Epidural lead electrode and insertion needle

Tissue stimulation apparatus for positive positioning of an electrode-bearing lead proximous to tissue which is to be stimulated electrically, the invention particularly includes a body penetration and insertion assembly which carries an elongated flexible strip of physiologically inert plastic material having at least one electrode positioned thereon into contacting relation with said tissue. The insertion assembly comprises a hollow needle having a slot formed longitudinally along the length of one wall thereof, the slot allowing transverse removal of the flexible lead from the needle after proper positioning of the lead and after removal of the needle from the body. The present slotted assembly allows use of a flexible electrode lead having electrical connections at the external end thereof which are too large to pass through the hollow needle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to surgical apparatus and, more particularly, to an 
electrode lead and insertion assembly for positioning a tissue stimulating 
electrode in electrical contact with living tissue which is to be 
stimulated, 
2. Brief Description of the Prior Art 
Electrical stimulation of living tissue has previously produced beneficial 
therapeutic results ranging from stimulation of heart function to relief 
of severe pain states which are unresponsive to more conventional 
treatment. Implantable electrode leads have come into use which can be 
positioned in contact with tissue to be stimulated without the need for 
major surgery, the usually flexible electrode leads being carried by 
hollow rigid insertion needles which penetrate the skin and body wall to a 
suitable depth. The flexible electrode lead is then fed into a desired 
position relative to the tissue which is to be stimulated through the 
inserted needle, the needle then being withdrawn from the body over the 
entire length of the electrode lead while maintaining the lead in the 
desired position within the body. In such prior systems, the anterior end 
of the electrode lead could not be fitted with electrical connections or 
electrical components which could not be drawn through the hollow needle. 
In prior practice, it is therefore necessary for the surgeon to attach or 
form electrical connections to the electrode lead after the needle is 
pulled from the anterior end of the lead. Such connections, made under 
operating room conditions by medical personnel, are time consuming and 
often not comparable to the quality of electrical connections made under 
more controlled manufacturing conditions. The invention thus provides, 
among other things, the capability of implanting an electrode lead through 
the skin, which lead has electrical connections at its anterior end which 
are too large to pass through surgical insertion needles. Electrode leads 
which are pre-fabricated and/or connected to electrostimulation devices 
prior to implantation can therefore be conveniently used with substantial 
savings of time and with greater reliability than has previously been 
possible. 
SUMMARY OF THE INVENTION 
The present invention provides an electrode-bearing lead assembly which is 
capable of rapid penetration of the skin and body wall enclosing the 
tissue which is to be stimulated without the need for multiple incisions. 
The present assembly effectively carries an extremely flexible conductive 
lead into contact with the tissue, following which certain elements 
thereof are removed leaving the electrode lead in contact with the tissue. 
The flexible electrode lead than allows free movement of the body and of 
the stimulated tissue while maintaining electrical contact therewith and 
without damaging the tissue. In particular, the present structure allows 
the use of a flexible electrode lead assembly which has electrical 
connections attached to its external, non-implanted end, which connections 
are too large to pass through a conventional insertion needle, such as a 
Tuohy needle. In order to accomplish this desirable function, the present 
structure is provided with a rigid, external sleeve-like needle which 
penetrates the skin and body wall, the flexible electrode lead being fed 
through the needle into contact with the selected tissue. The needle is 
provided with a longitudinal slot extending the full length thereof so 
that the flexible electrode lead can be removed transversely from the 
needle on removal of said needle from the body, electrical connections 
existing on the external end of the electrode lead being left intact 
during removal of the lead from the needle. 
Although the present invention can be practiced with electrode leads of 
varying description, the lead itself is preferably formed of a flexible, 
physiologically inert material. The body of the lead also serves to 
encapsulate and thus insulate multistranded, helical electrically 
conductive wires which usually extend throughout the lead from a unipolar 
electrode or bipolar electrodes at the distal, or implanted, end thereof 
to the anterior or external end of the lead, which external end is 
connected to a source of electrical energy. The electrode lead is 
preferably formed with an oval or rectangular cross-section along its 
length, i.e., the body of the lead is "flattened" in order to prevent 
rotation when placed into contact with tissue to be stimulated. When the 
present electrode lead is used to stimulate spinal cord tissue, the 
flattened conformation of the present lead also enables a better fit 
within the epidural space. The electrode lead can further be configured at 
the inner end thereof with a rounded tip which slopes from the upper 
surface of the lead to cause the lead to more naturally follow a desired 
path on insertion of the lead into an operative position, such as within 
the spinal column. 
Accordingly, it is an object of the invention to provide an electrode lead 
assembly for insertion of an electrode-bearing flexible lead into the body 
and positioning therein with a minimum of surgical invasion. 
It is a further object of the invention to provide an electrode lead 
assembly capable of implanting at least one end of a flexible, 
electrode-bearing lead into contact with tissue to be electrically 
stimulated, following which certain elements thereof can be removed 
leaving the implanted portion of the assembly in contact with said tissue, 
the elements of the assembly removed from the body being transversely 
withdrawn from the lead. 
It is another object of the invention to provide an electrode lead assembly 
wherein a hollow, rigid body-penetrating portion thereof, through which a 
flexible, electrode-bearing lead is fed into the body, is formed with a 
longitudinal slot along its length to allow removal of the lead from said 
portion in a direction transverse to the longitudinal axis of the lead, 
thereby to allow leads having large electrical connections on the external 
ends thereof to be removed from said portion without disconnection of 
reforming of said electrical connections. 
It is yet another object of the invention to provide an electrode lead 
assembly wherein a flexible lead has a shaped inner end portion to 
facilitate positioning of the lead in a desired relation to tissue which 
is to be electrically stimulated. 
Further objects and advantages of the invention will become apparent in 
light of the following description of the preferred embodiments of the 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While the invention relates to apparatus for inserting an insulated 
electrically conductive lead and electrode structure through a body wall 
and into contact with living tissue which is to be electrically 
stimulated, the following description particularly relates the use of the 
invention to stimulation of the spinal cord, particularly the lumber 
region thereof, such as is practiced in the relief of chronic intractable 
pain. Certain features of the invention particularly apply to this 
therapeutic procedure while other features of the invention can be more 
generally applied. Thus, even though the use of the invention is described 
hereinafter for a particular application, it is to be understood that such 
description is for the purpose of illustration only and does not limit the 
application and scope of the invention. 
Referring now to the drawings and in particular to FIG. 1a, the present 
electrode lead and insertion assembly can be understood to comprise a 
tubular insertion sleeve 10 having an enlarged, essentially semi-circular 
head 12 disposed on the outer end thereof. The inner end of the sleeve 10 
is seen to be formed into a sharpened oblique point 14. The point 14 may 
curve slightly from the longitudinal axis of the sleeve 10 in order to 
facilitate useage thereof for particular applications such as will be 
described hereinafter. The point 14 may further be formed with an opening 
16 disposed in the upper surface of the sleeve 10 as seen in FIG. 1a, the 
opening 16 being formed in that surface of the sleeve 10 toward which the 
point 14 curves. The enlarged head 12 has an aperture 18 formed therein 
which has its longitudinal axis disposed parallel to the longitudinal axis 
of the sleeve 10, the aperture 18 being spaced from the juncture of the 
sleeve 10 and the head 12 and can be conveniently aligned with said sleeve 
along a radius of the head 12 which is perpendicular to the straight side 
of said head. The sleeve 10 and head 12, which can conveniently be 
integrally formed of a material such as stainless steel, are essentially 
similar to a known surgical tool usually referred to as a Tuohy needle. 
The head 12 is grasped by a surgeon and used to apply pressure to the skin 
and underlying tissues of an animal, such as Homo sapiens, through the 
sleeve 10, the sleeve 10 being sufficiently rigid and the point 14 
sufficiently sharp to enable penetration thereof through the skin and 
tissues. 
The sleeve 10 differs markedly from prior surgical instruments in that a 
longitudinal slot 20 is formed in a side wall of the sleeve 10 and extends 
along the full length thereof. The slot 20 essentially lies in the plane 
defined by the straight line formed by the straight side of the head 12 
and the line intersecting the juncture of the sleeve 10 and head 12 and 
which is parallel to the longitudinal axis of said sleeve. Thus, the 
opening provided by the slot 20 is transverse to the body of the sleeve 10 
and "faces" to one side thereof. The sleeve 10 is preferably formed with 
an oblong cross-section, i.e., flattened on opposing surfaces relative to 
circular, along its length, such cross-section particularly allowing the 
accommodation of a flattened electrode lead within the lumen, i.e., the 
hollow interior channel, defined by said sleeve. While the sectional 
conformation of the sleeve 10 as shown and described herein is preferable 
in most applications, it is to be understood that differing sleeve 
cross-sections could be provided for accommodation of electrode leads of 
varying conformation. 
As will be appreciated relative to the ensuing description referenced both 
to FIGS. 1a and 1b, a stylet 22 is seen to be insertable into the sleeve 
10 from the outer end thereof, the stylet 22 comprising a solid needle 24 
and an enlarged head 26 formed on the outer end of said needle. The needle 
24 has a cross-section which is similar in geometric contour to the 
cross-section of the sleeve 10, the needle 24 being dimensionally smaller 
than the interior channel defined by the sleeve 10 so that said needle 24 
can be inserted into said sleeve to cause substantially all of the 
volumetric space within the sleeve to be occupied by said needle. Since 
the stylet 22 is seen to be partially inserted into the sleeve 10 in FIG. 
1a, it is not possible to fully observe the shape of the inner end of the 
stylet. Although not a major feature of the invention, the inner end of 
the needle 24 as seen in FIG. 1b is preferably formed with a curve which 
is essentially congruent with the curve of the point 14 of the sleeve 10 
as described hereinabove. The inner end of the needle 24 is also 
preferably formed with a sharpened, essentially rounded point 28 which is 
contiguous to a flat surface 30 lying immediately to the rear of the point 
28. The plane of the surface 30 lies essentially parallel to the plane of 
the flattened upper surface of the sleeve 10, the surface 30 being of 
sufficient dimensional size to occupy the opening 16 in the point 14 of 
said sleeve. The inner end of the assembly, when the stylet 22 is fully 
inserted into the sleeve 10, thereby presents an essentially smooth 
surface without jagged contours which could act to tear tissue in an 
undesired fashion. The inner end of the needle 24 may further be formed 
with a depression 32 immediately to the rear of and contiguous to the 
surface 30, the depression 32 allowing said needle to bend more readily as 
needed to conform to the contours of the sleeve 10. The head 26 of the 
stylet 22 can conveniently be formed of a flat, rectangular plate having a 
pin 34 extending from the inner face thereof, the pin 34 aligning with the 
aperture 18 formed in the head 12 to provide a more positive connection 
therebetween when the stylet 22 is fully inserted into the sleeve 10. That 
portion of the head 26 extending outwardly from contact with the head 12 
takes the form of a flap which can be used to withdraw the stylet 22 from 
the sleeve 10. The purpose of the stylet 22, as will be more appreciated 
from the following description, is to prevent tissue and liquid matter 
from entering the interior of the sleeve 10 on insertion thereof into the 
body. 
Referring now to FIG. 2, the manner in which the apparatus of FIG. 1a is 
utilized in treatment of intractable pain in the human body can be seen. 
In treatment of the kind to be described hereinafter, electrical 
stimulation of tissue in the lumbar region of the spinal cord is effected 
by an electrode implanted in contact with or in proximity to the spinal 
cord. The implanted electrode is electrically connected by means of a 
flexible, conductive lead to a source of electrical energy which can be 
located either internally or externally of the body. The assembly of FIG. 
1a, and particularly the sleeve 10, is used to implant the electrode and 
flexible head. As seen in FIG. 2, the stylet 22 is fully inserted into the 
sleeve 10, the assembly being then inserted into the body through a 
selected portion of the dorsal surface of the abdomen, the point 14 of the 
sleeve 10 entering the spinal foramen either between or to the side of the 
spinous processes on adjacent lumbar vertebrae. The head 12 and the head 
26 on the stylet 22 are used to apply force to the sleeve 10 to cause 
penetration of the skin and tissue overlying the spinal column. The 
upwardly curved point 14 of the sleeve 10 better enables the sleeve to be 
positioned such that an electrode-bearing electrical lead assembly to be 
described hereinafter can be more readily located in a desired position. 
The stylet 22 serves inter alia to prevent tissue from entering the 
volumetric space within the sleeve 10 on insertion of the sleeve into the 
body. When the sleeve 10 is located in the substantially correct position, 
i.e., with the tip 14 positioned externally of and adjacent to the dura 42 
as will be fully described hereinafter, the stylet 22 is fully withdrawn 
from the sleeve 10. 
Referring now to FIGS. 3a and 3b the manner in which the tip 14 of the 
sleeve 10 is positioned within the spinal foramen of the spinal column is 
illustrated. Viewing the spinal column in section between two lumbar 
vertebrae, the dura 40 is seen to surround the spinal cord 42. The tip 14 
of the sleeve 10 is positioned by "feel" near the outer surface of the 
dura 40 prior to removal of the stylet 22. When the stylet 22 is removed 
from the sleeve 10, a hollow needle 44 is inserted into the sleeve 10 to 
enable exact positioning of the tip 14 of the sleeve relative to the dura 
40. As best seen in FIG. 3b, the needle 44 is formed with a hollow body 
member 46 having a cross-section congruent with the cross-section of the 
sleeve 10, the member 46 fitting substantially flushly within the sleeve 
10. At the outer end of the body member 46, the needle 44 is fitted with a 
circular stop plate 48 which is surmounted by an open-ended cup 50, the 
lumen within the body member 46 extending into and communicating with the 
volumetric space defined by the cup 50. On full insertion of the needle 44 
into the sleeve 10, the stop plate 48 abuts the outer surface of the head 
12, thereby properly positioning the open inner end of the needle 44 at 
the open surface 30 of the sleeve 10. Physiological saline solution is 
then introduced into the cup 50 of the needle 44 and the entire lumen of 
the needle 44 is filled with the saline solution. The cup 50 is also 
filled with the saline solution sufficiently to form a meniscus therein 
which is visible at the open end thereof. The sleeve 10 with the needle 44 
inserted thereinto can then be moved relative to the dura 40 to create a 
"potential space" between the dura 40 and surrounding tissues at the point 
where the tip 14 of the sleeve 10 contacts the outer surface of the dura. 
The manner in which the meniscus of the saline solution in the cup 50 
responds to inward movement of the sleeve 10 enables the tip 14 of said 
sleeve to be accurately positioned in a desired location relative to the 
dura. If the dura 40 is inadvertently penetrated by the tip 14 of the 
sleeve 10, cerebral spinal fluid will move through the body member 46 of 
the needle 44 and into the cup 50, thereby signalling the user of the 
apparatus that the sleeve 10 has been inserted too deeply into the spinal 
foramen. When the tip 14 of the sleeve 10 is properly positioned, the 
needle 44 is removed. 
Prior to discussion of the actual insertion of an electrode-bearing, 
flexible lead into the spinal foramen, a description of a preferred lead 
assembly follows. Referring particularly to FIGS. 4 and 5, the inner end 
portion of a flexible lead 60 is seen to be generally oblong or oval in 
cross-section, i.e., the lead 60 has a flattened body portion formed of a 
flexible, electrically insulative, and physiologically inert material such 
as the plastic materials now being used for similar structures. The lead 
60 could alternatively be of a rectangular cross-section or other oblong 
section capable of providing the functions described herein. For certain 
applications, the lead 60 could also be circular or semi-circular in 
cross-section, the sleeve 10 being formed to accommodate the lead 60. 
Corners of the tip 62 of the lead 60 are seen to be generally rounded 
transversely, the tip 62 sloping on the underside thereof along the 
longitudinal axis of the lead. This sloped tip 62, which is shaped 
substantially like the front end "running" portion of a sled, enables the 
lead 60 to deflect in a desired direction along the dura 40 when brought 
into contact therewith as will be more fully described hereinafter. The 
lead 60 has electrodes 64 disposed on the lower surface thereof, the 
electrodes 64 each being electrically connected by means of helical wires 
66 to a source of electrical stimulation energy (not shown). The wires 66 
each consist of multiple, redundant strands 68 of an electrically 
conductive wire material such as is well-known in the art. Each strand 68 
is capable of providing a current flow adequate to maintain a desired 
level of electrical output from the electrodes 64. Thus, if fatigue 
failure or other factors cause breakage of one or more of the strands 68, 
the electrical stimulation system will remain capable of functioning as 
long as one of the strands remains intact in each of the wires 66. The 
helical nature of the wires 66 also allows substantial elongation and 
bending without breakage of the strands 68. The wires 66 are essentially 
encapsulated within the body of the flexible lead 60 to electrically 
insulate said wires. The electrodes 64 are both fixed in position on one 
face, i.e., the "lower" surface, of the lead 60, the relative spacing and 
position of the electrodes 64 being incapable of changing after 
implantation of the inner end of the lead 60. In addition, the disposition 
of both electrodes 64 on the surface of the lead 60 which is to face the 
dura 40 (as will be described in more detail hereinafter) enables the 
greater portion of the electrical stimulation energy applied through the 
electrodes to be directed into the spinal cord rather than be dispersed 
through surrounding tissue and bone. The lead 60 is made with flat upper 
and lower surfaces, i.e., in the aforementioned substantially oval 
sectional conformation, in order that the lead 60 can fit more efficiently 
and effectively within the epidural space, i.e., the potential space 
previously mentioned. The flat upper and lower surfaces of the lead 60 
also act to prevent rotation of the lead about its own longitudinal axis 
after implantation within the epidural space. The lead 60 can further be 
provided with a mesh sleeve 70 which is slidable over the lead 60. The 
sleeve 70 can be formed of Dacron, a product of E. I. duPont Corporation, 
or other physiologically inert material formed into a mesh. The sleeve 70 
can be positioned along the lead 60 internally of the body in proximity to 
the entry point of the lead in the spinal column, medical silastic being 
used to fix the sleeve 70 to the lead at that point. Tissue growing into 
the mesh of the sleeve 70 anchors the lead 60 into place. Although the 
lead 60 is described as having a bipolar electrode arrangement, it is to 
be understood that a unipolar electrode arrangement could be provided on 
the lead 60. 
Referring now to FIG. 6, it can be seen that the lead 60 is insertable into 
the sleeve 10, which sleeve has been inserted into a desired relation to 
the dura 40 as described hereinabove. The dimensions of the lead 60 are 
such that said lead can be inserted through the sleeve 10 without binding 
of the flexible material forming the lead and without damage to the 
electrodes 64. The lead 60 may optionally be provided with a stiffening 
member (not shown), such as a wire or the like, disposed longitudinally 
thereof to facilitate insertion of the lead into the sleeve 10 and 
subsequent removal of the sleeve from the lead. The lead 60 is inserted 
into the sleeve 10 with the electrode-bearing surface facing downwardly 
relative to the body of the individual into which the lead is being 
implanted. When the tip 62 of the lead 60 exits the tip 14 of the sleeve 
10, the sloped underside of the tip 62 deflects against the dura 40 and is 
directed upwardly along the outer surface of the dura. The electrodes 64 
are thus brought into contact with the dura 40 and face the spinal cord. 
The lead 60 is connected through the wires 66 to a source of electrical 
energy during this procedure in order that the lead can be positioned 
along the spinal cord at a location best suited for relief of the pain 
condition against which electrical stimulation is to be applied. The 
individual undergoing the procedure is conscious during the procedure and 
indicates subjective sensations produced by varying positions of the lead 
60 along the spinal cord, the positon of the lead 60 being controlled from 
the outer end of the sleeve 10 by "feeding" of the lead through the 
sleeve. 
When the lead 60 is most advantageously positioned relative to the spinal 
cord, the sleeve 10 is withdrawn from the body along the lead 60 as seen 
in FIG. 7, the head 12 being used to pull the sleeve 10 from the body. In 
prior art electrode lead implantation procedures, the implantation needle 
corresponding to the sleeve 10 must be pulled along the full length of the 
lead and over the outer end thereof, thereby requiring the use of 
electrical connectors on the outer end of the lead which are small enough 
to fit within the lumen of the prior art insertion needle. Electrical 
connection to the external electrical source also must be disconnected to 
allow removal of the insertion needle from the lead. With the present 
invention as seen in FIG. 8, the body of the lead 60 can be removed from 
the sleeve 10 in a direction transverse to the longitudinal axes of the 
lead and sleeve through the slot 20 formed in the side wall of said 
sleeve. The use of electrical connectors on the outer end of the lead 60 
which are larger than the inner dimensions of the sleeve 10 is therefore 
possible. Prefabricated sterile leads can be manufactured for implantation 
with the present invention which will reduce the complexity and temporal 
length of the implantation procedure. Prefabricated leads which are 
manufactured with permanent electrical connections to electrical 
pulse-producing apparatus is also now made possible by the present 
invention. 
Referring now to FIG. 9, a sleeve 100 is an alternate embodiment thereof 
can be seen to have an enlarged end member 80 slidably received on the 
outer end thereof, the sleeve 100 not having fixed structure such as the 
head 12 formed thereon. The end member 80 is slotted along its length, the 
dimension of the slot 82 being sufficiently large to allow the lead 60 but 
not the sleeve 100 to pass therethrough. Therefore, the end member 80 can 
be utilized in the manner of the head 12 of FIG. 1 inter alia to insert 
the sleeve 100 into the body and to remove said sleeve from the body The 
end member 80 can be slidably removed over the outer end of the sleeve 
100, the lead 60 then being transversely removed from the end member 
through the slot 82. The lead 60 is then removed from the sleeve 100 
through the slot 200 in a manner similar to that previously described. As 
seen in FIG. 9, the slot 82 is formed in the end member 80 on the side 
thereof opposite the slot 200 in the sleeve 100. The end member 80 thus 
serves to maintain the structural integrity of the sleeve 100 while 
preventing the lead 60 from inadvertently slipping through the slot 200. 
While the invention has been described relative to useage as means for 
implantation of an electrode-bearing lead in the body and for electrical 
stimulation of a portion of the spinal cord for relief of intractable 
pain, it is to be understood that the present assembly finds utility for 
other therapeutic application not explicitly described herein. Further, 
modification of the invention can be made in light of the teachings 
provided hereinabove. For example, the present structure can alternatively 
include a slotted sleeve which extends between the outer end of the sleeve 
10 and the opening 16 or any portion of such distance, the slotted sleeve 
being essentially concentric with the sleeve 10 to retain the lead 60 
within the sleeve 10 on insertion of the assembly into the body. This 
slotted sleeve could then be removed from the sleeve 10 in the same manner 
as the sleeve 10 is removed from the lead 60 or in the manner that the 
member 80 is removed from the sleeve 100. The head 12 could be retained on 
the sleeve 10 with use of such an outer slotted sleeve. Accordingly, in 
light of the foregoing, the invention is to be limited in scope only by 
the recitations of the appended claims.