Apparatus and Method for Optimum Electrode Placement in the Treatment of Disease Syndromes Such as Spinal Curvature

Spinal curvature has been known to man since he first assumed the erect posture. Scoliosis, a lateral curvature of the vertebral column and rotation around its longitudinal axis, is a progressive condition often associated 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 idiopatic scoliosis is genetic, its true cause has not been found. Also, there is no known preventative or cure for idiopathic scoliosis and treatment remains a matter of correcting the curvature after it has developed. The curvature 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 instances, 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 technique requires the almost constant wearing of a cumbersome external device over a period of several years. This type of treatment is very expensive and, at best, can only prevent a scoliotic curve from progressing. Thus, even the best bracing techniques fall far short of leaving the patient with a corrected mobile spine. In addition, because the brace is typically used during adolescence it has often left the patient with significant psychological problems.

In contrast to the bracing technique, various spinal fusion techniques have provided satisfactory correction of the spinal curvature in those patients, usually young, whose spines were flexible at the time of fusion. However, the patient is left with a rigid spine. Because these fusion techniques 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 on ever increasing stress on those lower discs that remain mobile.

In addition to bracing and spinal fusion techniques, there are suggestions 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 stimulation 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 overcomes the worsening of the compensating curve(s) attending known prior art electrical treatments.

The present invention consists essentially of sleeve means, means for positioning one end of the 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.

In an preferred embodiment, 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 inserted into the paraspinal muscle and removed while leaving the sleeve within the muscle.

A helical electrode is mounted on an elongated tool capable of imparting 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 helical 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.

FIG. 1 is a diagrammatical illustration of a typical scoliotic curve of the spinal column and the electro-spinal instrumentation system of the present invention.

FIG. 2 illustrates a preferred embodiment of the needle electrode employed in the system of the present invention.

FIG. 3 illustrates a preferred embodiment of the probe-sleeve assembly employed in the system of the present invention.

FIG. 4 illustrates a preferred embodiment of the tool used to secure the electrode within the paraspinal muscles in the system of the present invention.

FIG. 5 illustrates a cross-section taken along the line 5--5 in FIG. 4.

FIG. 6 illustrates a preferred embodiment of the electrode employed in the system of the present invention.

FIG. 7 illustrates a cross-section taken along the line 7--7 in FIG. 6.

FIG. 8 illustrates the assembly of the preferred embodiments illustrated in FIGS. 4-7.

FIGS. 9 and 10 illustrate the schematic circuits of the electronic transmitter and receiver of the electro-spinal instrumentation system.

FIG. 1 is a diagrammatic illustration of the spinal column and a typical 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 verterbra 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 of the vertebrae in the spinal column. That is, vertebra 11 is the highest vertebra with its superior border inclined toward the thoracic concavity while vertebra 14 is the lowest vertebra with its inferior border inclined 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 vertebrae 11, 12 and 14, as determined by the above definitions, are commonly employed to measure the amount of curvature, the particular measurement methods being well known to those skilled in the art. In the spinal column illustrated, both the thoracic and lumbar curvatures are approximately 65.degree. when measured by the Cobb method.

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 contraction of those paraspinal muscles which extend sufficiently beyond the major curve to have a worsening effect on the compensatory curve. With reference to the curve 10 illustrated in FIG. 1, this is accomplished by placing the electrodes 15 within the deeper paraspinal muscles proximate the convex side of the curve (the right side for curve 10).

The electro-spinal instrumentation system illustrated in FIG. 1 is provided to exercise the paraspinal muscles to cause them to hypertrophy or strengthen through the application of electrical stimulating impulses to three electrodes 15, at least two of said electrodes being active electrodes and one of the electrodes being an indifferent electrode. The electrodes 15 are placed in a manner described hereinafter in greater detail at varying depths within 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 imbalance in comparison with the muscles on the concave side of the curve 10 through the remaining growing years of the child and that muscle imbalance will arrest, or work to correct the convexity of the spinal column 10.

The electrodes 15 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 18 over the subcutaneous implant position of the receiver 17. The antenna 18 is electrically connected by a lead 19 to the output jack of a radio frequency pulse generating transmitter 24.

In operation by the patient, the radio frequency transmitter 24 is conveniently 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 receiver 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 FIG. 1. Likewise, the impulses received by receiver 17 and applied to the electrodes 15 are depicted as wave form B in FIG. 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 produced, 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 without causing fatigue. The preselected rate, amplitude and pulse width of the stimulating pulses may comprise a rate of 30 pulses per second at an amplitude between the electrodes 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 in conjunction with FIGS. 9 and 10. The surgical procedure for implanting the receiver and electrodes will now be described.

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 correction of the curvature as a result of an induced 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 accomplished through the use of needle electrodes such as that illustrated in FIG. 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 manipulation. 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 electrodes of FIG. 2 will be required to establish the optimal electrode sites, the sites which maximize straightening of the spinal curvature as a result of induced muscle contraction. The optimal sites may be established visibly by repeatedly repositioning the needle electrodes of FIG. 2 within the paraspinal muscles and electrically inducing a contraction of those muscles. Alternatively, the optimal 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 sites for electrode securement are established, the needle electrodes are withdrawn. A blunt probe fitted with a sleeve is then 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 FIG. 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 30 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 FIG. 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 resulting 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 penetration depths and the muscle stimulated at each depth through a stimulating signal applied at the tip electrode 29. The penetration depth which maximizes 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 FIG. 4, there is shown a tool 35 which is used to secure a helical electrode within the paraspinal muscles at the sites and penetration depths established with the needle electrode of FIG. 2 and the probe of FIG. 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. FIG. 5 is a cross-section taken along the line 5--5 in FIG. 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 convenient manner.

Referring now to FIG. 6, there is shown a helical electrode 40 which is a preferred electrode embodiment within the system of the present invention. 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 direction. The cooperation between the member 41 and the muscle tissue is analogous to the operation of a cork screw and electrodes such as that illustrated in FIG. 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 cyclindrical portion 43 and a generally flat or tab portion 44. The cylindrical portion 43 of the electrode body 42 has a diameter approximating that of the tool of FIG. 4 and the portion 44 of the electrode body 42 is composed of a central portion 47 which accommodates an electrically conductive lead 48 and extending members or wings, 45 and 46, which are sufficiently 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 electrical insulation in known manner.

Referring now to FIG. 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 43 of the electrode 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 correspond with the number of coils in the member 41.

With the electrode 40 mounted on the tool 35 as illustrated in FIG. 8 and with the sleeve 26 in the optimal position relative to the paraspinal muscles, as described above, the tool-electrode combination is inserted within 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 withdrawn from the muscle 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 device (not shown) permits, the slot 27 in sleeve 26 may be eliminated inasmuch 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 maximize the correction in the spinal curvature through an electrically induced contraction of the paraspinal muscles. While the electrodes are in direct contact with the muscle tissue, it is believed that contraction of the muscle is induced chiefly through nerve stimulation as a result of a lower nerve threshold.

Turning now to FIGS. 9 and 10, there is shown in detail a circuit diagram of the transmitter and receiver of the electro-spinal instrumentation system. As mentioned 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 circuit, the pulse train duration also being adjustable by further elements of the circuit. In the circuit of FIGS. 9 and 10, the transmitter includes a power source consisting, for example, of a nine-volt battery 50 of a conventional 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 FIG. 10. The cycler circuit 53 comprises a cyclic timer with on and off times individually selectable at the time of manufacture from one millisecond to one hour. In this particular application, the cycler may be designed to have an on-time adjustable 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 voltage is applied from the output terminal 54 to the pulse rate oscillator circuit 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 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 resistor element for adjusting the width of its output pulse. The radio frequency 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 train 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 wave form A in FIG. 1. In the radio frequency oscillator circuit 60, an amplitude control circuit is provided to adjust the voltage amplitude of the radio frequency energy pulses.

The antenna 18 is electrically connected to the output of the radio frequency oscillator circuit 60, and, as described hereinbefore, is used to couple the radio frequency pulses through the skin of the patient to the receiver circuit. As depicted in FIG. 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 circuit of FIG. 10, the battery power source 50 is electrically connected in series through the switch 51 to the input terminal 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 astable 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 oscillator 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 preselected 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 count is reached by the second counter 72, it develops 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 signal developed by the first astable multi-vibrator 64 is conducted by conductor 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 established 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 circuit 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 70 provides that, when the power supply is applied by the closing switch 51 (FIG. 9) by the patient, the counts in both counters are Reset to zero by supply voltage 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 manner 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 following 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 of a power switching transistor 86. The positive going voltage applied to the base of transistor 83 turns transistor 83 "on" which lowers the voltage 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 FIG. 9, it comprises a reference voltage source including the transistor 88, the resistors 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 resistor 97, resistor 98 and capacitor 99. The source voltage is applied across reference voltage divider resistors 90 and 91, the junction of which are 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 94, 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. As 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 resistors 100 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 gate control resistor 99.

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 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 100 and 102, the transistor 104 is concurrently normally non-conductive. The pulse width control elements of circuit 58 comprises variable pulse width control resistor 106, resistor 108, capacitor 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 polarity 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 by conductor 118 to the junction of resistors 100 and 102. Normally, while transistor 104, is non-conductive, transistor 114 is conductive, reflecting 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 raising the potential on conductor 118. The increased potential on conductor 118 is reflected through resistor 110 and conductor 103 back to the base of transistor 104, latching it in positive feedback 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 circuit 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 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 RF stimulation signal is adjustable by an amplitude control element of the circuit 60.

The RF oscillator circuit 60 includes: (1) a Colpitts oscillator comprising 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 KHz, during the duration of the output pulse of circuit 55; (a) an emitter-follower amplifier responsive to the RF signal comprising transistor 130 and resistors 132, 134, and 136 and capacitor 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 oepration, 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 130. Transistors 130 and 140 amplify and reflect the oscillations to the resonating antenna circuit, and the inductor 142 provides a low impedance to high 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.

The radio frequency signals are detected by a sympathetically tuned receiver circuit 17, comprising the inductance 62 of the receiver antenna, capacitors 154, 156 and 158, diode 160 and resistor 162, which are all connected in a well known receiver configuration to detect 460 KHz signals, rectify the detected signals and filter them to produce the pulse train of wave from B of FIG. 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 advantageously employed with three electrodes, two negative stimulating electrodes 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 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 advantageous for its further reduction of muscle fatigue. It is further contemplated 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 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. It is expected that, during 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 possibility of over correction.

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.