Method for non-invasive electrical stimulation of epiphyseal plate growth

Epiphyseal growth plate stimulation in the bone of a living body is achieved by applying electrodes non-invasively to a body and supplying to said electrodes an AC signal in the range of about 2.5 to 15 volts peak-to-peak at a frequency of about 20-100 KHz.

TECHNICAL FIELD 
This invention relates to a non-invasive method for stimulating growth in 
the epiphyseal plate in the bone of a living body by electrical 
stimulation. 
BACKGROUND OF THE INVENTION 
Bone formation arises by a transformation of connective tissue, and may be 
preceded either by the laying down of cartilage, or by direct 
transformation of fibrous tissue. In bones which have been preformed in 
cartilage, a portion of the cartilage persists throughout the period of 
growth as a cartilage plate. This cartilage continues to grow, and is 
constantly replaced by bone, resulting in lengthwise bone growth. The 
cartilage with its surrounding tissues, also contributing to growth, has 
been called the growth apparatus. In long bones the growth apparatus is at 
the epiphyses or ends of the bones. 
The length of the bone is controlled by the rate of growth of the 
epiphyseal line, which is the small cartilage plate at the end of the 
bone. Various stimuli have been implemented in trying to stimulate bone 
growth at the epiphyseal line. These stimuli have included periosteal 
irritation, radiation, medullary plugging, creation of an arteriovenous 
fistula, sympathetic denervation, heat, insertion of foreign objects into 
the epiphyses/metaphyses, and electricity. The methods of electrical 
stimulation have included electrolysis, i.e. the use of implanted 
dissimilar metals to produce a small current, direct current, 
electromagnetic fields and electric fields, both static and dynamic. 
Efforts using electrolysis electrical stimulation have included inserting 
dissimilar metal strips into the metaphyses close to the growth plate on 
mongrel dogs, and creating a current of 10-20 microamperes between the two 
strips. However any positive results obtained were insignificant. Further 
work using bimetallic strips resulted in the stimulation of longitudinal 
growth, but the stimulus was unpredictable. 
Other work has included that of Bassett who in 1974 showed that a 
capacitively coupled asymmetric electrostatic field increased the repair 
rate of fibular osteotomies in a rabbit. Watson in 1975 reported an 
increase in the length of embryonic chick tibiae grown in vitro in a 
pulsed square wave 1000 V/cm electric field. However, Watson obtained no 
positive results with a static field. Louis Norton in 1974 reported 
increased metabolic activity in the metatarsus bones of newborn chicks in 
response to a 5 Hz unidirectional signal ranging from 163 V to 490 V 
applied between two electrode capacitive plates. In 1977, Norton reported 
an increase in cAMP in response to a 900 V 5 Hz unidirectional signal, 
which increase tailed off at voltages above 1250 V. In 1976 Rodan and 
Norton demonstrated an enhanced incorporation of 3H-thymidine, in 
chondrocyte cultures, in response to a 1166 V/cm signal oscillating at 5 
Hz. Similar results were reported by Norton working with membranous bone 
from rat calvaria in 1977. 
In 1981, I reported electrical enhancement of growth plate DNA synthesis in 
vitro with low voltage capacitive coupling. In this experiment, 
costochondral junctions were excised from rats and were anchored to 
tightly sealed Petri dishes and grown in tissue culture medium. The Petri 
dishes were stimulated for 24 hours between intimately contacting, 
parallel, stainless steel plates using a stimulation signal of 10 V 
peak-to-peak, at a frequency of 60 KHz, with and without 50% amplitude 
modulation. Analysis of the samples indicated increased DNA synthesis of 
the experimental (stimulated) group relative to the control (unstimulated) 
group. However, the experiments were limited to in vitro specimens 
stimulated in Petri dishes. 
In early 1982, I reported stimulation of in vitro epiphyseal plate growth 
by a time varying electric field using stimulation signals of 5-80 V 
peak-to-peak, frequencies between 30 and 120 KHz, and 0%, 50% and 100% 
modulation. Stimulatory effects of increased DNA synthesis was noted 
particularly over the range of 5-50 volts peak-to-peak and over a 
frequency range of 30-60 KHz. Again, this experiment was limited to in 
vitro specimens of costochondral junctions of rats stimulated in Petri 
dishes. While increased DNA synthesis was observed in this and the former 
experiment, both experiments were limited to in vitro specimens. 
Therefore, it was still not known whether certain stimulation signals 
would result in longitudinal bone growth at the epiphyseal growth plate in 
vivo, (i.e. in living bodies). 
SUMMARY OF THE INVENTION 
In accordance with the present invention, bone growth at the epiphyseal 
growth plate in a living body is promoted by non-invasively applying 
electrodes to a subject's body in the vicinity of the epiphyseal growth 
plate of a bone and supplying to the electrodes an AC stimulation signal 
having a frequency of about 20-100 KHz. By applying the signal in this 
manner, intermittently or continuously for a sufficient period of time, an 
increase in bone growth is effected as compared with bone growth that 
would occur naturally. 
For better understanding of the above and other features and advantages of 
the invention, reference is made to the following detailed description of 
a preferred procedure according to the invention taken in conjunction with 
the following drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
While this invention may be practiced in many different forms, there is 
shown in the drawings and will herein be described in detail one specific 
method, with the understanding that the present disclosure is to be 
considered as an exemplification of the principles of the invention and is 
not intended to limit the invention to the precise method illustrated. 
FIG. 1 shows a signal frequency generator 10 which generates an AC 
stimulation signal having a frequency within the range of about 20-100 
KHz. The waveform of the AC stimulation signal is preferably an 
unmodulated symmetrical sinewave having a peak-to-peak amplitude within 
the range of about 2.5-15 volts peak-to-peak and more preferably within 
the range of about 5-10 volts peak-to-peak. The frequency generator 10 can 
be a Wave Tech Model 148 Function Generator. The stimulation signal is 
supplied by the wires 12 to a pair of stimulation electrodes 14 
non-invasively applied to the skin of a living body at positions in the 
vicinity of the epiphyseal growth plate of a bone. In order to achieve 
good electrical contact, the skin of the subject can be shaved initially 
and periodically to remove any hair, and a conductive jelly such as K-Y 
lubricating jelly (Johnson & Johnson) can be applied to the skin before 
the electrodes are non-invasively applied or reapplied to the skin. 
It should be understood that the electrodes should preferably be positioned 
relatively close to the epiphyseal growth plate of a bone. However, the 
electrodes may be applied at locations remote from the epiphyseal growth 
plate, where that proves necessary or desirable because of the particular 
bone selected to be stimulated. 
While the electrodes 14 are preferably bare metal placed in direct contact 
with the skin after the application of K-Y gel, one or both of the 
electrodes may be coated with dielectric material such as Mylar film 15. 
EXAMPLE 
Efficacy of the procedure according to the invention has been established 
in the following clinical experiment. 
A total of 80 seven-week old New Zealand white rabbits were selected for 
uniform growth and were distributed into four equal groups with each group 
having 10 control (unstimulated) animals and 10 experimental (stimulated) 
animals. The right proximal medial and lateral tibial epiphyses of all of 
the rabbits were shaved, and then a pair of electrodes 14 in the form of 
1.8 sq. cm. stainless steel plates was placed in parallel over the medial 
and lateral right tibial shaved areas of each rabbit. The electrodes were 
held in place by a plastic jig and moleskin wrap, which allowed for 
relatively normal weight bearing and free range of motion at the knee. The 
lead wires to the electrodes 14 were Teflon coated and encased in springs 
to prevent the animals from chewing the wires, and were connected to a 
rotating electrical connector at the top of the cage which allowed the 
wires to be untangled without disconnecting the wires, while also allowing 
the animal ample scope of movement. 
At the onset of the experiment (day 0) all animals received 3 mg/kg of 
intravenous oxytetracycline via the ear vein. Oxytetracycline has been 
found to have a strong affinity for mineralizing cartilage and bone 
tissue, and accumulates in skeletal locations where new bone matrix or 
hyaline cartilage is mineralizing. Since a rapid intraveneous pulse is 
given, an instantaneous fluorescent marker is established at the 
epiphyseal-metaphyseal border to provide a label parallel to the border. 
As bone increases in length the label remains incorporated in the 
metaphysis. When examined under ultraviolet light, the marker or label 
fluoresces green-yellow and is thus distinct from surrounding structures, 
and provides a means of measuring longitudinal bone growth. 
All animals received a second injection of oxytetracyline 2 days after the 
first injection (day 2). Commencing at the time of the second injection, 
the animals were reshaved, K-Y lubricating jelley was applied to the skin 
and electrodes 14 were reapplied to the right tibial area to insure good 
electrical contact, and the experimental animals in each group were 
stimulated with a continuous low voltage 60 KHz symmetrical sine wave 
signal from the generator 10 for two days (from day 2 to day 4). 
The signals were provided by a number of generators 10, with each generator 
servicing five animals. The amplitude of the signal for group 1 was 2.5 
volts peak-to-peak, for group 2 it was 5 volts, for group 3 it was 10 
volts, and for group 4 it was 20 volts. The signal was monitored every 
eight hours with a Techtronics T922 Oscilloscope. 
The currents passing through the electrodes 14 were calculated from the 
voltage drop across a 100 ohm resistor placed in series with the 
electrodes as measured by a Hewlett Packard Digital Multimeter. The rms 
current across the pairs of electrodes 14 for the stimulated animals in 
group 1 was 1.24 mamps .+-.0.32 (range 0.54-2.44), 1.10 mamps .+-.0.42 
(range 0.18-3.04) for the animals in group 2, 1.53 mamps .+-.0.64 (range 
0.08-8.36) for the animals in group 3 and approximately 7 mamps for the 
animals in group 4. The control animals received no stimulation during 
this period. 
The jigs used to hold the electrodes in place caused pedal edema to develop 
in some animals, and this condition was graded on a scale of 0-3 
(0=absent, 1=mild, 2=pitting and 3=weeping) on both days 2 and 4. The 
animals were weighed on days 0 and 4. 
On day 4, 96 hours after the first injection, all animals were sacrificed 
and the tibiae were dissected and stored in 40% ethyl alcohol for a 
maximum of 16 hours. The midlateral proximal tibiae were then 
longitudinally cut into sagittal or planar section slices approximately 
100 microns in thickness using a Buehler "Isomet" low speed diamond saw, 
exercising care to obtain sections perpendicular to the growth plate. A 
slab of proximal tibia was then ground down to 10 microns on a Buehler 
Grinder No. 320. The specimens were kept water wet during the entire 
procedure. Each specimen was then dehydrated in ethyl alcohol and 
permanently mounted on a microscopic slide with Eukitt's Mounting Media 
and kept out of direct light to minimize fading of the tetracycline label. 
Longitudinal growth was quantified using microscopic epifluoresence and a 
Zeiss MOP-3 measurement system. All specimens were read blindly. The 
longitudinal distance between the first and the second oxytetracycline 
line (indicating growth during the unstimulated period, days 0-2) and the 
second oxytetracycline line and the bone-cartilage junction (indicating 
growth during the stimulated period, days 2-4) was measured in both the 
control and experimental animals under 16.times.magnification. 
Each distance was calculated from the mean of twelve separate measurements 
taken at equal intervals across the growth plate of each specimen. An 
eyepiece grid was used to ensure uniform specimen alignment and equal 
measurement intervals. The precision of the system was tested beforehand 
by performing ten consecutive measurements on the same specimen. 
DATA ANALYSIS 
Two basic analyses of the data were made. In the first analysis the growth 
in the stimulated (experimental) animals was compared to growth in the 
unstimulated (control) animals for the stimulation period (days 2-4) only. 
This analysis was done for all four groups. In the second analysis, only 
the data for the stimulated animals in group 3 was analyzed. In this 
analysis, the growth in stimulated animals during the stimulation period 
(days 2-4) was compared to the growth of the same animal during their 
unstimulated period (days 0-2). 
1. First Analysis 
For the first analysis, the longitudinal proximal tibial growth data was 
tabulated, and ratios of right-to-left (i.e. R/L) growth for this 2 day 
stimulation period (days 2-4) were calculated for both the stimulated 
(experimental) animals and unstimulated (control) animals, (see Tables I, 
II, III, and IV). While 10 control and 10 experimental animals were 
initially present in each group, in some cases 1 or 2 animals were 
eliminated from the table for various reasons. 
As mentioned, only the right tibia of each experimental animal was 
stimulated. By measuring both the right and left tibiae for all animals, 
and then by calculating a ratio of right/left (R/L) for the tibiae of each 
animal, control for any growth or disease mechanisms that might be 
naturally occurring in the animal was obtained. 
As seen in Table I and FIG. 2, the group 1 animals (2.5 volts stimulation) 
experienced a 4.3% increase in length from 1.16 average ratio R/L to 1.21 
average ratio R/L. However, under statistical analysis using the "group-t" 
test, the results were not statistically significant. The correlation 
coefficients for current, weight gain and edema (r=0.27, 0.14 and 0.07 
respectively) revealed no statistical significance when compared to 
growth. 
For group 2 animals (5.0 volts stimulation) in Table II, a 9.2% increase in 
length was obtained, from 1.09 average ratio R/L to 1.19 average ratio 
R/L, (see FIG. 3). This result is statistically significant (p 0.05) under 
group t-test analysis. Again, no significant linear correlation appears to 
exist between longitudinal growth and either current, weight change or 
edema (with correlations of r=0.28, 0.43 and 0.10 respectively). 
Table III and FIG. 4 illustrate that the group 3 animals (10.0 volts 
stimulation) experienced an 7.8% increase in bone length, from 1.15 
average ratio R/L to 1.24 average ratio R/L, which was also statistically 
significant (p 0.02) under group t-test anaylsis. Again, there was no 
significant correlation between growth and current, weight change or edema 
(with correlations of r=0.23, 0.06 and 0.23 respectively). 
TABLE I 
______________________________________ 
Longitudinal Proximal Tibial Growth with 
Stimulation of 2.5 Volts P-P 
(50 units = 1 mm) 
______________________________________ 
Control Experimental 
R L R L 
______________________________________ 
33.02 29.80 32.76 
32.75 
33.82 26.68 30.03 
27.67 
32.89 30.65 31.80 
25.81 
35.33 29.32 37.36 
30.73 
28.17 26.38 32.39 
27.28 
34.28 33.10 32.79 
26.68 
35.48 29.41 39.92 
29.20 
32.51 25.43 42.92 
32.93 
33.35 
25.97 
(-x) 33.19 28.85 34.81 
28.78 
(SD) 2.3 2.54 4.28 2.77 
(SE) 0.81 0.90 1.43 0.92 
______________________________________ 
R/L R/L 
______________________________________ 
1.11 1.00 
1.27 1.09 
1.07 1.23 
1.21 1.22 
1.07 1.19 
1.04 1.23 
1.21 1.37 
1.28 1.30 
1.28 
(-x) 1.16 1.21 
(SD) 0.10 0.11 
(SE) 0.03 0.04 
4.3% .uparw. 
NS 
______________________________________ 
TABLE II 
______________________________________ 
Longitudinal Proximal Tibial Growth with 
Stimulation of 5 Volts P-P 
(50 units = 1 mm) 
______________________________________ 
Control Experimental 
R L R L 
______________________________________ 
37.87 34.16 36.23 
27.78 
37.00 35.88 41.12 
32.90 
38.67 34.71 23.54 
19.58 
29.33 32.11 32.35 
29.93 
27.21 23.48 34.28 
30.52 
32.32 27.83 30.42 
26.65 
36.93 32.73 27.73 
23.99 
27.38 24.88 33.28 
26.76 
38.85 
32.86 
(-x) 33.34 30.72 33.09 
27.89 
(SD) 4.86 4.71 5.44 4.30 
(SE) 1.72 1.66 1.81 1.43 
______________________________________ 
R/L R/L 
______________________________________ 
1.11 1.30 
1.03 1.25 
1.11 1.20 
0.91 1.08 
1.16 1.12 
1.16 1.14 
1.13 1.16 
1.10 1.24 
1.18 
(-x) 1.09 1.19 
(SD) 0.08 0.07 
(SE) 0.03 0.02 
9.2% .uparw. 
P&lt;0.05 
______________________________________ 
TABLE III 
______________________________________ 
Longitudinal Proximal Tibial Growth with 
Stimulation of 10 Volts P-P 
(50 units = 1 mm) 
______________________________________ 
Control Experimental 
R L R L 
______________________________________ 
36.16 31.73 43.90 
34.02 
32.85 29.68 34.75 
26.52 
36.91 31.54 29.18 
24.69 
37.34 32.97 42.30 
31.18 
41.42 34.15 33.74 
29.00 
33.14 26.63 41.63 
36.24 
36.03 33.72 43.38 
34.96 
36.60 33.13 37.34 
30.16 
(-x) 36.31 31.69 38.28 
30.85 
(SD) 2.67 2.49 5.37 4.08 
(SE) 0.94 0.88 1.90 1.44 
______________________________________ 
R/L R/L 
______________________________________ 
1.14 1.29 
1.11 1.31 
1.17 1.18 
1.13 1.36 
1.21 1.16 
1.25 1.15 
1.07 1.24 
1.11 1.24 
(-x) 1.15 1.24 
(SD) 0.06 0.08 
(SE) 0.02 0.03 
7.8% .uparw. 
p&lt;0.02 
______________________________________ 
TABLE IV 
______________________________________ 
Longitudinal Proximal Tibial Growth with 
Stimulation of 20 Volts P-P 
(50 units = 1 mm) 
______________________________________ 
Control Experimental 
L R L R 
______________________________________ 
30.30 31.43 28.06 
30.43 
25.68 33.25 32.63 
30.55 
27.43 32.42 35.53 
37.36 
27.80 32.25 26.86 
28.55 
24.76 25.75 29.39 
31.81 
27.07 30.78 29.13 
33.89 
31.41 36.82 28.28 
38.52 
31.11 37.50 30.41 
34.87 
32.29 38.09 29.00 
35.68 
28.53 33.33 
(-x) 28.64 33.16 29.92 
33.63 
(SD) 2.55 3.67 2.65 3.49 
(SE) 0.08 1.16 0.88 1.16 
______________________________________ 
R/L R/L 
______________________________________ 
1.04 1.08 
1.30 0.94 
1.18 1.05 
1.16 1.06 
1.04 1.08 
1.14 1.16 
1.17 1.36 
1.21 1.15 
1.18 1.23 
1.17 
(-x) 1.16 1.12 
(SD) 0.08 0.12 
(SE) 0.02 0.04 
3.6% .dwnarw. 
NS 
______________________________________ 
As shown in Table IV and FIG. 5, the group 4 animals (20.0 volts 
stimulation) experienced a 3.6% decrease in growth, from 1.16 average 
ratio R/L to 1.12 average ratio R/L. However, the results under group 
t-test analysis were not statistically significant. The correlation 
coefficients of weight gain and edema were 0.21 and 0.98 respectively. 
FIG. 6 illustrates the dose-response curve for the effect of stimulating 
the proximal tibial growth plate in the in vivo rabbit. The vertical axis 
is the mean stimulated growth, in percent, of the stimulated tibiae in 
each group, using the unstimulated animals in that respective group as a 
base. The points plotted are 4.3% for the 2.5 volt group, 9.2% for the 5 
volt group, 7.8% for the 10 volt group and -3.6% for the 20 volt group. A 
clear dose-response curve was obtained with the most growth experienced 
using a 5 volt signal. It appears that an optimal window of about 2.5 to 
15 for the voltage parameter was obtained, above and below which either 
negative or insignificant results were experienced. 
2. Second Analysis 
While the results discussed above in the first data analysis were obtained 
by comparing the growth observed during the stimulation period (days 2-4) 
of the stimulated animals with the unstimulated or control animals during 
the stimulation period, in the second analysis the growth during the 
stimulated period (days 2-4) was compared to the growth during the 
unstimulated period (days 0-2) for only the stimulated animals in group 3, 
i.e. the 10 volt group. 
Using a "paired t-test" the length change of days 0-2 was compared to that 
of days 2-4 and expressed as a ratio or percent difference. The double 
tetracycline label technique allowed the use of the unstimulated growth 
period (days 0-2) in each animal to serve as a control or base for the 
stimulated period (days 2-4) in that animal, thereby eliminating any error 
introduced by animal-to-animal variation. 
However, the transverse oxytetracycline label which was deposited at day 0 
was lost on many of the animals, because bone material which is about 96 
hours old reaches the medullary canal (the hollow portion of the bone) and 
experiences remodelling to define this hollow canal. Therefore, only 3 
animals in group 3 retained their transverse day 0 tetracycline label in 
both of their tibiae. 
As shown in FIG. 7, a mean 17.8% increase in length was seen (p 0.05, n=3, 
paired t-test) when the growth during the stimulation period (days 2-4) 
was compared to the growth during the nonstimulation period (days 0-2) in 
these three animals. Thus on the basis of this analysis alone a 10 volt 
peak-to-peak 60 KHz sine wave signal applied to electrodes in contact with 
the skin at appropriate positions relative to the epiphyseal growth plate 
was shown to induce epiphyseal plate growth in living beings. 
The above experiments were actually carried out in four stages over a 6 
month period, with one group in each stage. The 10 volt group, or group 3 
was carried out first and generated the data for the second analysis as 
shown in FIG. 7. After it was determined that the first oxytetracycline 
line was lost in a large number of animals after 96 hours in the 10 volt 
group, the first oxytetracycline line was withheld for the 5.0 volt group, 
the 2.5 volt group and the 20 volt group which were carried out in the 
order just mentioned. 
CONCLUSIONS 
The results from both data analyses clearly show that longitudinal growth 
in bones can be accelerated by applying a continuous low voltage 60 KHz 
symmetrical sine wave signal of proper peak-to-peak amplitude via 
electrodes applied to appropriate positions relative to the epiphyseal 
growth plate of a bone. 
Further, Tables I-IV show that there is no statistical difference between 
the left experimental legs and the left control legs, indicating that 
little if any distal stimulatory growth effect occurs in the left leg of 
an animal as a result of a stimulation signal applied to the right leg of 
that animal. In fact, the left legs in the experimental animals were 
shorter than the left legs in the control animals in the 2.5 volt, 5 volt 
and 10 volt groups. Therefore, it appears that epiphyseal growth plate 
stimulation can be limited to certain bones to at least a certain degree. 
It is to be understood that the invention is not limited to the precise 
method shown and described, and no limitation is intended or should be 
inferred. It can be appreciated that numerous variations and modifications 
may be effected without departing from the true spirit and scope of the 
novel concept of the invention. It is of course intended to cover by the 
appended claims all such modifications as fall within the scope of the 
claims.