U.S. patent application number 09/983292 was filed with the patent office on 2002-03-07 for cochlear implant electrode array.
Invention is credited to Dadd, Fysh, Darley, Derek Ian, Parker, John L., Treaba, Claudiu-Gheorghe.
Application Number | 20020029074 09/983292 |
Document ID | / |
Family ID | 3764581 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020029074 |
Kind Code |
A1 |
Treaba, Claudiu-Gheorghe ;
et al. |
March 7, 2002 |
Cochlear implant electrode array
Abstract
An electrode array for a cochlear implant is formed with a
carrier made, for example from silicone, is preshaped and is formed
with a lumen. The array is shaped to assume a first. The array can
be straightened, and held in a straight configuration by inserting
a stylet into the lumen. The array relaxes to a shape matching the
curvature of the cochlea when the lumen is removed. The electrodes
of the array are disposed on one side of the array to face the
modiolus when the array is inserted into the cochlea.
Inventors: |
Treaba, Claudiu-Gheorghe;
(Wollstonecraft, AU) ; Dadd, Fysh; (Leichhardt,
AU) ; Darley, Derek Ian; (Cromer Heights, AU)
; Parker, John L.; (Roseville, AU) |
Correspondence
Address: |
GOTTLIEB RACKMAN & REISMAN PC
270 MADISON AVENUE
8TH FLOOR
NEW YORK
NY
100160601
|
Family ID: |
3764581 |
Appl. No.: |
09/983292 |
Filed: |
October 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09983292 |
Oct 23, 2001 |
|
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09454976 |
Dec 3, 1999 |
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Current U.S.
Class: |
607/137 |
Current CPC
Class: |
A61F 11/20 20220101;
A61N 1/0541 20130101 |
Class at
Publication: |
607/137 |
International
Class: |
A61N 001/05 |
Foreign Application Data
Date |
Code |
Application Number |
May 21, 1999 |
US |
PCT/AU99/00391 |
Claims
1. A cochlear electrode array kit for stimulating an auditory nerve
of a patient, said electrode array kit comprising: an elongated
carrier having a carrier surface and a lumen extending
longitudinally through said carrier; a plurality of electrodes
disposed on said carrier surface; and a plurality of wires
connected to said electrodes and embedded in said carrier to
provide signals to said electrodes; wherein said elongated carrier
is arranged and constructed to have a first configuration in which
said carrier is insertable into said cochlea and a second
configuration in which after insertion, said electrodes are
positioned to apply stimulation to said auditory nerve; and a
stylet sized to fit into said lumen and extend substantially
through said carrier, said stylet, said wires and said carrier
cooperating to change said elongated carrier between said first and
second configuration.
2. The cochlear electrode array kit of claim 1 wherein said carrier
is biased toward said first configuration when said stylet is
inserted into said carrier.
3. The cochlear electrode array kit of claim 2 wherein said lumen
has a cross-sectional dimension which increases as said elongated
carrier changes shape from said first to said second configuration
to allow said stylet to be withdrawn.
4. The cochlear electrode array kit of claim 1 wherein said
elongated carrier is made of a silicone material.
5. The cochlear electrode array kit of claim 1 wherein said stylet
is made of a malleable, biocompatible material.
6. The cochlear electrode array kit of claim 5 wherein said
malleable, biocompatible material is platinum.
7. The cochlear electrode array kit of claim 1 wherein said stylet
includes a tip, said tip being more flexible than the rest of said
stylet.
8. The cochlear electrode array kit of claim 1 wherein said
elongated carrier includes a tip, said tip being more straight and
flexible than the rest of the said elongated carrier.
9. The cochlear electrode array kit of claim 1 wherein said stylet
has a variable stiffness.
10. A cochlear electrode array for a cochlear implant comprising:
an elongated carrier having a proximal end and a distal end with an
outer surface defining a inner side and an outer side opposite said
inner side; a plurality of electrodes on said outer surface; and
wires connected to said electrodes and extending to said proximal
end.
11. The cochlear electrode array of claim 10 wherein each of said
electrodes is connected to one of said leads.
12. The cochlear electrode array of claim 10 wherein at least one
of said electrodes is connected to at least two of said leads.
13. The cochlear electrode array of claim 10 wherein each of said
electrodes comprises a ring collapsed to form a U-shaped
member.
14. The cochlear electrode array of claim 13 wherein said elongated
carrier has a longitudinal axis and wherein said rings are arranged
orthogonally to said longitudinal axis.
15. The cochlear electrode array of claim 14 wherein said
electrodes form a channel, said leads being disposed in said
channel.
16. The cochlear electrode array of claim 10 wherein said elongated
carrier is shaped into a curved configuration to fit inside the
cochlea of a person, said cochlea including a modiolus, said
electrodes being oriented on said inner side to face said modiolus
when said carrier is inserted into the cochlea.
17. The cochlear electrode array of claim 10 wherein said outer
surface is smooth along said outer side to prevent any damage to
the cochlea as said carrier is inserted into the cochlea.
18. The cochlear electrode array of claim 10 wherein said
electrodes are disposed on said inner side.
19. A cochlear electrode array comprising: an elongated carrier
having a proximal end and a distal end, an inner surface with a
plurality of electrodes; said elongated carrier being formed with a
lumen extending through said carrier, said elongated carrier being
held in a first configuration by an external member inserted into
said lumen; said elongated carrier having a memory to assume a
second configuration, and said elongated carrier being arranged to
assume to said second configuration when said external member is
removed from said lumen.
20. The cochlear electrode array of claim 19 wherein said elongated
carrier is constructed and arranged to assume a curved
configuration matching the shape of the cochlea when no member is
inserted into said lumen.
21. The cochlear electrode array of claim 19 wherein said body is
arranged to be retained in said first configuration when the
external member is located into the lumen, said carrier being
substantially straight in said first configuration.
22. A method of making a cochlear electrode array for implantation
into the cochlea of a patient as part of a cochlear implant system
comprising: forming an elongated blank around a curved production
stylet; removing said curved production stylet to create a lumen
through said elongated blank; straightening said elongated blank
and inserting a straight production stylet into the said lumen;
attaching electrodes and wires to said elongated blank; and
withdrawing said straight production stylet.
23. The method of claim 22 further comprising generating each said
electrode by the steps of providing a ring of a conductive
material, threading one of said wire through said ring and
collapsing said rings to grip said one of said wires.
24. The method of claim 23 wherein said step of collapsing includes
electrowelding said ring.
25. The method of claim 23 wherein each said ring is collapsed into
a U-shaped electrode.
26. The method of claim 25 wherein the said elongated blank is
formed with a channel.
27. The method of claim 26 wherein the said wires are placed into
the said channel formed in the said elongated blank.
28. The method of claim 27 wherein each of said u-shaped electrodes
with its said attached wire is placed one-by-one into said channel
starting from the tip of the said elongated blank, such that each
electrode covers the wires of the electrodes which have been
previously placed on the blank.
29. The method of claim 22 further comprising positioning said
blank with said electrodes into a curved die and applying a
moulding material to said blank and said electrodes to form a
unitary carrier.
30. The method of claim 22 wherein said production stylet is
withdrawn from said body first to generate said lumen, said blank
is straightened and a second straight stylet inserted to hold said
blank in a straight configuration before said electrodes are
attached to said blank.
31. A method of making a cochlear electrode array for implantation
into the cochlea of a patient as part of a cochlear implant system
comprising: providing a plurality of electrodes, each electrode
being attached to a wire; positioning said electrodes in a spaced
relationship in a moulding die with said wires extending toward one
end of said moulding die; and applying a moulding material into
said moulding die to form a carrier with said electrodes and wires
being embedded in said moulding material.
32. The method of claim 31 wherein said electrodes are formed by
providing a plurality of rings; welding a wire to each ring; and
collapsing each of said rings to form a U-shaped electrode
element.
33. The method of claim 32 further comprising positioning said
electrodes in said moulding die to form a channel and positioning
said wire in said channel.
34. The method of claim 33 further comprising inserting into said
moulding die a production stylet before said moulding materials is
applied, and removing said production stylet from said carrier to
form a lumen therein.
35. The method of claim 31 further comprising providing said
moulding die in a first shape having a first curvature smaller than
the curvature of the shape of the cochlea.
36. The method of claim 32 comprising forming the said electrode
array such that after straightening said electrode array will relax
to a second relaxed curve having a second curvature larger than
said first curvature.
37. The method of claim 33 wherein the second relaxed curvature
matches the curvature of the human cochlea.
38. A stylet insertion jig, stylet and precurved cochlear electrode
array combination for forming a straightened cochlear electrode
array, said combination comprising: a precurved cochlear electrode
array having a longitudinal lumen adapted to receive a stylet; an
elongated stylet having a long axis; a jig including: a chassis
upon which is mounted a variable engagement means arranged to
position said array and said stylet relative to each other, an end
section of said lumen intersecting said long axis of said variable
engagement means operative to insert said stylet into said lumen;
an electrode array straightening means mounted on said chassis and
engaging said array and operative to straighten said array.
39. A combination according to claim 39, wherein said stylet is
formed of a malleable material having an annealed tip at a first
end and a loop at a second end, said loop forming a means of
engagement.
40. A combination according to claim 39, wherein said straightening
means cooperates with said variable engagement means to
incrementally straighten said precurved electrode array during
insertion of said stylet.
41. A stylet insertion jig for straightening a precurved cochlear
electrode array having a lumen and for inserting a stylet into said
lumen, said jig comprising: a chassis upon which is mounted a
variable engagement means arranged to position said array and said
stylet relative to each other, an end section of said lumen
intersecting said long axis of said variable engagement means
operative to insert said stylet into said lumen; an electrode array
straightening means mounted on said chassis and engaging said array
and operative to straighten said array.
42. A stylet insertion jig according to claim 41, wherein said
straightening means cooperates with said variable engagement means
to incrementally straighten said precurved electrode array during
insertion of said stylet.
Description
FIELD OF INVENTION
[0001] This invention pertains to cochlear electrode arrays shaped
to a predetermined curvature, and more particularly to a cochlear
electrode array which has a first preselected shape suitable for
insertion into the body of a patient, and a second shape suitable
for providing a specific function, or stimulus.
BACKGROUND OF THE INVENTION
[0002] Cochlear implant systems are used to aid patients having a
hearing deficiency. More particularly, these systems include a
microphone receiving ambient sounds and converting the sounds into
corresponding electrical signals, signal processing means of
processing the electrical signals and generating cochlea
stimulating signals and an electrode array for applying the cochlea
stimulating signals to the cochlea of the patient. It is known in
the art that the cochlea is tonotopically mapped. In other words,
the cochlea can be partitioned into regions, with each region being
responsive to signals in a particular frequency range. This
property of the cochlea is exploited by providing the electrode
array with a plurality of electrodes, each electrode being arranged
and constructed to deliver a cochlea stimulating signal within a
preselected frequency range to the appropriate region. The
electrical currents and electric fields from each electrode
stimulate the auditory nerve cells disposed in the modiolus of the
cochlea. Several electrodes may be active simultaneously.
[0003] It has been found that in order for these electrodes to be
effective, the required magnitude of the currents flowing from
these electrodes is a function of the distance between the
electrodes and the modiolus. If this distance is great, the
threshold stimulation current magnitude must be larger than if the
distance is smaller. Moreover, the current from each electrode may
flow in all directions, resulting in the area of the cochlea
stimulated by a single electrode being undesirably large. Therefore
the electrical stimulation is not well localised to a particular
site on the cochlea. In order to reduce the threshold stimulation
amplitude and to improve localisation, it is advisable to keep the
distance between the electrode array and the modiolus as small as
possible. This is best accomplished by providing an electrode array
having a shape which generally follows the shape of the modiolus.
In contrast during insertion, the electrode array should be
generally straight, because otherwise the insertion procedure is
too cumbersome and difficult. Consequently there is a problem due
to the hitherto conflicting design objectives that the electrode
array be straight during insertion but curved during use.
[0004] Several methods and means of curving the electrode array and
therefore overcoming the above-described problem have been
attempted. These attempts fall generally in two categories. The
first category consists of arrays that are formed in a straight
configuration, and are mechanically manipulated into a curved
configuration by an external device which exerts pressure against
the outside wall of the cochlea. These arrays are designed so that
part of the array is pressed against the outside wall of the
cochlea, and another part is thereby pressed against the inside
wall. These types of arrays may be of a two-part design (such as
commonly assigned U.S. Pat. Nos. 5,645,585 and 5,545,219,) or they
may be of a space-filling design. Both share the disadvantage of
exerting a permanent pressure against both the inside and outside
wall of the cochlea. The space-filling designs have an additional
disadvantage that they displace the cochlear fluid, which may have
adverse affects on the patient.
[0005] The second category consists of arrays which are shaped into
a curved configuration and are then straightened for insertion.
Examples of arrays falling into this second category include an
electrode array having an electrode carrier provided with a
longitudinal element arranged on one side of the carrier which is
constructed to change its dimension once the array is inserted. For
example, the longitudinal element could include a hydrogel such as
PAA (Polyacrylic Acid) which expands after insertion by absorbing
water from the cochlear fluid, as described in commonly assigned
U.S. Pat. No. 5,578,084. Alternatively, the longitudinal element
could be a bimetallic filament (such as nickel/titanium filament)
which is shaped to allow the electrode carrier to take a straight
configuration at room temperature but bends into a preselected
shape once it is exposed to body temperature.
[0006] Commonly assigned U.S. Pat. No. 5,653,742 discloses another
electrode array falling into the second category. In this patent,
the array is encapsulated into a stiffening sheath which holds the
array in a linear configuration. The sheath is made of a
biosorbable material such as polyvinyl alcohol (PVA) which
dissolves in the cochlear fluid after insertion.
[0007] While the arrays from this second category remove the
disadvantage of the static pressure against the walls of the
cochlea, they have other disadvantages in that the surgeon cannot
control the point in the surgical procedure at which the array
curves, and the array cannot be restraightened during surgery to
allow a second attempt at insertion if the first attempt fails.
OBJECTIVES AND SUMMARY OF THE INVENTION
[0008] In view of the above-mentioned disadvantages of the prior
art, it is an objective of the present invention to provide a
cochlear electrode array which has a first, relatively straight
configuration so that it can be readily implanted, using a stylet
which, after insertion is readily removed and a second, curved
configuration to conform to the cochlea of a patient.
[0009] A further objective is to provide an array which is small
relatively in cross-sectional area, so as to facilitate insertion
and minimise the displacement of the cochlea fluid.
[0010] Another objective is to provide an array which can be
manufactured relatively easily and inexpensively.
[0011] Other objectives and advantages of the invention shall
become apparent from the following description.
[0012] Briefly, an electrode array in accordance with this
invention includes an elongated carrier which supports a plurality
of electrodes suitable for defining an electrode array for
application for cochlear stimulation signals, and wires attached to
the electrodes to provide cochlear stimulation signals in the usual
manner. The carrier is preferably preshaped into a curved
configuration selected to insure that the electrodes are disposed
in close proximity to the modiolus of the scala tympani.
Importantly, the carrier is formed with a lumen which is designed
to accept one or more surgical stylets. Prior to insertion of the
carrier into the cochlea, the stylet is introduced into the carrier
to insure that the carrier is maintained in a substantially
straight configuration. As the array is inserted into the cochlea,
the stylet is slowly withdrawn allowing the array to assume a
curved configuration. Preferably the stylet is relatively stiff
along its entire length except for its tip. The tip is annealed to
render it more malleable then the rest of the stylet to allow the
array to flex easily as it is being inserted.
[0013] Preferably, the electrodes are disposed on an inner surface
of the carrier, so that when the carrier is implanted, the
electrodes are facing the modiolus. Each electrode may be formed
from a ring with a wire threaded through the ring, the ring then
being collapsed into a U-shaped electrode element to grip the wire.
The electrodes and wires are then embedded into the carrier.
[0014] Several methods for producing the electrode array can be
used. For example, a blank may be formed around a curved production
stylet, and the stylet may be withdrawn from the blank to form a
lumen. The electrodes and their wires are attached to the blank and
a moulding material is applied to complete the carrier.
[0015] After the carrier and its electrodes are completed, it may
be packaged in its curved configuration together with an
appropriate surgical stylet, and a straightening jig. Prior to
surgery, the straightening jig is used to simultaneously straighten
the carrier and insert the -stylet into the lumen of the carrier.
The stylet is stiffer or more rigid then the carrier so that once
the stylet is inserted into the lumen, the electrode array thus
formed can be removed from the jig with the carrier maintaining its
straight configuration for insertion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1a shows a plan view of a cochlear implant array
constructed in accordance with this invention in a relaxed
state;
[0017] FIG. 1b shows a side elevational view of the electrode array
of FIG. 1a;
[0018] FIG. 1c shows an end elevational view of the electrode array
of FIGS. 1a and 1b;
[0019] FIG. 2a shows an enlarged cross sectional view of the distal
end of the electrode array of FIGS. 1 a-c;
[0020] FIG. 2b shows an enlarged cross sectional view of the array
taken along lines II-II in FIG. 2a;
[0021] FIG. 2c is similar to FIG. 2b and shows the array with the
surgical stylet in place;
[0022] FIG. 2d is similar to FIG. 2b with two surgical stylets;
[0023] FIG. 3 shows a somewhat diagrammatic view of a cochlear
array as it is inserted into the cochlea;
[0024] FIG. 4a shows a production stylet with spacers used to make
a blank;
[0025] FIG. 4b shows a blank being formed;
[0026] FIG. 4c shows details of the blank tip;
[0027] FIG. 4d shows a side view of an electrode ring;
[0028] FIG. 5 shows an alternate technique of making the array;
[0029] FIG. 6 shows in cross-section the attachment of an electrode
ring to a blank;
[0030] FIGS. 7a-7d show the electrode array being inserted into the
cochlea; and
[0031] FIGS. 8a and 8b show an orthogonal view of a jig used to
straighten the array prior to surgery.
DETAILED DESCRIPTION OF THE INVENTION
[0032] A preferred embodiment of the invention shall now be
described in conjunction with the figures. Starting with FIGS.
1a-1c, an electrode array 10 constructed in accordance with this
invention is shown in a state wherein it follows the natural
curvature of the cochlea of an adult. This electrode array consists
of an elongated carrier 12 having a straight portion 14 and a
portion 16 which has a spiral shape. Portion 16 subtends an arc of
about 450.degree., as shown. The array 10 is provided with a
plurality of electrodes shown in FIGS. 2a, 2b and described below.
These electrodes have been omitted from FIGS. 1a-c for the sake of
clarity. The carrier 12 is made of a plastic material, such as
medical grade silicone rubber, as described in more detail
below.
[0033] Portion 14 is provided with a ring 18 to indicate insertion
depth, especially during extraction of the stylet (described
below). The ring 18 is used for holding the array 10 during the
insertion. From ring 18, portion 14 widens slightly to form two
tubes 22 and 24. Tube 22 is formed with a plurality of
longitudinally spaced external ribs 26, provided to allow fixation
using bone cement or platinum ties (not shown). Tube 22 holds a
plurality of wires 36 discussed below which extend from the
receiver/stimulator 23 to the electrodes of portion 16. Tube 24
encloses a lumen 30 which extends through the length of the
electrode array 10. Lumen 30 is fabricated using a production
stylet 31, and is used to house a surgical stylet 44, as described
bellow.
[0034] Referring now to FIGS. 2a and 2b, portion 16 has a plurality
of electrodes 32 arranged on an inner surface 34, i.e., the surface
facing the modiolus 33, as shown in FIG. 3. Each electrode 32 is
connected to one or more wires 36. Advantageously the electrodes 32
form a channel for the wires 36 connected to the electrodes 32. The
electrodes 32 and wires 36 are embedded in the plastic material 38
forming the carrier 12.
[0035] With reference to FIGS. 4a-4d, a method of making the array
10 is now described. First, the production stylet 31 is cut to size
from platinum wire coated with polytetrafluroethene i.e. "teflon".
A plurality of donut shaped spacers 40 made of silicone are
inserted over the production stylet 31 as seen in FIG. 4a.
Importantly at its tip 31A, (FIG. 4c) the teflon coating is removed
from the production stylet 31 thereby forming the narrow section at
the end of the lumen. Next, the stylet 31 with the spacers 40 is
inserted into a curved die (not shown) and a silicone material is
poured into the curved die and cured to form a moulded blank 42
which includes the production stylet 31 and the spacers 40 embedded
therein. The spacers 40 insure that the production stylet is
positioned at a predetermined location within the moulded blank 42.
The die is shaped to insure that the blank 42 has an end section
16A which is not curved but is formed so that it is relatively
straight. This section 16A may have a length of about 0.7 mm. The
bare tip 31A of production stylet 31 is disposed in this end
section 16A. After the moulded blank 42 is cured, it is removed
from the die.
[0036] The production stylet is then withdrawn from the moulded
blank 42 leaving behind the lumen 30 having a tip 30A which is
narrower then the rest of the lumen. The spacers 40 are also left
behind on removal of the production stylet. The non-stick property
of the teflon facilitates the easy removal of production stylet 31
from the cured silicon array, thereby leaving a smooth lumen 30
behind. Prior to the removal of the molded blank from the moulding
die, the lumen 30 is, of course, circular.
[0037] In a separate operation a plurality of electrodes 32 are
formed and attached to corresponding wires 36 as follows. First
several rings made of platinum are provided. A typical array may
have 22 electrodes in which case the following sized rings may be
used: 6 rings with an outer diameter of 0.6 mm, 6 rings with an
outer diameter of 0.63 mm and 10 rings with an outer diameter of
0.65 mm.
[0038] A parylene-coated Pt/Ir wire is connected to each of the
rings as follows. The wire is placed inside the ring and welded,
and then the ring is then collapsed and welded also, using a
welding electrode to form a U-shaped electrode 32 shown in FIG. 4d.
The wire 36 extends away from the electrode 32.
[0039] Generally, every electrode 32 is connected in this manner to
a single wire 36. However, with the technique described above it is
relatively easy to connect two or more wires, such as wire 36A, to
each electrode 32 as well. Multiple wires provide redundancy in
case one of them breaks, and importantly, also provide greater
mechanical flexibility for a given electrical resistance.
[0040] The moulded blank 42 is next manually straightened and
placed into a production jig 43 adapted to hold the moulding blank
42 in the straight configuration (FIG. 5). The production jig
preferably comprises a flat piece of chrome-plated brass with
indents to hold the electrodes in correct position for attachment
to the production stylet. In this configuration a second production
stylet 46 is inserted into the lumen 30 to hold the moulded blank
42 straight. The second production stylet 46 is straight, and
preferably is made of stainless steel. Once the second production
stylet 46 has been fully inserted into the lumen 30, the production
jig 43 is removed. Next, each of the electrodes 32 is glued in one
of the recesses 41 on the blank 42 as shown in FIG. 5, using a dab
of silicone. Recesses 41 are formed by the shape of the die used to
mould the blank. The blank 42 is then backfilled with a silicone
filler material and the whole array is cured to complete the array
10. Upon addition of the silicon filler material and curing spacers
40 and the added filler amalgamate to form an homogeneous whole.
The second production stylet 46 is then removed.
[0041] The array may alternatively be fabricated by the following
method. A set of electrodes are formed by pressing rings of
platinum into a U-shape. The electrode furthest from the tip of the
electrode array is placed in a straight welding die (not shown),
where a wire is welded to that ring. A droplet of silicone is
placed in the trough of the electrode. A second electrode is then
placed in the welding die, and a wire is welded to it. The wire
from the second electrode is bedded down into the silicone droplet
in the trough of the first electrode. A droplet of silicone is then
placed in the trough of the second electrode. A third and
subsequent electrodes are placed in a similar fashion. Additional
droplets of silicone may be placed in the earlier electrodes if
necessary to capture all of the wires.
[0042] Once all of the electrodes have been welded and assembled in
the straight welding die the production stylet is pressed on top of
the wires and silicone in the troughs of the electrodes. Each
electrode trough is then partially filled with more silicone. The
whole assembly is then placed in an oven to cure the silicone.
[0043] The assembly is then removed from the straight die and
carefully curved to match the shape of a curved moulding die. The
assembly is then placed in the curved moulding die and the space in
the die is packed with silicone material. A matching die cover is
placed over the assembly and pressed down. The die is then placed
in an oven to cure the silicone. The die is then open to allow the
resulting electrode array to be removed from the die.
[0044] The array 10 may alternatively be fabricated by placing a
production stylet 31, U-shaped electrodes 32 and wires 36 into a
curved moulding die (not shown). The electrodes are placed in the
die one at a time, starting at the base, with the wire from each
electrode passing through the trough formed by the previously
inserted electrodes. Once all of the electrodes 32 have been placed
in the die the whole space is packed with silicone material, and a
matching die cover is placed over and pressed down over the
moulding die. The array is cured, and then removed from the die,
and the production stylet removed from the array.
[0045] After completion, the array 10 is attached to the cochlear
implant receiver/stimulator 23 in the same fashion as prior art
electrode arrays.
[0046] The assembly formed of the array 10 and the
receiver/stimulator 23 is packaged and shipped in an electrode
array kit which also includes a surgical stylet 44 and, optionally,
a straightening jig 48.
[0047] The surgical stylet 44 is formed from an uncoated wire of a
malleable, biocompatible wire such as platinum, having a diameter
of about 0.125 mm. A length of wire of about 3 mm forms the tip of
the surgical stylet 44 is annealed to thereby making it more
flexible. The opposite end of stylet 44 is curved to form a loop
44A to allow the manipulation of the stylet 44.
[0048] The straightening jig 48 shown in FIGS. 8a and 8b is used to
straighten the array 10 prior to surgery as shall now be described.
The jig 48 contains a fixed platform 110 and a moving carriage 120
which can slide on platform 110 along a pair of rails 102, 104.
Platform 110 is also provided with a pin 130 disposed at one end of
the platform 110 as shown. Also attached to the platform is a
stationary wall 140.
[0049] The carriage 120 is formed with a trough 106 extending
longitudinally through the carriage 120. On one side of this trough
106, the carriage 120 is provided with an extension 106-108
disposed in parallel with and adjacent to stationary wall 140 as
shown. The carriage 120 also has a top surface with ribs 112 which
allow a person to move the carriage 120 on top of platform 110.
[0050] Before surgery, the array 10 is positioned on platform 110
so that the portion 16 is disposed adjacent to the stationary wall
140 and the portion 14 extends between the stationary wall 140 and
the extension 108 and into the trough 106. In this position, the
portion 14 of the array 10 is captured by the carriage 120.
[0051] Surgical stylet 44 is positioned so that its tip is inserted
into the lumen 30 while the remainder of the stylet 44 extends from
the carriage 120 to the pin 130 with the loop 44A being fitted over
the pin 130 as shown in FIG. 8a. The array 10 is now ready to be
straightened.
[0052] Because the carriage 120 grips the electrode array 10, as
the carriage 120 is moved in the direction of arrow A in FIG. 8a,
the portion 16 of the array 10 is forced to unravel slowly between
the stationary wall 140 and extension 108. Simultaneously with the
unravelling or straightening of portion 16, the array 10 is pulled
over the surgical stylet 44 like a stocking. Once the array 10 is
fully straightened the stylet 44 is fully inserted into lumen 30,
and the straightened array 10 with stylet 44 in place can be
removed from the jig 48.
[0053] Preferably, the straightening jig 48 is packed with the
electrode array 10, with the surgical stylet 44 being partially
inserted into tube 24 of array 10. This allows the array 10 to be
stored with the portion 16 in its moulded state, yet is ready to be
easily straightened by the surgeon just prior to use.
[0054] In an alternate embodiment, the array 10 is straightened
prior to shipment using the straightening jig 48, and the surgical
stylet 44 is inserted to hold the array 10 straight. In this
embodiment the kit shipped to the surgeon need not include the jig
48 since it is not necessary. However, this alternative may be less
desirable since the array 10 may be in the straight configuration
for a relatively long time period and may lose its curved natural
or relaxed shape.
[0055] The surgical use of a cochlear implant utilising the
inventive electrode array 10 will now be described. First, the
array 10 is straightened and held in this configuration using the
jig 48. Simultaneously the surgical stylet 44 is fully advanced
into lumen 30 as described above and in FIGS. 8a and 8b. With the
array 10 straight, the lumen 30 assumes a tight oval
cross-sectional shape which grips the surgical stylet so that it
will not easily fall out.
[0056] In the following description it is assumed that the surgeon
is now ready to insert the array 10 into the patient's cochlea.
[0057] As described above, the end 31A of production stylet 31 is
narrower than the rest of the stylet 31. Therefore the resulting
lumen 30 has a narrower end 30A as well. When the surgical stylet
44 is inserted into the lumen 30, its tip is wedged into and forms
in interference fit with the end 30A of the lumen 30 so that the
surgical stylet 44 is retained in the lumen 30 until it is forcibly
removed. As previously mentioned, this tip is annealed to make it
softer then the rest of the stylet 44.
[0058] After the surgical stylet 44 is fully inserted into the
lumen 30, the array 10 and stylet 44 are removed from the jig 48
and the jig is discarded. (Of course, if the array 10 is shipped
with the surgical stylet 44 in place, this step is omitted).
[0059] Referring now to FIGS. 7a-7d, a surgeon inserts the array 10
as follows. First, he makes an incision in the cochlea 48 in a
normal fashion to generate a small access 50 in its sidewall. The
surgeon inserts the tip 10A of the array 10 through the access 50
slowly. (FIG. 7b) As the array 10 is introduced, it starts curving
to follow the curvature of the outer wall 45 of the cochlea until
the final position shown in FIG. 7c is reached. The insertion is
made easier because the array has no electrodes along the outside
surface, just a smooth surface of silicone. This minimises friction
between the array 10 and the outer wall 45 of the cochlea. The
friction is also reduced because the stylet is made of a malleable
material. Therefore the array 10 with the stylet 44 inside conforms
to the shape of the outer wall 45 cochlea without applying any
substantial static outward pressure as would be the case if the
stylet 44 was in elastic deformation.
[0060] The insertion is further assisted by the straight preferred
feature portions on the tips of the array 10 and stylet 44,
respectively, which help to prevent the array 10 from folding
over.
[0061] During the insertion, the surgeon can judge the position of
the array 10 within the cochlea by the relative positions of mark
18. When the mark 18 reaches the access hole 50, the surgeon knows
that the final position of the array 10 has been reached. At this
point the surgeon removes and discards the surgical stylet 44 as
indicated in FIG. 7d by arrow A. Once the stylet tip pulled out of
the narrowed portion 30A of lumen 30, the whole stylet 44 is much
easier to pull out since it is resting rather loosely therein, as
explained above, and shown in FIG. 2c. The array 10 is curved
during the insertion, and so the lumen 30 opens allowing the stylet
44 to be freely removed. Furthermore, the array 10 has now assumed
a curved shape similar to the relaxed shape shown in FIG. 2a. This
causes the lumen 30 to assume a more open shape, which allows the
surgical stylet 44 to be easily removed.
[0062] Once the surgical stylet 44 is removed, the array 10 relaxes
away from the outer wall 45 of the cochlea 48, to reach its final
position adjacent to the inner 47 wall of the cochlea and the
modiolus. Importantly, the array 10 is in a resting position and is
not pressing against the modiolus.
[0063] In summary, the electrode array 10 of the present invention
is fabricated in a curved shape (FIGS. 1a and 1b). It has a lumen
30 which allows a surgical stylet 44 to be inserted to hold the
array straight for surgical insertion (FIGS. 2a and 2b).
Importantly, the lumen 30 is fabricated so that the opening is
almost round when the array 10 is in its relaxed or curved
configuration. When the array 10 is straight, the lumen 30
constricts and holds the stylet 44. These features allow the stylet
44 to be withdrawn easily from the lumen 30 of the electrode array
10 after the array 10 has been inserted into the cochlea 48, since
the array is curved by contact with the outer wall 45 of the
cochlea 48. After the surgical stylet 44 is removed, the array 10
assumes its fully curved shape, and achieves a final position lying
close to the modiolus.
[0064] Preferably the cross-sectional shape of the electrode
carrier is not round, but is approximately square with rounded
corners (FIGS. 2b, 2c). This reduces the possibility that the array
10 will twist during insertion.
[0065] The lumen 30 is a dynamic feature in that it changes its
shape depending on the curvature of the array 10: when the array 10
is in its curved state the lumen 10 is open and round. When the
array 10 in its relaxed curved state (somewhat less curved than the
moulded shape) the lumen is open and elliptical in shape.
[0066] When the array 10 is straightened, the walls of the lumen 30
collapse closing the lumen 30 such that the surgical stylet 44 is
gripped and held in. This ensures that the stylet 44 will not fall
out of the lumen during transportation or manipulation prior to
surgery as the array is held straight.
[0067] During insertion into the cochlea the array becomes
partially curved. This causes the lumen to open. After insertion
the lumen is open which releases the stylet allowing it to be
easily removed.
[0068] Preferably the lumen is of a reduced diameter for a small
distance at its tip (FIG. 4c). The surgical stylet is frictionally
fit into this reduced diameter section, so that it is firmly held
there. Throughout the remainder of the distance of the lumen and
stylet the stylet is a loose fit so that it can be easily
removed.
[0069] Preferably the shaped lumen is fabricated by removing the
teflon from the production stylet for a length of 0.15 mm, from the
point where the production stylet passes the last electrode. Thus
the lumen will be a constant diameter of 0.18 mm until the last
0.15 mm where the diameter will be 0.127 mm. The surgical stylet is
0.125 mm and since neither the lumen nor the stylet are preferably
round, there will be a friction fit over the last 0.15 mm. This has
the advantage that the surgical stylet is locked into the tip of
the electrode array, and the initial force for removal of the
stylet is comparatively high. Once the surgical stylet is withdrawn
0.15 mm, however, the stylet is then easily removed. Therefore, the
surgical stylet is unlikely to be dislodged accidentally, yet is
relatively easy to remove intentionally.
[0070] Preferably the tip of the electrode array is moulded
straight, while the remainder of the array is curved . This helps
to prevent the array tip from folding over during insertion. The
carrier is moulded with a continuing tightening curve until
approximately 0.7 mm before the tip. The last 0.7 mm of the
electrode is fabricated straight. Because the tip is not
predisposed to curving, even if the stylet withdraws slightly
during insertion, it would require a large force to be applied
during insertion to cause the electrode to double back on itself.
In this manner, the surgical stylet 44 has a variable flexibility
along its length. In an alternate embodiment two stylets 44-1 and
44-2 may be inserted into lumen 30 with one of them (for instance
44-2) extending only partially along the length of array 10 (as
shown in FIG. 2d).
[0071] The array shown in FIGS. 1a-1c could be designed in other
ways as well. For example, the array could be moulded from two dies
to form two halves which can then be glued together.
[0072] Alternatively, the array could be formed in two separate
parts--a straight electrode carrier with a channel, and a curved
tube. The tube could then be glued into the channel so as to create
a curved array with a lumen which is open (round) when the array is
in its curved shape.
[0073] Obviously, modifications could be made to the invention
without departing from its scope as defined in the appended claims.
For example, it is possible make and use an array with a stylet
without the special shaped lumen.
* * * * *