Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02472669 2004-06-28
Multi-Piece Modular Patellar Prosthetic System
Field of the Invention
The present invention relates to a modular knee prosthetic system used to
replace the
natural knee and, more particularly, to a mufti-piece modular patellar
prosthetic system
having various baseplates and articulation components that are interchangeable
with each
other.
Background of the Invention
In the United States alone, over 200,000 knee replacements are performed each
year.
Degenerative arthritis, or the gradual degeneration of the knee joint, is the
most common
reason for these replacements. In this form or arthritis, cartilage and
synovium surrounding
the knee wear down so underlying bones grind directly on each other.
In knee arthroplasty, portions of the natural knee joint are replaced with
prosthetic
components. These components include a tibial component, a femoral component,
and a
patellar component. The femoral component generally includes a pair of spaced
condyles
that articulate with the tibial component. These condyles form a trochlear
groove in which
the articulating surface of the patellar component moves. The components are
made of
materials that exhibit a low coefficient of friction when they articulate
against one another.
When the articulating ends of both the femur and tibia are replaced, the
procedure is
referred to as total knee replacement or TKIt. Much effort has been devoted to
performing
TKR that restores normal, pain-free functions of the knee for the lifetime of
the prosthetic
components.
Unfortunately, patients can experience problems with the prosthetic knee after
a total
knee replacement surgery. If a problem occurs, a patient may need a revision
surgery
wherein some or all of the prosthetic components are replaced. Historically,
problems
associated with the patellar prosthesis are responsible for as many as
50°l0 of all knee implant
revisions. More particularly, complications with the patello-femoral joint or
patello-femoral
dysfunction are the primary cause of failure in TKR.
One option in a TKR or revision surgery is to implant a prosthetic patellar
component. The patellar component has a metallic back or baseplate that is
permanently
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fixed to the patellar bone. Metal baseplates were introduced to provide a more
even stress
distribution on the natural patella and provide the option for either cement
or cementless
fixation. An articulation or bearing component is permanently connected to the
baseplate to
form the prosthetic patellar component. The articulation component is formed
from metal or
S a polymer, such as ultra-high molecular weight polyethylene (IJHMWPE).
Despite current advances in the design of prosthetic knees, the patellar
component
still fails and must be replaced in a revision surgery. Failure of the
patellar component
occurs for a multitude of reasons. In some instances, the articulation
component becomes
loose or worn through repeated use. Obviously then, this component must be
replaced.
As one disadvantage with current patellar components, replacement of the
articulation
or bearing component during a revision surgery can be impractical, difficult,
or unhealthy for
the natural patella. After the initial TKR surgery, the baseplate becomes
firmly fixed to the
host patellar bone. In present patellar prosthetic designs, the articulation
component is
permanently attached to the baseplate. So, removal of the articulation
component alone is
not an option. Instead, both the baseplate and the articulation component must
be removed
and then replaced. Removing the baseplate from the natural patellar bone is
undesirable since
healthy bone stock can be damaged or removed from the patella. Further, the
stress
associated with removing the baseplate during a revision surgery can fracture
the natural
patella. The patellar bone stock may already be thin or weak, and forcing or
prying the
baseplate from the bone can damage the patella.
Since removing the baseplate from the patella can have serious, unwanted
consequences, surgeons have few options. Manufacturers do not provide modular
articulation components that are designed to be removed from the baseplate
during a revision
surgery. In the past, some attempts have been made to forceably remove or pry
apart the
articulation component from the baseplate during a revision surgery.
Manufacturers,
however, would not recommend such a procedure if the components were not
designed for
this use.
It, therefore, would be advantageous to provide an implantable modular
patellar
prosthetic system having various baseplates and articulation components that
are
interchangeable with each other.
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Summary of the Invention
The present invention is directed toward a modular patellar prosthetic system
used to
replace a portion of the natural knee and, more particularly, to a mufti-piece
modular patellar
prosthetic system having various baseplates and articulation components that
are
interchangeable with each other.
Each baseplate has a fixation surface and a bearing surface. The fixation
surface is
adapted to engage patellar bone and includes a plurality of pegs that extend
outwardly from
the surface to penetrate bone.
Each articulation component has an articulation surface and a bearing surface.
The
articulation surface has a smooth contour that is adapted to articulate with
the femur or
femoral prosthesis at the patello-femoral joint. This surface may have various
shapes known
to those skilled in the art, such as a hyperbolic paraboloid or dome-like
configuration. The
bearing surface of the articulation component is adapted to engage, either
directly or
indirectly, the bearing surface of the baseplate. In some embodiments, these
surfaces are
configured to slideably contact or articulate with each other. In other
embodiments, the
articulation component and baseplate anti-rotationally lock together.
An attachment mechanism couples the baseplate to the articulation component so
the
bearing surfaces are adjacent each other. The attachment mechanism is a
separate
component from the articulation component and baseplate and can have a variety
of
configurations to enable the articulation component to engage and disengage
from the
baseplate. In one embodiment, the attachment mechanism has a disc shape with a
locking
mechanism; and in other embodiments, the attachment mechanism has a ring
shape. The
attachment mechanism serves an important function as it enables the
articulation component
to attach and detach from the baseplate and provides a modular interface
between the
articulation component and various baseplates.
As one important advantage of the present invention, the articulation
component is
removeably connectable to the baseplate. In other words, even after the
baseplate becomes
permanently connected to the patellar bone, an articulation component can be
readily
attached or detached from the baseplate. During a revision surgery then,
healthy bone stock
of the natural patella will not be damaged or removed since the baseplate can
be left attached
to the patella.
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As another advantage, an articulation component can be relatively easily
removed
from or attached to the baseplate. As such, nominal stress is placed on the
natural patella as
an old articulation component is removed and a new one is attached. The
natural patella is
thus less likely to fracture or otherwise become damaged during replacement of
the
S articulation component.
As yet another advantage of the invention, multiple articulation components
can be
easily attached to an implanted baseplate. During a revision surgery then, the
implanted
articulation component can be removed from the baseplate and replaced with a
new, sterile
one. Further, multiple articulation components having various sizes and shapes
can be
attached to the baseplate. As such, the surgeon can choose from a variety of
articulation
components to meet the specific needs of the patient.
As yet another advantage, multiple articulation components can connect to
multiple
baseplates. The articulation components and baseplates can have different
sizes and shapes
and can interchange and connect to each other. The interchangeability between
the various
components gives the surgeon a wide array of options in selecting various
articulation
components and baseplates to meet the needs of the patient.
As yet a further advantage, the attachment mechanism is a separate component
from
the articulation component and baseplate. This mechanism enables the
articulation
component to be easily and repeatedly attached and detached from the
baseplate.
Other objects and advantages of the present invention will be apparent from
the
following descriptions of a preferred embodiment with reference to the
drawings.
Brief Description of the Drawings
FIG. 1 is a top perspective view of a modular knee prosthetic system according
to the
invention that includes multiple baseplates removeably connectable with three
different
articulation components.
FIG. 2 is a bottom perspective view of the modular knee prosthetic system of
FIG. 1.
FIG. 3 is a side view of one baseplate embedded in patellar bone with the
three
articulation components of FIG. 1 superimposed on the baseplate to illustrate
the different
sizes of articulation components.
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FIG. 4 is an exploded top perspective view of an alternate embodiment of a
modular
knee prosthesis useable with the modular knee prosthetic system of the present
invention.
FIG. 5 is an exploded bottom perspective view of the modular knee prosthesis
of FIG.
4.
FIG. 6 is an exploded top perspective view of another alternate embodiment of
a
modular knee prosthesis useable with the modular knee prosthetic system of the
present
invention.
FIG. 7 is an exploded bottom perspective view of the modular knee prosthesis
of FIG.
6.
FIG. 8 is a side perspective view of an assembled modular knee prosthesis of
FIGS. 6
and 7.
FIG. 9 is another side perspective view of the assembled modular knee
prosthesis of
FIG. 8.
FIG. 10 is an exploded top perspective view of another alternate embodiment of
a
modular knee prosthesis useable with the modular knee prosthetic system of the
present
invention.
FIG. 11 is an exploded bottom perspective view of the modular knee prosthesis
of
FIG. 10.
FIG. 12 is a top perspective view of another modular knee prosthetic system
that
includes a baseplate removeably connectable with three different articulation
components.
FIG. 13 is a bottom perspective view of the modular knee prosthetic system of
FIG.
12.
FIG. 14 is a top perspective view of the modular knee prosthetic system of
FIGS. 12
and 13 with a baseplate that is removeably connectable with five different
articulation
components.
Detailed Description of the Preferred Embodiment
FIGS. 1-3 show a modular knee prosthetic system or kit 10 having a plurality
of
individual, implantable patellar prostheses. Prostheses of different sizes are
shown wherein
each prosthesis includes an articulation or bearing component 12A~ i2C, an
attachment
mechanism 13A-Y3C, and a base component or baseplate l4A.and 14B.
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The articulation components and baseplates are shown relative to mutually
orthogonal
reference axes X, Y and Z (FIG. 3). When a prosthesis is implanted, reference
axes X, Y and
Z correspond, generally, to well known and accepted anatomical directional
terms. The X
axis extends generally in the medial-lateral direction, the Y axis extends
generally in the
inferior-superior direction, and the Z axis extends generally in the posterior-
anterior
direction. If the prosthesis were implanted on the Ieft patella of a human
patient, the ends of
each of the X, Y, and Z axes marked with an arrowhead would point generally in
the medial,
superior, and posterior directions, respectively.
The present invention may be utilized in various knee surgeries known to those
skilled in the art. As an example, during a TKR surgery, the patella is
resected in a plane
generally perpendicular to the anterior-posterior direction to remove a
posterior portion of the
patellar bone, leaving a resected planar bony surface 15 (FIG. 3). When a
prosthesis is
implanted, the Z axis lies perpendicular to the resected planar bony surface
15 of a patella 17,
and the X and Y axes lie parallel to the resected planar bony surface.
The articulation components of the present invention are constructed of a
biocompatible material having desirable wear and bearing friction properties,
such as
biocompatible metals and ultra-high molecular weight polyethylene (UIiMWP).
Examples
of a suitable materials are Metasul~ and Durasul~ articulation components
manufactured by
Centerpulse Orthopedics Inc. of Austin, Texas.
Articulation component 12 includes two primary surfaces: An articulation
surface 16
and a planar bearing surface 18 oppositely disposed from the articulation
surface. The
bearing surface 18 is generally perpendicular to the Z axis and spaced from
the articulation
surface 16 to define a thickness. A wall 20 extends around the outer perimeter
of the
articulation component and generally has an elliptical or round shape.
Articulation surface 16, in the preferred embodiment shown, is a hyperbolic
paraboloid, also known as a "saddle" shape, in which the intersection of the
surface 16 and
wall 20 defines an undulating edge 22. Points 24 and 26 are at opposite ends
of the "saddle"
and designate the locations at which undulating edge 22 is at its maximum
spacing from
planar bearing surface 18. Points 24 and 26 are on the minor axis of wall 20,
and are disposed
relative to each other generally in the inferior-superior direction along the
Y axis. Points 28
and 30 are at opposite sides of the "saddle" and designate the locations at
which undulating
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edge 22 is at its minimum spacing from planar bearing surface 18. Points
28wand 30 are on
the major axis of wall 20, and are disposed relative to each other generally
in the medial-
lateral direction, along the X axis. Articulation surface 16, so configured,
ideally provides
congruent sliding contact over an extensive range of articulation between
articulation
component 12 and the patellar articulation surface of a femoral prosthesis
component (not
shown) at the patello-femoral joint. Undulating edge 22 at points 24 and 26 at
the high ends
of the "saddle" functionally defines a ridge that can track the intercondylar
groove of the
femoral component during flexion and extension of the knee joint.
The baseplates of the present invention are constructed of a biocompatible
material
having desirable wear, bearing friction, and bone engaging properties that are
known to those
skilled in the art. Examples of such a material are UHMWPE, titanium, titanium
alloys,
zirconia ceramics, aluminum oxide ceramics, and cobalt chromium alloys.
Baseplate 14 includes a fixation surface 32 for engaging patellar bone 17, a
planar
bearing surface 34 generally perpendicular to the Z axis and spaced from the
fixation surface
32, and an outer wall 36 that extends around the perimeter and is generally
parallel to the Z
axis. The baseplate generally has an elliptical or round shape to match the
size and shape of
the articulation component 12.
Fixation surface 32 includes a generally planar surface portion 38 adapted to
engage
resected planar bony surface 15 generally parallel thereto. The surface
portion 38 can be
adapted to directly engage and integrate with the patellar bone with or
without bone cement.
Planar surface portion 38, for example, can include surface texturing (such as
grit-blasting or
other roughened, textured surface) to promote osseointegration of baseplate
14. A coating of
hydroxyapatite, ceramic, or porous metal are examples of surface texturing
known to those
skilled in the art. Such coatings can be applied with plasma spraying or
sintering techniques.
Suitable metals for sintering include titanium and its alloys and cobalt
chromium alloys.
Other materials and methods for providing a surface that favors
osseointegration are well
known in the art.
Fixation surface 32 also includes a plurality of pins or pegs 40 that extend
downward
from the surface. These pegs are evenly and symmetrically spaced apart and are
integrally
connected to fixation surface 32. The pegs 40 are sized and shaped to be
received in
correspondingly shaped bores 42 in patella 17 (FIG. 3). Specifically, each peg
has a
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r
cylindrical body portion with a tapered or conical distal end. One skilled in
the art will
appreciate that the pegs can have various configurations and textures, such as
a straight,
ribbed, or tapered shape with a macro-textured surface to enhance fixation
with bone cement
or osseointegration.
One important advantage of the present invention is that the articulation
component
12 is removeably connectable to the baseplate 14. Even after the baseplate
becomes
permanently connected to the patellar bone, an articulation component can be
readily or
easily attached and detached from the baseplate. The removeable or detachable
connection
between the baseplate and articulation component provides a modular knee
prosthesis. As
shown in FIGS. 1-3, a plurality of articulation components 12A-I2C can connect
to a
plurality of baseplates 14A-14B. Each of the three articulation components has
a similar
shape with a different size. Three different sizes are shown, such as large,
medium, and
small sizes. Likewise, each of the baseplates has a similar shape with a
different size. Two
different sizes are shown, such as large and small. Together, the plurality of
baseplates and
plurality of articulation components form a modular knee prosthetic system.
FIG. 3 also illustrates how each articulation component would fit on one of
the
baseplates. It is important to note that any one of three different
articulation components
12A-12C are engageable with and removable from any one of the baseplates 14A-
14B. One
skilled in the art will appreciate that the number of sizes can increase or
decrease to offer a
more diversified modular prosthetic knee system. Further, a variety of
different shapes for
both the articulation components and baseplates can be offered to provide a
diversified
modular knee prosthetic system.
During a TKR or other knee surgery, the surgeon can select any one of various
sized
and shaped articulation components to connect to any one of various sized and
shaped
baseplates. During a revision surgery for example, the implanted articulation
component
may be damaged, worn, or otherwise need replaced. The articulation component
can be
easily removed from the baseplate and replaced with a new, sterile one. At the
same time
though, the baseplate can be left undisturbed and attached to the patellar
bone. Thus, a new
and different articulation component can be engaged and connected infra-
operatively to an
existing baseplate previously implanted in the patient.
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The coupling or attachment mechanism 13 enables the articulation corriponent
12 and
baseplate 14 to be connectable to and removeable from each other.
Specifically, in the
preferred embodiment, the attachment mechanism 13 has a flat, thin disc-shape
with a first
locking surface or side 46 adapted to engage the bearing surface 18 of the
articulation
S component 12 and a second locking surface or side 48 adapted to engage the
bearing surface
34 of the baseplate 14. The attachment mechanism 13 is provided as a
completely separate
component from both the articulation component 12 and baseplate 14 and has a
locking
mechanism 49 that enables the attachment mechanism to permanently connect to
the
articulation component and removeably connect to the baseplate.
The locking mechanism 49 includes a hub or pin 50 located in the center of the
disk
and two wings or shoulders 52 located on the periphery of the disk. On the
first locking
surface 46, the hub 50 projects outwardly and has cylindrical or tapered
conical shape with a
flat top surface 53. Hub 50 is hollow and includes a keyway or locking recess
54 projecting
inwardly from the second locking surface 48. This keyway generally has an
elongated
rectangular shape and provides access to the enlarged hollow section inside
the hub.
Each wing 52 extends upwardly from the first locking surface 46 and has an
elongated, thin, rectangular shape defined by an inside wall 55 and an outside
wall 56. The
wings extend around the outer perimeter of the first locking surface 46 and
thus have a
curved shape.
The bearing surface 18 of the articulation component 12 has a centrally
located bore
or recess 58. This recess is sized and shaped to receive the hub 50 on locking
mechanism 49.
Articulation component 12 also includes a pair of cutouts or recesses 60 along
the outer
perimeter or wall 20. These cutouts are sized and shaped to receive the wings
52 of locking
mechanism 49.
The bearing surface 34 of the baseplate 14 has a centrally located and
outwardly
extending pin 62. This pin has an elongated rectangular head portion 63 that
is sized and
shaped to extend into and through the keyway 54 of the second locking surface
48 of locking
mechanism 49.
In operation, articulation component 12 and baseplate 14 are configured to
engage
each other in a removable locking or snap-retaining relationship.
Specifically, the locking
mechanism 49 is shaped and sized to connect to the articulation component 12.
As the first
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locking surface 46 of the locking mechanism 49 is pressed or abutted against
the bearing
surface 18 of the articulation component 12, hub 50 projects into and engages
with recess 58.
At the same time, wings 52 project into and engage with cutouts 60. The wings
52 can be
configured to be resilient and slightly deform outwardly to engage cutouts 60.
The connection between the articulation component 12 and the attachment
mechanism 13 can be designed to be either permanent (i.e., not removable) or
removable.
Once the two components are connected, wings 52 are locked into cutouts 60 and
prevent the
attachment mechanism and articulation component from rotating relative to each
other.
An impouant advantage of the present invention is that the articulation
component 12
can repeatedly attach and detach from the baseplate 14. In this operation, the
second locking
surface 48 of attachment mechanism 13 is shaped and sized to removeably
connect to and
lock with the bearing surface 34 of the baseplate 14. As these two surfaces
are pressed or
abutted against each other, the head portion 63 of pin 62 extends through
keyway 54 and into
the hollow portion of hub S0. The articulation component 12 and accompanying
attachment
mechanism 13 can then be rotated 90° in either a clockwise or
counterclockwise direction to
secure and Iock the baseplate 14 to the articulation component 12.
In order to remove the articulation component 12 from the baseplate 14,
articulation
component 12 and accompanying attachment mechanism 13 can then be rotated
90° in either
a clockwise or counterclockwise direction to unlock the components.
FIGS. 1-3 show an attachment mechanism 13 formed as a disk with a locking
mechanism adapted to engage both the articulation component and baseplate. One
skilled in
the art will appreciate that attachment mechanism can be altered without
departing from the
scope of the invention. As an example, the components of the locking mechanism
can be
switched, moved, and altered. Other embodiments as well are within the scope
of the
invention, and some of these embodiments are shown in the subsequent figures.
Another advantage of the present invention is that the articulation component,
baseplate, and attachment mechanism are each formed as single, unitary pieces
that are
connectable together. The attachment mechanism enables the articulation
component to
removeably connect to the baseplate.
FIGS. 4 and 5 show an alternate modular knee prosthesis 70 that can be used
with the
various embodiments of the present invention. The prosthesis includes an
articulation
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component 72, a baseplate 74, and an attachment mechanism 76. The articulation
component
and baseplate generally have a configuration similar to the articulation
component 12 and
baseplate 14 shown and described in connection with FIGS. 1-3. The primary
differences
between these embodiments centers around the attachment mechanism 76 and how
it
S connects the articulation component to the baseplate.
Articulation component 72 has a bearing surface 80 with a circular channel or
groove
82 that includes a recess 84 extending around the inner wall. The baseplate 74
includes a
circular or annular protrusion 86 that extends outwardly from the bearing
surface 88. The
protrusion 86 has a rectangular cross-section with four rectangular legs 90
extending
outwardly from the annular body. Each leg includes a lip, shoulder, or tang
91. The
protrusion 86 is shaped and adapted to be received in the channel 82 of the
articulation
component 72.
The attachment mechanism 76 includes an annular or ring-shape body 94 with a
locking mechanism formed as four rectangular cutouts 96 and a recess 98. The
recess
extends around an outer perimeter or surface of the body and is sized and
shaped to receive a
locking ring 100.
In operation, articulation component 72 and baseplate 74 are configured to
engage
each other in a locking relationship such that the two components can be
connected and
removed from each other. The attachment mechanism 76 is sized and shaped to
fit into the
circular recess 84 of the articulation component 72. Locking ring 100 fits in
both recess 98
and recess 84 to connect and lock the attachment mechanism 76 to the
articulation
component 72.
As the bearing surface 80 of the articulation component is pressed or abutted
against
the bearing surface 88 of the baseplate 74, the protrusion 86 extends into the
channel 82 so
legs 90 engage and protrude into cutouts 96. Simultaneously, the locking ring
100 snaps
over the lips 91 of protrusion 86 to secure and lock the baseplate to the
articulation
component. When articulation component 72 and baseplate 74 are engaged and
locked
together, the planar bearing surfaces of both components lie in direct
parallel engagement
each other. These surfaces are free to slideably engage so the articulation
component can
rotate relative to the baseplate. One skilled in the art will appreciate that
the tolerances of
these components could also be modified to make this assembly a non-rotateable
assembly.
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For example, especially tangs 91 can be configured to engage the inner wall of
recess 84 and
prevent relative movement between the components.
FIGS. 6-9 show another alternate modular knee prosthesis 110 that can be used
with
the various embodiments of the present invention. The prosthesis includes an
articulation
component 112, a baseplate 114, and an attachment mechanism 116. The
articulation
component and baseplate generally have a configuration similar to the
articulation
component 12 and baseplate 14 shown and described in connection with FIGS. 1-
3. The
primary differences between these embodiments centers around the attachment
mechanism
116 and how it connects the articulation component to the baseplate.
Articulation component 112 has a smooth, planar bearing surface 120. Two
oppositely disposed cutouts 122 are formed along the outer perimeter or wall
124 of the
articulation component. These cutouts include a ridge or shoulder 126.
Baseplate 114 has a smooth, planar bearing surface 130. Four equally spaced
cutouts
or recesses 134 are formed along the outer perimeter or wall 135. Each cutout
134 includes a
ledge 136 that partially extends around the length of the cutout. A gap or
opening 138 is
formed between an end wall of the cutout and the end of the ledge 136.
Attachment mechanism 116 enables the articulation component 112 and baseplate
114 to be connectable to and removable from each other. Specifically, the
attachment
mechanism 116 has a flat, thin disc-shape with a first locking surface or side
140 adapted to
engage the bearing surface 120 of the articulation component 112 and a second
locking
surface or side 142 adapted to engage the bearing surface 130 of the baseplate
114. The
attachment mechanism 116 is provided as a completely separate component from
both the
articulation component 112 and baseplate 114 and has a locking mechanism 149
that enables
the attachment mechanism to permanently connect to the articulation component
and
removeably connect to the baseplate.
The locking mechanism 149 includes two wings or shoulders 152 located on the
periphery of the disk. Each wing 152 extends upwardly from the first locking
surface 140
and has an elongated, thin, rectangular shape defined by an inside wall 155
and an outside
wall 156. A lip or ridge 157 extends along the inside wall 155. The wings
extend around the
outer perimeter of the first locking surface and thus have a curved shape. The
locking
mechanism 149 also includes four arms 160 that extend outwardly from the
second locking
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surface 142. These arms have an "L" shape with a lip or tab 162 and are
equally spaced
around the outer perimeter of the attachment mechanism 116.
In operation, articulation component 112 and baseplate 114 are configured to
engage
each other in a removable locking or snap-retaining relationship.
Specifically, the locking
S mechanism 149 is shaped and sized to connect to the articulation component
112. As the
first locking surface 140 of the locking mechanism 149 is pressed or abutted
against the
bearing surface 120 of the articulation component 112, wings 152 project into
and engage
with cutouts 122. As the wings are pressed into the cutouts, the ridges 157 of
wings 152 snap
over the shoulders 126 to lock the attachment mechanism 116 to the
articulation component
112. The wings 152 can be configured to be resilient and slightly deform
outwardly so the
ridges 157 fit over the shoulders 126.
The connection between the articulation component 112 and the attachment
mechanism 116 can be designed to be either permanent (i.e., not removable) or
removable.
Once the two components are connected, wings 152 are locked into cutouts 122
and prevent
the attachment mechanism and articulation component from rotating relative to
each other.
As the bearing surface 120 of the articulation component 112 and second
locking
surface 142 of attachment mechanism 116 are pressed or abutted against the
bearing surface
130 of the baseplate 114, the arms 160 on the second locking surface 142 of
the attachment
mechanism 116 extend through the openings 138 of each cutout 134. The
attachment
mechanism 116 and attached articulation component 112 are then rotated so the
tabs 162 are
positioned under ledge 136. FIGS. 6 and 7 illustrate a locking rotation (shown
with an arrow
and "Lock") needed to connect the articulation component to the baseplate. In
this position,
the articulation component is engaged and locked with the baseplate. Further,
the planar
bearing surfaces of both components lie in direct parallel engagement each
other. These
surfaces slideably engage while the components are locked and unlocked, but
otherwise the
articulation component does not rotate relative to the baseplate.
FIGS. 6-9 show an attachment mechanism 116 formed as a disk with a locking
mechanism adapted to engage both the articulation component and baseplate. One
skilled in
the art will appreciate that attachment mechanism can be altered without
departing from the
scope of the invention. As an example, the components of the locking mechanism
can be
switched, moved, and altered. FIGS. 10 and 11 show one such embodiment.
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In FIGS. 10 and 11, the articulation component 170, baseplate 172, and
attachment
mechanism 174 generally have a configuration similar to the corresponding
components
shown and described in connection with FIGS. 6-9. The primary differences
between these
embodiments centers around the attachment mechanism 174 and how it connects
the
articulation component to the baseplate. Specifically, the four arms 176
(previously shown
in FIGS. 6-9 at 160 on the attachment mechanism 116) now extend outwardly from
the
bearing surface 180 of the baseplate 172. Further, the cutouts 182 and
corresponding
openings 184 (previously shown in FIGS. 6-9 at 134 and 138, respectively, on
the baseplate
114) are now positioned along an outer perimeter 186 of attachment mechanism
174.
Articulation component 170 engages, locks, unlocks, and disengages from
baseplate
172 in a manner similar to the articulation component 112 and baseplate 114
described in
FIGS. 6-9. FIGS. 10 and 11 illustrate one example how the attachment mechanism
can be
altered from another embodiment without departing from the scope of the
invention.
As previously shown and discussed in connection with FIGS 1-3, the modular
knee
prosthetic system of the present invention can have a plurality of
articulation components
with different sizes and a plurality of baseplates with different sizes. In
these figures, the
various articulation components have saddle shapes, while the baseplates use a
central pin to
engage and connect with the attachment mechanism and accompanying articulation
component. One skilled in the art, though, will appreciate that the
articulation component,
attachment mechanism, and baseplate can be modified without departing from the
scope of
the invention. FIGS. 12 and 13 illustrate one such example.
FIGS. 12 and 13 show a modular knee prosthetic system or kit 210 having a
plurality
of individual, implantable patellar prostheses. Prostheses of different sizes
are shown
wherein each prosthesis includes an articulation or bearing component 212A-
212C, an
attachment mechanism 213, and a common baseplate 214.
Articulation component 212 includes two primary surfaces: An articulation
surface
216 and a planar bearing surface 218 oppositely disposed from the articulation
surface. The
bearing surface 218 has a configuration similar to the bearing surface 80 of
articulation
component 72 shown and described in connection with FIGS. 4 and 5. In FIGS. 12
and 13,
though, the ring-shaped attachment mechanism 213 (previously shown in FIGS. 4
and 5 at
76) is integrally formed into a circular channel or groove 220 of bearing
surface 218.
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The articulation surface 216 of the articulation component 212 has~'a rounded
or
dome-like shape. Specifically, a tapered or conical section 222 extends
inwardly from a side
perimeter or wall 224. This tapered section abuts a generally flat top section
226.
Baseplate 214 includes a fixation surface 232 for engaging patellar bone and a
planar
bearing surface 234. The baseplate 214 has a configuration that is identical
to the baseplate
74 shown and described in connection with FIGS. 4 and 5.
As shown in FIGS. 12 and 13, the attachment mechanism 213 includes a circular
locking wire or ring 238. This ring can be positioned into and out of the
channel 220 of the
articulation component to engage and lock the baseplate 214 when the
articulation
component is connected to the baseplate. The articulation component 212
attaches and
detached from the baseplate 214 in a manner similar to the articulation
component 72 and
baseplate 74 of FIGS. 4 and S. This ring may also serve as an x-ray marker to
aid in the
location of the bearing component in the unlikely event that the bearing
component should
become dislodged from the baseplate component (for example, due to trauma). A
metallic
ring would be useful if the other components were fabricated from materials
such as
UI~VIWPe.
FIG. 14 further illustrates the diversification of the modular knee prosthetic
system
250 of the present invention. Prosthetic combinations of different sizes and
shapes are
available and possible wherein each prosthesis includes an articulation
component 252A-
252E, an attachment mechanism (not shown), and a baseplate 256. These
components attach
and detach from one another in a manner similar to the components shown and
described in
connection with FIGS. 4, 5, 12, and 13.
It is important to note that the prosthetic system 250 of FIG. 14 includes a
plurality of
articulation components having different sizes and shapes. Components 252A and
252E
have articulation surfaces with saddle shapes, whereas components 252B-252D
have
articulation surfaces with dome-like shapes. One skilled in the art will
appreciate that the
number and sizes and shapes of both the articulation components and baseplates
can increase
or decrease to offer a more diversified modular prosthetic knee system.
The articulation component of the present invention can enjoy various degrees
of
freedom of movement relative to the baseplate. The term "degree of freedom" is
used in its
ordinary engineering sense to mean freedom of a component to rotate about or
translate along
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a line that is parallel to one axis of a three-axis Cartesian coordinate
system fixed in
orientation relative to the reference component. The freedom to rotate about
such a line
comprises one degree of rotational freedom, and the freedom to translate along
such a line
comprises one translational degree of freedom. A component can enjoy a maximum
of six
degrees of freedom, in which case the component can rotate about any axis and
can translate
along any axis. Essentially, a component with six degrees of freedom is
unconstrained by any
other component.
United States Patent Number 5,702,465 entitled "Patella Prosthesis Having
Rotational
and Translational Freedom" is incorporated herein by reference and teaches an
articulation
component and baseplate having two degrees of freedom. The present invention
can be
employed with the embodiments taught therein.
Further, the present invention can be utilized with various prosthetic knee
designs,
including both mobile bearing and fixed knee designs.
Even further, one skilled in the art will appreciate that the attachment
mechanism
used to connect the articulation component to the baseplate may be modified
without
departing from the scope of the invention. For example, the male and female
components on
the articulation component could be switched with the corresponding components
on the
baseplate.
Further yet, it is important to reiterate that the present invention includes
a family of
baseplates, a family or articulation components, and a family of attachment
mechanisms that
all can be produced and packaged separately or together with the intention of
producing a
modular prosthetic knee system. The articulation components and baseplates can
be
assembled intra-operatively in a mix and match fashion to meet the needs of
the patient.
Further, the present invention contemplates multiple components in a family of
articulation
components and baseplates that can be removed or replaced with like or
different
components from the family. A large family of components can serve a wide
array of patient
needs and give the surgeon modularity between components even during intra-
operative
assembly.
Although illustrative embodiments have been shown and described, a wide range
of
modifications, changes, and substitutions is contemplated in the foregoing
disclosure and in
some instances, some features of the embodiments may be employed without a
IOI-440 16
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corresponding use of other features. Accordingly, it is appropriate that the
appended claims
be construed broadly and in a manner consistent with the scope of the
embodiments disclosed
herein.
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