U.S. patent number 3,842,841 [Application Number 05/193,728] was granted by the patent office on 1974-10-22 for constant current power pack for bone healing and method of use.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Navy. Invention is credited to Carl T. Brighton, Zachary B. Friedenberg, William Redka.
United States Patent |
3,842,841 |
Brighton , et al. |
October 22, 1974 |
CONSTANT CURRENT POWER PACK FOR BONE HEALING AND METHOD OF USE
Abstract
Bone fracture healing through use of direct current of from 5 to
20 microamperes applied between a cathode inserted into a fracture
or the site of a bone defect and an anode taped to the skin near
the cathode implantation site is disclosed. A power source capable
of delivering such current constantly despite increasing tissue
resistance also is provided.
Inventors: |
Brighton; Carl T.
(Philadelphia, PA), Friedenberg; Zachary B. (Philadelphia,
PA), Redka; William (Philadelphia, PA) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (Washington,
DC)
|
Family
ID: |
22714785 |
Appl.
No.: |
05/193,728 |
Filed: |
October 29, 1971 |
Current U.S.
Class: |
607/52; 602/2;
607/64; 607/75 |
Current CPC
Class: |
A61N
1/205 (20130101); A61B 17/58 (20130101); G05F
3/24 (20130101) |
Current International
Class: |
A61B
17/58 (20060101); A61N 1/372 (20060101); A61N
1/375 (20060101); A61N 1/20 (20060101); G05F
3/24 (20060101); G05F 3/08 (20060101); A61n
001/20 () |
Field of
Search: |
;128/419R,421D,422,2.1P,2.1R,82.1,92R ;307/297,304,251 ;323/4,16
;3/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Friedenberg et al., "Surgery Gynecology & Obstetrics," Vol.
131, No. 5, Nmber 1970, pp. 894-899. .
Friedenberg et al., "Surgery, Gynecology & Obstetrics," Vol.
127, No. 1, July 1968, pp. 97-102. .
Assimacopoulous, "The American Surgeon," Vol. 34, No. 6, June 1968,
pp. 423-431. .
Bassett et al., "Nature" Vol. 204, Nov. 14, 1964, pp.
652-654..
|
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Sciascia; R. S. Vautrain, Jr.; C.
E.
Claims
What is claimed is:
1. A system for expediting the healing of bone fractures and bone
defects in a living being comprising:
constant current source means for providing a constant value of
current despite changes in load;
means for connecting said constant current means to the living
being, such connection acting to produce current flow into said
fracture or defect,
said connecting means including further means for application
internally of said living being at the fracture or defect site,
said constant current being a selected value within a predetermined
microampere range so as to promote bone formation at the fracture
or bone defect site and avoid fibrous tissue formation in other
areas of the living being.
2. The system as defined in claim 1 wherein said connecting means
includes means for external application to the skin surface, the
internal means being a cathodic electrode,
the external means being an anodic electrode.
3. The system as defined in claim 1 wherein said constant current
means comprises miniature solid state means suitable for mounting
on the living being in close proximity to said fracture or
defect.
4. The system as defined in claim 1 wherein said cathodic electrode
is positionable within said fracture or defect.
5. The system as defined in claim 1 wherein said current is in the
range of from substantially 5 microamperes to substantially 20
microamperes.
6. A system for supplying a constant current within a selected
amperage range to a bone fracture or a bone defect in a living
being to promote healing thereof comprising:
a pair of n-channel field-effect transistors, each having a source,
drain and gate electrode;
a dc power source, having a positive and a negative terminal,
the drain electrode of one of said transistors being connected to
the positive terminal of said power source and the source electrode
of said one transistor being connected to the drain electrode of
the other of said transistors;
a variable resistor;
the gate electrode of said one transistor and the source electrode
of said other transistor being connected to one side of said
variable resistor;
means for connecting the negative terminal of said power source to
the site of a bone fracture or bone defect; and
means for completing the electrical circuit through the living
being to a junction of the gate electrode of said other transistor
and the other side of said variable resistor, the value of said
variable resistor being adjusted for the desired current value of
the cascaded transistors and the current valve being maintained
notwithstanding changes in impedance across the fracture or defect
tissue.
7. The system as defined in claim 6 wherein said means for
connecting the negative terminal comprises a cathodic electrode for
implantation in the fracture or defect and said means for
completing the electrical circuit comprises an anodic electrode for
application to the skin of the living being.
8. The system as defined in claim 6 wherein said power source is a
7-volt battery, and said battery, said field-effect transistors and
said variable resistor can provide a current output in the range of
from 1 to 20 microamperes.
9. The system as defined in claim 6 wherein the current through
said fracture or defect site is constant at a selected value in the
range of from 5 microamperes to 20 microamperes to promote bone
formation in the region of said cathodic electrode and avoid
fibrous tissue formation in the region of said anodic
electrode.
10. The system as defined in claim 6 wherein said power source is
suitable for mounting on the living being in close proximity to
said fracture or defect.
11. The method of promoting the healing of a bone fracture or bone
defect in a living being comprising:
inserting a first electrode into a site within the fracture or
defect;
applying a second electrode to the skin surface of the living being
at a location in the vicinity of said fracture or defect;
connecting constant dc current means across said electrodes,
thereby producing a constant flow of current therebetween,
regardless of load changes; and
adjusting said current flow to a predetermined value between 5 and
20 microamperes.
12. The method of claim 11 including the step of mounting the
current means on the living being in close proximity to the
fracture or defect.
13. The method claim 11 wherein said first electrode is connected
to the negative terminal of said current source.
Description
The present invention concerns bone healing with the assistance of
electric current and, more particularly, bone fracture healing
through the use of direct current from a portable power source.
The application of direct current to a bone fracture in an effort
to influence regeneration has been the subject of several past
efforts. Among early efforts, a 1 microampere current was passed
through the femur for a period of 3 weeks with the result that a
ridge of callus was formed from pole to pole. More callus was noted
at site of the cathode than at that of the anode. Bony callus
developed with amperages between 1 and 100 microamperes, and
cartilaginous callus appeared when the current exceeded 100
microamperes. Bone destruction resulted when currents greater than
1,000 microamperes were passed through the femur. A subsequent
effort resulted in bone production from a current actually
delivered to the bone of from 0.7 microampere to slightly more than
3 microamperes, this production reaching a peak within 2 weeks
after which no significant increase in bone formation occurred.
These and other efforts, however, were inconclusive because a
constant current source to the bone was not available, current
provided to the bone decreasing as tissue resistance developed at
the electrode sites. The need for using a constant current as well
as wider range of current to study the galvanometabolic behavior of
bone was recognized. The present invention is the result of an
attempt to study the galvanometabolic behavior of bone with a
constant current source that was not influenced by tissue
resistance in vivo. Such a power pack heretofore was not
available.
The present invention is a practical application of the use of
direct current to influence bone formation, the current being
maintained constant by a portable direct current source. The entire
device is encapsulated in silicone and includes a power pack of a
plurality of batteries, appropriate electronics to assure that a
constant direct current is provided and a silicone seal to protect
both the device and the person using it. The device is sufficiently
compact to be strapped or taped to the leg, arm or body of the
user. Current is delivered to the fracture source by implantation
of the power pack cathode lead into the body near the fracture and
the application of the anode to the skin on the remote side of the
fracture from the cathode preferably by means of a surface
electrode.
Accordingly, it is an object of the present invention to provide a
method of and means for promoting the healing of bone fractures and
bone defects.
It is another object of the invention to provide a method of and
means for portable bone fracture healing and bone defect healing
which supplies a constant current throughout the time current is
delivered to the fracture region.
A further object of the invention is to provide a method of and
means for for supplying a constant current to healing fractures and
bone defects to promote and/or accelerate healing by means which
may be taped to and worn by the person during those normal
activities which are permitted by the nature of the fracture.
Other objects, advantages and novel features of the invention will
become apparent from the following detailed description thereof
when considered in conjunction with the accompanying drawing in
which like numerals represent like parts throughout and
wherein:
FIG. 1 is a perspective view of the power pack and its external
appendages;
FIG. 2 is a schematic diagram of a constant current power
supply;
FIG. 3 is a schematic diagram of a fractured ankle bone showing
placement of electrodes;
FIG. 4 is a top plan view of a surface anode; and
FIG. 5 is a bottom plan view of the anode of FIG. 4.
FIG. 1 is a view in perspective of the complete fracture healing
device 11 having a pair of test leads, or wires, 12 and 13 and a
pair of leads 15 and 16 with healing electrodes 23 and 24 extending
therefrom. The pack contains, not necessarily in the succession
recited, a battery or batteries in a compartment 18, necessary
electronics to provide a constant current supply source in a
compartment 19 and a silicone seal and miscellaneous connections in
a compartment 20. The entire pack may be encapsulated in
methacrylate plastic or a like substance. Test leads 12 and 13 are
connected to test equipment, not shown, so that the operation of
the device may be constantly monitored. Lead 15 ends in a bare-wire
region 23 which comprises a cathode which is implanted in the
region of the fracture by the insertion of bare wire region 23,
while lead 16 is connected to an anode 24 which, in this
embodiment, is shown as a wire mesh which is to be applied to the
surface of the skin on the remote side of the fracture from the
position where cathode wire 23 is inserted.
FIG. 2 schematically illustrates a power supply which may be used
to produce the desired constant DC current flow across the bone
fracture. Electrodes 15 and 16 are adapted to be connected across
output terminals 30 and 31 respectively, and the impedance across
these electrodes, which changes during the bone healing process, is
automatically compensated for by the control circuit to maintain a
present, constant, microampere current level through the treatment
site tissue.
The control elements of the power supply are a pair of n-channel
field-effect transistors, Q1 and Q2. These transistors are
effectively connected in series with a resistive network, R1 and
R2, across the output electrodes and a bias source 33. More
specifically, the drain electrode 35 of Q1 is connected to the
positive terminal of battery 33 while the source electrode 36 of
this transistor is directly connected to the drain 37 of Q2. The
source electrode 38 of this second transistor is connected to one
side of the resistance network, the other side of which is
connected to the positive side of the output terminal 31. The gate
electrode 40 of Q1 is directly tied to the source electrode 38 of
Q2, and the gate electrode 41 of Q2 is connected to the junction 42
of R1 and R2. For calibration and monitoring purposes, voltage
output readings may be taken across R2 via test leads 12 and
13.
FIG. 3 is a schematic view of an X-ray of the lower leg and foot 25
of a person in which a fracture exists in the region indicated in
26. The fracture area is enlarged on the order of two or more times
to more clearly illustrate the placement of healing electrode 23
therein. Electrode 23 is inserted in the fracture opening with the
conductive part of the electrode, i.e., the exposed bared wire,
preferably being placed within the periphery of the bone sections.
Anode 24 is applied to the skin, in this case along the vertical
surface of the instep, while power pack 11 is positioned and
carried by the user above the ankle. The power pack may be attached
to the person by tape, strap or other conventional means. Test
electrodes 12 and 13 are shown available for connection as desired
to a monitoring device for reviewing the operation of the power
source.
The operation of this circuit is such that the variations in the
impedence of the load, i.e., of the fracture tissue, connected
across the output terminals 30 and 31, will not change the
predetermined current level. The field-effect transistor (FET)
because of its characteristic is readily applicable as a constant
current element. As shown in FIG. 2, Q1 and Q2 are cascaded to
decrease the circuit output conductance as the voltage across the
transistor or the load impedence change, the key consideration in
operation of the constant current source. Resistor R.sub.1 adjusts
current output level, provides bias for the circuit, and develops
feedback to further decrease output conductance. As long as the
voltage across the field-effect transistor is larger than the
pinch-off voltage, the FET is operating in the constant current
region of its characteristic, thus a change in the load impedence
will change the load circuit by only a small factor because of the
low output conductance of the circuit. R2 is in series with the
load and is used merely to develop monitoring voltage across
it.
In order to set the current level, R1 may be adjusted to an
appropriate value as determined by the voltage reading across R2.
In one practical embodiment, 33 was a 7 volt battery, R2 = 1,000
ohms and R1 = 3 .times. 10.sup.6 ohms, 8 .times. 10.sup.5 ohms 4
.times. 10.sup.5 ohms 15 .times. 10.sup.4 ohms for currents of 1
microampere, 5 microampere, 10 microampere and 20 microampere
outputs.
FIGS. 4 and 5 are front and back plan views, respectively, of one
embodiment of an anode 24 which may be used with the device. This
embodiment is preferably made of a face plate 50 of metal to which
is soldered a stainless steel mesh 51. This form of anode may be
constructed by cutting a square of stainless steel sheathing
preferably 0.7 mm. thick to a size slightly greater than 2 cm.
.times. 2 cm. The additional material in excess of 2 cm. is then
turned up to form a shallow well. A small hole 52 preferably 1/64
inch in diameter is then drilled in the center of the well and
thereafter stainless steel mesh 51 is cut to size, inserted in the
well and then soldered along all 4 edges of the plate. A tube 53 is
then soldered to the hole in the back of the plate with the end
flush against the plate. Four small wire eyelets 54 - 57 may be
soldered to the corners of plate 50 to permit fixing the plate
against the skin of a person. A polyethelene tubing 58 is then
attached to tube 53 to permit the instillation of electrolytic
paste into the well through tubing 58.
In practice, compartment 18 preferably houses 51/2 volt batteries
connected in series with field-effect transistors Q1 and Q2. The
entire capsule is sealed with silicone, methacrylate plastic or
similar sealing compounds while the multi-strand stainless steel
wires 12, 13, 15 and 16 are covered with Teflon insulation. Anode
24, shown in FIG. 1, is one form of anode which is to be placed on
the surface of the skin, with the wire mesh attached thereto in
such a manner as to permit a conductive paste, not shown, to be
installed therein in order to make an effective circuit with the
implanted cathode. If the anode is to be implanted, it, like
electrode 23, is bared of its cover for the last 1/4 inch or
more.
In animal experiments, the entire power pack, except for the two
monitoring wires, was implanted under the skin on the back of the
animal. The cathode and anode wires were run subcutaneously along
the limb to the fracture or bone defect site. The cathode was
inserted into the fracture or bone defect site and held there with
chromic sutures. The anode was fastened in the nearby soft tissue
with chromic sutures. Current output was monitored at will by means
of the monitoring leads protruding through the skin.
In human subjects, the entire power pack is sterilized in a gas
autoclave, or, if replaceable cathodes are used, only the cathode
is sterilized. Only the cathode is inserted into the patient at the
fracture, nonunion, or bone defect site. The anode is taped to the
surface of the skin near the cathode implantation site, and the
power pack is strapped to the limb or to the outside of a cast
encasing the limb. The cathode may be modified such that the
multi-strand stainless steel wire is replaced by a more rigid
stainless steel pin covered with Teflon. If the multi-strand
cathode is used, a small incision must be made in the skin and
underlying subcutaneous tissue in order to insert the cathode into
the fracture or bone defect site. If the stainless steel pin
cathode is used, no incision is made. The pin is simply pushed
through the skin and soft tissue into the underlying bony fracture
or defect. Placement and location of the pin is determined by X-ray
evaluation.
The present invention has been successful in promoting bone growth
in rabbits which were divided into three groups, one in which 1 to
5 microamperes current were applied, another in which 10 to 20
microamperes were applied and another where 50 to 100 microamperes
were applied. In the 1 to 5 microampere group, little reaction was
noted at the implant site at either the anode or the catode site.
In the 10 to 20 microampere group, a dark discoloration was noted
around the anodal site but no discoloration was noted in the
vicinity of the cathode. At 50 to 100 microamperes, marked
discoloration occurred at both electrode sites.
Microscopic examination showed that bone formation occurred
predominately around the cathode site. The optimum range of current
for such formation was 5 to 20 microamperes with diminution of bone
production above 20 microamperes. The bone formed appeared to be
predominantly osteoblastic in type, with some areas of
fibro-osseous metaplasia. The areas of bone formation were
contiguous with, and surrounded areas of, cartilage which, in turn,
surrounded the electrode sites. Cartilage production, which
appeared to be hyaline in type, occurred around both poles to a
limited extent, with the optimum production again being reached
between 5 to 20 microamperes at the cathode. No appreciable change
was noted in the capillaries or blood vessels. There was a reversal
of electrodal relationships relative to fibrous tissue formation,
with the greatest production occurring at the anode. A gradual
increase of anode fibrous tissue formation was seen up to 10
microamperes, after which there was a sharp decline at the higher
microamperages. Tissue destruction was markedly prevalent at the
anode in virtually every instance, with a maximum being attained at
20 microamperes and persisting through 100 microamperes. Tissue
destruction at the cathode was minimal until 100 microamperes, when
the severity approached that found at the anode. Tissue destruction
was that of fibrinoid necrosis, extending from the immediate area
around the electrode to destruction of the entire marrow content
between the two electrodes, and involved the cortical endosteum,
with many of the lacunae being empty. Bone formation ranged from a
thin shell rimming the cathode to a filling of the medullary cavity
between the two electrodes.
It will be appreciated that the present invention provides a novel
method of treating both delayed and nonunion fractures as well as
bony defects by use of constant current as described herein. The
invention has produced accelerated fracture healing. The bony
healing promoted by the present invention is accomplished without
any requirement for surgery whereas methods presently available for
achieving bony union require bone graft surgery.
The foregoing is accomplished through the use of a constant 10
microampere current which is available regardless of changing
tissue resistance. This current may be obtained from portable power
pack 11 which is sterilizable and therefore readily usable. The
preferred electrodes are an implantable cathode and a surface
anode. The individual components of the power pack may be varied as
to construction materials so long as the output of the unit is a
constant current regardless of changing resistance. Further
research, utilizing power packs with greater current outputs and
cathodes with a much greater surface area, may indicate a use of
this system in the treatment of large bone defects. Although the
cathode must be placed in the fracture, nonunion or bony defect
site, the anode, though described as preferably being placed on the
remote side of the site from the cathode, may be placed anywhere so
long as it completes a circuit with the cathode. Obviously, other
modifications and variations of the present invention are possible
in the line of the above teachings.
* * * * *