AU2006252212A1 - Improved cochleostomy sealing - Google Patents

Description

P001 Section 29 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Improved cochleostomy sealing The following statement is a full description of this invention, including the best method of performing it known to us: c IMPROVED COCHLEOSTOMY SEALING FIELD OF THE INVENTION C 5 The present invention relates to cochlear implant devices, and in particular, to their electrical efficiency.

BACKGROUND OF THE INVENTION SA cochlear implant prosthesis is a surgically implantable device that provides hearing sensation to individuals with severe-to-profound hearing loss who receive limited benefit from hearing aids.

C Cochlear implants are designed to substitute for the normal hearing mechanism (function of the outer, middle ear and part of the inner ear including the hair cells), transforming sound energy into electrical energy that will initiate impulses in the auditory nerve. An electrode array that is inserted into the cochlear stimulates different auditory nerve fibres depending on the frequency of the signal received from an external microphone and processor system.

The electrode array is inserted during an operation that usually takes between 2-3 hours depending on the device to be implanted. An incision is made behind the ear to expose the temporal bone; the temporal bone consists of the squamous, the mastoid, the tympanic, zygomatic and petrous segment. All implants require the opening of the mastoid bone which leads to the middle ear.

A shallow recess is then created to hold the implant package in place and level with the bone. Next a hole is drilled which allows the surgeon access into the cochlea. This hole is known as a cochleostomy the opening from the middle ear to the perilymphatic spaces of the cochlea. A cochleostomy can be formed through the round window, the oval window, the promontory or through the apical turn of the cochlea.

The electrode array is then gently threaded into the shell like structure of the cochlea and the wound closed; the cochleostomy remains open and heals with scar tissue over the next few days.

Once implanted, cochlear implants require electrical energy to operate. In conventional devices, this energy is typically supplied by batteries fitted in the external components of the cochlear implant, which is generally connected to the 0 implant via an inductive power transfer arrangement. It is envisaged that future C generations of implants will be fully implantable, with an implanted battery. In aeither case, battery life and energy efficiency are important issues.

STo create the perception of sound, cochlear implants pass electrical c 5 current through the electrodes inserted in the cochlea. The perceived loudness of the sound is monotonically related to the amplitude and duration of the current c-i pulse, and therefore the energy of the stimulation.

C It is conventional during surgical implantation to use a tissue graft from the C patient to provide a circumferential seal at the cochleostomy, primarily to reduce C 10 the risk of meningitis resulting from communication between the inner ear and the C middle ear.

However, there is evidence to suggest that a significant amount of stimulus current flows out of the cochlea and back to the reference electrode via the cochleostomy, and so does not contribute to the desired neural stimulation.

It is an object of the present invention to provide a cochlear implant prosthesis, and method of implantation, which improve the electrical efficiency of the prosthesis.

SUMMARY OF THE INVENTION In a broad form, the present invention provides a seal for use with a cochlear implant which is effective to operatively reduce current flow through a cochleostomy and thereby improve the electrical efficiency of a cochlear implant prosthesis.

In one aspect, the present invention provides an electrode array for a cochlear implant prosthesis, said array being adapted to be inserted through a cochleostomy, said array including an electrically insulating plug operatively adapted to surround the array and substantially seal the cochleostomy.

According to another aspect, the present invention is an implantable prosthesis including such an electrode array.

According to another aspect, the present invention provides a cochlear implant kit, including at least a cochlear implant, said implant including an electrode array, and an electrically insulating plug operatively adapted to surround the array and to operatively substantially seal a cochleostomy.

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According to a further aspect, the present invention provides a seal for a c cochlear implant prosthesis, said prosthesis including an electrode array aoperatively adapted to be inserted through a cochleostomy, said seal being Sformed from a electrically insulating material and being operatively adapted to c 5 surround said electrode array and substantially seal said cochleostomy.

The present invention further provides, in a cochlear implant implantation procedure, a method of providing an electrical seal for a cochleostomy, said c implant prosthesis having an electrode array inserted via said cochleostomy, c including at least the steps of

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a) providing an insulating plug adapted to surround the array; and b) placing the plug in the cochleostomy so that it surrounds the array and substantially seals said cochleostomy.

According to a further aspect, the present invention provides a seal for a cochlear implant prosthesis, said prosthesis including an electrode array operatively adapted to be inserted through a cochleostomy, said seal being formed from a electrically insulating material and being operatively adapted to surround said electrode array and substantially seal said cochleostomy.

For the purpose of power reduction it is desirable to reduce the amount of electrical current required to stimulate the auditory nerve. During stimulation, as much as possible the current flowing from the electrode within the cochlea must be directed towards the auditory nerve. Any leakage of current through paths other through than the auditory nerve should therefore be minimised in order to reduce the power consumption of the implant. The present invention accordingly allows current leakage via the cochleostomy of a hearing implant prosthesis to be reduced. As a consequence, the current levels used for stimulation can be decreased as the implant's energy is used more efficiently.

Although many different stimulation approaches have been proposed and used, in each scheme the energy for the stimulations is provided by the implant, and conventionally this is supplied ultimately by the batteries in the external component. Hence, the degree to which the energy supplied by the batteries is effectively delivered impacts upon battery life.

N BRIEF DESCRIPTION OF THE DRAWINGS c An illustrative embodiment of the present invention will be described with Ureference to the accompanying figures, in which: Figure 1 is a schematic diagram of the cochlea showing a conventional C 5 intra-cochlear electrode insertion with cochleostomy sealed using muscle/fat tissue; cFigure 2 is a schematic diagram of the cochlea showing an improved ccochleostomy seal using a moulded insulating plug; SFigure 3 is a schematic of a inverted funnel-shaped seal in isolation; Figure 4 is a schematic diagram of the cochlea showing the inverted funnel C shaped seal in use; Figure 5 is a schematic illustration of an alternative structure for the seal; and Figure 6 is a schematic diagram showing a close up of the inserted funnel shaped seal in use as in figure 4.

DESCRIPTION OF PREFERRED EMBODIMENT The present invention may be implemented in a variety of ways and the embodiments illustrated are to be considered only as illustrative constructions.

More particularly, the present invention is potentially useful for other related purposes, other than sealing a cochleostomy created as described previously.

For example, the present invention may be applied to seal an existing orifice between the middle ear and the. inner ear, for example the round window. The present invention may be used to seal any opening created between the middle ear and the perilymph, whether this is intended to be used as a conduit for a part of an implanted device, or to be sealed completely after surgery. The term cochleostomy should accordingly be understood for the purposes of this application in this expansive sense. Such sealing may have further advantages, for example reducing the chance of the recipient contracting meningitis. It may also reduce the risk of unintended explantation.

Figure 1 is a schematic of the cochlear 10 showing a conventional, prior art intra-cochlear electrode insertion, where the cochleostomy 15 is sealed using a graft of the patient's tissue, typically muscle and fat. The cochleostomy 15 is shown in the wall of the cochlea 20 itself, and is situated in the middle ear space c o Figure 2 shows schematically an improved cochleostomy seal according to Sone implementation of the present invention, using a deformable insulating plug c 5 30 to provide the cochleostomy seal. The plug 30 illustrated is preferably formed from a soft, deformable grade of silicone elastomer. This allows the plug 30 to be cinserted into the cochleostomy 15, and then elastically conform to the generally c irregular shape of the cochleostomy SThe plug 30 may be formed around the electrode lead 35 so that it can C 10 slide along the lead 35. In practice, the surgeon would insert the electrode lead c 35 through the cochleostomy 15 and into the cochlea 20 in the conventional manner. This process is well understood in the art, and described in the literature, and conventional aspects of this process will not be further described in detail. A standard reference for such a process is described in "Surgical Techniques for Cochlear Implants", Noel L. Cohen, Chapter 8, p 151 in "Cochlear Implants", Waltzman, S.B. and Cohen, L. L. (1997) ISBN 0-86577-882-5, the disclosure of which is hereby incorporated by reference.

The extent of insertion will vary significantly from patient to patient, depending upon the peculiarities of the anatomy of the patient, the specific surgical procedure used by the surgeon, and the precise location of the cochleostomy 15. It is expected that the most improvement in leakage reduction will be for the basal electrodes, as these electrodes have the shortest leakage path. It therefore also follows that greater improvement may be seen in short or partial electrode arrays, for example as used in electro-acoustic stimulation.

After the array 35 has been inserted as far as desired, the plug 30 may be slid along the electrode lead 35 and through into the cochleostomy 15. It then provides a seal of insulating material within the cochleostomy 15, thereby increasing the impedance of the undesired current path through the cochleostomy to the reference electrode located outside the inner ear. It will be appreciated that as the surrounding structures to the plug 30 are partially conductive, a substantial current may still leak through this general path, but the leakage through the cochleostomy site will be reduced.

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The plug 30 shown in figure 2 is generally toroidal in shape, as it surrounds c the array and fills the space between the array 35 and the cochleostomy However, any other suitable shape may be used. One such suitable shape would be an inverted funnel 40, as shown in figure 3 in isolation from the electrode array 35 on which it would be formed and in figure 4 in use. The funnel tip 45 would easily pass through the cochleostomy 15, or other hole for which the plug can be c- used, with the body 50 of the plug able to deform on insertion to substantially seal cthe cochleostomy or hole 15. The base portion 55 of the funnel would remain on c the outer side of the cochleostomy or hole 15, allowing for easy removal should that be necessary. This shape allows the seal to flex and conform to the c cochleostomy shape.

The sealing of the cochleostomy by the inverted funnel shaped plug 40 is shown in close-up in figure 6. The inverted funnel shaped plug 40 is either fixed on electrode lead 35 or capable of sliding along the lead 35 once the lead is in a suitable position. In either case, the inverted funnel shaped plug 40 is shown in position sealing the cochleostomy 15 with the funnel base 55 on the outer side of cochleostomy The plug 30 could be formed of any suitable inert biocompatible material, which is operatively an insulator, but is preferably made of silicone. The plug may be formed of different materials or from a single material. It could be partly formed from a more stiff material, with the outer portions being resilient in order to provide the necessary conformable seal. The seal 30 could be formed from a suitable polymer putty material in situ. It could be formed, with a slit or the like, to allow it to be attached around the electrode lead 35 after insertion. The key requirement is that it be formed of an insulating material and substantially seal the cochleostomy 15 so as increase the impedance of the leakage path. If different shapes or forms of electrode array 35 are used, then the shape of the seal 30 will need to be adapted to suit the shape of the array or lead 35 which passes through the cochleostomy Alternatively, as in figure 5, the plug 30 can be formed by moving a hard, space-filling, hollow cylinder or cone inside a hollowed portion of the electrode array 35. The hard object deforms the soft material of the electrode array outwards. The hard object 30 is initially located near the proximal end of the electrode array 35 so that it does not interfere with the normal insertion of the C array 35. After insertion of the array 35 the hard object 30 is slid along the array to the cochleostomy 15 where it deforms the sides of the electrode array Ssufficiently to seal the cochleostomy 15. This has the advantage there are no c 5 places where two separate insulator parts abut, to create a potential space for infection, thereby reducing the risk of infection.

cAlternatively, the plug 30 can be formed by being moulded, as part of the C electrode moulding process, at an appropriate point along the length of the c electrode array 35. This approach has the same advantage as the sliding space C 10 filling plug of figure 5 in that it has no separate insulator parts abutting and c therefore has a reduced risk of infection. It also has the advantage of not requiring a small device to be moved, relative to the array 35, in the confined space and delicate structures of the inner ear during implantation. However, this approach potentially requires that insertion be conducted to a specific depth, thereby limiting surgical flexibility.

The seal 30 could be specifically shaped to fit an actual aperture, for example the oval window. Alternatively, it could be formed in situ, for example by a fast curing sealant injected around the cochleostomy 15. Any effective artificial seal which can be positioned as required may be used to implement the invention.

The efficacy of this approach has been investigated using an animal model. Experiments on two Guinea Pigs, with a total of three ears investigated acutely have been performed. In these experiments, the bulla (middle ear cavity) was exposed, a cochleostomy was drilled over the round window and a four electrode array was inserted. Stimulation was applied between the most apical intracochlear electrode (ICE) and a monopolar ball electrode inserted in the temporalis muscle.

Monopolar Electrical Auditory Brainstem Response (EABR) thresholds and the voltage waveform between the stimulus electrodes (to deduce impedance) were measured. In the last of the three ears investigated the voltage between the two most basal ring electrodes was also measured during the stimulus pulse (to determine the current flow along the cochlea at a point near the cochleostomy).

0 To calibrate this measurement a known current pulse had been previously c applied between the most apical ICE and another ring electrode (on a separate Sarray) held by hand in the cochleostomy.

SFour different methods of sealing the cochleostomy were used: no sealing; c 5 small piece of muscle of approx. the volume of the cochleostomy; larger piece of muscle several times the volume of the cochleostomy (residual muscle extending S out of the cochleostomy) and otoform paste (one ear only).

SOtoform paste is a settable silicone material, used in hearing aid fitting and csimilar applications, which is initially mouldable but which then sets to a soft deformable consistency.

CN In every ear the EABR thresholds, the impedance and the current flow at the cochleostomy varied depending on the plug type used. The following table shows the four sealing methods and how those parameters varied: Plug material EABR T Impedence Cochleostomy current Large muscle largest lowest largest Small muscle 2 n d largest 2 n o lowest 2 na largest No seal 3 rd largest 3 rd lowest 3'r largest Otoform putty Smallest highest smallest The smallest EABR threshold (otoform putty) was about 40% smaller than the largest threshold (large muscle). The impedance results varied by around from smallest to largest. The current flow through the cochleostomy varied from 84% of total current (large muscle) to 70% (otoform putty).

The results are consistent with a significant proportion of the stimulus current flowing through the cochleostomy. Different sealing arrangements appear to change the amount of current flow through the cochleostomy and thereby change the EABR threshold. The changes in impedance and cochleostomy current flow as measured by the voltage on the basal two rings are consistent with this model. These results indicate it is possible to lower thresholds by effective sealing of the cochleostomy.

Another perspective is that any T and C decrease gained from using the plug will manifest itself as a decrease in power consumption of the implant and a subsequent increase in battery life. Power consumption of the implant can be divided into two parts power consumed to run the implant electronics (WE)and c power consumed to deliver current to the auditory nerve The decrease in T/C level current will manifest itself as a proportional decrease in WN. For present Simplant designs the ratio of WN to WE is about 50:50 for high rate strategies. If, for C 5 example, it is assumed that the plug provides a 10% decrease in T/C level this would translate to about a 5% decrease in overall implant power consumption for chigh rate strategies, less for lower rate strategies. However, the most recent tests cshow that the plug yields an improvement of between 20-40% decrease in T/C c level, indicating at lease a 10% improvement in power consumption.

Variations and additions are possible to the structures described within the c general scope of the present invention. For example, the present invention could be employed in addition to a tissue graft type sealing approach.

Although the present invention has been principally described with reference to a cochlear implant prosthesis, it will be appreciated that this construction can readily be applied to other implant prostheses in which there are electrical losses due to a cochleostomy or similar opening. It will also be understood that although the description has referred principally to an implant with an external receiver stimulator unit, the present invention is equally applicable to a totally implanted device.

It will also be appreciated that although this invention has been principally used to provide sealing at the cochleostomy there are other openings between the cochlea and the middle ear that may pass similar current and that may also provide similar benefit by being sealed. These include the round window and the oval window. Similar stand-alone insulating plugs (not connected to the electrode array) may be inserted into these other openings, providing a further decrease in power consumption. It will be understood that the present invention may also be applied to seal a cochleostomy which is not intended to remain open, for example in some form of totally implanted device which does not require a physical conduit to remain out of the inner ear.

2006252212 21 Dec 2006

Claims (11)

1. 3. An electrode array according to claim 1, wherein the plug is formed by a slidable element which is operatively moveable within a hollow portion of the electrode array, the surface of the array being deformed outwards by the slidable element, such that the slidable element can be moved within said hollow portion to provide said plug and seal the cochleostomy
2. 4. An electrode array according to claim 1, wherein the plug is formed from a resilient, deformable material so that operatively it conforms substantially to the surface of the cochleostomy. An electrode array according to claim 1, wherein the plug is moulded onto the electrode array.
3. 6. An electrode array according to claim 1, wherein the plug is formed from deformable material.
4. 7. An electrode according to any one of the preceding claims, wherein the plug is formed from silicone.
5. 8. An electrode array according to any one of the preceding claims, wherein the plug is of an inverted funnel shape.
6. 9. An electrode array according to any one of the preceding claims, C wherein when the plug is in operation a portion of the plug remains on the outer side of the cochleostomy. An implantable prosthesis including an electrode array according to any one of the preceding claims. c- 11. A cochlear implant kit, including at least a cochlear implant, said n implant including an electrode array, and an electrically insulating plug operatively IND adapted to surround the array and to operatively substantially seal a Scochleostomy.
7. 12. A kit according to claim 11, including an array according to any one of claims 1 to 9.
8. 13. In a cochlear implant implantation procedure, a method of providing an electrical seal for a cochleostomy, said implant prosthesis having an electrode array inserted via said cochleostomy, including at least the steps of a) providing an insulating plug adapted to surround the array; and b) placing the plug in the cochleostomy so that it surrounds the array and substantially seals said cochleostomy.
9. 14. A seal for a cochlear implant prosthesis, said prosthesis including an electrode array operatively adapted to be inserted through a cochleostomy, said seal being formed from a electrically insulating material and being operatively adapted to surround said electrode array and substantially seal said cochleostomy. A plug adapted to seal an opening between the inner ear and the middle ear, said plug being an electrical insulator. INO
10. 16. A plug according to claim 15, wherein the plug is adapted to be c inserted into the round window or oval window, so as to provide an electrical seal aand increase the impedance across the round or oval window.
11. 17. A plug according to claim 15, wherein the plug includes an orifice to permit the passage of part of an implantable device. (Ni C 18. A plug according to claim 15 wherein the plug is formed from a (N In resilient, deformable material so that operatively it conforms substantially to the INO surface of the opening. DATED this 18th day of December 2006 COCHLEAR LIMITED WATERMARK PATENT TRADE MARK ATTORNEYS BUILDING 1 BINARY CENTRE RIVERSIDE CORPORATE PARK 3 RICHARDSON PLACE NORTH RYDE NSW 2113 AUSTRALIA