U.S. patent application number 12/177091 was filed with the patent office on 2009-03-26 for coupling apparatus for a bone anchored hearing device.
This patent application is currently assigned to COCHLEAR LIMITED. Invention is credited to Peter Elmberg, Erik Holgersson, Lars Jinton.
Application Number | 20090082817 12/177091 |
Document ID | / |
Family ID | 40265117 |
Filed Date | 2009-03-26 |
United States Patent
Application |
20090082817 |
Kind Code |
A1 |
Jinton; Lars ; et
al. |
March 26, 2009 |
COUPLING APPARATUS FOR A BONE ANCHORED HEARING DEVICE
Abstract
A coupling apparatus for a bone anchored hearing device for
anchoring hearing aid devices or extra-oral prostheses in the form
of ear and orbital prostheses in the skull bone. The apparatus
comprises a screw-shaped anchoring fixture configured to be
inserted into the skull bone and a skin-penetrating abutment
coupled to the fixture by a screw connection. The fixture comprises
a main body with an external screw thread and a flange having a
substantially planar bottom surface. The flange is configured to
stop the anchoring element from penetrating through the skull bone.
The skin-penetrating abutment comprises a substantially conical
outer surface. The upper end surface of the fixture is designed
with an open cavity with a tapered inner contour forming a seat for
the bottom part of the abutment. The bottom part of the abutment is
configured to create a good connecting fit between the fixture and
abutment.
Inventors: |
Jinton; Lars; (Molndal,
SE) ; Holgersson; Erik; (Gothenburg, SE) ;
Elmberg; Peter; (Kallered, SE) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W., SUITE 1100
WASHINGTON
DC
20006
US
|
Assignee: |
COCHLEAR LIMITED
Lane Cove
AU
|
Family ID: |
40265117 |
Appl. No.: |
12/177091 |
Filed: |
July 21, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60951169 |
Jul 20, 2007 |
|
|
|
60951163 |
Jul 20, 2007 |
|
|
|
Current U.S.
Class: |
606/301 ;
606/305; 606/308 |
Current CPC
Class: |
H04R 25/606 20130101;
A61C 8/0066 20130101; A61C 8/0069 20130101; A61C 8/0025 20130101;
H04R 2460/13 20130101; A61B 17/8615 20130101; A61B 17/863
20130101 |
Class at
Publication: |
606/301 ;
606/305; 606/308 |
International
Class: |
A61B 17/04 20060101
A61B017/04 |
Claims
1. A coupling apparatus for anchorage of a prosthesis to a
patient's skull bone, comprising: an elongate anchoring fixture
comprising an external screw thread for penetrating the bone, and a
flange that abuts the bone when the fixture is implanted, wherein a
proximate end of the fixture has an open cavity with a tapered
interior contour; and a skin-penetrating abutment detachably
connectable to said fixture comprising a substantially conical
exterior surface having a tapered exterior contour that fits within
the tapered interior contour of the open cavity.
2. The coupling apparatus of claim 1, wherein said prosthesis is a
hearing prosthesis.
3. The coupling apparatus of claim 1, wherein the flange has a
width that is greater than a peak diameter of the external screw
threads.
4. The coupling apparatus of claim 3, wherein the width of the
flange exceeds the peak diameter of the external screw threads by
about 10-20%.
5. The coupling apparatus of claim 1, wherein the flange comprises
a flared external top portion and a cylindrical portion adjacent to
the flared external top portion.
6. The coupling apparatus of claim 1, wherein the abutment sleeve
further comprises an upper end and an inner annular flange disposed
within the upper end.
7. The coupling apparatus of claim 1, wherein the elongate
anchoring fixture further comprises an elongate coupling shaft to
securely couple the elongate anchoring fixture and the
skin-penetrating abutment.
8. The coupling apparatus of claim 7, wherein the elongate coupling
shaft comprises a screw head.
9. The coupling apparatus of claim 8, wherein the screw head
comprises an internal hex or multi-lobular configuration for a
cooperating insertion tool.
10. The coupling apparatus of claim 9, wherein the screw head has
an external hex geometry and a bore with an internal screw
head.
11. The coupling apparatus of claim 9, wherein the screw head has
an external thread and a bore with an internal unigrip
configuration.
12. The coupling apparatus of claim 8, wherein the abutment sleeve
further comprises an internal shoulder having a central opening for
the elongate coupling shaft.
13. A coupling apparatus for a bone anchored prosthesis comprising:
a bone anchor fixture comprising an outer screw thread and a flange
having a flared outer top surface and a bottom portion configured
to prevent the bone anchor fixture from penetrating through the
bone; and an abutment sleeve coupled to the bone anchor fixture
comprising a tapered outer surface adjacent to the flared outer top
surface of the flange; wherein the flared outer top surface of the
bone anchor fixture and the tapered outer surface of the abutment
sleeve define an outer contour having a substantially hourglass
shape having a waist and a waist angle.
14. The coupling apparatus of claim 13, wherein the outer contour
is substantially smooth.
15. The coupling apparatus of claim 13, wherein the waist angle is
greater than 90.degree..
16. The coupling apparatus of claim 13, wherein the abutment sleeve
is coated with a material to reduce the shear modulus.
17. The coupling apparatus of claim 16, wherein the material is
selected from the group consisting of: a biocompatible polymer, a
ceramic material, and a combination thereof.
18. The coupling apparatus of claim 17, wherein the material has a
thickness of about 0.001 .mu.m to about 50.0 .mu.m.
19. The coupling apparatus of claim 17, wherein the shear modulus
is reduced to less than 35 GPa.
20. The coupling apparatus of claim 13, wherein the abutment sleeve
is coated with a surface increasing material.
21. The coupling apparatus of claim 20, wherein the surface
increasing material provides a roughness value of about 0.5 .mu.m
to about 10 .mu.m.
22. A coupling apparatus for a bone anchored prosthesis comprising:
a bone anchor fixture comprising an outer screw thread and a flange
having an open cavity and tapered inner side walls disposed within
the open cavity; and an abutment sleeve comprising a tapered outer
surface configured to be seated within the tapered inner side walls
of the bone anchor fixture.
23. The coupling apparatus of claim 22, wherein the tapered inner
side walls of the bone anchor fixture and the tapered outer surface
of the abutment sleeve have first and second cone angles,
respectively.
24. The coupling apparatus of claim 23, wherein the first and
second cone angles are identical.
25. The coupling apparatus of claim 23, wherein the first and cone
angles have a difference of about 1.degree. to about 5.degree..
26. The coupling apparatus of claim 23, wherein the first and
second cone angles are in the range of about 30.degree. to about
40.degree. relative to a vertical axis.
27. A healing cap for use with a coupling apparatus for a bone
anchored prosthesis comprising: a platform comprising a central
opening and one or more protruding members configured to removably
attach the healing cap to coupling apparatus; a cap for the central
opening; and a flexible band connecting the platform and the
cap.
28. The healing cap of claim 27, wherein the one or more protruding
members are provided around the central opening to define an
annular space.
29. The healing cap of claim 28, wherein the cap further comprises
a lower, cylindrical sleeve-shaped portion configured to be
inserted into the annular space.
30. A coupling apparatus for a bone anchored prosthesis comprising:
bone anchor means comprising a screw means configured to be
installed into the bone and a flange means configured to prevent
the screw means from penetrating through the bone; abutment means
coupled to the bone anchor means for penetrating the skin; and
coupling means for securely and removably coupling the bone anchor
means and the abutment means.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/951,169, entitled "Coupling Apparatus for a Bone
Anchored Hearing Device," filed Jul. 20, 2007 and U.S. Provisional
Application No. 60/951,163, entitled "Bone Anchor Fixture for a
Medical Prosthesis," filed Jul. 20, 2007. These applications are
hereby incorporated by reference herein.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates generally to hearing devices
and, more particularly, to a coupling apparatus for bone anchored
hearing devices.
[0004] 2. Related Art
[0005] For persons who cannot benefit from traditional, air
conduction hearing aids there are other types of hearing aids on
the market commonly referred to as bone anchored hearing aids. Bone
anchored hearing aids mechanically transmit sound information to a
person's inner ear via the skull bone by means of a vibrator. Such
hearing aid devices are typically connected to a percutaneous
implant in the form of a titanium screw implanted in the skull bone
behind the external ear so that sound is transmitted via the skull
bone to the cochlea (inner ear). This enables the hearing aid to be
effective regardless of whether there is disease or damage in the
middle ear. Moreover, penetration of the skin makes the vibratory
transmission very efficient.
[0006] Bone anchored hearing aids were initially developed to
rehabilitate certain types of hearing-impaired patients. They may
also be utilized for other indications such as stuttering and for
certain non-medical applications. A bone anchored hearing aid may
be connected to an implant by means of a bayonet coupling, a
snap-in coupling, a magnetic coupling or the like. One example of
this type of hearing aid device is the BAHA.RTM. bone anchored
hearing aid, described in U.S. Pat. No. 4,498,461 and commercially
available from Cochlear Bone Anchored Solutions AB (previously
Entific Medical Systems AB) in Goteborg, Sweden.
[0007] Typically, the implant connecting the hearing aid to the
skull generally comprises two components: a bone attachment piece
that is attached or implanted directly into the skull bone and a
skin penetrating piece coupled to the bone attachment piece. This
two-piece design facilitates the installation of the implant in two
sequential steps. In the first step, the bone attachment piece is
installed into the skull and the surrounding tissue is allowed to
heal for a period of time that may last up to a few months. In the
second step, the skin penetrating piece is coupled to the bone
attachment piece. In the event that the skin penetrating piece
becomes damaged, it may be replaced without removing the anchoring
fixture from the skull. Moreover, this permits the hearing aid to
be changed or upgraded, if necessary, without removing the bone
attachment piece from the skull.
[0008] A well-known problem with many of these conventional
percutaneous implants is the increased risk of infections and
inflammation that results from bacterial colonization in the area
surrounding the skin-implant interface. Oftentimes, unwanted
pockets and gaps are formed between the skin and the implant. In
conventional implants such gaps are dimensioned so as to provide an
ideal environment for bacterial growth, inflammation and infection
in the tissue surrounding the implant.
[0009] Another problem with these conventional percutaneous
implants is the risk of micro-leakage and bacterial colonization
from gaps formed between the two components. Such gaps result from
insufficient connection between bone attachment piece and the skin
penetrating piece, imperfections in the contact surfaces of the two
components, incorrect tightening torque, or a combination of the
foregoing factors.
SUMMARY
[0010] In one embodiment, a coupling apparatus for anchorage of a
prosthesis to a patient's skull bone is disclosed. The coupling
apparatus comprises an elongate anchoring fixture comprising an
external screw thread for penetrating the bone, and a flange that
abuts the bone when the fixture is implanted. The fixture has a
proximate end having an open cavity with a tapered interior
contour. The skin-penetrating abutment is detachably connectable to
the fixture and comprises a substantially conical exterior surface
with a wider proximate region and a narrower distal region having a
tapered exterior contour that fits within said tapered interior
contour of the open cavity.
[0011] In another embodiment, a coupling apparatus for a bone
anchored prosthesis is disclosed. The coupling apparatus comprises
a bone anchor fixture and an abutment sleeve coupled to the bone
anchor fixture. The bone anchor fixture comprising an outer screw
thread and a flange. The flange has a flared outer top surface and
a bottom portion configured to prevent the bone anchor fixture from
penetrating through the bone. The abutment sleeve is coupled to the
bone anchor fixture and comprises a tapered outer surface adjacent
to the flared outer top surface of the flange. The flared outer top
surface of the bone anchor fixture and the tapered outer surface of
the abutment sleeve define an outer contour having a substantially
hourglass shape having a waist and a waist angle.
[0012] In yet another embodiment, a coupling apparatus for a bone
anchored prosthesis is disclosed. The coupling apparatus comprises
a bone anchor fixture comprising an outer screw thread and a flange
having an open cavity and tapered inner side walls disposed within
the open cavity. The coupling apparatus further comprises an
abutment sleeve comprising a tapered outer surface configured to be
seated within the tapered inner side walls of the bone anchor
fixture.
[0013] In a further embodiment, a healing cap for use with a
coupling apparatus for a bone anchored prosthesis is disclosed. The
healing cap comprises a platform having a central opening and one
or more protruding members configured to removably attach the
healing cap to coupling apparatus. A cap is provided for the
central opening of the platform and a flexible band connects the
platform and the cap.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Embodiments of the present invention are described herein
with reference to the attached drawing sheets in which:
[0015] FIG. 1 is a perspective view of the coupling apparatus in
accordance with one embodiment of the coupling apparatus;
[0016] FIG. 2 is a side view of the embodiment of the coupling
apparatus illustrated in FIG. 1;
[0017] FIG. 3 is a cross-sectional side view of the embodiment of
the coupling apparatus illustrated in FIG. 1;
[0018] FIG. 4 is a partial view of a proximate end of the fixture
illustrating the tapered connection between the fixture and the
abutment components of the coupling apparatus illustrated in FIG.
1, in accordance with one embodiment of the coupling apparatus;
[0019] FIG. 5 is a perspective view of one embodiment of an
elongate coupling shaft having a screw head with an external hex
and a bore with an internal screw thread;
[0020] FIG. 6A is a side view of a healing cap with the coupling
apparatus illustrated in FIG. 1, with the healing cap in a closed
orientation;
[0021] FIG. 6B is a perspective view of the healing cap illustrated
in FIG. 6A;
[0022] FIG. 7A is a side view of the healing cap illustrated in
FIGS. 6A and 6B, with the healing cap in an open orientation;
and
[0023] FIG. 7B is a perspective view of the healing cap illustrated
in FIG. 7A.
DETAILED DESCRIPTION
[0024] Aspects and exemplary embodiments of the invention disclosed
herein are generally directed to a bone anchored coupling apparatus
in which the surfaces of an implanted fixture component and an
associated abutment component are configured so as to reduce gaps
thereby minimizing undesirable micro-leakage, preferably regardless
of any imperfections in the mating surfaces and a range of
tightening torques.
[0025] In certain embodiments, the coupling apparatus has a smooth
outer contour facing the surrounding soft tissue to minimize
unwanted pockets or gaps in the tissue-device interface. In
particular embodiments, the regions of the fixture and the abutment
components which mate with each other have inverse conically-shaped
regions such that, when mated, the fixture forms the bottom of an
hourglass shape while the abutment forms the top of the hourglass
shape. Preferably, the dimensions of the hourglass configuration
are such that the patient's skin abuts the narrow region of the
hourglass configuration.
[0026] In certain embodiments, the upper end surface of the fixture
has an open cavity with a tapered interior surface forming a seat
for the tapered exterior side wall of the abutment. This preferably
creates a good connecting fit between the fixture and abutment so
as to reduce the risk of micro-leakage.
[0027] A well known problem with percutaneous implants is infection
and inflammation at the skin-implant interface resulting from
bacterial colonization in the area around the interface. The
coupling apparatus disclosed herein increases the integration of
the skin to the coupling apparatus thereby decreasing the
likelihood that a gap will form between the two. Such gaps are,
unfortunately, an ideal environment for the bacteria. By creating
an integration of the skin to the coupling apparatus the adverse
skin reactions associated with bone anchored percutaneous implants
may be reduced.
[0028] Integration between the skin and the implant occurs when the
soft tissue encapsulates the implant in fibrous tissue and does not
readily dissociate itself from the implant. U.S. Provisional Patent
Application No. 60/951,163, entitled "Bone Anchor Fixture for a
Medical Prosthesis", filed Jul. 20, 2007, discloses a surface
modification which reduces certain adverse skin reactions, and
which may be implemented in embodiments of the present invention.
In other embodiments the abutment sleeve is coated to reduce the
shear modulus, as described in greater detail below.
[0029] Embodiments of the coupling apparatus may be used in
connection with hearing aid devices of the bone conduction type,
that is, hearing aid devices by which the sound is transmitted via
the skull bone directly to the inner ear of a person with impaired
hearing. However, embodiments of the coupling apparatus may also be
configured for use in connection with other types of hearing aid
devices anchored in the skull bone and for ear or orbital
prostheses which are also anchored in the skull bone. Other
applications of the coupling apparatus are also contemplated.
[0030] Embodiments of the bone anchored coupling apparatus will be
described below with reference to the accompanying drawings. FIG. 1
is a perspective view of a bone anchored coupling apparatus 30
according to one embodiment. Coupling apparatus 30 is illustrated
in FIG. 1 with a screw-shaped bone anchor fixture 1 and a
skin-penetrating abutment sleeve 2. The two components are
connected by an elongate coupling shaft or an abutment screw 3
having, in one embodiment, a cylindrical screw head 4. Screw head 4
has an internal hex or multi-lobular configuration 5 for a
cooperating insertion tool, which is not part of the invention and
therefore not illustrated here.
[0031] In an alternate embodiment depicted in FIG. 5, a coupling
shaft 3 is illustrated as having a screw head 4 with an external
hex geometry 29A and a bore with an internal screw thread 30. The
external hex geometry 29A may be used for the screw tightening and
the internal screw thread 30 may be used for connecting measuring
probes or the like for controlling purposes, such as a Resonance
Frequency Analyzer (RFA) probe for measuring implant stability and
osseointegration. In one embodiment, an M 1.6 screw is used. In
combination with the conical fit between the fixture 1 and the
abutment sleeve 2, the M 1.6 screw provides sufficient torque to
secure the assembly and improved elastic deformation of the screw.
This reduces the likelihood of the coupling assembly 30 become
disassembled or unscrewed.
[0032] In the alternative embodiments, rather than external hex
geometry 29A, screw head 4 has outer threads and an internal
ungrip. Such an embodiment may be suitable for connecting certain
RFA probes.
[0033] Fixture 1 may be made of any material that has a known
ability to integrate into surrounding bone tissue, a phenomenon
commonly referred to as osseointegration. In one embodiment,
fixture 1 is made of titanium. Fixture 1 has a main body with an
outer screw thread 6 which is intended to be installed into the
skull bone. Fixture 1 also comprises a flange 7 configured to
function as a stop when fixture 1 is installed into the skull bone.
Flange 7 prevents the screw thread 6 from completely penetrating
through the skull bone. Fixture 1 may further comprise a
tool-engaging socket having an internal grip section (now shown)
for easy lifting and handling of fixture 1. Tool-engaging socket
and the internal grip section are described and illustrated in
co-pending U.S. Provisional Application No. 60/951,163, entitled
"Bone Anchor Fixture for a Medical Prosthesis," filed Jul. 20,
2007, which is hereby incorporated by reference herein.
[0034] The main body of fixture 1 has a length sufficient to
securely anchor the fixture 1 into, without penetrating entirely
through, the skull bone. The length of the main body may therefore
depend on the thickness of the skull bone at the implantation site.
In one embodiment the main body has a length that is no greater
than 5 mm, measured from the planar bottom surface 10 of the flange
7 to the end of the distal region 1B. In another embodiment, the
length of the main body is from about 3.0 mm to about 5.0 mm.
[0035] In the embodiment depicted in FIGS. 1-3, the main body has a
tapered apical proximate end 1A, a straight, generally cylindrical
body, and a screw thread 6. The distal region 1B of fixture 1 is
fitted with three self-tapping cutting edges 8 formed into the
exterior surface of the fixture. Further details of the
self-tapping features are described in International Patent
Application WO 02/09622, which is hereby incorporated by reference
herein.
[0036] A clearance or relief surface 9 may be provided adjacent to
the self-tapping cutting edges 8. This design is advantageous
because it reduces the squeezing effect between the fixture 1 and
the bone during installation of the screw by creating more volume
for the cut-off bone chips.
[0037] As more clearly illustrated in FIGS. 2 and 3, flange 7 has a
planar bottom surface 10 for resting against the outer bone
surface, indicated by 11 in FIG. 2, when anchoring fixture 1 has
been screwed down into the skull bone. Again, flange 7 prevents the
fixture 1 from completely penetrating through the skull bone.
Preferably, flange 7 has a diameter which exceeds the peak diameter
of the screw threads 6. In one embodiment, the diameter of the
flange 7 exceeds the peak diameter of the screw threads 6 by
approximately 10-20%. Although flange 7 is illustrated in FIGS. 1-5
as being circumferential, flange 7 may be configured in a variety
of shapes so long as flange 7 has a diameter or width that is
greater than the peak diameter of the screw threads 6. Also, the
size of flange 7 may vary depending on the particular application
for which the coupling apparatus 30 is intended.
[0038] The outer peripheral surface 36 of flange 7 has a
cylindrical part 12 and a flared top portion 13. Upper end 7A of
flange 7 is designed with an open cavity 14A having a tapered inner
side wall 14. The tapered inner side wall 14 is adjacent to the
grip section (not shown). The interior of the flange 7 further
includes an inner bottom bore 15 having internal screw threads for
securing a coupling shaft 3.
[0039] In one embodiment, increased stability to the coupling
between fixture 1 and abutment sleeve 2 is provided by having the
length of the open cavity 14A extends from flange 7 to the distal
region 1B of fixture 1. Tapered inner side wall 14 forms a seat for
abutment sleeve 2 to create a good connecting fit between the
fixture 1 and abutment sleeve 2. As shown in FIG. 4, a cone angle
33 is defined by the tapered interior contour 14 relative to a
vertical axis. In one embodiment, the cone angle 33 may be in the
range of approximately 30-40 degrees.
[0040] In the embodiments illustrated in the figures, the flange 7
has a smooth, open upper end 7A and does not have a protruding hex.
The smooth upper end 7A of the flange 7 and the absence of any
sharp corners provides for improved soft tissue adaptation. Flange
7 also comprises a cylindrical part 12 which, together with the
flared upper part 13, provides sufficient height 34 in the
longitudinal direction for internal connection with the abutment
sleeve 2. FIG. 4 illustrates the tapered seat 14 seated within the
height 34 of flange 7.
[0041] The skin penetrating part of the implant includes the
abutment sleeve 2. In one embodiment, abutment sleeve 2 has an
inner annular flange 16 at its upper edge 17A configured to
cooperate with other components (not shown) by means of snap-in
connection or the like. Abutment sleeve 2 has an internal shoulder
18 with a central opening for a connecting shaft or coupling shaft
3 and a number of peripherally arranged through holes or recesses
19 used for a tool such as that illustrated in WO 2004/105650,
which is hereby incorporated by reference herein.
[0042] It should be appreciated that the fixture 1, abutment sleeve
2 and coupling shaft 3, may be delivered separately or they may be
delivered in the form of a pre-mounted device as illustrated in WO
2004/105650. In accordance with one embodiment, the coupling
apparatus 30 is delivered to the surgeon pre-mounted in its package
to facilitate installation of the entire device in a single step.
Abutment sleeve 2 may be pre-mounted to the fixture 1 at the
manufacturing site with the correct tightening torque to obviate
the need for the surgeon to know the correct tightening torque or
to handle the separate pieces of the coupling apparatus 30.
[0043] In contrast to traditional implants which require an outer
fixture hex for tool engagement, the coupling apparatus 30 may be
installed by using the recesses 19 in the abutment sleeve 2. These
recesses 19 are located on the upper part of the coupling apparatus
30 and are more visible than a traditional outer hex.
[0044] According to the embodiment shown in FIG. 3, the abutment
sleeve 2 has a substantially curved, conical outer surface with an
upper edge 17A and a bottom, fixture-connecting part 17B. The upper
edge 17A may have a width or diameter that is larger than that of
the bottom, fixture connecting part 17B. The bottom part 17B of the
outer surface has a contour 20 adapted to be seated with the
tapered inner contour 14 of the fixture to create a good connecting
fit between the fixture 1 and abutment sleeve 2. The two conical
shaped surfaces not only provides an axially well-defined fit when
assembled together, they also provides for easy disassembly.
[0045] It would be desirable to reduce the risk for micro-leakage
from the coupling apparatus 30. Designing the upper part of the
fixture 1 and the lower part of the abutment sleeve 2 with a
conical fit reduces the risk for gaps and unwanted micro-leakage,
regardless of any imperfections in the contact surfaces or
incorrect tightening torques.
[0046] As shown in FIG. 4, the tapered portion 20 of the abutment
sleeve 2 is characterized by a cone angle 32. The cone angle 32 is
configured so as to securely couple the fixture 1 and the abutment
sleeve 2 without significant gaps. Preferably, the cone angles 32
and 33 are in the range of about 30.degree. to about 40.degree.,
with little or no difference between the cone angles 32 and 33. In
one embodiment, the cone angles 32 and 33 are substantially the
same. In another embodiment, the difference between the cone angles
32 and 33 is about 1.degree. to about 5.degree., and more
preferably about 1.degree..
[0047] It would also be desirable to reduce the risk of infections
and inflammation that results from bacterial colonization in the
unwanted pockets and gaps that are formed between the skin and the
implant. As illustrated in FIG. 2, an hourglass waist angle 38 is
generally defined between the exterior peripheral surface 36 of
flared portion 13 of flange 7 and the tapered lower portion 20 of
abutment sleeve 2. The hourglass waist angle 38 provides a smooth
outer contour to the facing soft tissue such that unwanted pockets
and gaps are not formed between the surrounding tissue and the
coupling apparatus 30. This smooth contour facilitates integration
between the coupling apparatus 30 and the surrounding tissue to
substantially eliminate gaps and unwanted pockets where bacteria
might grow. This is in contrast to many traditional implant devices
in which a comparatively sharp interface is formed with the
contacting tissue. The embodiment depicted in FIG. 2 show an
hourglass waist angle is greater than 90.degree..
[0048] In certain embodiments, the skin-contacting surface of
abutment sleeve 2 may be modified in such a way that the shear
modulus of the skin-contacting part of abutment sleeve 2 is reduced
to less than 35 GPa. The surface of the skin-contacting part of the
percutaneous implant abutment sleeve 2 may be coated with a
biocompatible polymer or a ceramic material. In accordance with one
aspect of the embodiments, the coating has a thickness of
approximately 0.001-50.0 .mu.m. A surface increasing treatment may
be provided resulting in a roughness value S.sub.a of 0.5-10 .mu.m
in place of or in addition to the coating. These modifications to
the skin-contact surface generally reduce the shear modulus and
certain adverse skin reactions. Surface modifications of this type
are discussed in more detail in the co-pending patent application
incorporated by reference elsewhere herein.
[0049] In certain embodiments, the abutment sleeve is coated with a
material to reduce the shear modulus. Such a material may be, for
example, a biocompatible polymer, a ceramic material, and/or a
combination thereof. In one specific embodiment, the material has a
thickness of about 0.001 .mu.m to about 50.0 .mu.m. In the same or
other embodiments, the shear modulus is reduced to less than 35
GPa. In the same or other embodiments, the abutment sleeve is
coated with a surface increasing material. Such a material may be
such that it provides a roughness value of about 0.5 .mu.m to about
10 .mu.m. Further details of the above and other features may be
found in Swedish Patent Application No. 0701244-6, which is hereby
incorporated by reference herein.
[0050] The coupling apparatus 30 may also be designed in such a way
that it is easy to handle together with instruments and components
used for installation and control of the implant device. As noted,
surgical techniques normally used for installing the implants have
been carried out as a two-step procedure. In the first step the
implant is inserted and maintained unloaded during a healing period
of about a couple of months. During this healing period it is
important to avoid micro-leakage from the coupling apparatus and
bacteria colonization.
[0051] FIGS. 6-7 depict a healing cap 37 that may be used in
connection with the coupling apparatus 30. As illustrated in FIGS.
6-7, the healing cap 37 comprises a snap-in platform 24, a cap 22,
and a flexible band 23 connecting the snap-in platform 24 and the
cap 22. This design makes it easy and safe for the surgeon to
handle.
[0052] Snap-in platform 24 includes a central through opening 25
and a lower, central protruding portion 26 with a number of
protruding, flexible members 27 arranged to cooperate with said
inner annular flange 16 on the abutment sleeve 2. Cap 22 comprises
a lower, cylindrical sleeve-shaped portion 28 arranged to be
inserted into the annular spacing formed between the flexible
members 27 and the protruding screw head 4 of the coupling shaft 3.
Cap 22 provides a closure for the through hole in the abutment
sleeve 2 as well as a locking member for snap-in platform 24.
Healing cap 37 is preferably made of a plastic material.
[0053] FIGS. 6-7 depict the sleeve-shaped portion 28 having a
cylindrical shape. It is understood, however, that the
sleeve-shaped portion 28 may have any other shape, such as a
squared, rectangular, rounded or polygonal shape, depending on the
connecting parts.
[0054] The entire implant device--including fixture 1, abutment
sleeve 2, abutment screw 3 and healing cap 37 (discussed
below)--may be installed in a single session followed by a healing
period, instead of the traditional multi-step procedure in which
the fixture is separately installed and followed by a healing
period before the remaining parts, the abutment sleeve, abutment
screw and healing cap, are installed.
[0055] Further features and advantages of the present invention may
be found in U.S. Provisional Application No. 60/951,169, entitled
"Coupling Apparatus For a Bone Anchored Hearing Device," and filed
Jul. 20, 2007, and U.S. Provisional Application No. 60/951,163,
entitled "Bone Anchor Fixture for a Medical Prosthesis," and filed
Jul. 20, 2007, which are hereby incorporated by reference
herein.
[0056] The invention described and claimed herein is not to be
limited in scope by the specific preferred embodiments herein
disclosed, since these embodiments are intended as illustrations,
and not limitations, of several aspects of the invention. Any
equivalent embodiments are intended to be within the scope of this
invention. Indeed, various modifications of the invention in
addition to those shown and described herein will become apparent
to those skilled in the art from the foregoing description. Such
modifications are also intended to fall within the scope of the
appended claims.
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