Note: Descriptions are shown in the official language in which they were submitted.
Title of the Invention:
A method for fixin~ an eleetrieal eleetrode to bone tissue,
and a_ eleetrical eleetrode for carrying out the method.
T_ nical Field
The present invention relates to a method for fixing
an electrode to bone tissue or hard tissue for eleetrically
stimulating a healing process therein, the electrode being
of the kind having a rigid electrode tip and a highly
flexible electrically insulated cable attaehed thereto.
The invention also relates to an electrical eleetrode
with which the method can be carried out.
Baekground Art
.
Several deviees are known to -the art by means oE whieh
healing oE bone tissue is promoted by eleetrieally stimula-
ting the bone tissue with the aid of one or more electrodes
applied to the fraeture point of a broken limb, these
devices ineluding means whereby an eleetrie eurrent or an
eleetrie voltage ean be applied to the eleetrode.
Sueh deviees and eleetrodes are normally used to
avoid the necessity of carryiny out surgery on the damaged
bone. To his end it is known to affix one or more elec-
-trodes in the region adjacent the fracture surface and to
connect -the electrodes to an electrieal s-timulating device,
located externally on a fractured limb being treated, or
on a plaster cast placed therearound.
A variety of such electrodes, which are affixed to
bone tissue and connected to a source of electric eurrent
or voltage for the purpose of stimulating a bone healing
process (osteogenesis), are known to the art.
Eleetrodes used within the medical field for this
purpose can be divided into two separate categories, eaeh
relating to the nature of the tissue to which electrodes
are -to be applied and the manner in which they are used.
Thus, eleetrodes of the firs-t category are particularly
designed for insertion into soft tissue and there to be
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firmly and reliably held in good electrical contact with
the soft tissue, normally muscle tissue, these electrodes
normally being used to evaluate muscle tension etc.. The
electrodes belonging to the second category are particu-
larly designed for attachment to bone tissue or hardtissue, so as to be firmly seated in good electrical
contact with the hard tissue while being insulated from
the soft tissue, in order to stimulate osteogenesis.
The present invention relates to the second category
of electrode.
The U.S. Patent Specification No. 3,842,841, which
relates to an electrode of this second category, discloses
the use oE an external anode which is secured to the outer
surface of the skin, and a cathode which comprises a long
rigid stainless steel wire covered with an electrically
insulatec1 material, such as polytetrafluoroethylene. This
steel wire is pressed through the skin, i.e. percutaneous
insertion, whilst screening the damaged area with X-rays
(radioscopy), and pushed into the bone close to a fracture
or area of diseased bone to be treated.
It i.s also known to use a handdrill to assist the
insertion of these rigid electrodes some short di.stance
into the bone tissue, so that the electrode tip is firmly
seated therein.
Disclosure of the Present Invention
_
Technical Problem
__
With reference to the present state of the art as
described above it is obvious that one technical problem
encountered in this field is that of providing a method
and an electric electrode by means of which an electrode
tip can be firmly attached to bone tissue with the aid of
simple means, whilst still permitting the use of a flexible,
electrically insulated connecting cable extending between
a source of electric current or electric voltage and the
electrode tip.
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A further technical problem is that of being able
to find ways and means whereby the irritation experienced
as the skin is penetrated, due to muscle contraction and
prevalent with steel-wire bone electrodes, can be elimi-
nated.
With such electrode there is a grave risk that the
rigid steel wire will break off within the bone, if an
excessive load is applied thereto. Consequently, a further
technical problem in this art is one of eliminating this
risk.
Another technical problem related hereto is to be
found in the provision of a method and an electrode having
a rigid electrode tip and a flexible connecting cable
which can be provided with a non-breakable connection
between the electrode tip and the cable, since this would
eliminate the need of surgery to remove any part oE a
broken electrode still attached to the tissue and extending
therebeyond, such surgery oEten bein~ necessary with
present day methods and electrodes.
Still another technical problem is that of providing
a method by which a rigid electrode having a flexible
connecting cable can be attached to bone tissue through a
pre-bore, where the electrode tip is fully inserted into
the bone tissue and can be left there without discomfort
to the patient.
A further technical problem is one of designing an
electrode which fulfills the aforementioned requirements
and which enables the connecting cable to be readily
removed, without surgical involvement, when it is consi-
dered that the rigid electrode tip can be left in the bonetissue.
A further technical problem is one of providing means
whereby an electrode tip can be introduced into bone
tissue in a direction de-termined by a guide tube firmly
held by soft tissue.
Still another technical problem is one of enabling a
pre-bore to be formed in bone tissue with the aid of simple
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means, and of enabling the electrode tip to be readily introduced
into such a pre-bore.
Sum~ary oE the ~nvention
The present invention provides a method which enables
the rigid tip of an electrode connected to a highly flexible
connecting cable insulated electrically against surrounding softer
tissue, to be attached to bone tissue (hard tissue). Thus, the
present invention is a method for attaching through soft tissue
an electrode to bone -tissue, said electrode having a rigid elect-
rode tip and a flexible electric cable connected to the electrodetip and beingelectrically insulated agalnst surrounding so:Et -tissue,
comprising the steps oE: applying one end o:E an elongatecl guide
means having a longitudinally extending channel to an outer sur-
face of soft tissue adjacent a selected location of bone tissue;
moving the one end of the elongated guide means through the soft
tissue towards the bone tissue; preforming a hole in the bone
tissue by introducing a member through said channel; introducing
through the channel an electrode having a rigid electrode tip,
a flexible cable connected thereto and means for stifEening the
cable, said cable stiffening means releasably connected with said
electrode tip; displacing the cable stiffening means through the
guide means so as to move the electrode tip into contact with the
bone tissue adjacent said hole; threading the electrode tip into
the bone tissue adjacent said hole so that said elec-trode tip is
located i.n the bone tissue; and removing the stiffening means and
the guide means so as to leave a part of the flexible cable exposed
above the outer surface of the soft tissue, whereby the cable
may be connected -to an electric current or voltage .source and
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said electrode tip may remain in the bone tissue af-ter treatment.
According to the invention there is arranged in the
channel a pointed member which extends beyoncl one end thereof
when it is pushed through the soft tissue. Optionally, the
pointed member may be pressed in a manner -to plastically deform
the bone tissue, so as to form a part which co-acts with the
electrode tip.
In accordance with one advantageous feature of the
invention, the electrode tip is inserted into the bone tissue
with the aid of an axially directed force, wherewith the aid
of rotation movement applied to a pointed part provided with
cutting screw-threads.
According to one embodiment the bore may have a narrow
outermost part and a ~roader part, in which the cross-sectional
area of the narrow part is somewhat smaller than the cross-
sectional area of the electrode tip, while the cross-sectional
area of the broader part is equal to or somewhat greater than
the cross-sectlonal area of the electrode tip.
In accordance with another embodiment a drill is inserted
through a channel in a guide means for forming a desired hole in
the bone tissue. When the electrode tip is provided with cutting
screw-threads, the diameter of the drill is smaller than the
diameter of the screw-threaded part of the electrode tip. The
drill is removed prior to inserting the electrode and the tube
through the channel.
The present invention also relates to an electric
electrode designed for application to bone tissue (hard tissue),
the electrode being provided with a rigid electrode tip and
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having a flexible electrical connecting cable connected to said
tip, characterized in that the connection between the electrode
tip and the connecting cable is such that the cable is withdrawn
from its co-operation with the electrode tip when a pulling force
is exerted in the longitudinal direction of the cable.
The electrode tip is suitably provided, adjacent the
point at which it is connected to the cable, with a fitting which
is able to co-act with one end of the tube to prevent rotation
thereof. The connecting cable comprises a helically wound wire
enclosed in an electrically insulating sleeve or sheath.
Both the helically wound wire and the insulating sleeve
are flrmly secured in relation to the electrode tip. The wire
can be removed by withdrawing it Erom the insulating sleeve.
The sleeve can be removed by pulling the same in a direction
away from the electrode tip, therewith leaving the electrode tip
firmly screwed into the bone tissue.
As will be understood, when wishing to remove the
electrode completely there is nothing to prevent the connecting
cable from being stretched somewhat away from the electrode tip
and the tube being caused to embrace the cable, so that one end
of thetube can be displaced down through the soft tissue and
optionally through the bone tissue against the electrode, and
there caused to co-act with the fitting or coupling means formed
on the electrode tip, thereby to enable the electrode -tip to be
rotated out of the bone tissue, to permit the connecting cable
and the electrode tip to be removed.
Advantages
Those advantages primarily characteristic of a method
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and an electrode in accordance with the present invention
are to be Eound in the possibilities provided thereby of
applying a rigid electrode tip to bone tissue and, when the
electrode tip is connected to the bone tissue, of
enabling a flexible cable to be connected to an electrical
current or voltage source, for the electrical stimulation
of the bone healing process.
_ _ _ _ _ _
The primary characterizing features of a method
according to the present invention are set forth in the
characterizing clauses of the following Claims 1-3, while
the primary characterizing features of an electrode
according to the invention are defined in the characterizing
clauses of the following Claims 10-14.
Short Description oE the Drawlngs
An embodiment illustrating the significant charac-
terizing features of an electric electrode and a ~ethod
according to the invention for attaching the electric
electrode to bone tissue will now be described with
reference to the accompanying drawings, said embodiment
being that preferred at present, in which drawings
Figure 1 is a perspec-tive view of a guide means, one
end of which is applied to -the outer surface of soft
tissue located ad~acent a bone fracture;
Figure 2 is a side view of a first embodiment of a
drill which can be used to drill a hole in bone tissue;
Figure 3 illustrated the drill bit in larger scale
of the drill illustrated in Figure 2;
Figure 4 is a side view of a second embodiment of a
drill for drilling a hole in bone tissue;
Figure 5 illustrates in larger scale the drill bit
of the drill shown in Figure 4;
Figure 6 illustrates in perspective the manner of
applying one end of the guide means to the outer surface of
bone tissue or hard tissue, and further illustrates a
manner of screwing an electric electrode percutaneously
to bone tissue; and
Figure 7 is a perspective view, in larger scale, of
the electrode tip of an electric electrode with a connec-
ting cable connected thereto.
Description of Preferred Embodiments
Figure 1 illustrates in perspective a guide means
generally shown at 1, comprising an elongated guide tube 3
having extending axially therein a channel 2 which is open
at both ends thereof. One end, 3a, of the guide tube 3 is
intended -to be placed against an outer surface 4 of soft
tissue 5, in the immediate vicinity of a fracture 6 loca-
ted between two shafts of bone 7, 7', and further comprising
holder means 8 which is connected at one end 8a thereof
to the upper end 3b of the guide tube 3, and the other end
8b of which serves as a handgrip.
The holder means 8 connec-ted to the end 3b of the
guide tube is intended for controlling the alignment of
the guide means 1, such that an extension 2' of the channel
2 is positioned in or within a region of bone tissue where
-the electrode tip is to be applied. This area is referenced
7a in Figure 1 and forms a poin-t on the bone tissue.
The region where the electrode tip should be applied can
be determined by X-ray screening or radioscopy , in a
known manner. The guide tube 3 is then pressed through the
skin, so that the end 3a of the tube is located at the
point or location 7a.
In the illustrated embodiment, insertion of the tube
3 through the skin is facilitated by means of a needle-
like member 9 having a pointed part 9a and being arranged
for axial movement in said channel. The end of the member
9 remote from said pointed part is provided with a push
plate 9b. The length of the needle~like member 9 is
slightly greater than the length of the guide tube 3, and
in its initial position the member 9 is wi-thdrawn in the
channel of the guide means 3.
In this posi-tion, the soft tissue 5 forms a means for
guiding and positioning the guide tube 3.
When the pointed part 9a is pressed against the
location 7a on a bone shaft, the bone is plastically
deformed to provide a gripping surface for a drill and/or
a screw having self--cutting threads. The needle-like
piercing member 9 is removed when the guide tube has been
inserted to the desired position in the soft tissue.
Although the present invention can be applied to secure
electrode tips to bone tissue without previously drilling
a hole therein, it has been found that certain problems
can occur when no such pre-bore is formed. One such
problem is the risk of the bone tissue splitting.
In order to avoid this problem; there is preferably
formed in the bone tissue 7 a pre-bore having a diameter
which is slightly.s~aller than the ou-ter diame-ter of the
el.ec-trode -t.ip. To -this end there is provided in accordance
wi-th the invention a drill havinc,~ the form illustrated in
Figure 4.
When the electrode tip is to be embedded deep in the
bone -tissue, there is used a pre-bore formed by a drill of
the kind illustrated in Figure 2. The drill illustrated in
Figure 2 is generally reEerenced 10 and has at one end
1Oa thereof connecting means 11 for connecting the drill to
a drilling machine, while the other end 1Ob of the drill
carries a drill bit 12~ The drill bit 12 is shown in larger
scale in Fi~ure 3, and has edge portions 13,14, where the
distance "al' is such as to substantially correspond to the
distance "a" in Figure 7. Thus, -the distance "a" between
the surface flanking said edge por-tions 13,14 shall
correspond to the maximum width of the electrode tip, or
shall be slightly greater than said width.
When attaching the actual electrode tip to bone tissue,
it is proposed, in accordance with the invention, that there
is formed a pre-bore with the aid of a drill 15, which is
provided at one end 15a thereof with connecting means 16
for connecting the drill to a drilling machine, and which
has at the other end 15b thereof a drill bit 17. The drill
bit 17 is shown i.n larger scale and in more detail in
1 0
Figure 5, ~rom which the orientation of edge portions 18,
19 can be seen. The drill 15 is intended to form in bone
tissue 7 a hole 7b having a diame-ter "b", said hole beiny
smaller than the hole 7c of diameter "a".
The narrower part of the drill 15 is arranged for
co-action with the electrode tip 20 via a tensioning or
clamping action.
The electrode tip may be provided with barbs for
solely pressing the tip in-to the hole.
In the illustrated embodiment, the electrode tip 20
is provided with self-cutting screws, and the distance or
diameter "b" shall be adapted to the root diameter of the
screw thread.
Positioning of the guide means 1 in the soft tissue
5 ensures that the two drills 15 and 10 are aligned in
one and the same direction.
As wlll be seen more clearly from Figure 6, with the
guide tube 3 located in the desired position and guidecl by
the soft tissue 5, there is now passed through the channel
2 in -the guide tube 3 firstly an electrode 20 having a self-
tappiny, rigid electrode tip 21 and a highly flexible
connecting cable 22 connected thereto, and secondly a tube
25 which embraces the cable and which co-acts with the
electrode tip via coupling means, the lower part 25a of
the tube 25 being provided wi-th said coupling means 26
arranged to co-act with corresponding coupling means 27
provided on the upper part of -the electrode tip 20, the
coupling means 27 of this embodiment having the form of a
regular hexacon. This is shown in more detail in Figure 7.
The upper part 26b of the tube 25 is pro~ided with a
knob 28, by means of which the electrode tip 20 can be
caused to rotate and a downwardly directed force can be
exerted for screwing the tip into the bone or bone tissue
7.
It will also be seen from Figure 6 that the tube 25
and the guide means 1 can be moved relative to one another,
such that the electrode tip 20 will pass through the channel
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1 1
2 and beyond the soft tissue 5, to co-act with the bone
tissue.
Thus, the electrode tip 21 can be screwed into the
bone tissue 7, by rotating the tube 25 with the aid of
knob 28, while exerting pressure against the bone tissue.
By then removing the tube 25 and the guide means 1,
preferably together, part of the flexible cable extending
above the outer surface 4 of the soft tissue 5 can be
connected to a source of electric current or voltage, not
shown. This part of the flexible cable has been referenced
22a.
The bore comprising holes 7b and 7c should be drilled
to a depth such as to enclose the whole of the electrode
tip 20. As will be understood, the hole can be made deeper
than that il]ustrated in Figure 6.
Figure 7 illustrates in larger scale in relation to
Figure 6 the pointed part of the electric electrode according
to the invention, arranged -to be firmly screwed into bone
tissue 7. The electrode is provided with a rigid electrode
tip 21, having the form of a self-tapping or self-cutting
screw. The electrode tip is also provided with a cutting
edge 21a, having a cavity in which bone cuttings are
accommodated. Connected to the electrode 20 i5 a flexible
connecting cable 22 which is electrically insulated against
surrounding soft tissue. This insulation is referenced 30
and has the form of an insulating sleeve or sheath.
Arranged between the electrode tip 20 and the cable
22 is an electrical connection so constructed that when
pulling in the direction of cable 22, the end part 22b of
the cable will separate from the connecting part 31 of the
electrode tip 20.
As will be seen from the Figure, the electrode tip
20 is provided, adjacent the connecting part 31, with
coupling means or a fitting 27 arranged to co-act with one
end 25a of the tube 25 in a manner to hold the same against
axial rotation, in a manner ]cnown per se, via a corres-
ponding coupling means provided on said one end.
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The cahle 2~ comprises a helically and tightly
wound wire 33 encased in an electrically insulating hose
30. Both the helically wound wire 33 and the hose 30 are
fixed in relation to the part 31 of the electrode tip 20,
by clamping the wire 33 by means of a sleeve 31a and by
threading the electrically insulating hose 30 over the
sleeve 31a. When the wire 33 is removed by withdrawing it
from the hose or sheath 30, complete withdrawal of the
wire will also release the hose 30 from its co-action with
the sleeve 32, permitting the hose 22 to be also removed,
soth the wire and the hose can be removed by pulling the
same away from the electrode tip.
In so doing, the electrode tip 20 will be left
seated in the bone tissue 7, fully embraced thereby.
When wishing to also remove the electrode tip 20
from the bone tissue 7, it is proposed in accordance with
the invention that the connecting cable 22 is stretched up
from the electrode tip 21 and that the tube 25 is passed
over the cable 22 such that the coupling means 26 on the
tube-end 25a are brought into co-action with the coupling,
means 27 for the electrode tip20, so as to enable the
electrode to be fully removed from the bone tissue 7, by
rotating the electrode tip 20 in a direction in which it
is screwed out of said bone tissue, without requiring
surgical intervention.
As will be understood, the drills 10 and 15 may each
be provided with graduations (mm-scale), to enable the
depth of the drilled hole to be established in relation to
the upper edge part oE the guide tube 3.
As will be understood, the invention is not restric-
ted to the aforedescribed embodiments, given by way of
example onl~, and that the modifications can be made within
the scope of the following claims.
