Field of the invention
[0001] The present invention is generally related to the field of hearing aid devices based
on bone conduction.
Background of the invention
[0002] For most patients conductive hearing loss can be treated with classical hearing aids
or by performing middle ear surgery. There are however patients for whom surgical
intervention is impossible or no classical hearing aid can be applied. One such example
relates to children born with major aural atresia who present with malformed middle
ears, have no external ear canal and no auricle allowing for placement of a classical
air-conduction hearing aid.
[0003] For these patients the only functional solution is a hearing aid that operates via
bone conduction. A bone conduction device (BCD) comprises a BCD transducer and a mechanical
coupling to the human body. A BCD transducer is provided with a microphone (Mic),
an amplification processor (Amp), a battery (Bat) and an actuator (Act) (Fig.1.).
The microphone captures an acoustic input signal and converts it into an electrical
signal, the amplification circuit processes the received electrical signals and generates
control signals to cause the actuator to vibrate. The actuator of a BCD is an electromagnetic
or piezoelectric vibrator that transmits vibrations in the audible range to a recipient's
inner ear. These vibrations stimulate the sensory cells located at the basilar membrane
of the cochlea and evoke hearing sensations. There are different implementations of
BCDs available, from non-implantable external BCDs to (semi-)implantable BCDs. Depending
on the type of the BCD, the mechanical vibration is transferred to the inner ear by
coupling vibrations of the transducer to the skin covering the skull, directly to
the skull bones, to the middle ear ossicles or to the bony or membranous parts of
the inner ear.
[0004] Conventionally, an external non-implantable BCD is connected to a metallic diadem
or an elastic head band that is worn on the head. The function of this diadem (see
Fig.2a) or the head band (Fig.2b) is to press the BCD against the skin ensuring coupling
of the vibrations to the skull bone. These solutions have however, several disadvantages.
First of all, patients, even little children, are forced to wear an aesthetically
compromising bulky metallic diadem or an elastic head band with a BCD vibrator fixed
to it. Also, the pressure exerted by the metallic diadem or the elastic head band
often causes pain reactions. Last but not least, problem with the coupling of the
vibrations to the skull by pressing the BCD against the skull skin is the damping
of the vibrations through the skin. The damping can amount up to 20dB for the speech
frequencies above 1kHz. The recent trials of replacing the coupling through the metallic
diadem by using the adhesive tape glued to the skin covering the mastoid process of
the temporal bone, as described e.g. in
JP2001087142 A, are cosmetically more acceptable, but still show the disadvantage of vibration damping
by the skin.
[0005] Since the 1980s implantable screw fixtures made of titanium of tantalum have been
introduced, based on the phenomenon of osseointegration. These screw fixtures are
surgically placed directly into the skull bone and allow for coupling of the BCD transducers
directly to the skull through a BCD attachment piece, called a percutaneous coupling
abutment, that penetrates the skin (Fig.1). Examples can be found amongst others in
US2010/112519 A1,
US2004/234091 A1 and
US2006/093175 A1. Osseointegration is the formation of a direct interface between an implant and bone,
without intervening soft tissue. The direct structural and functional connection between
living bone and the surface of a load-bearing artificial implant ensures increased
mechanical stability of the implant.
[0006] The main advantage of direct contact of the osseointegrating screw fixture with the
skull bone is that one gets rid of the damping of the vibrations through the skin.
This solution has, however, also an important disadvantage. The percutaneous coupling
abutment penetrating through the skin causes very frequent infections and inflammatory
reactions around the osseointegrating fixture screw and the percutaneous coupling
abutment that require medical intervention and sometimes lead even to the loss of
the osseointegrating fixture screw.
[0007] This problem has recently been solved by coupling BCD transducers directly to the
osseointegrating fixture screw without percutaneous abutment. In this way the BCD
vibrating transducer remains under the skin and is powered by an external (transcutaneous)
BCD processor sending the power and the microphone signal to the implanted vibrating
transducer by a radiofrequency link. The external (transcutaneous) BCD processor is
held in place by magnets contained in the implanted vibrating transducer and in the
external BCD processor. An illustration can be found in
US2004/032962 A1.
[0008] However, solutions wherein a BCD is coupled to an osseointegrating fixture screw,
either in a percutaneous or a transcutaneous implementation, can only be considered
in patients older than 4 year, as the bone needs to be thick enough (more than 3-4mm)
to allow reliable placement and fixation of the osseointegrating titanium or tantalum
fixture screw. This means that it is impossible to apply this solution in children
under 4 years old.
[0009] Therefore children with congenital aural atresia have to use the vibrators attached
to metallic head diadems, elastic head bands or glued to the skin. All these solutions
are not comfortable and not optimal from the audiological point of view, because of
the above-mentioned acoustic damping through the skin.
[0010] Consequently, there is a need for improvement, so that also children younger than
four years can benefit from bone conduction devices with osseointegrated coupling.
Summary of the invention
[0011] It is an object of embodiments of the present invention to provide for a device that
allows for coupling of a bone conduction device (BCD) to the skull bone, wherein the
above-mentioned drawbacks are avoided or overcome, and in particular the limitation
that such coupling of a bone conduction device by means of an osseointegrating screw
cannot be applied in the case of very young children.
[0012] The above objective is accomplished by the solution according to the present invention.
[0013] In a first aspect the invention relates to a device for coupling a bone conduction
device, comprising a plate arranged for osseointegration and a coupling abutment for
attaching an acoustic BCD to the plate.
[0014] The proposed solution indeed allows for coupling a BCD. The device of the invention
comprises a plate, preferably a metallic plate, arranged for allowing and stimulating
the adhesion and proliferation of osteoinducible cells on its surfaces and the acoustic
bone conduction device can be fixed to that plate via the coupling abutment. The proposed
solution can be used for any person in which general anaesthesia can be applied. This
means in practice that even children of only 6 months of age can receive the proposed
device. There is no need any more to wait until the bone has reached a certain thickness
as is the case in the prior art solutions.
[0015] In a preferred embodiment the device of the invention is made of titanium or tantalum.
These materials have the advantageous property of easy osseointegration with the bone.
Alternatively, the plate can be made of another metal or of another material allowing
for osseointegration with living bone.
[0016] In embodiments of the invention the plate comprises a plurality of screw holes, which
can be used for primary fixing the plate by means of screws, for example bioresorbable
screws, before the osseointegration process ensures the final fixation of the plate
to the bone.
[0017] In advantageous embodiments the device for coupling according to this invention comprises
at least one cut-out. By providing at least one cut-out additional area is created
for bone growth.
[0018] In preferred embodiments the plate, e.g. metallic plate, comprises a transversal
connection whereon said coupling is provided.
[0019] In embodiments of the invention the plate is ring shaped. In some embodiments the
plate is elliptic.
[0020] Advantageously, a surface of the plate has a lattice or mesh structure arranged for
inducing bone formation and osseointegration.
[0021] In one embodiment the surface of the plate that faces the skull of the patient is
customized to the 3D anatomy of a patient's skull. That surface may be provided with
a lattice or mesh structure.
[0022] In a preferred embodiment the plate comprises at least one position marker. This
may facilitate the correct positioning of the plate on the bone surface.
[0023] In another embodiment the part of the coupling abutment closest to the plate is polished.
[0024] In one embodiment a part of said coupling closest to said plate is covered by hydroxyapatite.
This offers the advantage of an improved healing of the skin and infection prevention.
Alternatively, another healing coating can be used, for example antibacterial or steroid
releasing coatings.
[0025] In another embodiment the plate comprises one or more extensions. These extensions
further increase the contact surface with the bone.
[0026] In another aspect the invention relates to a kit of parts comprising a device for
coupling as previously described and fixation means for fixating an acoustic bone
conduction device to the plate of the device.
[0027] Preferably the fixing means comprises metallic screws or bioresorbable screws or
bone cement.
[0028] For purposes of summarizing the invention and the advantages achieved over the prior
art, certain objects and advantages of the invention have been described herein above.
Of course, it is to be understood that not necessarily all such objects or advantages
may be achieved in accordance with any particular embodiment of the invention. Thus,
for example, those skilled in the art will recognize that the invention may be embodied
or carried out in a manner that achieves or optimizes one advantage or group of advantages
as taught herein without necessarily achieving other objects or advantages as may
be taught or suggested herein.
[0029] The above and other aspects of the invention will be apparent from and elucidated
with reference to the embodiment(s) described hereinafter.
Brief description of the drawings
[0030] The invention will now be described further, by way of example, with reference to
the accompanying drawings, wherein like reference numerals refer to like elements
in the various figures.
Fig.1 illustrates a prior art solution with a percutaneous osseointegrating screw
fixture.
Fig.2a and 2b illustrate a metallic diadem and a head band as used in prior art solutions.
Fig.3a illustrates an above view of the ring shaped osseointegration-enabled scaffold
plate with integrated coupling abutment according to the present invention. Fig.3b
shows the undersurface of the plate.
Fig.4 illustrates an embodiment where the osseointegration-enabled scaffold plate
and the coupling abutment are produced as two separate pieces that can be connected
together with e.g. a screw.
Fig.5 illustrates a lattice structure as found at the undersurface of the scaffold
plate in certain embodiments.
Fig.6 illustrates the use of an (arrow) marker on the scaffold plate to ease a correct
positioning.
Fig.7 illustrates an osseointegration-enabled scaffold plate provided with cut-outs
(shown as cross-hatched areas) in an embodiment with a separate coupling abutment
fixed to the osseointegration-enabled scaffold plate by a screw.
Fig.8 illustrates a scaffold plate provided with one or more extensions. The undersurface
with the mesh structure is being shown.
Fig.9 illustrates the connecting parts being undercut to facilitate removal of the
coupling abutment.
Detailed description of illustrative embodiments
[0031] The present invention will be described with respect to particular embodiments and
with reference to certain drawings but the invention is not limited thereto but only
by the claims.
[0032] Furthermore, the terms first, second and the like in the description and in the claims,
are used for distinguishing between similar elements and not necessarily for describing
a sequence, either temporally, spatially, in ranking or in any other manner. It is
to be understood that the terms so used are interchangeable under appropriate circumstances
and that the embodiments of the invention described herein are capable of operation
in other sequences than described or illustrated herein.
[0033] It is to be noticed that the term "comprising", used in the claims, should not be
interpreted as being restricted to the means listed thereafter; it does not exclude
other elements or steps. It is thus to be interpreted as specifying the presence of
the stated features, integers, steps or components as referred to, but does not preclude
the presence or addition of one or more other features, integers, steps or components,
or groups thereof. Thus, the scope of the expression "a device comprising means A
and B" should not be limited to devices consisting only of components A and B. It
means that with respect to the present invention, the only relevant components of
the device are A and B.
[0034] Reference throughout this specification to "one embodiment" or "an embodiment" means
that a particular feature, structure or characteristic described in connection with
the embodiment is included in at least one embodiment of the present invention. Thus,
appearances of the phrases "in one embodiment" or "in an embodiment" in various places
throughout this specification are not necessarily all referring to the same embodiment,
but may. Furthermore, the particular features, structures or characteristics may be
combined in any suitable manner, as would be apparent to one of ordinary skill in
the art from this disclosure, in one or more embodiments.
[0035] Similarly it should be appreciated that in the description of exemplary embodiments
of the invention, various features of the invention are sometimes grouped together
in a single embodiment, figure, or description thereof for the purpose of streamlining
the disclosure and aiding in the understanding of one or more of the various inventive
aspects. This method of disclosure, however, is not to be interpreted as reflecting
an intention that the claimed invention requires more features than are expressly
recited in each claim. Rather, as the following claims reflect, inventive aspects
lie in less than all features of a single foregoing disclosed embodiment. Thus, the
claims following the detailed description are hereby expressly incorporated into this
detailed description, with each claim standing on its own as a separate embodiment
of this invention.
[0036] Furthermore, while some embodiments described herein include some but not other features
included in other embodiments, combinations of features of different embodiments are
meant to be within the scope of the invention, and form different embodiments, as
would be understood by those in the art. For example, in the following claims, any
of the claimed embodiments can be used in any combination.
[0037] It should be noted that the use of particular terminology when describing certain
features or aspects of the invention should not be taken to imply that the terminology
is being redefined herein to be restricted to include any specific characteristics
of the features or aspects of the invention with which that terminology is associated.
[0038] In the description provided herein, numerous specific details are set forth. However,
it is understood that embodiments of the invention may be practiced without these
specific details. In other instances, well-known methods, structures and techniques
have not been shown in detail in order not to obscure an understanding of this description.
[0039] The invention presents a device that facilitates the osseointegrated coupling of
a bone conduction device (BCD) to the skull of a patient. It is a major advantage
of the proposed device that it can be used even for children as young as 6 months
of age, i.e. as soon as a general anaesthesia can be applied. This is in great contrast
to the prior art solutions as indicated in the background section.
[0040] The device according to the invention comprises an osseointegration-enabled scaffold
plate, hereafter sometimes also referred to as 'scaffold plate' or just 'plate', provided
with a coupling abutment (further in this description also shortened to 'abutment')
for attaching a BCD (Fig.3a and 3b). A scaffold plate is a 3D matrix, for example
a metallic 3D lattice or mesh, that allows and stimulates the adhesion and proliferation
of osteoinducible cells on its surfaces.
[0041] The osseointegration-enabled scaffold plate and the abutment can in some embodiments
be manufactured as one integrated piece. In alternative embodiments they can be produced
as two or more pieces to be connected together with e.g. one or more screws or other
fixation means (Fig.4.).
[0042] The scaffold plate can have different shapes in different embodiments of the invention,
ranging for example from regular circular to oval or irregular, without however being
limited thereto. In advantageous embodiments the plate, preferably a metallic plate,
of the scaffold is ring shaped, for example as a circular or an elliptic ring. Such
embodiments were already illustrated in Fig.3. Such a ring provides the main stability,
strength, and fixation to the device.
[0043] The coupling abutment for attachment of a BCD is for example cylindrically or conically
shaped. Preferably the coupling abutment is positioned centrally on the scaffold plate.
However, excentric positions are also possible in other embodiments.
[0044] In some embodiments the coupling abutment will pierce the skin once placed, so allowing
for fixation of a BCD, for example a commercially available percutaneous BCD. In other
embodiments the abutment does not pierce the skin and allows for connecting an implantable
BCD with the vibrating part remaining under the skin.
[0045] The coupling abutment is in some embodiments so oriented that, when the device is
applied to a patient, the abutment is perpendicular to the skin surface. In that way
the abutment is also positioned perpendicular to the underlying bone so that collision
is avoided between the BCD and the patient's skull. However, in some patients it may
be more advantageous to deviate from a 90-degree angle between the osseointegration-enabled
scaffold plate and the axis of the coupling abutment. An inclination relative to the
X, Y or Z axis may then be applied.
[0046] The coupling abutment can in preferred embodiments have different lengths and shapes
making it suitable for connecting different percutaneous BCDs with the vibrating element
placed above the skin surface as well as implantable BCDs wherein the vibrating part
remains under the skin. The abutment is advantageously so shaped that the connecting
parts of commercially available bone conduction devices fit inside or around the coupling
abutment by means of fit geometry or threads. The abutment may have a length between
for example 1 and 15 millimetres. The abutment may be cylindrically or conically shaped.
In order to optimize the piercing through the skin and to minimize the risk of local
infections, a part of the abutment penetrating through the skin may be polished or
covered with other biocompatible materials, for example hydroxyapatite or other coatings
improving healing of the skin or preventing infection around the coupling abutment,
for example antibacterial or steroid releasing coatings.
[0047] The device according to the present invention is preferably made in titanium or tantalum.
Titanium and tantalum are preferred materials because of their strength and hardness.
Further they are easily osseointegrated with the bone in the form of a direct structural
and functional connection between living bone and the surface of a load-bearing artificial
implant that ensures increased mechanical stability of the implant. However, also
other metals or biocompatible materials can be applied.
[0048] In advantageous embodiments the plate of the device can be primarily attached to
the skull of the patient by means of screws, for example metallic or bioresorbable
screws. The osseointegration-enabled scaffold plate is then provided with a plurality
of screw holes, for example two or three or more screw holes. The screws hold the
device in place during the period of osseointegration. The screw holes may be counterbore
structures in certain embodiments. In other embodiments also other methods for fixation
to the patient's skull can be envisaged, for example by means of bone cement. The
screws can be positioned perpendicular to the bone structure or with an inclination
increasing the mechanical stability of the device.
[0049] Eventually the scaffold plate gets itself osseointegrated in the bone. In this way
the scaffold replaces the osseointegrating fixture applied in the prior art solutions
as discussed in the background section.
[0050] In order to obtain good osseointegration of the scaffold it is important to ensure
that the undersurface of the scaffold plate (i.e. the surface of the plate that faces
the skull of the patient), makes good and tight contact with the bone. In order to
achieve this the scaffold plate can in some embodiments of the device according to
the invention be custom made following the three-dimensional (3D) structure of the
skull bone. This can be achieved by means of a customised manufacturing, for example
based on a computer tomography (CT) scan or a cone-beam computer tomography (CBCT)
scan of the patient's skull with subsequent 3D reconstruction of the bone surface.
The CT or CBCT images of the patient, including the temporal and parietal region,
are collected to obtain a DICOM (Digital Imaging and Communications in Medicine) format
image data set. Using three-dimensional reconstruction software for 3D design, a 3D-model
of the patient is acquired from the DICOM format image data.
[0051] The data, e.g. the image data, concerning the design of the device may next be transformed
into 3D printable and machinable data.
[0052] The post-processing of the appliance may be performed by using a computer numerical
control centre or a numerically controlled milling machine, and manually drilling,
grinding and polishing. Additional surface treatments can be applied to the device,
to optimize for example the osseointegration, the soft tissue integration, sound conduction
and healing. This can contain, but is not limited to, an acid etching process, a specialized
coating, anodization or any other chemical/mechanical treatment.
[0053] In order to facilitate and shorten the process of osseointegration, the surface of
osseointegration-enabled scaffold plate having contact with the bone can be provided
with a lattice or mesh structure capable of inducing bone formation. Fig.5 provides
an example of such a mesh structure.
[0054] In advantageous embodiments the plate, e.g. metallic plate, comprises, for example
on its outer ring, one or more markings that facilitate the correct positioning of
the scaffold plate on the bone surface. The markers, for example arrows, can define
e.g. the top-down direction or point at the predefined landmarks (Fig.6).
[0055] In an embodiment of the device of the invention, the osseointegration-enabled scaffold
plate has a form of a disc, e.g. a circular or elliptic disc, with a flat, non-customized
undersurface. In order to obtain good and tight contact of the flat undersurface of
such scaffold plate with the bone, the bone has to be first flattened with a burr
in such embodiments. An advantage of this solution is that this type of scaffold is
suitable for different patients and avoids the necessity for customized 3D prints.
Additionally, due to its axial symmetry, such a 'ready-for-all' embodiment can be
positioned at all axial angles and does not require markers defining the directions
or pointing at the predefined landmarks.
[0056] In some embodiments the scaffold plate comprises two or more cut-outs with a connecting
part in between the cut-outs, as shown in Fig.7. In some embodiments the connecting
parts between the cut-outs may form the shape of a cross. Providing these cut-outs
is advantageous in that in such a way additional area for bone growth is created,
which may reduce the period of time required for the osseointegration. In Fig.7 an
embodiment with a separate coupling abutment is shown. Such abutment is fixed to the
osseointegration-enabled scaffold plate by a screw. As mentioned above the BCD can
fit inside or around the coupling abutment by means of fit geometry or threads.
[0057] In another embodiment the osseointegration-enabled scaffold plate is provided with
one or more extensions, as depicted in Fig.8. This increases the surface of the contact
with the bone, facilitates osseointegration and ensures increased strength of the
coupling to the bone. These extensions can be provided with additional screw holes
for the primary fixation. The different extensions do not necessarily have all the
same shape or size. The number and the size of these extensions can be defined on
basis of the preoperative CT or CBCT scans in such a way that optimal fixation points
relative to the patient's anatomy can be obtained.
[0058] An abutment for coupling a BCD can be attached to the scaffold plate or to the connecting
part between the cut-outs. As already mentioned above in certain embodiments this
abutment may be integrated with the connecting part of the plate or fixed to it with
for example a screw. In preferred embodiments the abutment is centrally positioned
on the connecting part. However, as mentioned above, excentric positions are also
possible in some embodiments.
[0059] In yet another embodiment, illustrated in Fig.9, the connecting parts in between
the cut-outs, lateral relating to the abutment, can be recessed or undercut in order
to facilitate the removal of the part of the device comprising the coupling abutment
in case a problem occurs. In this case there is no need for extensive drill-out of
the bone and removal of the whole already osseointegrated scaffold plate.
[0060] In another aspect the invention relates to kit of parts comprising a device for coupling
a bone conduction device as described above and fixation means for fixing of the osseointegration-enabled
scaffold plate to the bone as well as screw(s) for connecting of the coupling abutment
to the osseointegration-enabled scaffold plate.
[0061] While the invention has been illustrated and described in detail in the drawings
and foregoing description, such illustration and description are to be considered
illustrative or exemplary and not restrictive. The foregoing description details certain
embodiments of the invention. It will be appreciated, however, that no matter how
detailed the foregoing appears in text, the invention may be practiced in many ways.
The invention is not limited to the disclosed embodiments.
[0062] Other variations to the disclosed embodiments can be understood and effected by those
skilled in the art in practicing the claimed invention, from a study of the drawings,
the disclosure and the appended claims. In the claims, the word "comprising" does
not exclude other elements or steps, and the indefinite article "a" or "an" does not
exclude a plurality. A single processor or other unit may fulfil the functions of
several items recited in the claims. The mere fact that certain measures are recited
in mutually different dependent claims does not indicate that a combination of these
measures cannot be used to advantage. A computer program may be stored/distributed
on a suitable medium, such as an optical storage medium or a solid-state medium supplied
together with or as part of other hardware, but may also be distributed in other forms,
such as via the Internet or other wired or wireless telecommunication systems. Any
reference signs in the claims should not be construed as limiting the scope.
1. Device for coupling a bone conduction device, comprising a plate arranged for osseointegration
and a coupling abutment for attaching an acoustic bone conduction device to said plate.
2. Device for coupling as in claim 1, implemented in titanium or tantalum or in another
biocompatible material.
3. Device for coupling as in any of the previous claims, wherein said plate comprises
a plurality of screw holes for fixing said metallic plate.
4. Device for coupling as in any of the previous claims, wherein said plate comprises
at least one cut-out.
5. Device for coupling as in any of the previous claims, wherein said plate is ring shaped.
6. Device for coupling as in claim 5, wherein said plate is elliptic.
7. Device for coupling as in claim 5 or 6, wherein said plate comprises a transversal
connection whereon said coupling is provided.
8. Device for coupling as in any of the previous claims, wherein a surface of said plate
has a structure arranged for inducing bone formation and osseointegration.
9. Device for coupling as in claim 8, wherein said surface provided with said structure
is customized to the 3D anatomy of a patient's skull.
10. Device for coupling as in any of the previous claims, wherein said plate comprises
at least one position marker.
11. Device for coupling as in any of the previous claims, wherein a part of said coupling
abutment closest to said plate is polished.
12. Device for coupling as in any of the previous claims, wherein a part of said coupling
abutment closest to said plate is covered by hydroxyapatite.
13. Device for coupling as in any of the previous claims, wherein said plate comprises
one or more extensions.
14. Kit of parts comprising a device for coupling as in any of the previous claims and
fixing means for fixating an acoustic bone conduction device to said plate of said
device.
15. Kit of parts as in claim 14, wherein said fixing means comprises metallic screws or
bioresorbable screws or bone cement.