U.S. patent application number 13/763145 was filed with the patent office on 2014-08-14 for bearing fixation.
This patent application is currently assigned to BIOMET MANUFACTURING CORPORATION. The applicant listed for this patent is BIOMET MANUFACTURING CORPORATION. Invention is credited to Aaron P. SMITH.
Application Number | 20140228966 13/763145 |
Document ID | / |
Family ID | 50185030 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140228966 |
Kind Code |
A1 |
SMITH; Aaron P. |
August 14, 2014 |
BEARING FIXATION
Abstract
Disclosed is a bearing liner engageable within a shell member
with an integrated projection portion. The integrated projection
portion may deform a selected amount during positioning of the
bearing liner within the shell. The shell may include a
complementary engaging portion.
Inventors: |
SMITH; Aaron P.; (Warsaw,
IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BIOMET MANUFACTURING CORPORATION |
Warsaw |
IN |
US |
|
|
Assignee: |
BIOMET MANUFACTURING
CORPORATION
Warsaw
IN
|
Family ID: |
50185030 |
Appl. No.: |
13/763145 |
Filed: |
February 8, 2013 |
Current U.S.
Class: |
623/22.15 ;
623/22.38 |
Current CPC
Class: |
A61F 2002/30367
20130101; A61F 2002/30331 20130101; A61F 2002/3412 20130101; A61F
2002/305 20130101; A61F 2/34 20130101 |
Class at
Publication: |
623/22.15 ;
623/22.38 |
International
Class: |
A61F 2/34 20060101
A61F002/34 |
Claims
1. A system for an acetabular prosthesis to fix a bearing liner
within a shell, comprising: a shell member having an exterior
configured to engage an anatomy and a concave interior; a bearing
liner having an exterior wall surface configured to be received
within the concave interior of the shell member, the exterior wall
surface extending from a rim of the bearing liner towards an apex
of the bearing liner along a substantially continuous curve, and an
axial fixation projection extending from the substantially
continuous curve of the exterior surface; wherein the axial
fixation projection has a first projection surface extending from
the exterior surface a first distance and at least one second
surface extending towards the exterior surface at an acute angle
relative to the first projection surface; wherein at least 51
percent of the material that forms the axial fixation projection is
between a midline of the axial fixation projection and the apex of
the bearing; wherein the axial fixation projections engages the
shell to engage the bearing liner within the concave interior of
the shell.
2. The system of claim 1, wherein the first projection surface is
substantially perpendicular to a bearing liner axis extending from
the apex past the rim.
3. The system of claim 2, wherein the rim defines a bearing plane
and the bearing liner axis is substantially perpendicular to the
bearing plane and intersects the apex.
4. The system of claim 1, wherein the concave interior is
substantially hemispherical.
5. The system of claim 1, wherein the shell defines a groove formed
into a wall surface of the concave interior, wherein the axial
fixation projection is received within the groove when the bearing
liner is seated within the shell.
6. The system of claim 1, further comprising: proximal femoral
member configured to be implanted into a femur to articulate within
the positioned bearing liner.
7. The system of claim 1, wherein the at least one second surface
includes a plurality of second surfaces that together extend from
an exterior end of the first projection surface to the
substantially continuous curve of the exterior surface of the
bearing liner.
8. A system for an acetabular prosthesis to fix a bearing liner
within a shell, comprising: a shell member having an exterior
configured to engage an anatomy and a concave interior surface
extending from a shell rim to a shell apex, an engagement groove is
defined through the concave interior surface; a bearing liner
having an exterior wall surface configured to be received within
the concave interior of the shell member, the exterior wall surface
extending from a rim of the bearing liner towards an apex of the
bearing liner along a substantially continuous curve, an
asymmetrical axial fixation projection extending from the
substantially continuous curve of the exterior wall surface;
wherein the asymmetrical axial fixation projection has a first
configuration where a volume of material of the asymmetrical axial
fixation projection is biased towards the apex of the bearing
liner; wherein the asymmetrical axial fixation projection engages
the engagement groove of the shell to engage the bearing liner
within the concave interior of the shell in a locking configuration
that is deformed from the first configuration due to insertion into
the shell and engaging the engagement groove in a second
configuration.
9. The system of claim 8, wherein the groove is substantially
continuous around the concave interior surface.
10. The system of claim 8, wherein the axial fixation projection is
discontinuous around the exterior of the bearing liner.
11. The system of claim 8, wherein the asymmetrical axial fixation
projection includes a first projection surface extending from the
exterior surface substantially perpendicular to a central axis of
the liner and having a surface end a first distance from the
exterior surface and positioned a first distance from the rim of
the liner; wherein the asymmetrical axial fixation projection
further includes at least one second surface extending towards the
central axis at an acute angle relative to the first projection
surface and positioned a second distance from the rim, wherein the
second distance is less than the first distance.
12.-17. (canceled)
Description
FIELD
[0001] The subject disclosure is related to fixing a deformable
member to a second member, and particularly to fixing a liner to a
shell.
BACKGROUND
[0002] This section provides background information related to the
present disclosure, which is not necessarily prior art.
[0003] A subject can have a portion replaced with a replacement
member. For example, a human patient subject can have a portion of
the anatomy replaced with a prosthetic member. The reason for the
replacement can be due to injury, disease, or other failing of the
natural anatomy.
[0004] A prosthetic member can be used to replace a portion of the
anatomy to substantially recreate or mimic the natural anatomy and
physiology. For example, an acetabular prosthesis can be positioned
in a prepared acetabulum of a patient to achieve a substantially
natural or selected interaction of a femur and an acetabulum. It is
understood in a complete or total hip arthroplasty that a proximal
femoral portion may also be replaced.
[0005] An acetabular prosthesis can include a shell component that
contacts a pelvis within an acetabulum. The shell can either
interact with the natural femur or with a proximal femoral
prosthesis directly, or a bearing can be placed in the shell. A
bearing can be fixed in the shell using a separate element that is
positioned between the bearing and the shell, such as with the
RINGLOC.RTM. sold by Biomet, Inc.
SUMMARY
[0006] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0007] An acetabular prosthesis can be positioned in a patient to
replace an acetabulum that is damaged or defective. The acetabular
prosthesis can be placed in the patient after properly preparing
the acetabulum to receive the acetabular prosthesis. The acetabular
prosthesis can generally be formed of at least two pieces,
including an external shell that is positioned in contact or
cemented to the acetabulum of the pelvis and a bearing liner (also
referred to herein alone as a liner or bearing) that is positioned
and selectively fixed within the shell. Both the shell and the
liner can include convex exterior surfaces and concave interior
surfaces. The convex exterior surface of the shell can engage the
bone of the pelvis and the convex exterior of the liner can engage
the concave interior of the shell. The concave interior of the
liner can then articulate relative to a proximal femur portion. The
proximal femur can be a prosthetic member or natural proximal
femur.
[0008] The liner can be engaged to the shell with an engagement
portion defined by the liner. The engagement portion defined by the
liner may engage and/or interact with the internal surface of the
shell to selectively deform the liner during insertion of the liner
into the shell. The engagement portion of the liner may then engage
or be received by a depression formed within the shell. Once
engaged with the depression the liner is substantially fixed to the
shell for the purpose of the implantation.
[0009] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
[0010] The drawings described herein are for illustrative purposes
only of selected embodiments and not all possible implementations,
and are not intended to limit the scope of the present
disclosure.
[0011] FIG. 1 is an exploded view of a shell and bearing liner,
according to various embodiments;
[0012] FIG. 2 is a cross-section view of the shell of FIG. 1;
[0013] FIG. 3 is a cross-section view of the bearing liner of FIG.
1;
[0014] FIG. 4 is a detail cross-section view of an engagement
portion taken from FIG. 3;
[0015] FIG. 5 is a detail cross-section view of an engagement
portion, according to various embodiments;
[0016] FIG. 6 is a detail cross-section view of an engagement
portion, according to various embodiments;
[0017] FIG. 7A is a detail cross-section view of the bearing liner
being inserted into the shell;
[0018] FIG. 7B is a detail cross-section view of the bearing liner
seated in the shell;
[0019] FIG. 7C is a detail cross-section view from FIG. 7B; and
[0020] FIG. 8 is an environmental view of the shell and bearing
liner relative to a subject.
[0021] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0022] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0023] With reference to FIG. 1, an acetabular prosthesis system
can include a shell 20 and an acetabular liner 30. The shell 20 can
include an exterior convex surface 40 that is configured to contact
an acetabulum of a pelvis. The shell 20 can include throughbores,
such as an apical throughbore defined by a sidewall 44 and one or
more screw of fixation throughbores 46 defined by through sidewalls
48. The throughbores 46 extend from an interior concave surface 50
to the exterior convex surface 40. The apical hole 42 can generally
be used for fixation and positioning of the acetabular shell 20 in
the acetabulum. The fixation bore 46 can be used for passing a
screw or other fixation member into the acetabular portion during
implantation and fixation of the acetabular shell 20. It is
understood that a plurality of the fixation throughbores 46 can be
provided at various positions of the shell 20 and a user can
selectively pass screws for fixing the shell 20 to the acetabulum
of the subject. Additional mechanisms or features can be used to
fix the shell to the pelvis as well, for example, projections or
spikes, a porous coating or porous outer surface portion.
[0024] The acetabular shell 20 can also include other features,
such as the anti-rotation depressions 56 formed near an upper
surface or a rim 58 of the acetabular shell 20. The acetabular
shell 20, including the anti-rotation depressions 56 can engage the
liner 30 to hold the liner substantially rotationally fixed
relative to the shell 20. Additionally, the shell 20 can include an
interior groove or depression 60 formed as a substantially annular
or circumferential depression within the concave surface 50 of the
acetabular shell 20.
[0025] The groove 60 formed within the shell 20 can be a groove
formed within the shell similar to the groove formed in the shell
of the acetabular shell used in the Ringloc.RTM. acetabular
prosthesis sold by Biomet, Inc. having a place of business in
Warsaw, Ind. The groove 60 formed in the interior surface 50 of the
acetabular shell 20 can be formed with appropriate dimensions. The
dimensions, as discussed further herein, can assist in fixation of
the liner 30 relative to the shell 20 during and after an
implantation of the liner 30 into the shell 20. Generally, the
depression 60 substantially extends around the interior 50 of the
shell 20 for fixing the liner 30 within the shell 20. It is
understood, however, that alternative or additional fixation
mechanisms can be provided or formed within the shell 20 to engage
the liner 30.
[0026] With continuing reference to FIG. 1, and additional
reference to FIG. 3, the acetabular liner 30 can include an outer
convex surface 70 and an inner concave surface 72. A liner rim 74
can be formed near an upper or equator region of the liner 30
positioned away from an apex 76 of the liner 30. A wall thickness
between the interior concave surface 72 and the exterior convex
surface 70 can be provided. It is understood that the wall
thickness 78 can be substantially uniform or vary between the apex
76 and the rim 74 of the liner 30. The variation of the thickness
of the wall of the liner 30 can be provided for various purposes
such as insertion of the liner 30 within the shell 20 and other
bearing characteristics, such as wear resistance or weight
bearing.
[0027] Additionally, the liner 30 can be provided with a one or
more anti-rotation projections 80 that extend from the outer
surface 70 of the liner near the rim 74. The anti-rotation
projections can engage the anti-rotation depressions 56 defined by
the shell 20 for substantially rotationally fixing the liner 30
relative to the shell 20. Additionally, the anti-rotation
projections 80 can assist in aligning the liner 30 relative to the
shell 20. The anti-rotation projections can also assist in aligning
the bearing 30 within the shell to ensure proper fixation
therein.
[0028] Additionally, an axial fixation projection 90 can be formed
to extend from the surface 70 of the liner 30. The axial fixation
projection 90 can be formed as a substantially continuous
projection around an exterior of the liner 30. Alternatively, the
projection 90 can be formed as a segmental projection including
discreet projection regions around the exterior of the liner 30.
The axial fixation projection 90 may be formed to engage the axial
fixation depression 60 within the shell 20 during an implantation
and positioning of the liner 30 within the shell 20. As discussed
herein, the geometry of the axial fixation projection 90 can
interact with the inner surface 50 of the shell 20 during
positioning of the liner 30 within the shell 20 and engage the
depression 60 within the shell 20 for fixing the liner 30 within
the shell 20.
[0029] With continuing reference to FIG. 3 and additional reference
to FIG. 4, the axial fixation projection 90 is shown in detail. The
projection 90, illustrated in FIG. 4, is a manufactured or first
configuration of the projection 90. As discussed herein, the
projection can deform to engage and/or seat in the shell 20. The
liner 30 can define a central axis 100 that extends substantially
through the apex 76 of the liner 30. The central axis 100 is also
generally perpendicular to a place defined near and/or by a rim of
the liner 30. An apical or distal surface 102 of the axial fixation
projection 90 can be formed to be substantially perpendicular or at
a right angle to the axis 100 of the liner 30. The perpendicular
surface 102 of the axial fixation projection 90 can extend a
distance 104 from the exterior surface 70 of the liner 30. The
distance 104 of the edge or surface 102 can provide, as discussed
further herein, a sufficient or selected amount of material of the
projection 90 to deform relative to the shell 20 for fixation
within the depression 60 of the shell 20. The axial fixation
projection 90 can further include a first parallel extending wall
106 that extends a parallel distance 108 of about 0.4 mm to about
0.6 mm, including about 0.5 mm. The parallel wall 108 extends
substantially parallel to the central axis 100 of the liner 30. The
parallel wall 106, however, can form an angle towards the central
axis 100 from the perpendicular wall 102, such as about 68.degree.
relative to the perpendicular wall 102 of the axial fixation
projection 90. A third angled wall 110 can extend from the parallel
wall 106 to a juncture 111 along a distance 112. The distance 112
can be about 0.6 mm to about 0.8 mm, including about 0.7 mm. The
angled wall 110 can extend at an angle towards the central axis 100
from the wall 106 at a generally acute angle towards the central
axis 100 of the liner 30.
[0030] The exterior surface 70 generally defines an arc having a
center defined relative to the liner 30. The exterior surface 70 is
substantially continuous from the rim of the liner to an apex of
the liner 30. The projection 90, including the various surfaces
102, 106, and 110 generally extends or diverges from the exterior
surface 70 of the liner 30. Additionally, the measurements are
exemplary regarding a liner generally having a diameter of about 31
mm. It is understood that the specific dimensions of the projection
90 can, therefore, differ based upon the dimensions of the liner
30.
[0031] According to various embodiments, the axial fixation
projection 90 is formed of the same material as the remainder of
the liner 30. Further, the projection 90 can be formed as one piece
with the liner 30. For example, the liner 30 can be molded to
include the projection 90 as an integral portion of the liner
30.
[0032] The projection 90 can be provided such that a majority of
the material within the axial projection 90 is positioned below a
midline 140 of the projection 90. The midline 140 is at the
mid-point of the total axial distance of the projection 90. The
total axial distance of the projection 90 can generally be defined
as a distance between where the first surface 102 extends at 102a
from the external surface 70 of the liner 30 to a point 110a where
the surface 110 rejoins and/or extends from the external surface 70
of the liner 30. Accordingly, with reference to FIG. 4, the midline
140 of the projection 90 can be defined generally along line 140.
Generally, the midline 140 is a first axial distance 140a from a
line through the point 102a and a second axial distance 140b from a
line through point 110a. The first axial distance 140a and the
second axial distance 140b are equal when the line 140 is a
true-mid-line. The lines through the points 102a and 110a are
perpendicular to the central axis 100.
[0033] A vertical line or plane 142 is also defined relative to the
liner 30. The vertical line 142 may be substantially parallel with
the central axis 100 of the liner 30 and intersect the point 110a,
where the wall 110 rejoins the outer surface 70. The mid-line 140
may be substantially perpendicular to the vertical line 142.
[0034] The mid-line 140 can define a boundary or a plane that
divides material of the projection 90 between the rim and the apex
of the liner 30. The vertical line 142 can define a central
boundary of the projection 90. A majority, such as at least 51% of
a volume of the material that defines the axial fixation projection
90 is between the mid-line 140 and the apex 76 of the liner 30 and
the vertical line 142 and the outer edge of the projection 90.
Thus, less than 51% of the volume of the material that defines the
axial fixation projection 90 is between the line 140 and the upper
rim 74 of the liner 30 and the vertical line 142 and the outer edge
of the projection 90. According to various embodiments, however
without being bound by the theory, providing a majority of the
material in the axial fixation projection 90 closer to the apex 76
can allow for the projection 90 to deform as the liner 30 is moved
into the shell 20. When the projection 90 deforms, the projection
90 can engage the depression 60 of the shell 20 after positioning
the liner 30 within the shell 20 in a seated or changed
configuration that is different from the original or manufactured
configuration illustrated, for example, in FIG. 4.
[0035] According to various embodiments, as illustrated in FIG. 5,
an alternative axial fixation projection 190 is illustrated. The
liner 30 can include the exterior surface 70 and an axial fixation
projection 190 that is substantially bulbous or curved. The
projection 190 can include an exterior surface 192 that is
substantially continuous from the first extension point 194 from
the exterior surface 70 to the second diversion point 196, where
the axial fixation projection 190 rejoins the exterior surface 70.
A vertical line 198 extend substantially parallel to the central
axis 100 of the liner and intersects the diversion point 194
(nearest the rim of the liner. The axial fixation projection 190
can include a majority of a volume of the material defined within
the axial fixation projection 190 between a mid-line 200 and the
apex 76 of the liner 30 and the vertical line 198 and an outer edge
of the projection. Again, the mid-line 200 can be equidistant from
lines that are perpendicular to the central axis 100 through the
respective points 194 and 196.
[0036] According to various embodiments, with reference to FIG. 6,
a liner 230 can be formed similar to the liner 30. The liner 230,
however, can include a generally cylindrical outer surface region
232, such as near a rim of the liner 230. An axial fixation
projection 234 can be formed to have a generally bulbous of
continuous outer surface 236 or to have any appropriate geometry,
such as that discussed above. The outer surface of the projection
234 can diverge/converge from the outer surface 232 of the liner
230 at a first divergence point 238 and converge or diverge at a
second divergence point 240. A mid-line 242 can be defined as a
line that is half way between the first point 238 and the second
point 240. The outer surface region 232 can be substantially
parallel to a central axis 244 of the liner 230. Thus, the outer
surface 232 can define a substantially vertical line. Near an apex
of the liner 230 a curved outer surface region 246 can be defined
by the liner 230. The axial projection 234, however, can be defined
substantially entirely within the cylindrical outer surface region
232.
[0037] Accordingly, it is understood that a specific geometry of
the axial fixation projection or the liner is not required. For
example, the axial projection need not include the specific
dimensions illustrated in FIG. 4 and the liner need not be entirely
curved. Nevertheless, the axial fixation projection may include
dimensions where a majority of the volume of the material of the
axial fixation projection is between the mid-line of the axial
fixation projection and the apex of the liner 30.
[0038] Generally, according to various embodiments, the axial
fixation projection 90, 190, 236 initially or is manufactured and
provided to include a majority, such as more than 51%, of a
material of the axial fixation projection, between the respective
midlines and the apex of the liner 30. For example, regarding the
axial fixation projection 90 at least 51% of the material that is
included in the axial fixation projection 90 is below the midline
140. Thus, the projection 90, 190, 236 according to various
embodiments, is asymmetrical about the mid-line 140, 200.
[0039] With reference to FIGS. 7A-7C, the liner 30 is initially
placed relative to the shell 20 in the manufactured configuration
where a majority of the material of the axial fixation projection
is between the midline and the apex of the liner 30. The liner 30
is then moved into and may be positioned within the shell 20 by
applying a substantially axial force in the direction of Arrow A
that can generally be along the axis 100 of the liner 30. As the
liner 30 is pressed into the shell 20, the axial fixation
projection 90 engages the inner wall surface 50 of the shell
20.
[0040] As the axial fixation projection 90 engages the inner wall
surface 50 of the shell 20, the projection 90 is urged generally in
the direction of Arrow B that is substantially in a direction
opposite of Arrow A. The projection 90 is generally forced in the
direction of Arrow B due to a reaction of pressing the liner 30
into the shell 20. Friction caused between the projection 90 and
the inner surface 50 of the shell 20 causes the projection 90 to be
urged in the direction of Arrow B. The material of the projection
90 generally does not compress or collapse, but may be mobile under
the force of the insertion of the liner 30 into the shell 20. A
movement zone can be formed near or at the interface of the
projection 90 with the outer surface 70 of the liner 30. The
movement zone can include movement of the material from the
projection 90 towards the rim 74 of the liner 30. In other words,
there is movement of material in the projection 90 from below the
mid-line 140 (i.e. an area or volume between the apex 76 and the
mid-line 140) to an area above the mid-line 140 (i.e. an area or
volume between the rim 74 and the mid-line 140). As the liner 30 is
pressed into the shell 20 the friction or engagement between the
projection 90 and the inner surface 50 of the shell 20
continues.
[0041] As the liner 30 moves into a substantially seated position,
as illustrated in FIG. 7B and 7C, the projection 90 achieves a
substantially locking configuration, which can also be viewed a
reverse pullout ramp configuration. In the locking configuration,
which can be a second and/or deformed configuration, a portion of
the material of the projection 90 that was between the mid-line 140
and the apex 76 of the liner 30 has moved between the line 140 and
the rim 74 of the liner 30. In the locked configuration, the
projection 90, 190, according to various embodiments, may be
asymmetrical about the mid-line 140, 200 and biased towards the rim
74 of the liner 30.
[0042] In the locked configuration, the material of the projection
90 has been altered or moved to engage the depression or groove 60
of the shell 20 in a locked configuration. The surface of the
deformed projection that was initially provided as surface 110 is
substantially perpendicular to the central axis of the liner 30 and
would engage a surface 60a of the depression prior to other
surfaces of the deformed projection. Moreover, the initially
provided surface 102 and part or all of surface 106 are angled
towards the rim 74 and the central axis 100 of the liner 30.
[0043] The movement of the material from the projection 90 from the
manufactured configuration (also referred to as the initial
configuration) to the locked configuration, as illustrated in FIGS.
7B and 7C, can provide a substantially strong push-out and
lever-out force of the liner 30 relative to the shell 20.
[0044] The amount of material that moves from the initial position
(e.g. as illustrated according to various embodiments in FIGS. 4-6)
to the locked position (e.g. as illustrated in FIGS. 7B and 7C)may
be selected based upon various considerations and selections. For
example, the amount of material that moves can be selected based on
materials for the liner 30, the various dimensions of the axial
fixation projection 90 (e.g. the first wall 102), the distance from
the rim 58 to the recessed depression 60 of the shell 20, and other
factors. Generally, according to the various embodiments,
projection 90 may include at least 51% of the material of the
projection between the mid-line and the apex of the liner and in
the locked configuration the projection 90 has at least 51% of the
material moved between the mid-line 140 and the rim 74.
[0045] The liner 30 can be pre-assembled to the shell 20 prior to
insertion into a patient. Alternatively, and according to various
embodiments, however, the shell 20 can initially be positioned
within a patient 320, as illustrated in FIG. 8, and then the liner
30 can be positioned within the shell 20. Assembly of the liner 30
into the shell 20 and positioning the shell 20 into the patient 320
can be performed according to various and commonly known methods,
such as that used with the RINGLOC.RTM. prosthesis system sold by
Biomet, Inc. having a place of business in Warsaw, Ind. Generally,
the liner 30 can be pressed into the shell 20 using an insertion
tool that can apply enough force to overcome the friction between
the projection 90 and the inner surface 50 of the shell 20 and
allow the projection 90 to deform for engagement into the groove of
the shell 20.
[0046] As discussed above, the projection 90 can be formed with the
other portions of the liner 30 according to generally known
manufacturing techniques. Generally, the liner 30 can be molded
using generally known molding and forming techniques. Accordingly,
the projection 90 need not be an additional piece that is added to
the liner or to the assembly of the shell 20 with the liner 30. The
projection 90 being integral with the liner 30 allows for an
efficient assembly of the liner 30 with the shell 20. Additionally,
additional machining and manufacturing steps for a separate locking
mechanism may not be required. Further, the material forming the
projection 90 can generally be substantially anatomically and
physiologically compatible and additional materials need not be
offered to the assembly.
[0047] The interaction of the liner 30, including the projection
90, with the inner surface 50 of the shell 20 can provide for a
substantially strong lever-out and push-out force. Various
standards have been developed in the art to measure forces that act
on acetabular prostheses to attempt to disassemble or disconnect
the liner 30 from the shell 20. For example, a lever out test,
according to the standard ASTM F1820-97 (2009) can measure the
amount of force required to lever out the liner 30 from the shell
20. Generally, the liner 30 can be assembled into the shell 20. The
shell 20 is then held fixed within an assembly and a leaver arm
engages the liner 30 by being pressed into the liner 30 across the
diameter of the liner 30. The lever arm is then pressed over a
fulcrum to apply a force to attempt to lever out the liner 30 from
the shell 20. Generally, the lever out force of the liner 30
including the projection is about 140 foot/pounds (ft/lb) to about
190 ft/lb, including about 160 ft/lb to about 190 ft/lb, and
further including about 170 ft/lb to lever out the liner 30 from
the shell 20.
[0048] Additionally, a push-out force test can also be performed
according to the standard ASTM F1820-97 (2009) standard. In a
push-out test, the liner 30 is assembled into the shell 20 and the
shell 20 is supported by an assembly while the liner 30 is free to
move when a force is applied. The force is supplied through the
apical hole 42 with a push bar. The push-out force for the liner 30
with the projection 90 assembled within the shell 20 can generally
be about 320 ft/lb to about 400 ft/lb, including about 350 ft/lb to
about 380 ft/lb, and further including about 370 ft/lb.
Accordingly, the assembly of the liner 30 into the shell 20
including only the axial fixation projection 90 can provide a
substantial lever-out and push-out forced resistance. Additionally,
it is understood, that the other configurations, including that
illustrated in FIG. 5, can include similar lever-out and push-out
force resistance given the configuration of the axial fixation
projection 190 to interact with the shell 20. Generally, the
achieved lever-out and push-out forces can be achieved when the
projection, according to various embodiment, can achieve the seated
or deformed configuration that moves the selected amount of
material past a mid-line of the projection. Further, it is
understood, that the material of the projection 90 remains in the
second or implanted configuration after implantation until acted
upon by a member that produces the forces discussed above. That is,
the projection 90 does not substantially elastically deform, but
maintains the implanted configuration.
[0049] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not
intended to be exhaustive or to limit the disclosure. Individual
elements or features of a particular embodiment are generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be used in a selected embodiment, even if
not specifically shown or described. The same may also be varied in
many ways. Such variations are not to be regarded as a departure
from the disclosure, and all such modifications are intended to be
included within the scope of the disclosure.
* * * * *