropriate setting,
e.g., five seconds on then one second off.
[0075] 4. After each stimulation pulse, series of pulses, or some
predefined interval, any change in impedance is sensed, preferably
by one or more electrodes 156 and 158 of implantable stimulator
150. These responses are converted to data and telemetered out to
external electronic appliance 200 via Function 3.
[0076] 5. From the response data received at external appliance 200
from the implantable stimulator 150, or from other assessment, the
stimulus threshold for obtaining a reflex response is determined
and is used by a clinician acting directly 212 or by other
computing means 218 to transmit the desired stimulation parameters
to the implantable stimulator 150 in accordance with Function
2.
[0077] 6. When patient 170 desires to invoke an electrical
stimulation to alleviate symptoms (e.g., pain, loss of function,
etc.), patient 170 employs handheld controller 180 to set the
implantable stimulator 150 in a state where it delivers the
prescribed stimulation pattern.
[0078] 7. Patient 170 employs controller 180 to turn off stimulator
150, if desired.
[0079] 8. Periodically, the patient or caregiver recharges the
power source/storage device 162 of implantable stimulator 150 in
accordance with Function 1 described above (i.e., transmit
electrical power).
[0080] For the treatment of any of the various types and degrees of
chronic pain, it may be desirable to modify or adjust the
algorithmic functions performed by the implanted and/or external
components, as well as the surgical approaches, in ways that would
be obvious to skilled practitioners of these arts. For example, it
may be desirable to employ more than one implantable stimulator
150, each of which could be separately controlled by means of a
digital address. Multiple channels and/or multiple patterns of
stimulation might thereby be programmed by the clinician and
controlled by the patient in order to deal with bilateral, complex,
or multidimensional pain such as may occur as a result of spinal
cord injury and failed back surgery syndrome (FBSS), for
example.
[0081] In one preferred embodiment, microstimulator 150, or a group
of two or more microstimulators, is controlled via closed-loop
operation. A need for and/or response to stimulation is sensed via
microstimulator 150, or by an additional microstimulator (which may
or may not be dedicated to the sensing function), or by another
implanted or external device. If necessary, the sensed information
is transmitted to microstimulator 150. Preferably, the stimulation
parameters used by microstimulator 150 are automatically adjusted
based on the sensed information. Thus, the stimulation parameters
are adjusted in a closed-loop manner to provide stimulation
tailored to the response to stimulation.
[0082] For instance, in one embodiment of the present invention, a
first and second "stimulator" are provided. The second "stimulator"
periodically (e.g. once per minute) records a level of e.g., neural
activity, which it transmits to the first stimulator. The first
stimulator uses the sensed information to adjust stimulation
parameters according to an algorithm programmed, e.g., by a
physician. For example, amplitude of stimulation may be increased
in response to increased neural activity. More preferably, one
"microstimulator" performs both the sensing and current generating
functions.
[0083] For example, as seen in FIG. 6, a first microstimulator 150,
implanted in or adjacent the spine of patient 170, provides
electrical stimulation via electrodes 156 and 158 to a first
location; a second microstimulator 150' provides electrical
stimulation to a second spinal location; and a third
microstimulator 150" provides electrical stimulation to a third
spinal location. As mentioned earlier, the implanted devices may
operate independently or may operate in a coordinated manner with
other similar implanted devices, other implanted devices, or other
devices external to the patient's body, as shown by the control
lines 222, 223 and 224 in FIG. 6. That is, in accordance with one
embodiment of the invention, the external controller 220 controls
the operation of each of the implanted microstimulators 150, 150'
and 150". According to another embodiment of the invention, an
implanted device, e.g. microstimulator 150, may control or operate
under the control of another implanted device(s), e.g.
microstimulator 150' and/or microstimulator 150". That is, a device
made in accordance with the invention may communicate with other
implanted stimulators, other implanted devices, and/or devices
external to a patient's body, e.g., via an RF link, an ultrasonic
link, a thermal link, or an optical link. Specifically, as
illustrated in FIG. 6, microstimulator 150, 150', and/or 150", made
in accordance with the invention, may communicate with an external
remote control (e.g., patient and/or physician programmer 220) that
is capable of sending commands and/or data to implanted devices and
that is capable of receiving commands and/or data from implanted
devices.
[0084] Microstimulators made in accordance with the invention
further incorporate, in one embodiment, first sensing means 228 for
sensing therapeutic effects, clinical variables, or other
indicators of the state of the patient, such as impedance, EMG,
ENG, and/or EEG. The stimulators additionally or alternatively
incorporate second means 229 for sensing levels and/or changes in
pain medication and/or sympathetic discharge and/or other markers
of the potential for pain. The stimulators additionally or
alternatively incorporate third means 230 for sensing electrical
current levels and waveforms supplied by another source of
electrical energy. Sensed information may then be used to control
the parameters of the stimulator(s) in a closed loop manner, as
shown by control lines 225, 226, and 227. Thus, the sensing means
may be incorporated into a device that also includes electrical
stimulation means, or the sensing means (that may or may not have
stimulating means), may communicate the sensed information to
another device(s) with stimulating means.
[0085] While a microstimulator may also incorporate means of
sensing pain, it may alternatively or additionally be desirable to
use a separate or specialized implantable device to sense and
telemeter physiological conditions/responses in order to adjust
stimulation parameters. This information may then be transmitted to
an external device, such as external appliance 220, or may be
transmitted directly to implanted stimulator(s) 150. However, in
some cases, it may not be necessary or desired to include a sensing
function or device, in which case stimulation parameters are
determined and refined, for instance, by patient feedback.
[0086] As described earlier, microstimulator 150 includes means to
stimulate intermittently or continuously. Specific stimulation
parameters provide therapeutic advantages for various forms of
pain.
[0087] According to one therapeutic alternative, pain is alleviated
with decreased excitement of targeted neural tissue, e.g., at
decussation of the spinothalamic tract, at the ventral commissure
116. High-frequency electrical stimulation (e.g., greater than
about 100-150 Hz) is likely to produce such inhibition. Depending
on the specific condition of a patient, this therapy is most likely
to provide relief to patients with chronic peripheral pain, such as
peripheral neuropathy and complex regional pain syndrome (CRPS),
among other problems. Alternatively or additionally, the patient
may be treated with decreased excitement of other areas of the
spinal cord through which pain signals travel, such as Lissauer's
tract, or at other locations along the spinothalamic tract 118.
[0088] According to another therapeutic alternative, pain is
alleviated with increased excitement of one or more of dorsal
column(s) 120 (cuneate fasciculus 122 and/or gracile fasciculus
124), dorsal root(s) 110, and/or spinal nerve(s) 112, at e.g.,
T8-S5, and/or more preferably T10-S1. Low-frequency electrical
stimulation (e.g., less than about 100-150 Hz) is likely to produce
such excitement. This therapy is most likely to provide relief to
patients with CRPS and FBSS, among other problems.
[0089] As mentioned earlier, large diameter fibers (e.g., A-.alpha.
and/or A-.beta. fibers) respond to relatively lower current density
stimulation vis--vis small diameter fibers (e.g., A-.delta. and/or
C fibers). These A-.delta. and C fibers are generally responsible
for carrying pain and temperature signals, while the A-.alpha. and
A-.beta. fibers generally carry pressure, light touch, and
proprioceptive information. Therefore, pain may be masked,
decreased or removed by activating the larger A-.alpha. and/or
A-.beta. fibers, so the signals from the A-.delta. and/or C fibers
are "masked", or "gated." For example, microstimulator(s) 150 may
be implanted on or adjacent a dorsal column 120 or a dorsal root
110 of one or more of L2, L3, L4, and L5 to treat pain at the front
of a patient's leg (see FIG. 1B). The microstimulator(s) are
preferably programmed to provide relatively low-current stimulation
pulses (e.g., at less than about 1-10 mA, depending on proximity of
the stimulator to the target neural tissue), which is likely to
cause the sensation of pressure, light touch, proprioceptive, and
other non-nociceptive sensations. These sensations may be
sufficient to mask or block the pain signals.
[0090] If, instead or additionally, the pain is located at the back
of a patient's leg and/or in the foot, stimulation applied to one
or more nerve fibers of L1-L5, S1, and S2 may provide relief. As
used herein, nerve fibers include spinal nerve(s), spinal nerve
root(s), and areas in and around the spinal cord, such as
Lissauer's tract, the ventral commissure, the spinothalamic tract,
the dorsal column, among other things. Chronic pain in the arms may
best be relieved with stimulation of one or more nerve fibers of
C5, C6, C7, C8, and T1. Chronic cervical pain may best be relieved
with stimulation of one or more nerve fibers of C2-C5, while
chronic pain in the lower back may best be treated with stimulation
of one or more nerve fibers of L1-L5, and S1. Pain elsewhere in the
back may best be treated with stimulation of one or more nerve
fibers of T1-T12. Pain in the head/neck region, such as headache,
migraine, facial pain, and/or occipital neuralgia may be best
treated with stimulation of one or more nerve fibers of C1-C8.
[0091] As described earlier, chronic pain is often reported in the
pelvic region. For pain in this area, preferred locations for a
stimulator(s) include one or more of the nerve fibers of T10-T12,
L1, and L2 (mainly for pain in the front half of the pelvis),
and/or L1-L5 and S1-S5 (for pain in the back half of the
pelvis).
[0092] In yet another alternative, sensing means described earlier
may be used to orchestrate first the activation of
microstimulator(s) targeting one or more nerves to control pain in
one area, and then, when appropriate, the microstimulator(s)
targeting nerves that control pain in another area and/or by a
different means. Alternatively, this orchestration may be
programmed, and not based on a sensed condition.
[0093] While the invention herein disclosed has been described by
means of specific embodiments and applications thereof, numerous
modifications and variations could be made thereto by those skilled
in the art without departing from the scope of the invention set
forth in the claims.
* * * * *