U.S. patent application number 11/401727 was filed with the patent office on 2007-10-11 for acetabular cup conversion ring.
Invention is credited to Richard A. Berger, Erin M. Johnson, Archie W. Newsome, Randy L. Schlemmer.
Application Number | 20070239283 11/401727 |
Document ID | / |
Family ID | 38330460 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070239283 |
Kind Code |
A1 |
Berger; Richard A. ; et
al. |
October 11, 2007 |
Acetabular cup conversion ring
Abstract
An acetabular implant for hip replacement surgery includes a
shell component and first and second alternative bearing components
interchangeably engageable with the shell component to provide a
choice in bearing materials. The shell component has an engagement
mechanism suitable for locking engagement with the first
alternative shell component. A conversion ring is lockingly
engageable with the shell component to adapt the shell component to
provide an engagement mechanism suitable for locking engagement
with the second alternative shell component.
Inventors: |
Berger; Richard A.;
(Chicago, IL) ; Johnson; Erin M.; (Columbia City,
IN) ; Newsome; Archie W.; (Mentone, IN) ;
Schlemmer; Randy L.; (Bremen, IN) |
Correspondence
Address: |
John F. Hoffman, Esq.;BAKER & DANIELS LLP
Suite 800
111 East Wayne Street
Fort Wayne
IN
46802
US
|
Family ID: |
38330460 |
Appl. No.: |
11/401727 |
Filed: |
April 11, 2006 |
Current U.S.
Class: |
623/22.29 |
Current CPC
Class: |
A61F 2/30721 20130101;
A61F 2002/30378 20130101; A61F 2002/30024 20130101; A61F 2002/30607
20130101; A61F 2002/30616 20130101; A61F 2250/0036 20130101; A61F
2002/30827 20130101; A61F 2002/305 20130101; A61F 2220/0025
20130101; A61F 2002/3069 20130101; A61F 2310/00179 20130101; A61F
2220/0033 20130101; A61F 2002/3241 20130101; A61F 2002/30822
20130101; A61F 2002/30324 20130101; A61F 2002/30405 20130101; A61F
2002/30881 20130101; A61F 2002/30026 20130101; A61F 2002/30614
20130101; A61F 2/34 20130101; A61F 2310/00011 20130101; A61F
2002/30593 20130101; A61F 2002/30891 20130101; A61F 2002/30474
20130101; A61F 2002/30014 20130101; A61F 2250/0018 20130101; A61F
2002/30604 20130101; A61F 2250/0021 20130101; A61F 2002/4641
20130101; A61F 2002/30016 20130101; A61F 2002/30332 20130101; A61F
2002/30487 20130101; A61F 2002/30136 20130101; A61F 2250/0019
20130101; A61F 2002/30594 20130101; A61F 2230/0004 20130101; A61F
2002/30495 20130101; A61F 2250/0062 20130101 |
Class at
Publication: |
623/022.29 |
International
Class: |
A61F 2/34 20060101
A61F002/34 |
Claims
1. A conversion ring for converting an acetabular shell component
engagement mechanism from a first engagement mechanism engageable
with a first alternative bearing component to a second engagement
mechanism engageable with a second alternative bearing component,
the conversion ring comprising: a ring shaped body having a
sidewall defining an outer surface and an inner surface and
extending axially from a first end to a second end; a first
engagement mechanism formed on the outer surface, the first
engagement mechanism of the conversion ring being releasably
engageable with the first engagement mechanism of the acetabular
shell component in axial locking arrangement; and a second
engagement mechanism formed on the inner surface, the second
engagement mechanism of the conversion ring being releasably
engageable with the second engagement mechanism of the second
alternative bearing component in axial locking arrangement, the
first and second engagement mechanisms being of different types
selected from the group consisting of snap-fit, press-fit,
taper-fit, and threaded-fit engagement mechanisms.
2. The conversion ring of claim 1 wherein the first engagement
mechanism comprises a snap-fit and the second engagement mechanism
comprises a taper-fit.
3. The conversion ring of claim 2 wherein the first engagement
mechanism comprises a plurality of annular projections formed on
the outer surface of the body.
4. The conversion ring of claim 2 wherein a portion of the sidewall
is slit to allow the conversion ring to resiliently compress and
expand.
5. The conversion ring of claim 4 wherein the sidewall includes
multiple slits extending part-way through the sidewall between the
first and second ends, adjacent slits alternately originating from
the first and second ends to form the sidewall into a serpentine
sidewall.
6. The conversion ring of claim 1 wherein the conversion ring is
provided in a plurality of configurations each configured to adapt
the shell component to receive a differently configured second
alternative bearing component.
7. The conversion ring of claim 1 wherein the first end defines a
first opening and the second end defines a second opening, the
first opening being able to receive the alternative bearing
component and the second opening permitting the alternative bearing
component to project through the body.
8. A kit of acetabular components for assembling an acetabular
joint prosthesis including a shell component and a bearing
component disposed in the shell, the kit comprising: a shell
component having an external surface shaped for engagement with an
acetabulum and an internal cavity, the cavity including a first
engagement mechanism; a first bearing component having an external
surface, the external surface defining a complimentary first
engagement mechanism engageable with the first engagement mechanism
of the shell component, a conversion ring having a sidewall
defining an outer surface and an inner surface and extending
axially from a first end to a second end, the outer surface
defining a complimentary first engagement mechanism releasably
engageable with the first engagement mechanism of the shell
component, the inner surface defining a second engagement
mechanism; a second bearing component having an external surface,
the external surface defining a complimentary second engagement
mechanism releasably engageable with the second engagement
mechanism of the conversion ring, such that the conversion ring is
insertable into the shell component to convert the shell component
from the first engagement mechanism to the second engagement
mechanism, the first and second engagement mechanisms being of
different types selected from the group consisting of snap-fit,
press-fit, taper-fit, and threaded-fit engagement mechanisms.
9. The kit of claim 8 wherein the first engagement mechanism
comprises a snap-fit and the first bearing component and the
conversion ring each include an external surface having a
relatively resilient portion for snapping into the shell
component.
10. The kit of claim 9 wherein the second engagement mechanism
comprises a taper-fit and the inner surface of the conversion ring
defines a tapered surface such that the ring is intraoperatively
engageable with the shell to convert the shell from a snap-fit to a
taper-fit engagement mechanism.
11. The kit of claim 10 wherein the snap-fit mechanism comprises an
annular projection formed on each of the first liner and conversion
ring and an annular groove formed in the shell.
12. The kit of claim 11 wherein the snap-fit mechanism comprises
first and second annular grooves formed in the shell, the grooves
being spaced apart axially with the second annular groove being
further into the shell than the first annular groove, the first
bearing component comprising an annular projection engageable with
the first annular groove and the conversion ring comprising an
annular projection engageable with the second annular groove.
13. The kit of claim 10 wherein the taper-fit is self locking.
14. The kit of claim 8 wherein the first bearing component
comprises a polymer body having an external surface engageable with
the internal cavity of the shell, the external surface including a
relatively flexible shell engagement portion and the second bearing
component comprises a relatively rigid non-polymeric body having a
relatively rigid external surface, the relatively rigid external
surface defining a tapered engagement surface.
15. The kit of claim 8 wherein the first engagement mechanism
comprises a snap-fit and the conversion ring is resiliently
collapsible upon insertion into the shell to engage the snap-fit
mechanism.
16. The conversion ring of claim 15 wherein a portion of the
sidewall is slit to allow the conversion ring to resiliently
compress and expand.
17. The conversion ring of claim 16 wherein the sidewall includes
multiple slits extending part-way through the sidewall between the
first and second ends, adjacent slits alternately originating from
the first and second ends to form the sidewall into a serpentine
sidewall.
18. The conversion ring of claim 15 wherein engagement of the
second bearing component with the conversion ring prevents the
conversion ring from collapsing.
19. The conversion ring of claim 8 wherein the conversion ring is
provided in a plurality of configurations each configured to adapt
the shell component to receive a differently configured second
alternative bearing component.
20. A conversion ring for converting an acetabular shell component
engagement mechanism from a first engagement mechanism engageable
with a first alternative bearing component to a second engagement
mechanism engageable with a second alternative bearing component,
the conversion ring comprising: a ring shaped body having a
sidewall defining an outer surface and an inner surface and
extending axially from a first end to a second end, a portion of
the sidewall being slit to allow the conversion ring to resiliently
compress and expand radially, the sidewall including multiple slits
extending part-way through the sidewall between the first and
second ends, adjacent slits alternately originating from the first
and second ends to form the sidewall into a serpentine sidewall; a
first engagement mechanism formed on the outer surface, the first
engagement mechanism of the conversion ring being releasably
engageable with the first engagement mechanism of the acetabular
shell component in axial locking arrangement; and a second
engagement mechanism formed on the inner surface, the second
engagement mechanism of the conversion ring being releasably
engageable with the second engagement mechanism of the second
alternative bearing component in axial locking arrangement.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to acetabular implants for hip
replacement surgery. In particular, the present invention relates
to acetabular implants including a shell component and alternative
bearing components interchangeably engageable with the shell
component to provide a choice of bearing materials.
BACKGROUND
[0002] Total hip replacement surgery is commonly performed to
alleviate pain and loss of function in injured or diseased hip
joints. During this surgery, the articulating surfaces of the hip
joint are replaced with prosthetic bearing components. The
replacement components generally include a femoral component having
a convex bearing surface and an acetabular cup component having a
mating concave bearing surface.
[0003] Modular prosthetic components have become popular because
they allow the surgeon to assemble components in a variety of
configurations at the time of surgery to meet specific patient
needs and surgeon preferences. For example, modular acetabular
components generally include separate shell and liner components
that can be assembled in a variety of configurations of shell
surface finish, shell outer diameter, liner inner diameter, and
liner bearing material. With a modular acetabular component, it is
desirable to lock the shell and liner together to prevent expulsion
of the liner and to minimize debris producing wear between them.
Typically, the engagement mechanism is formed adjacent the equator
of a hemispherical shell and liner to maximize the engagement area
and the resulting holding power of the engagement mechanism.
[0004] Various liner bearing materials are in use. The liners vary
in hardness, friction coefficient with different paired ball heads,
weight, and wear resistance. Polymers, including ultrahigh
molecular weight polyethylene (UHMWPE), are commonly used as
bearing materials paired with an opposing metal, ceramic, or other
composition ball head. The wear resistance of UHMWPE has been
improved by irradiating it to cause changes in its chemical and
mechanical properties. As the wear properties are improved the bulk
physical properties change also. Other materials, including metals
and ceramics, have also been used for acetabular bearings. These
materials vary from one another in terms of their hardness,
resilience, brittleness, and other physical properties. Because of
this variation, various mechanisms have been developed for engaging
acetabular liners with their mating shells. Different engagement
mechanisms are suitable for different liner and shell material
combinations. These engagement mechanisms include snap-fit,
cylindrical press-fit, taper-fit, threaded engagement, and other
suitable locking mechanisms. It is desirable to be able to
alternately fit different liners into a common shell to reduce
inventory while allowing surgeon choice in liner selection. It is
also desirable to allow intraoperatively changing from one liner to
another without having to remove a shell that has already been
placed in the surgical site during a primary surgery or one that
has become well fixed and only needs liner replacement in a
revision surgery.
[0005] U.S. Pat. No. 6,475,243 issued to Sheldon et al. Nov. 5,
2002. The '243 patent teaches a shell and liner arrangement that
permits alternative engagement of liners made of different
materials and having different engagement mechanisms. The '243
shell includes both a snap-fit engagement mechanism and a taper-fit
engagement mechanism formed in the interior of the shell adjacent
the shell equator. The snap-fit mechanism includes a pair of
annular grooves formed in the shell for receiving a pair of annular
projections protruding from the liner. One of the annular
projections deforms upon insertion of the liner into the shell and
snaps back into engagement with one of the annular grooves to
retain the liner in the shell. The other annular projection seats
in the other annular groove and engages a projection formed in the
groove to prevent rotation of the liner relative to the shell. The
snap-fit mechanism is suitable for relatively soft liner materials
that can deform to snap into the annular ring and that can deform
to engage the antirotation feature.
[0006] The taper-fit engagement mechanism includes a tapered seat
formed on the inside of the shell adjacent the equator for
receiving a liner having a tapered exterior surface. The taper-fit
engagement mechanism is suitable for relatively hard liner
materials. The annular grooves of the snap-fit engagement mechanism
are superimposed with the taper-fit engagement mechanism such that
the annular grooves interrupt the tapered seat and consequently
reduce the bearing area of the tapered seat and potentially create
stress risers at the taper surface.
[0007] U.S. Pat. No. 6,610,097 issued to Serbousek et al. Aug. 26,
2003. The '097 patent teaches a conventional hip cup arrangement
including a metal shell and a polyethylene bearing insertable into
the shell. The polyethylene bearing is part of a subassembly
including a metal liner permanently attached during manufacture to
the polyethylene bearing. The liner provides a metal taper surface
to facilitate taper seating of the subassembly into the shell.
SUMMARY
[0008] The present invention provides an acetabular implant for hip
replacement surgery including a shell component and first and
second alternative bearing components interchangeably engageable
with the shell component to provide a choice in bearing components.
The shell component has a first engagement mechanism suitable for
engaging the first alternative shell component. A conversion ring
is engageable with the shell component to adapt the shell component
to provide a second engagement mechanism suitable for engagement
with the second alternative shell component.
[0009] In one aspect of the invention, the conversion ring includes
a ring shaped body having a sidewall defining an outer surface and
an inner surface and extending axially from a first end to a second
end. A first engagement mechanism is formed on the outer surface
and is engageable with the first engagement mechanism of the
acetabular shell component in axial locking arrangement. A second
engagement mechanism is formed on the inner surface and is
engageable with the second engagement mechanism of the second
alternative bearing component in axial locking arrangement.
[0010] In another aspect of the invention, a kit includes a shell
component, first and second bearing components, and a conversion
ring having a sidewall defining an outer surface and an inner
surface and extending axially from a first end to a second end. The
outer surface defines a complimentary first engagement mechanism
engageable with the first engagement mechanism of the shell
component. The inner surface defines a second engagement mechanism
engageable with the second bearing component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Various examples of the present invention will be discussed
with reference to the appended drawings. These drawings depict only
illustrative examples of the invention and are not to be considered
limiting of its scope.
[0012] FIG. 1 is a perspective view of an illustrative exemplary
kit of acetabular components for assembling alternative acetabular
hip implants;
[0013] FIG. 2 is a cross sectional view of one illustrative
alternative acetabular hip component assembled from the kit of FIG.
1;
[0014] FIG. 3 is a cross sectional view of another illustrative
alternative acetabular hip component assembled from the kit of FIG.
1; and
[0015] FIG. 4 is an alternative arrangement for the snap-lock
mechanism of the acetabular hip component of FIG. 3.
DESCRIPTION OF THE ILLUSTRATIVE EXAMPLES
[0016] Embodiments of the present invention include an acetabular
cup conversion ring engageable with an acetabular shell component.
The shell component includes a first engagement mechanism for
engaging a first alternative bearing component to couple it to the
shell component. The conversion ring is engageable with the first
engagement mechanism to convert the shell component from the first
engagement mechanism to a second engagement mechanism suitable for
coupling a second alternative bearing component to the shell. Thus,
the conversion ring converts the shell first engagement mechanism
to provide a second alternative engagement mechanism for an
alternative bearing component to facilitate a choice in bearing
components. For example, alternative bearing components may be
provided that differ in material, size, shape, and/or other
parameter. For example, the alternative bearing components may be
provided in a variety of materials such as polyethylene,
crosslinked polyethylene, metal, ceramic, and/or other suitable
materials.
[0017] The conversion ring may be closed at one end or it may be
open at both ends to permit the bearing component to extend through
the ring. This allows the bearing component to occupy the full
depth of the shell component and thereby maximize the bearing
thickness at the polar region. The conversion ring may be generally
in the form of a hollow ring or band. The conversion ring may
include a first engagement mechanism formed on its outer surface
that is engageable with the first engagement mechanism formed on
the inside of the shell. The conversion ring may include a second
engagement mechanism formed on its inner surface that is engageable
with the second engagement mechanism of an alternative bearing
component. The first and second engagement mechanisms may be of the
same or a different type. Engagement mechanism types may include
snap-fit, press-fit, taper-fit, threaded, and/or other suitable
engagement mechanism types. The second engagement mechanism may be
configured for a particular type of bearing component. Multiple
conversion rings may be provided in a variety of configurations to
adapt a variety of different bearing components to a common shell.
For example, the first engagement mechanism may provide a snap-fit
to engage a relatively resilient bearing component directly in the
shell. A relatively rigid alternative bearing component may be more
suited to a taper-fit engagement mechanism. In this example, the
conversion ring would include a complimentary snap-fit engagement
mechanism on its outer surface engageable with the shell and a
complimentary taper-fit engagement mechanism on its inner surface
engageable with the alternative bearing component. In another
example, the first engagement mechanism may include a taper-fit
suited to the first bearing component and the second bearing
component may require a taper-fit having a different taper angle.
In this example, the conversion ring would have a taper-fit on both
its inner and outer surfaces but the angle of each taper-fit would
be different.
[0018] The conversion ring may be made of a variety of materials
including polymers, metals, ceramics, and combinations thereof.
Where a snap-fit engagement mechanism is employed for one of the
first and second engagement mechanisms, a degree of resiliency is
required to allow the snap-fit to function. The conversion ring, or
at least the snap-fit portion of the conversion ring, may be made
of a relatively resilient material to facilitate the snap fit.
Alternatively, the conversion ring may be made of a relatively
rigid material that is shaped to impart resiliency to selected
portions of the ring. For example, the conversion ring may be made
of a relatively rigid metal with a portion of the ring being
removed to allow the ring to compress and expand to function in a
snap-fit engagement mechanism. For example the conversion ring may
be cut through its sidewall to allow the ring to compress to a
smaller diameter. In another example, the ring sidewall may remain
a continuous band but may include multiple cuts extending part-way
through the sidewall and originating on alternating opposite sides
to form the sidewall into a serpentine sidewall that is more
resilient than the uncut sidewall.
[0019] FIGS. 1-3 depict an illustrative example of an acetabular
cup assembly 10 including a shell component 12 and alternative
first and second bearing components 14, 16. The shell component 12
includes a hollow hemispherical body 18 extending from an
equatorial rim 20 to a polar end 22 along an axis 23 and defining a
convex exterior surface 24 and a concave interior surface 26. The
rim 20 defines a circular opening 28 communicating with the
interior surface 26. A first engagement mechanism 30 in the form of
a snap-fit engagement mechanism is formed on the interior surface
26 adjacent the rim 20. The engagement mechanism includes an
annular groove 32 formed into the body 18.
[0020] The first bearing component 14 includes a hollow
hemispherical body 40 extending from an equatorial rim 42 to a
polar end 44 along an axis 45 and defining a convex exterior
surface 46 and a concave interior surface 48. The first bearing
component includes a complimentary snap-fit engagement mechanism
including an annular projection 50 sized to fit within the annular
groove 32. When the first bearing component 14 is pressed into the
shell component 12, the annular projection 50 deforms resiliently
to fit through the opening 28 and snaps into the groove 32 to
retain the first bearing component 14 in the shell component 12. In
the illustrative example, the first bearing component 14 is made of
polyethylene.
[0021] The second bearing component 16 includes a hollow
hemispherical body 62 extending from an equatorial rim 64 to a
polar end 66 along an axis 67 and defining a convex exterior
surface 68 and a concave interior surface 70. The illustrative
second bearing component 16 is made of a relatively rigid material
such as metal or ceramic and includes a tapered exterior surface 72
adjacent to the rim 64.
[0022] A conversion ring 80 includes a hollow body 82 having an
axis 83 extending from a first end 84 to a second end 86 along the
axis 83. The conversion ring 80 includes an outer surface 88
adapted to engage the shell component 12. The outer surface 88
includes an annular projection 90 engageable with the annular
groove 32 of the shell component 12. The conversion ring includes a
tapered inner surface 92 engageable with the tapered exterior
surface 72 of the second bearing component 16. In the illustrative
example, the conversion ring 80 and second bearing component 16
engage one another in a self-locking taper engagement. The
illustrative conversion ring 80 is made of a relatively rigid
material, such as metal, to provide rigid support to the relatively
rigid second bearing component 16 and to facilitate a tight
self-locking taper-fit. The conversion ring 80 is intraoperatively
engageable and disengageable with the shell component 12 and the
second bearing component 16. Thus, intraoperative selection of a
conversion ring 80, a bearing component 16, and a shell component
12 is possible as well as intraoperative changing of the components
using manual manipulation and readily available tools. Similarly,
during a revision surgical procedure, the bearing 16, ring 80, and
shell 12 may be readily separated to facilitate replacement of the
bearing 16 and/or the ring 80.
[0023] The illustrative conversion ring 80 is provided with a
plurality of slits 94 cut part-way through the body 82 and
originating alternately from the first and second ends 84, 86 to
form a portion of the sidewall into a serpentine sidewall 96. In
the illustrative conversion ring 80, the serpentine sidewall 96 is
shown over a small portion of the body 82. The serpentine pattern
may also be formed in multiple discrete locations around the body
82 or it may be formed entirely around the body 82. When the
conversion ring 80 is pressed into the shell component 12, the
slits 94 allow the conversion ring 80 to compress to a smaller
diameter to permit the annular projection 90 to fit through the
opening 28 and snap into the groove 32 to retain the second bearing
component 16 in the shell component 12. A single slit 94 cut all
the way through the conversion ring 80 may be provided to permit
the conversion ring 80 to compress. However, the multiple
alternating slits 94 are advantageous since each slit 94 can be
much narrower than would be required by a single slit 94 to provide
the same degree of compressibility. By providing multiple narrow
slits 94, the localized interruption of the inner tapered surface
92 by each slit is minimized. The alternating pattern of slits also
provides for continuous, albeit serpentine, support of the second
bearing component around the entire circumference of the conversion
ring 80.
[0024] Once the conversion ring 80 is snapped into the shell
component 12, the conversion ring 80 resiliently expands to abut
the outer surface 88 of the conversion ring 80 against the interior
surface 26 of the shell component 12. This abutment prevents the
conversion ring 80 from expanding to a larger diameter when the
second bearing component 16 is inserted into the shell and ring
assembly. Likewise, the taper-fit engagement of the second bearing
component 16 with the conversion ring 80 prevents the conversion
ring from collapsing and exiting the shell 12 once the second
bearing component 16 is engaged with the conversion ring 80.
[0025] FIGS. 2-3 provide more detailed views of the illustrative
engagement mechanism. The first bearing component 14 snap-fit
engagement with the shell component 12 is shown in FIG. 2. The
conversion ring 80, second bearing component 16, and shell
component 12 engagements are shown in FIG. 3. The taper engagement
between the second bearing component 16 and the conversion ring 80
includes continuous taper surfaces 72, 92 providing support for the
bearing component at its equator. The illustrative annular
projection 90 of the conversion ring 80 includes a ramped leading
edge 100 angling outwardly from the outer surface 88 to ease
insertion of the conversion ring 80 into the shell component 12. A
seating portion 102 extends from the leading edge 100 generally
parallel to the outer surface 88. A shoulder 104 extends radially
inwardly from the seating portion 102. The annular groove 32 in the
shell component has a shape complimentary to the annular projection
90. As the conversion ring 80 is inserted into the shell component
12, the ramped leading edge 100 engages the opening 28 such that
continued axial pressure causes the conversion ring 80 to compress
and the annular projection 90 to slide along the inner surface of
the shell component 12 until it snaps into the annular groove 92.
With just the conversion ring 80 in the shell component 12, the
conversion ring 80 can be readily pried out of the shell component
12. When the bearing component 16 is seated in the conversion ring
80 it presses the conversion ring 80 into engagement with the shell
component 12 to prevent it from collapsing and being disengaged
with the shell component. Removal of the bearing component 16 again
frees the conversion ring 80 to be compressed and removed.
Preferably, the seating portion 102 bottoms in the annular groove
32 to form a press fit upon insertion of the bearing component 16
to prevent positioning of the conversion ring 80 in the shell
component 12.
[0026] FIG. 4 illustrates an alternative configuration of the
engagement mechanism comprising a second annular groove 34 spaced
axially into the cup from the first annular groove 32. The
conversion ring 80 may include a second annular projection 98
engageable with the second annular groove 32 to provide more
support for the conversion ring 80 and second bearing component 16
(as shown). Alternatively, one of the annular grooves 32, 34 may be
engaged by the first bearing component 14 and the other annular
groove may be engaged by the conversion ring 80 (not shown). For
example, the first bearing component 14 may engage the annular
groove 32 nearer the equator of the shell component 12 and the
conversion ring 80 may engage the annular groove 34 further from
the equator of the shell component 12. This arrangement may be
advantageous where, for example, the first annular groove 32 is
positioned to mate with existing bearing components with an annular
projection near the equator and where the second annular groove 34
and conversion ring annular projection 98 are positioned axially
inwardly from the equator to position them near a thicker portion
106 of the bearing component 16 to support the bearing component 16
at the thicker portion 106.
[0027] In use, a decision is made as to which of the alternative
bearing components 14, 16 is desired. If the first bearing
component 14 is to be used, it is snapped directly into the shell
component 12. If the second bearing component 16 is to be used, the
conversion ring 80 is first snapped into the shell component 12 to
convert the shell component engagement mechanism from a snap-fit to
a taper-fit. Then the second bearing component is pressed into the
shell and ring assembly. The conversion ring 80 may be used during
a primary hip surgery to allow an intraoperative choice of bearing
components 14, 16. The conversion ring 80 may be used during a
revision hip surgery to allow a previously implanted bearing
component to be replaced by a new bearing component having a
different engagement mechanism than the original without having to
remove the shell component 12. This is desirable, for example,
where the shell component 12 is well fixed in the acetabulum and
only the bearing component needs to be changed due to wear or the
need for a different bearing configuration such as a different
material, shape, or size. The conversion ring 80 also permits the
use of independently designed shell and bearing components with one
another such as a later designed liner with an earlier designed
shell or the use of components from distinct design families.
[0028] Although examples of an acetabular cup conversion ring and
its use have been described and illustrated in detail, it is to be
understood that the same is intended by way of illustration and
example only and is not to be taken by way of limitation. The
invention has been illustrated in use to convert a snap-fit shell
engagement mechanism to a taper-fit shell engagement mechanism.
However, the acetabular cup conversion ring may be configured to
convert any shell engagement mechanism into any other shell
engagement mechanism. Accordingly, variations in and modifications
to the acetabular cup conversion ring and its use will be apparent
to those of ordinary skill in the art, and the following claims are
intended to cover all such modifications and equivalents.
* * * * *