WO2014179267A1

WO2014179267A1 - Minimal trauma cochlear implant electrode

Info

Publication number: WO2014179267A1
Application number: PCT/US2014/035794
Authority: WO
Inventors: Anandhan Dhanasingh; Claude Jolly; Soeren Schilp; George ALEXIADES
Original assignee: MED EL Elektromedizinische Geraete GmbH
Current assignee: MED EL Elektromedizinische Geraete GmbH
Priority date: 2013-04-30
Filing date: 2014-04-29
Publication date: 2014-11-06
Anticipated expiration: 2015-10-30

Abstract

A cochlear implant electrode array includes electrode wires for carrying electrical stimulation signals. There is an electrode stimulation contact at a terminal end of each electrode wire for applying the electrical stimulation signals to adjacent neural tissue. An elongated electrode carrier is formed of resilient material that encases the electrode wires. The carrier has a center longitudinal axis and an outer surface with contact openings that expose the stimulation contacts. Resilient friction reduction rings are distributed along and protrude above the outer surface of the electrode carrier acting to limit contact area between the electrode carrier and a scala side wall during surgical insertion of the electrode array into a cochlea of an implanted patient.

Description

TITLE

Minimal Trauma Cochlear Implant Electrode

[0001] This application claims priority from U.S. Provisional Patent Application 61/817,438, filed April 30, 2013, which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to an implantable electrode arrangement for cochlear implant systems.

BACKGROUND ART

[0003] A normal ear transmits sounds as shown in Figure 1 through the outer ear 101 to the tympanic membrane 102 which moves the bones of the middle ear 103 that vibrate the oval window and round window openings of the cochlea 104. The cochlea 104 is a long narrow duct wound spirally about its axis for approximately two and a half turns. It includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The cochlea 104 forms an upright spiraling cone with a center called the modiolus where the spiral ganglion cells of the acoustic nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid-filled cochlea 104 functions as a transducer to generate electric pulses which are transmitted to the cochlear nerve 113, and ultimately to the brain.

[0004] Hearing is impaired when there are problems in the ability to transduce external sounds into meaningful action potentials along the neural substrate of the cochlea 104. To improve impaired hearing, auditory prostheses have been developed. For example, when the impairment is related to operation of the middle ear 103, a conventional hearing aid may be used to provide acoustic-mechanical stimulation to the auditory system in the form of amplified sound. Or when the impairment is associated with the cochlea 104, a cochlear implant with an implanted electrode can electrically stimulate auditory nerve tissue with small currents delivered by multiple electrode contacts distributed along the electrode.

[0005] Figure 1 also shows some components of a typical cochlear implant system where an external microphone provides an audio signal input to an external signal processor 111 in which various signal processing schemes can be implemented. The processed signal is then converted into a digital data format for transmission by external transmitter coil 107 into the implant 108. Besides receiving the processed audio information, the implant 108 also performs additional signal processing such as error correction, pulse formation, etc., and produces a stimulation pattern (based on the extracted audio information) that is sent through an electrode lead 109 to an implanted electrode array 110. Typically, this electrode array 110 includes multiple stimulation contacts 112 on its surface that provide selective stimulation of the cochlea 104.

[0006] The electrode array 110 contains multiple electrode wires embedded in a soft silicone body referred to as the electrode carrier. The electrode array 110 needs to be mechanically robust, and yet flexible and of small size to be inserted into the cochlea 104. The material of the electrode array 110 needs to be soft and flexible in order to minimize trauma to neural structures of the cochlea 104. But an electrode array 110 that is too floppy tends to buckle too easily so that the electrode array 110 cannot be inserted into the cochlea 104 up to the desired insertion depth. A trade-off needs to be made between a certain stiffness of the electrode array 110 which allows insertion into the cochlea 104 up to the desired insertion depth without the array buckling, and certain flexibility of the electrode array 110 which keeps mechanical forces on the structures of the scala tympani of the cochlea 104 low enough.

[0007] Recent developments in CI electrode array designs and surgical techniques are moving towards minimal trauma implantations. For preservation of residual hearing it is of particular importance to preserve the natural intra-cochlear structures. Therefore, the size and mechanical characteristics of the electrode array are critical parameters for the best patient benefit. Some electrode array designs are pre-curved, though a drawback of that approach is that a special electrode insertion tool is needed which keeps the electrode array straight until the point of insertion.

[0008] As documented by Erixon et al., Variational Anatomy of the Human Cochlea: Implications for Cochlear Implantation, Otology & Neurotology, 2008 (incorporated herein by reference), the size, shape, and curvature of the cochlea varies greatly between individuals, meaning that a CI electrode array must match a wide range of scala tympani (ST) geometries. Furthermore, recently published research by Verbist et al., Anatomic Considerations of Cochlear Morphology and Its Implications for Insertion Trauma in Cochlear Implant Surgery, Otology & Neurotology, 2009 (incorporated herein by reference) has shown that the human ST does not incline towards the helicotrema at a constant rate, but rather there are several sections along the ST where the slope changes, sometimes even becoming negative (i.e. downwards). The location and grade of these changes in inclination were also found to be different from individual to individual.

Consequently, CI electrode arrays should be highly flexible in all directions in order to adapt to individual variations in curvature and changes in inclination of the ST for minimal trauma implantation.

SUMMARY OF THE INVENTION

[0009] Embodiments of the present invention are directed to a cochlear implant electrode array which includes electrode wires for carrying electrical stimulation signals. There is an electrode stimulation contact at a terminal end of each electrode wire for applying the electrical stimulation signals to adjacent neural tissue. An elongated electrode carrier is formed of resilient material that encases the electrode wires. The carrier has a center longitudinal axis and an outer surface with contact openings that expose the stimulation contacts. Resilient friction reduction rings are distributed along and protrude above the outer surface of the electrode carrier acting to limit contact area between the electrode carrier and a scala side wall during surgical insertion of the electrode array into a cochlea of an implanted patient.

[0010] The rings have radial centers which may lie on the longitudinal axis of the electrode carrier, or they may be offset from the longitudinal axis of the electrode carrier. For example, the radial centers may be offset by a rotational angle from a centerline that passes through the stimulation contacts, which varies as a function of longitudinal position along the electrode carrier. Each ring has a diameter that may lie perpendicular to the longitudinal axis of the electrode carrier, or one or more non-perpendicular angles to the longitudinal axis of the electrode carrier. The rings may connected together in series to form one or more helical windings along the surface of the electrode carrier. And the rings may incorporate a friction-reducing lubricant material and/or a therapeutic drug adapted for release over a treatment period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 shows anatomical structures in a human ear having a cochlear implant system.

[0012] Figure 2 shows an example of a cochlear implant electrode with friction reduction rings according an embodiment of the present invention.

[0013] Figure 3 shows details of friction reduction ring offsets according to an embodiment of the present invention.

[0014] Figure 4 shows another example of a cochlear implant electrode according to an embodiment of the present invention.

[0015] Figure 5 shows another example of a cochlear implant electrode according to an embodiment of the present invention.

[0016] Figure 6 shows cross-section views of a cochlear scala with an implant electrode at various insertion angles.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0017] During surgical insertion of a cochlear implant electrode, the electrode carrier slides against one of the side walls of the scala tympani, either the outer lateral wall or the inner modiolus wall, or for some electrodes, against the basilar membrane (at the top of the scala tympani). This sliding action is known to create damage to the cochlear tissue structures and can lead to loss of any residual hearing that may be present. And once it has been inserted, the electrode contacts are either facing the modiolar wall close to the neural elements or they are facing the outer lateral wall which may result in high impedance. In addition, the electrode will be in different positions inside the scala tympani at different rotational turns of the cochlea. [0018] Embodiments of the present invention address these issues with a novel cochlear implant electrode array. Figure 2 shows a cochlear implant electrode array 110 which includes an electrode carrier 202 with a center longitudinal axis 203 made of resilient material (e.g., soft silicone) that encases the electrode wires that carry the electrical stimulation signals. Openings in the outer surface of the electrode carrier 202 expose electrode stimulation contacts 112 that are at the terminal end of each electrode wire for applying the electrical stimulation signals to adjacent neural tissue. There are resilient friction reduction rings 201 (e.g., soft silicone) which are distributed along and protrude above the outer surface of the electrode carrier 202. The friction reduction rings 201 act to limit contact area between the electrode carrier 202 and a scala side wall (the outer lateral wall or the inner modiolus wall) and thereby reduce the sliding friction created during surgical insertion of the electrode array 110 into the cochlea. The friction reduction rings 201 also help to reduce the electrode impedance by keeping some distance between the stimulation contacts 112 and the side wall of the scala tympani.

[0019] The electrode array 110 is a free fitting lateral wall electrode such that at different specific locations within the different turns of the cochlea, the electrode array 110 will be in different spatial positions within the scala tympani, sometimes closer to the outer lateral wall, sometimes closer to the upper basilar membrane, and sometimes closer to the inner modiolus wall. And the surgical insertion should be smooth (low friction) through the entire insertion path all the way from the outer basal turn to the inner apical turn. Thus rather than simple directed protrusions from the surface of the electrode carrier 202, the friction reduction rings 201 form a complete ring around the circumference of the electrode carrier 202. In order to support appropriate bending of the electrode array 110 according to the form of the cochlea, the entire electrode array 110 may have an oval shape. Alternatively just portions of the electrode array 110 such as the portions between the friction reduction rings 201 or just the friction reduction rings 201 may have an oval shape.

[0020] Though not limited to any particular height, the height of the friction reduction rings 201 might typically be between 10 and 50 μιη above the outer surface of the electrode carrier 202. The size and height of the friction reduction rings 201 may vary depending on the cross-sectional sizes of the electrode array 110 itself and of the scala tympani at the target locations after final placement, see Fig. 6. The height of the friction reduction rings 201 above the outer surface of the electrode carrier 202 may vary either in general or for specific friction reduction rings 201. Thus the height of an individual friction reduction ring 201 may sometimes be larger towards the outside (i.e., the lateral wall side) and sometimes larger at the inside (i.e., the modiolus wall side). In the specific embodiment shown in Fig. 2, each friction reduction ring 201 has a diameter 204 that lies perpendicular to the longitudinal axis 203 of the electrode carrier 202. In other specific embodiments, one or more of the friction reduction rings 201 may lie at one or more non- perpendicular angles to the longitudinal axis 203 of the electrode carrier 202.

[0021] As shown in Fig. 3, the radial centers 301 of the friction reduction rings 201 may be offset from the radial center 205 of the electrode carrier 202 (i.e. the longitudinal axis 203), and these offsets can have different orientation along the longitudinal axis 203 of the electrode carrier 202 so that the radial centers 301 of the friction reduction rings 201 may be offset by a rotational angle from a centerline that passes through the electrode stimulation contacts 112 which varies as a function of longitudinal position along the electrode carrier 202. And the friction reduction rings 201 may incorporate a friction- reducing lubricant material and/or a therapeutic drug adapted for release over a treatment period of time.

[0022] Figure 4 shows another example of a cochlear implant electrode 110 according to an embodiment of the present invention where the friction reduction rings 201 connected together in series to form a continuous helical winding 401 along the outer surface of the electrode carrier 202. Again the height of the helical winding 401 may vary as described above. Figure 5 shows an example of a related embodiment of an electrode array 110 wherein the friction reduction rings 201 are connected together in series to form two separate continuous helical windings 501 and 502 along the outer surface of the electrode carrier 202.

[0023] Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention.

Claims

CLAIMS What is claimed is:

1. A cochlear implant electrode array comprising:

a plurality of electrode wires for carrying electrical stimulation signals;

an electrode stimulation contact at a terminal end of each electrode wire for applying the electrical stimulation signals to adjacent neural tissue;

an elongated electrode carrier formed of resilient material encasing the electrode wires, having a center longitudinal axis and an outer surface with a plurality of contact openings exposing the stimulation contacts; and

a plurality of resilient friction reduction rings distributed along and protruding above the outer surface of the electrode carrier acting to limit contact area between the electrode carrier and a scala side wall during surgical insertion of the electrode array into a cochlea of an implanted patient.

2. An electrode array according to claim 1, wherein the rings have radial centers on the longitudinal axis of the electrode carrier.

3. An electrode array according to claim 1, wherein the rings have radial centers offset from the longitudinal axis of the electrode carrier.

4. An electrode array according to claim 3, wherein the radial centers are offset by a rotational angle from a centerline passing through the stimulation contacts that varies as a function of longitudinal position along the electrode carrier.

5. An electrode array according to claim 1, wherein each ring has a diameter that lies perpendicular to the longitudinal axis of the electrode carrier.

6. An electrode array according to claim 1, wherein each ring has a diameter that lies at a non-perpendicular angle to the longitudinal axis of the electrode carrier.

7. An electrode array according to claim 6, wherein the ring diameters lie at a plurality of different angles to the longitudinal axis of the electrode carrier.

8. An electrode array according to claim I, wherein the rings are connected together in series to form at least one helical winding along the surface of the electrode carrier.

9. An electrode array according to claim 8, wherein the rings form a plurality of helical windings along the surface of the electrode carrier.

10. An electrode array according to claim I, wherein the rings incorporate a therapeutic drug adapted for release over a treatment period of time.

11. An electrode array according to claim 1, wherein the rings incorporate a friction- reducing lubricant material.