Note: Descriptions are shown in the official language in which they were submitted.
9~
This invention relates to apparatus for use in the treatment of disease
syndromes causing spinal curvature and resulting skeletal imbalance in humans
by the selective application of electrical stimulation to the body.
This application is a division of our Canadian application Serial No.
242,742 filed December 30, 1975.
Spinal curvature has been known to man since he first assumed the erect
posture. Scoliosis, a lateral curvature of the vertebral column and rota-
tion around its longitudinal axis, is a progressive condition often associ-
ated with other spinal curvatures; kyphosis or humpback and/or lordosis or
swayback. Each of these conditions is debilitating and deforming to a degree
depending on the characteristics and extent of the curvature.
Idiopathic scoliosis accounts for the vast majority of all scoliosis
and is present in one out of ten children. While there is evidence that idio-
patic scoliosis is genetic, its true cause has not been found. Also, there
is no known preventative or cure for idiopathic scoliosis and treatment re-
mains a matter of correcting the curvature after it has developedO The curv-
ature in idiopathic scoliosis typically consists of a major curve, the curve
of greatest degree, and a minor curve or curves which form as a compensating ;
mechanism to keep the patient's head directly over the pelvis. In some in-
stances, more than one major curve may develop.
Among the more successful treatments for idiopathic scoliosis are the
long-term use of braces and spinal fusions. The bracing tec~mique requires
the almost constant wearing of a cumbersome external device over Q period of
several years. This type of treatment is very exp~nsive and, at best, can
; only prevent a scoliotic curve from progressing. Thus, even tlle best bracing
techniques fall far short of leaving the patient with a corrected mobile spine.
In additionj because the brace is typically used during adolescence it has
often left the patient with significant psychological problems.
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In contrast to the bracing technique, various spinal fusion techniques
have provided satisfactory correction of the spinal curvature in those pa-
tients, usually young, whose spines were flexible at the time of fusion.
However, the patient is left with a rigid spine. Because these fusion tech-
niques have been developed in relatively recent times, it is not known what
effect a spinal fusion will have during the adult life of the patient. Also,
the loss of mobility and disc spaces puts an ever increasing stress on those
lower discs that remain mobile.
In addition to bracing and spinal fusion techniques, there are sugges-
tions in the prior art of the use of electrical stimulation in the treatment
of scoliosis. The suggestions are in terms of transcutaneous stimulation.
Transcutaneous stimulation produces a contraction of at least the outer
paraspinal muscles. These muscles are longer than the muscles deeper in the
back and extend over many vertebral segments. Thus, while a transcutaneous
stimulation of the paraspinal muscles may have a beneficial effect on the
major spinal curve, the stimulation of the longer, outer paraspinal muscles
has the tendency to worsen the compensating curve. The electrical treatment
of spinal curvature is not an accepted practice and it is believed that the
tendency to worsen the compensating curve attending a transcutaneous stimu-
lation of the paraspinal muscles is a primary factor in the failure of such
a treatment to gain recognition.
The present invention provides a system for the electrical treatment
of scoliosis, and other spinal curvatures, capable of producing a correction
in the curvature without resort to cumbersome external bracing and without
loss of spinal mobility and disc spaces. The present invention also over-
comes the worsening of the compensating curve(s) attending known prior art
electrical treatments.
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The present invention involves means for positioning one end of a sleeve
means within the paraspinal muscles and means insertable through the other
end of the sleeve means for delivering and securing an electrode within the
paraspinal muscles adjacent the one sleeve means end. The electrodes are
connected to a source of stimulation impulses having alternating or cyclic
stimulation and rest periods and stimulation of the muscles may take place
~ while the patient relaxes or sleeps.
- According to the invention there is provided apparatus for use in the
treatment of disease syndromes causing spinal curvature and resulting skele-
tal imbalance in humans by the selective application of electrical stimu-
lation to the body comprising: pulse generator means for providing electrical
stimulation impulses having selective parameters sufficient to elicit a de-
sired muscular contraction response; electrode means electrically connectable
to said pulse generator means to receive the stimulation impulses and adapted
to apply the stimulatlon impulses to the body; muscle penetrating means
adapted to receive said electrode means for penetrating paraspinal muscles
of the body to position said electrode means within paraspinal muscles so
that the selective application of stimulation impulses to the paraspinal
muscles will be effective to cause their periodic contraction and relaxation;
and means associated with said electrode means for securing said electrode
means within the paraspinal muscles upon withdrawal of said muscle penetrat-
ing means from the paraspinal muscle.
In a preferred embodimemt, a probe having a blunt, muscle-penetrating
tip is fitted with a sleeve such that its tip extends from the sleeve. The
;~ blunt tip allows a muscle penetration with a minimum of muscle damage through
its ability to separate the muscles without severing them. The probe is in-
serted into the paraspinal muscle and removed while leaving the sleeve
within the muscie.
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A helical electrode is mounted on an elongated tool capable of impart-
ing a rotational force -to the electrode while allowing a disengagement with
electrode in one direction along the longitudinal axis of the tool. The
electrode-tool assembly is inserted through the sleeve and the electrode
secured in the paraspinal muscles by a rotational force applied to the tool.
After the electrode is secured, the tool is withdrawn from the sleeve and
the sleeve withdrawn from the muscle leaving the electrode secured within
the muscle.
Prior to positioning the probe, needle electrodes may be employed to
evaluate the effect of paraspinal muscle contraction produced by stimulation
of those muscles at several sites. When the needle electrode sites which
maximize the correction of the spinal curvature have been determined, the
blunt probes are inserted in those sites. The blunt probes may be provided
with electrode tips and the paraspinal muscles again stimulated at varied
penetration depths to establish the optimum depth for securement of the heli-
cal electrode. In this manner, the optimum site for the electrode as well
as the optimum electrode depth is established and the electrode is secured
at the established sites and to the established depths with a minimum of
tissue damage.
Figure 1 is a diagrammatical illustration of a typical scoliotic curve
; of the spinal column and the electro-spinal instrumentation system of the
present invention.
Figure 2 illustrates a pre~erred embodiment of the needle electrode em-
ployed in the system of ~he present invention.
Figure 3 illustrates a preferred embodiment of the probe-sleeve assembly
employed in the system of the present invention.
Figure 4 illustrates a preferred embodiment of the tool used to secure
the electrode within the paraspinal muscles in the system of the present in-
vention.
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Figure 5 illustrates a cross-section taken along tlle line 5-5 in
Figure 4.
Figure 6 illustrates a preferred embodiment of the electrode employed
in the system of the present invention.
Figure 7 illustrates a cross-section taken along the line 7-7 in
Figure 6.
Figure 8 illustra-tes the assembly of the preferred embodiments illus-
trated in Figures 4-7.
Figures 9 and 10 illustrate the schematic circuits of the electronic
transmitter and receiver of the electro-spinal instrumentation system; Fig. 10
is located on the first page of the drawings immediately under Figure 1.
Figure 1 is a diagrammatic illustration of the spinal column and a typi-
cal scoliotic curve under treatment by the electro-spinal instrumentation
system of the present invention. The curve is composed of a thoracic curve
10 bounded by vertebra 11 and vertebra 12 and a lumbar curve 13 bounded by
vertebra 12 and vertebra 14. Of course, the vertebrae 11, 12 and 14 which
bound the curves 10 and 13 are dependent on the curves in question and may
be any o~ the vertebrae in the spinal column. That is, vertebra 11 is the
highest vertebra with its superior border inclined toward the thoracic con-
cavity while vertebra 14 is the lowest vertebra with its inferior border in-
clined toward the lumbar concavity. Vertebra 12 is the lowest vertebra with
its inferior border inclined toward the thoracic concavity and the highest
vertebra with its superior border inclined toward the lumbar concavity. The
The vertebrae 11, 12 and 149 as determined by the above definitions, are
commonly employed to measure the amount of curvature, the particular measure-
ment methods being well known to those skilled in the art. In the spinal
column illus~rated, both the thoracic and lumbar curvatures are approxi-
mately 65 when measu-red by the Cobb method.
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A typical scoliotic curve has a major curve and a minor curve or
curves which form as a compensatory mechanism to maintain the head directly
over the pelvis. The present invention is directed to a straightening of the
major curve through an electrically induced contraction of the paraspinal
muscles in proximity to the convexity of the major curve and without a con-
traction of those paraspinal muscles which extend sufficiently beyond the
; major curve to have a worsening effect on the compensatory curve. With ref-
erence to the curve lO illustrated in Figure l, this is accomplished by plac-
ing the electrodes 15 within the deeper paraspinal muscles proximate the con-
vex side of the curve ~the right side for curve 10).
The electro-spinal instrumentation system illustrate~ in Figure 1
is provided to exercise the paraspinal muscles to cause them ~o hypertrophy
or strengthen through the application of electrical stimulating impulses
to three electrodes l5, at least two of said electrodes being active elec-
trodes and one of the electrodes being an indifferent electrode. The elec-
trodes 15 are placed in a manner described hereinafter in greater detail at
varying depths ~ithin the paraspinal muscles adjacent the major curve 10 of
the spinal column. It is believed that these muscles through the application
of electrical stimuli will hypertrophy and as a result induce a slight im-
2Q balance in comparison with the muscles on the concave side of the curve lO
through the remaining growing years of the child and that muscle imbalance
will arrest, or work to correct the convexity o the spinal column 10.
The electrodes lS are electrically connected to leads 16 that are
electrically connected to a biocompatible,subcutaneously implanted, electronic
radio frequency signal receiver 17.
The receiver 17 is placed subcutaneously in a surgical procedure
to be described following the placement of the electrodes 15. The patient, in
using the electrospinal instrumentation system, places a transmitting antenna
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18 over the subcutaneous implant position of the receiver 17. The antenna
18 is electrically connected by a lead l9 to the output jack of a radio fre-
quency pulse generating transmitter 24.
In operation by the patient, the radio frequency transmitter 24 is con-
veniently placed next to the patient's body while the patient is at rest,
and the antenna 18 is taped in place over the antenna of the implanted re-
ceiver 17. Then the patient turns on the transmitter, and the transmitter
24 cyclically produces a train of stimulating impulses at a rate that is
preset by the electronic circuitry of the transmitter.
The train of impulses produced by the transmitter 24 and transmitted by
antenna 18 is depicted as wave form A in Figure 1. Likewise, the impulses
received by receiver 17 and applied to the electrodes 15 are depicted as wave
- form B in Figure 1. During the "on" cycle of the transmitter 24, the train
- of pulses A is produced, each pulse having a preselected width and amplitude
recurring at a preselected rate. During the "off" cycle, no pulses are pro-
duced, and the muscles are allowed to rest. The time periods of the "on"
and "off" cycle may be one second and 5 seconds,-respectively, which allows
the stimulated muscles to contract and relax withou* causing fatigue. The
preselected rate, amplitude and pulse wldth of the stimulating pulses may
~i 20 comprise a rate of 30 pulses per second at an amplitude between the electrode
.
selectable from 0 to 10 volts and a pulse width of about 220 microseconds.
; These parameters are selectable by the surgeon at time of implant when the
operation of the system is tested and may be altered by the surgeon post-
.
~operatively as the patient's progress is monitored.
~ Further details of the circuit of the pulse generator and receiver will ~
;~ be described ln conjunction with Figures 9 and lO. The surgical procedure ,
for implanting the receiver and electrodes will not be described.
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After surgical incision and exposure of the paraspinal muscles, the
first step in the performance of the system of the present invention is the
identification of the optimal sites for the positioning of electrodes. The
optimal electrode sites are defined as those sites which maximize the correc-
tion of the curvature as a result of an i:nduced contraction of the paraspinal
muscles. It is contemplated that the present invention will be carried out
with three electrodes, two active electrodes and one indifferent electrode,
although other numbers of electrodes may be successfully employed. Also,
it is expected that the active electrodes will be negative inasmuch as this
provides a lower stimulation threshold.
The optimization of the sites for electrode placement may be accom-
plished through the use of needle electrodes such as that illustrated in
Figure 2. The needle electrode may have a portion 20 formed similarly to a
hypodermic needle and be provided with a knob 21 to facilitate its manipu- `
lation. The portion 20 is connected to an external source of stimulation
energy through a lead 22 and may be provided with a cutting surface 23 to
facilitate the placement of the electrode within the paraspinal muscles. It
is contemplated that several alternative placements of the needle elec-
trodes of Figure 2 Ylll be required to establish the optimal electrode sites,
the sites which maximize straightening of the spinal curvature as a result
of induced muscle contrac~ion. The optimal sites may be established visibly
,~ by repeatedly repositioning the needle electrodes of Figure 2 within the para-
spinal muscles and electrically inducing a contraction of those muscles.
Alternatively, the optlmal sites can be established through x-ray techniques
in which the degree of straightening is established, for several sites, by
. .
a~measurement of the curvature during stimulation.
Once the optimal sltes for electrode securement are established, the
needle electrodQs are withdrawn. A blunt probe fitted with a sleeve is then
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inserted within the muscle at each site established through the use of the
needle electrodes. A preferred embodiment of a blunt probe which may be
employed within the system of the present invention is illustrated at 25 in
Figure 3. The probe 25 has an elongated portion fitted with a sleeve 26
with the sleeve being provided with a slot 27 throughout its length. The
probe terminates at a blunt tip 28 which extends from the sleeve 26 and is
provided with an electrode 29 at its end. The electrode 29 is in electrical
communication with a lead 31 through which it may be connected to a source
of stimulation energy ~not shown) and is spaced from the end of the sleeve 26
to contact the muscle at generally the same location as a permanent electrode
inserted into the muscle through the sleeve 26. The probe may be provided
with an enlarged portion 32 which acts as a stop for the sleeve 26 and as
a handle to facilitate manipulation of the probe and the sleeve 26 may have
a tapered portion 30 conforming the blunt tip 28 of the probe.
A blunt probe 25 is inserted within the paraspinal muscle at each site
~ established as optimal through the use of the needle electrodes of Figure 2.
: The blunt tip 28 of the probe allows a penetration of the paraspinal muscles
through a separation of those muscles thereby minimizing the injury result-
m g from muscle penetration and the stop 32 causes the probe to carry the
sleeve 26 into the muscle tissue. Each probe is inserted to various pene-
tration depths and the muscle stimulated at each depth through a stimulating
signal applied at the tip electrode 29. The penetration depth which maxi-
mizes the correction of the spinal curvature can be established visibly or
through the use of x-ray techniques. Once the optimal penetration depth is
established, the probe is withdrawn from the paraspinal muscle leaving the
sleeve 26 in position in the muscle at the depth established for maximum
curvature correction.
Referring now to Figure 4, there is shown a tool 35 which is used to
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secure a helical electrode within the paraspinal muscles at the sites and pen-
etration depths established with the needle electrode of Figure 2 and the
probe of Figure 3. The tool 35 is essentially an elongated tubular member
having two slots on opposing sides thereof. One slot 36 extends from one
end of the tool 35 to a spot adjacent its other end to form a recess within
the tool. The other slot 37 extends from the same end of the tool 35 as the
slot 36 but need extend only far enough to accommodate the electrode to be
discussed below. Figure 5 is a cross-section taken along the line 5-5 in
Figure 4 and illustrates the slots 36 and 37 on opposing sides of the tool 35.
The tool 35 may be provided with a handle 38 to facilitate its manipulation
with the handle 38 being secured to the tool 35 in any con~enient manner.
Referring now to Figure 6, there is shown a helical electrode 40 which
is a preferred electrode embodiment within the system of the present inven-
tion. The electrode 40 has an exposed, electrically-conductive helical or
spiral member 41 which will engage and penetrate muscle tissue when rotated
in the proper direc~ion. The cooperation between ~he member 41 and the-muscle
tissue is analogous to the operation of a cork screw and electrodes such as
that illustrated in Figure 6 have been referred to in the prior art as cork
screw electrodes. The member 41 extends from an electrode body 42 which has
a first generally cylindrical portion 43 and a generally flat or tab portion
44.~ The cylindrical portion 43 of the electrode body 42 has a diameter ap-
proximating that of the tool of Figure 4 and the portion 44 of the electrode
body 42 is composed of a central portion 47 which accommodates an electri-
cally conductive lead 48 and extending members or wings, 45 and 46, which are
sufficlently extensive to be accommodated within the slots 36 and 37 of the
tool 35. The cork screw 41 is adapted for connection to an external source
of stimulation energy via the lead 48, the lead 48 being encased in an elec- ;
trical insuIation in known manner.
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.
Referring now to Figure 8, there is shown the electrode 40 mounted on
the tool 35. The wings 45 and 46 of the electrode body 42 are within the
slots 36 and 37 of the tool 35 with the cylindrical portion ~3 of the elec-
trode body 42 in abutment with one end of the tool 35. With this tool and
electrode configuration, tool 35 may be withdrawn from the electrode body 42
in one direction along its longitudinal axis while being capable of imparting
a force to electrode body 42 in the other longitudinal direction and will
transmit a rotational force to the electrode body 42 via the wings 45 and 46
in cooperation with the slots 36 and 37. The lead 48 lies within the slot 36
and emerges from the slot 36 at its end to be wrapped around the body of the
tool 35. The direction of wrapping of the lead 48 around the body of the
; tool 35 is selected such that the lead 48 will unwrap itself from the tool 35
as the tool 35 is rotated in the direction which will cause a penetration of
the muscle tissue by the cork screw 41. The number of wrappings may corres-
pond with the number of coils in the member 41.
With the electrode 40 mounted on the tool 35 as illustrated in Figure 8
and with the sleeve 26 in the optimal position relative to the paraspinal
muscles, as described above, the tool-electrode combination is inserted with-
in the sleeve 26, the tool 35 rotated thereby imparting a rotational force
to the electrode 40 and causing a penetration of the muscle tissue by the
cork screw 41 and tool 35 withdrawn from the sleeve leaving the electrode
secured within the muscle. The electrode 29 of the probe 25 is spaced from
the sleeve 26 during insertion such that the helical electrode will penetrate
to the depth established as optimal during stimulation with the electrode 29. . .
. . .
With the tool 35 withdrawn, the sleeve 26 is also with~rawn from the
moscle tissue with the slot 27:within the sleeve 26 allowing a disengagement
of the sleeve 26 from the lead 48. Of course~ if the end of lead 48 is free
and the nature of its electrical connection to the external stimulation
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device (not shown) permits, the slot 27 in sleeve 26 may be eliminated inas
much as the sleeve may be totally withdrawn over the lead 48. With the sleeve
26 withdrawn, the electrode 40 is in the optimal location to maximi7e the
correction in the spinal curvature through an electrically induced contrac-
tion of the paraspinal muscles. While the electrodes are in direct contact
with the muscle tissue, it is believed that contraction of the muscle is in-
duced chiefly through nerve stimulation as a result of a lower nerve thresh-
old.
Turning now to Figures 9 and 10, there is shown in detail a circuit
diagram of the transmitter and receiver of the electro-spinal instrumentation
system. As men~ioned hereinbefore, the transmitter 24 cyclically develops at
its antenna 18 a train of radio frequency energy stimulating impulses at a
predetermined rate, pulse-width and amplitude that are adjustable in the cir- " `~
cuit, the pulse train duration also being adjustable by further elements of
the circuit. In the circuit of Figures 9 and 10, the transmitter includes a
power source consisting, for example, of a nine-volt battery 50 of a conven-
tional dry cell type that may be depleted through use of the transmitter and
replaced as necessary by the patient. An on-off switch 51 is connected in
series with the battery and with the input terminal 52 of a cycler circuit 53,
the details of which will be explained with respect to Figure 10. The cycler
circuit 53 comprises a cyclic timer with on and off times individually selec-
table at the time of manufac~ure from one millisecond to one hour. In this
particular application, the cycler may be designed to have an on-time ad-
justable from one to five seconds and an off-time adjustable from five to
twenty-five seconds. During the on-time of the cycler circuit 53, supply vol-
tage is applied from the output terminal 54 to the pulse rate oscillator cir-
cuit 55. At all times that switch 51 is closed, supply voltage is applied by
; conductor 56 to the pulse width control circuit 58 and the radio frequency
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oscillator circuit 60, but neither of these circuits can operate as long as
source voltage is not applied to the pulse rate oscillator circuit 55. A
- filter capacitor 61 is connected across the input terminal 52 and circuit
ground.
The rate oscillator circuit 55 produces a train of pulses recurring at
a predetermined rate so long as supply voltage appears at the output terminal
54 of the cycler circuit 53, and the train of pulses is applied to the pulse
width control circuit 58. The pulse width control circuit 58 may comprise
a mono-stable multi-vibrator triggered by each pulse developed by the circuit
55 to produce a further pulse, the multi-vibrator having an adjustable re-
sistor element for adjusting the width of its output pulse. The radio fre-
quency oscillator 60 oscillates whenever an output pulse is received from
the pulse width control circuit 58 at a preselected frequency such as 460
kilohertz, resulting in a tràin of pulses each having a predetermined pulse
width and recurring at a preset rate during the on-time of cycler 53, each
pulse thereby comprising a burst of radio frequency energy as depicted as
~ave form A in Figure 1. In the radio frequency oscillator circuit 60, an
amplitude control circuit is provided to adjust the voltage amplitude of the
radio frèquency energy pulses.
- 20 The antenna 18 is electrically connected to the output of the radio ~re-
quency oscillator circuit 60, and, as described hereinbefore, is used to~
; couple the radio frequency pulses through the skin of the patient to the re- :.
. ~
ceiver circult. As depicted in Figure 1, the energy from the transmitting
antenna is coupled~with an antenna 62 within the receiver 17 where it is
: then detected and applied to the muscle through the leads 16 and electrodes
15.
Turning now to the~clrcuit of Figure 10, the battery power source 50 is
electrically connected in series through the switch 51 to the input terminal
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52. The cycler circuit 53 comprises a first astable multi-vibrator 64 that
oscillates at a frequency determined by the external R-C time components 65,
66 and 67. A first binary counter 68 receives impulses from the first a-
stable multi-vibrator 64 until it reaches a predetermined count, whereupon
the counter 68 develops or produces a high output state on conductor 69 that
is conducted to the A input of multi-vibrator 64 to halt its operation and is
also conducted to the A input of a second astable multi-vibrator 70. Astable
multi-vibrator 70 responds to the high state at its A input to generate and
apply pulses to second binary counter 72 which counts the number of pulses
developed by the second astable multi-vibrator 70 until it reaches a pre-
selected count. The frequency of the pulses developed by the second astable
multi-vibrator 70 is governed by R-C time components 73, 74 and 75.
When the full co1mt is reached by the second counter 72, it developes a
high output state on conductor 76 which is conducted through diode 77 to
the Reset input of the first counter 68 which in response thereto terminates
the high output state on conductor 69. At that moment, the low output state
applied to the A input of the first astable multi-vibrator 64 causes it to
start to oscillate, and the low output state applied to the A input of the
second astable multi-vibrator 70 causes it to cease oscillating. The output
20 signal developed by the first astable multi-vibrator 64 is conducted by con-
ductor 78 to the Reset input of counter 72 to terminate the high output state
on conductor 76, so that counter 68 is no longer reset and can count.
The oscillation frequencies of the astable multi-vibrators 64 and 70 are
establlshed by the charge times of the capacitors 67 and 75, respectively,
that are variable by adjustment of variable resistors 66 and 74, respectively.
In order to achieve consistent operation of the cycler 53, a Reset cir-
cuit comprising capacitor 79, resistor 80 and diodes 81 and 82 coupled between
; the power supply input 52 and the Reset inputs of counters 68 and 72 provides
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that, when the power supply is applied by the closing switch 51 ~Figure 9)
by the patient, the counts in both counters are Reset to zero by supply volt- `
age conducted through capacitor 79 and diodes 81 and 82. As supply voltage
rapidly increased across capacitor 79, the Reset signal rapidly dissipates
and the counters are rendered operational in the mamler described, and the
cycler circuit 53 operates at the start of its on-time cycle.
As mentioned hereinbefore, supply voltage is applied to rate oscillator
circuit 55 during the on-time cycle of the cycler 53, that is, the time fol-
lowing achievement of the full count in first counter 68 and while second
counter 72 is counting. More specifically, the high or relatively positive
output state of the first counter 68 is applied by conductor 69 to the base
of a switching transistor 83, the emitter-collector path of which is coupled
between ground potential and the junction of resistors 84 and 85. Resistor
84 is coupled to battery supply voltage, and resistor 85 is connected to the
base o~ a power switching transistor 86. The positive going voltage applied
to the base of transistor 83 turns transistor 83 "on" which lowers the volt-
age at the base of transistor 86 thus causing transistor 86 to turn "on" and
allows battery current to flow between input 52 and output 54. Thus battery
voltage is applied through transistor 86 to the rate oscillator circuit 55.
The astable multi-vibrators and counters are C-Mos integrated circuits
of types RCA-4047 and RCA-4040, respectively, available from RCA Corporation.
Referring now particularly to the rate oscillator circuit 55 of Figure 9,
; it comprises a reference voltage source including the transistor 88, the re-
sistors 90, 91, 92 and 93, the capacitor 94 and the diode 95 which apply a
reference voltage to an oscillator portion of the circuit 55 comprising a
programmable uni-junction transistor ~PUT) 96, a variable rate control re-
slstor 97, resistor 98 and capacitor 99. The source voltage is applied
across reference voltage divider resistors 90 and 91, the junction of which
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is connected to the base of transistor 88. Transistor 88 is thereby normally
biased to conduct source voltage to the junction of resistor 92 and capacitor
9~, less the forward voltage drop of transistor 88. The source voltage thus
applied through resistors 92, 93 and diode 95 is conducted to the gate to the
PUT 96 to establish a reference voltage level at its gate. Resistors 92 and
93 are selected to have relatively low and high impedances, respectively, and
therefore, capacitor 94, resistor 92 and diode 95 present a low impedance
voltage source in the forward direction of conduction, to the gate of PUT 96.
Conversely, to prevent the PUT 96 from being latched on by reverse current
flow, the resistor 93 presents a high impedance to the gate. The rate of
production of the pulses is controlled by the RC timing circuit comprising
the variable pulse rate control resistor 97, the resistor 98 and the capacitor
99 and the PUT 96. ~s source voltage is applied across the RC timing circuit,
voltage on capacitor 99 increases until that voltage reflected at the anode
of PUT 96 exceeds the reference voltage at its gate, whereupon the PUT 96 is
rendered conductive to produce an output pulse at its cathode. When the PUT
96 is rendered conductive, the voltage on capacitor 99 is discharged through
the resistors 100 and 102 only to the reference potential on its gate. The
PUT 96 is rendered conductive so long as the positive voltage applied to its
anode exceeds that applied to its gate. The values of capacitor 99 and re-
sistors lOO and 102 are selected to provide a positive spike output signal
that is applied to the pulse width control circuit 58 on conductor 103. The
rate of oscillation of the circuit 55, and thus the rate at which stimulation
pulses are produced is selectable by varying the pulse rate control resis-
tor 97.
The pulse width control circuit 58 operates as a monostable multi-
vibrator in response to the positive spike output signal of the circuit 55
to produce an output pulse having a uniform pulse width that is applied to
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the input of the RF oscillator circuit 60.
Since the cathode of PUT 96 is normally at ground potential reflected
through the circuit of resistors lOO and 102, the transistor 104 is concur-
rently normally non-conductive. The pulse width control elements of circuit
58 comprises variable pulse width control resistor 106, resistor 108, capaci-
tor 110 and resistor 112. The junction of resistor 112 and capacitor 110 is
connected to the collector of normally non-conductive transistor 104, and
capacitor 110 normally charges to a predetermined voltage of positive polar-
ity at the aforementioned junction. A second transistor 114 is connected at
its base to the junction of resistor 108 and capacitor 110, and its collector-
emitter path is connected in series with resistor 116 across supply voltage.
The junction of the resistor 116 and the collector of transistor 114 is
coupled b~ conductor 118 to the junction of resistors 100 and 102. Normally,
while transistor 104 is non-conductive, transistor 114 is conductive, reflect-
ing ground potential back to conductor 118.
When a spike potential is produced at the cathode of PUT 96 and applied
by conductor 103 to the base of transistor 104, transistor 104 is rendered
conductive. Capacitor 110 discharges through transistor 104 and resistors
106 and 108, and simultaneously renders transistor 114 non-conductive, thus
rais mg the potential on conductor 118. The increased potential on conductor
118 is reflected through resistor 100 and conductor 103 back to the base of
transistor 104, latching it in positlve feed-back conduction for so long as
capacitor 110 continues to discharge, that time period constituting the pulse
width of the transmitted stimulating impulses. The output pulse of the pulse
;~ width control circuie 58 is a square wave appearing on the conductor 119.
The conductor 119 is coupled to the input of the RF oscillator circuit
60, and the output pulse produced thereon triggers the oscillator circuit 60
into producing an RF~transmission signal of a pulse width determinable by the
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circuit 58 at a recurring rate established by the circuit 55 during the on-
time period of the cycler 53. The amplitude of the transmitted R~ stimula-
tion signal is adjustable by an amplitude control element of the circuit 60.
The RF oscillator circuit 60 includes: (1) a Colpitts oscillator com-
prising the transistors 120 and 122, the variable inductor 114, the capacitors
126 and 128, and the resistor 130 that produces an oscillatory signal at a
predetermined frequency, e.g., 460 ~Iz, during the duration of the output
pulse of circuit 55; ~a) an emitter-follower amplifier responsive to the RF
signal comprising transistor 131 and resistors 132, 134, and 136 and capaci-
tor 138 for capacitively coupling the RF signal to; (3) a class C operating
amplifier comprising transistor 140, inductor 142, variable amplitude control
resistor 144 and resistor 146 for further amplifying and isolating the RF
signal from the D.C. source voltage; and ~4) an oscillatory antenna circuit
comprising capacitors 148 and 150 that, in conjunction with the inductance of
antenna 18 oscillates sympathetically at the same radio frequency, e.g.,
~- 460 KHz.
In greater detail of operation, the Colpitts oscillator circuit includes
inductive and capacitive values that, when coupled to source potential through
conduction of transistors 120 and 122 in response to the positive output pulse
on conductor 119, establishes a rate of radio frequency oscillation at the
base of transistor 131. Transistors 131 and 140 amplify and reflect the os- `
cillations to the resonating antenna circuit, and the inductor 142 provides
a low impedance to hlgh frequency signals and a high impedance to the D.C.
source potential, so that transistor 140 can operate in the Class C state.
The current amplification factor of transistor 140 is adjustable by varying
resistor 144, a procedure that normally is done by the surgeon at the time of
implant and during post-operative treatment.
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The radio frequency signals are detected by a sympathetically tuned re-
ceiver circuit 17, comprising the inductance 62 of the receiver antenna, cap-
acitors 154, 156 and 158~ diode 160 and resistor 162, which are all connected
in a well known receiver configuration to detect 460 ~Iz signals, rectify the
detected signals and filter them to produce the pulse train of wave form B
of Figure 1. The leads 16 that couple the received RF stimulation signals
to the remote stimulation sites are connected as shown to the receiver circuit
17.
It is contemplated that the system of the present invention may be ad-
vantageously employed with three electrodes, two negative stimulating elec-
trodes and one positive indifferent electrode. It is further contemplated
that the stimulation employed will be intermittent bursts of bi-phasic square
wave pulses, the stimulation being provided for one to five seconds with
intervals between stimulation of five to twenty-five seconds. As is known in
the art, such intermittent stimulation prevents muscle fatigue. A duty cycle
~ratio of "on" time to "off" time) of one to five has been found to be ad-
vantageous for its further reduction of muscle fatigue. It is further con-
templated that the pulses will fall within the range of 30 to 60 pulses per
second with an amplitude of approximately 3 volts. During the determination
` 20 of the optimal location and penetration depth for the electrode, however, it
may be desirable to employ a stimulation amplitude of 10 volts or more. I~ is
expected thatj durm g treatment, stimulation will be provided for a period
of 8 to 10 hours during sleep and that treatment will continue at least until
the patient has achieved maturity, most likely until the patient is 16 to 18
years of age. However, as the desirable correction is approached treatment
may be conducted on an intermittent (non-daily~ basis to reduce the possi-
bility of over correction.
'.
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108~Z
Obviously, many modifications and variations of the present invention
are possible in light of the above teachings. For example, other electrode
configurations may be employed in place of the helical electrode described
in the preferred embodiment. Such electrodes may take the form of a needle,
with or without a barb, and extend from the electrode body 42 in the same
direction as the helical electrode to be positioned within the paraspinal
muscles through the use of the sleeve 26 and tool 35. It is therefore to
be understood that, within the scope of the appended claims, the invention
may be practiced otherwise than as specifically described.
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