U.S. patent application number 10/155568 was filed with the patent office on 2003-01-09 for surface sterilizable joint replacement prosthesis component with insert.
Invention is credited to Burstein, Albert, Gundlapalli, Rama Rao V., Heldreth, Mark, Smith, Todd.
Application Number | 20030009230 10/155568 |
Document ID | / |
Family ID | 27496163 |
Filed Date | 2003-01-09 |
United States Patent
Application |
20030009230 |
Kind Code |
A1 |
Gundlapalli, Rama Rao V. ;
et al. |
January 9, 2003 |
Surface sterilizable joint replacement prosthesis component with
insert
Abstract
A joint prosthesis (10) including a first component (12)for
cooperation with a first long bone (14) and a second component (16)
for cooperation with a second long bone (20) is provided. The joint
prosthesis (10) also includes a bearing component (222)
positionable between the first component (12) and the second
component (16) and cooperable with the first (12) and second (16)
components. The bearing component (222) has a reinforcing component
(236) having a first end (286) and a second end (294) and a
polymeric material (207). The polymeric material (207) surrounds at
least 99% of the surface area of the reinforcing component (236)
and is molded to the reinforcing component (236) so that the
material may be sterilized by a predominately surface sterilizing
technology. The bearing component (222) defines a first peripheral
region (271) and a second peripheral region (282). The first
peripheral region (271) is adjacent to the first end (286) of the
reinforcing component (236) and the second peripheral region (282)
is adjacent the second end (244) of the reinforcing component
(236). The first peripheral region (271) is cooperable with said
first component (12) and the second peripheral region (282) is
cooperable with the second component (16).
Inventors: |
Gundlapalli, Rama Rao V.;
(Leesburg, IN) ; Heldreth, Mark; (Mentone, IN)
; Smith, Todd; (Ft. Wayne, IN) ; Burstein,
Albert; (Sarasota, FL) |
Correspondence
Address: |
AUDLEY A. CIAMPORCERO JR.
JOHNSON & JOHNSON
ONE JOHNSON & JOHNSON PLAZA
NEW BRUNSWICK
NJ
08933-7003
US
|
Family ID: |
27496163 |
Appl. No.: |
10/155568 |
Filed: |
May 24, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60302115 |
Jun 30, 2001 |
|
|
|
Current U.S.
Class: |
623/20.28 ;
623/23.58; 623/901 |
Current CPC
Class: |
A61F 2220/0033 20130101;
A61F 2002/30364 20130101; A61F 2002/30957 20130101; A61F 2310/00029
20130101; A61F 2/3886 20130101; A61F 2310/00017 20130101; A61F
2310/00023 20130101; A61F 2002/30398 20130101; A61F 2/3868
20130101; B29C 43/006 20130101; B29C 43/18 20130101; A61F 2/30942
20130101; A61F 2220/0025 20130101; B29L 2031/7532 20130101; A61F
2002/30604 20130101 |
Class at
Publication: |
623/20.28 ;
623/23.58; 623/901 |
International
Class: |
A61F 002/38 |
Claims
What is claimed is:
1. A joint prosthesis, comprising: a first component for
cooperation with a first long bone; a second component for
cooperation with a second long bone; and a bearing component
positionable between said first component and said second component
and cooperable therewith, said bearing component including a
reinforcing component having a first end and a second end thereof
and a polymeric material surrounding at least 99% of the surface
area of the reinforcing component and molded thereto, so that the
material may be sterilized by a predominately surface sterilizing
technology, said bearing component defining a first peripheral
region thereof and a second peripheral region thereof, the first
peripheral region being adjacent the first end of the reinforcing
component and the second peripheral region being adjacent the
second end of the reinforcing component, the first peripheral
region being cooperable with said first component and the second
peripheral region being cooperable with said second component.
2. The joint prosthesis of claim 1, wherein the predominately
surface sterilizing technology comprises a gas plasma spray
process.
3. The joint prosthesis of claim 1, wherein said polymeric material
extends normally from the surface of said reinforcing component a
distance of at least 5 millimeters.
4. The joint prosthesis of claim 1, wherein said polymeric material
surrounds the reinforcing component on at least 99.5% of the
surface area of the reinforcing component.
5. The joint prosthesis of claim 1, wherein the reinforcing
component comprises: a first portion defining a first centerline
thereof; and a second portion defining a second centerline thereof,
said first centerline and said second centerline being
non-coincidental.
6. The joint prosthesis of claim 5, wherein the second centerline
is parallel and spaced from the first centerline.
7. The joint prosthesis of claim 1, wherein said polymeric material
comprises crosslinked ultra high molecular weight polyethylene
8. The joint prosthesis of claim 1, wherein the reinforcing
component defines a holding feature thereon for holding the
reinforcing component when placing the polymeric material onto the
reinforcing component.
9. The joint prosthesis of claim 5, wherein the reinforcing
component defines an orientation feature thereon for orienting the
reinforcing component with respect to at least one of the first
centerline and the second centerline when placing the polymeric
material onto the reinforcing component.
10. The joint prosthesis of claim 5, wherein the reinforcing
component defines a first recess on the first portion and a second
recess on the second portion, the first recess and the second
recess adaptable for holding the reinforcing component when placing
the polymeric material onto the reinforcing component.
11. The joint prosthesis of claim 10, wherein the first recess and
the second recess are oriented substantially concentric with at
least one of the first centerline and the second centerline.
12. The joint prosthesis of claim 5, wherein said reinforcing
component defines a first recess and a second recess on the first
portion, the first recess and the second recess adaptable for
holding the reinforcing component when placing the polymeric
material onto the reinforcing component.
13. The joint prosthesis of claim 12, wherein the first recess and
the second recess are oriented substantially perpendicular to the
first centerline and the second centerline.
14. A knee prosthesis, comprising: a femoral component for
attachment to a femur; a tibial tray for attachment to a tibia; a
bearing component positionable between said femoral component and
said tibial tray for cooperation with said femoral component and
said tibial tray, said bearing component including a reinforcing
component having a first end and a second end thereof and a
polymeric material, the polymeric material surrounding at least 99%
of the surface area of the reinforcing component and molded
thereto, so that the material may be sterilized by a predominately
surface sterilizing technology, said bearing component defining a
first peripheral region thereof and a second peripheral region
thereof, the first peripheral region being adjacent the first end
of the reinforcing component and the second peripheral region being
adjacent the second end of the reinforcing component, the first
peripheral region being cooperable with the femoral component and
the second peripheral region being cooperable with the tibial
tray.
15. The knee prosthesis of claim 14, wherein the predominately
surface sterilizing technology comprises a gas plasma spray
process.
16. The knee prosthesis of claim 14, wherein said polymeric
material extends normally from the surface of the reinforcing
component a distance of at least 5 millimeters.
17. The knee prosthesis of claim 14, wherein said polymeric
material surrounds the reinforcing component on at least 99.5% of
the surface area of the reinforcing component.
18. The knee prosthesis of claim 14, wherein the reinforcing
component comprises: a first portion defining a first centerline
thereof; and a second portion defining a second centerline thereof,
the first centerline and the second centerline being
non-coincidental.
19. The knee prosthesis of claim 18, wherein the second centerline
is parallel and spaced from the first centerline.
20. The knee prosthesis of claim 14, wherein the polymeric material
comprises crosslinked ultra high molecular weight polyethylene.
21. The knee prosthesis of claim 14, wherein the reinforcing
component defines a holding feature thereon for holding the
reinforcing component when placing the polymeric material onto the
reinforcing component.
22. The knee prosthesis of claim 18, wherein the reinforcing
component defines an orientation feature thereon for orienting the
reinforcing component with respect to at least one of the first
centerline and the second centerline when placing the polymeric
material onto the reinforcing component.
23. The knee prosthesis of claim 18, wherein the reinforcing
component defines a first recess on the first portion and a second
recess on the second portion, the first recess and the second
recess adaptable for holding the reinforcing component when placing
the polymeric material onto the reinforcing component.
24. A bearing component for use in knee joint arthroplasty, said
bearing component being positionable between a femoral component
and a tibial tray for cooperation with the femoral component and
the tibial tray, said bearing component comprising: a reinforcing
component having a first end and a second end thereof; and a
polymeric material, the polymeric material surrounding at least 99%
of the surface area of the reinforcing component, so that the
material may be sterilized by a predominately surface sterilizing
technology, said bearing component defining a first peripheral
region thereof and a second peripheral region thereof, the first
peripheral region being adjacent the first end of the reinforcing
component and the second peripheral region being adjacent the
second end of the reinforcing component, the first peripheral
region being cooperable with the femoral component and the second
peripheral region being cooperable with the tibial tray.
25. The bearing component of claim 24, wherein the predominately
surface sterilizing technology comprises a gas plasma spray
process.
26. The bearing component of claim 24, wherein said polymeric
material surrounds said reinforcing component on at least 99.5% of
the surface area of said reinforcing component.
27. The bearing component of claim 24, wherein said reinforcing
component comprises: a first portion defining a first centerline
thereof; and a second portion defining a second centerline thereof,
the first centerline and the second centerline being
non-coincidental.
28. The bearing component of claim 24, wherein said polymeric
material comprises crosslinked ultra high molecular weight
polyethylene.
29. The bearing component of claim 24, wherein said reinforcing
component defines a holding feature thereon for holding said
reinforcing component when placing said polymeric material onto
said reinforcing component.
30. The bearing component of claim 27, wherein said reinforcing
component defines a orientation feature thereon for orienting said
reinforcing component with respect to at least one of first
centerline and second centerline when placing said polymeric
material onto said reinforcing component.
31. The bearing component of claim 27, wherein said reinforcing
component defines a first recess on the first portion and a second
recess on the second portion, the first recess and the second
recess adaptable for holding said reinforcing component when
placing said polymeric material onto said reinforcing
component.
32. A method of manufacturing a polymeric bearing component for use
in joint arthroplasty and for cooperation with a first joint
component and a second joint component, comprising the steps of:
providing a reinforcing support having a first end and a second end
thereof; providing a molding die adapted for manufacturing the
bearing component for use in joint arthroplasty and having a first
mold portion and a second mold portion thereof, the first mold
portion adapted to provide a first surface and cooperation with the
first joint component and the second mold portion adapted to
provide a second surface for cooperation with the second joint
component; providing a positioning member for cooperation with the
reinforcing support and molding die; positioning the support in a
desired position within the molding die, with one of the first end
and at the second end located in the first mold portion;
maintaining the position of the support with the positioning member
in intimate contact with the support; adding moldable polymeric
material into the molding die; substantially surrounding the
support with the moldable material; heating and pressurizing the
mold; permitting the moldable material to cool to form the bearing
component and during the cooling and forming of the moldable
material removing the positioning member from the support while
maintaining a lower amount of one of heat and pressure on the mold
and allowing the polymeric material to replace the space occupied
by the positioning member; and removing the component from the
molding die.
Description
CROSS REFERENCE TO U.S. PROVISIONAL PATENT APPLICATION
[0001] This application is a Utility Application based upon U.S.
Provisional Patent Application, Serial No. 60/302,115 filed Jun.
30, 2001, entitled SURFACE STERILIZABLE JOINT REPLACEMENT
PROSTHESIS COMPONENT WITH INSERT.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] Cross reference is made to the following applications:
[0003] DEP 677 titled "JOINT PROSTHESIS MOLDING METHOD AND DIE FOR
PREFORMING THE SAME" and DEP 676 titled "JOINT REPLACEMENT
PROSTHESIS COMPONENT WITH NON LINEAR INSERT" filed concurrently
herewith which are incorporated herein by reference.
TECHNICAL FIELD OF THE INVENTION
[0004] The present invention relates generally to the field of
orthopaedics, and more particularly, to an implant for use in joint
arthroplasty.
BACKGROUND OF THE INVENTION
[0005] The invention relates to joint prostheses. More
particularly, the invention is directed to tibial components of
knee joint prostheses that can be configured to be either rotatable
or non-rotatable.
[0006] Joint replacement surgery is quite common and it enables
many individuals to function normally when otherwise it would not
be possible to do so. Artificial joints usually comprise metallic,
ceramic and/or plastic components that are fixed to existing
bone.
[0007] Knee arthroplasty is a well known surgical procedure by
which a diseased and/or damaged natural knee joint is replaced with
a prosthetic knee joint. A typical knee prostheses include a
femoral component, a patella component, a tibial tray or plateau,
and a tibial bearing insert. The femoral component generally
includes a pair of laterally spaced apart condylar portions, the
distal surfaces of which articulate with complementary condylar
elements formed in a tibial bearing insert.
[0008] The tibial plateau is mounted within the tibia of a patient.
Typically, the tibial bearing insert, which is usually made of
ultra high molecular weight polyethylene (UHMWPE), is mounted upon
the superior surface of the tibial plateau. The geometry and
structure of the tibial bearing insert varies depending upon the
needs and joint condition of a patient. Some tibial bearing inserts
are designed to be used with joint prostheses that are implanted
during procedures that retain one or both of the cruciate
ligaments. Others are implanted after removal of one or both of the
cruciate ligaments, and are thus structured to compensate for the
loss of these ligaments. Yet other tibial bearing inserts are used
with prostheses that provide enhanced stabilization to the knee
joint.
[0009] Recent total knee prostheses have been designed which allow
for increased freedom of rotation between the femur and the tibia.
To allow for this rotational motion, tibial bearing inserts have
been designed which allow for rotation of the insert on the tibial
tray or plateau. Typically the tibia bearing inserts have a central
stem which rotationally engages centrally in the tibial stem of the
tibial tray implant, thereby providing for the rotational motion.
Typically, there are no rotational constraints between the tibial
tray implant and the tibial bearing insert. Frequently, during
total knee arthroplasty, the posterior cruciate ligaments are
sacrificed and a substitute for the posterior cruciate ligaments is
required. Orthopaedic implants for total knee arthroplasty have
been developed which provide for the substitution of the posterior
cruciate ligament. Examples of such implants include the PFC Sigma
RP as described in U.S. Pat. No. 4,298,992 incorporated herein by
reference, and the LCS Complete total knee prosthesis, both of
which are sold by DePuy Orthopaedics, Inc., Warsaw, Ind.
[0010] These total knee prostheses are designed with tibial
components and femoral components which have in conjunction with
their articulating surface, a spine and cam mechanism, which is
used as a posterior cruciate substituting feature when the
posterior cruciate of the knee is sacrificed.
[0011] Such total knee replacement prostheses, which include a
spine and cam mechanism, typically contain tibial bearing
components manufactured from suitable plastic, usually UHMWPE. One
such construction use for a class of total knee replacement
prosthesis, which are known as constrained prosthesis, often
incorporate metal reinforcement rods in the construction of the
plastic bearing component. The bearing insert is constructed so
that the metal rod lies within the bearing, and thus provides
additional support for the central spine element of the bearing.
Such components are typically manufactured by machining or molding
the bearing component, drilling a central hole, and press fitting
the reinforcing metal rod. An example of such a component is
described in U.S. Pat. No. 5,007,933 to Sidebotham et al. hereby
incorporated in its entirety by reference.
[0012] In order to allow for desired kinematics of the knee during
a full range of motion, the spine and cam mechanism on the tibial
bearing insert may be placed in a suitable position, preferably
anterior to the center line of the insert in the anterior/posterior
direction. Designs of tibial inserts are available to help
reconstruct knees where the stabilizing soft tissue compromises
have been made or occurred due to various reasons. In such cases,
the tibial bearing inserts are required to experience greater loads
in the anterior/posterior and the medial/lateral directions. The
constrained inserts may be reinforced with a metal rod, as
mentioned earlier, to help distribute the loads experienced by the
spine of the polyethylene tibial bearing.
[0013] Total knee joint prostheses have been designed with the
spine and cam mechanism on the tibial bearing insert placed in a
position that the central axis of the distal stem portion of the
insert that engages the tibial tray, and the axis of the superior
spine portion that engages the cam of the femoral component, are
not necessarily collinear.
[0014] Unfortunately, this design does not allow for a straight
rod, commonly employed for reinforcement of tibial bearing inserts,
to be used.
[0015] It should be appreciated that a first rod could be inserted
inside the spine, and a second rod could be inserted in the stem of
the tibial tray portion of the bearing insert. However, the load on
the first rod would be transferred through the polymer portion of
the insert to the second rod. The polymer strength would then limit
the load carrying capacity of this configuration. Such a
configuration may not provide the required strength to sufficiently
support and reinforce the spine.
[0016] The present invention is directed to providing a tibial
bearing insert with sufficient strength at the spine to withstand
the loads of the knee prosthesis in the anterior/posterior and
medial/lateral direction, while preserving bearing wear resistance
when the central axis of the distal stem of the insert and the axis
of the superior spine are not necessarily co-linear.
SUMMARY OF THE INVENTION
[0017] The present invention is directed to an improved joint
prosthesis for total knee replacement which includes a spine and
cam mechanism. The cam mechanism being on the femoral component and
the spine being on the bearing component. The mechanism is capable
of withstanding the greater loads experienced in the
anterior/posterior and medial/lateral direction caused by the
substitution of the cam and spine for the posterior cruciate
ligament which may be sacrificed during total knee arthroplasty
while preserving bearing wear resistance.
[0018] The spine on the tibial bearing insert, according to the
present invention, is placed anterior to the centerline of the
insert in the anterior/posterior direction. Therefore, the distal
stem portion of the insert which engages the tibial tray and the
superior spine portion which engages the cam of the femoral
component are not in the same plane. The tibial bearing insert of
the present invention thus includes a rod placed internal to the
tibial bearing insert which includes an offset feature.
[0019] The knee prosthesis of the present invention thus includes a
first polymeric component and a reinforcing component including a
first portion on a first center line and a second portion on a
second center line such that the first portion may engage the
tibial tray and the second portion may be cooperating with the cam
mechanism in the femoral component of the knee prosthesis.
[0020] According to one embodiment of the present invention, there
is provided a joint prosthesis including a first component for
cooperation with a first long bone and a second component for
cooperation with a second long bone. The joint prosthesis also
includes a bearing component positionable between the first
component and the second component and cooperable with the first
and second components. The bearing component has a reinforcing
component having a first end and a second end and a polymeric
material. The polymeric material surrounds at least 99% of the
surface area of the first component and is molded to the first
component so that the material may be sterilized by a predominately
surface sterilizing technology. The bearing component defines a
first peripheral region and a second peripheral region. The first
peripheral region is adjacent to the first end of the reinforcing
component and the second peripheral region is adjacent the second
end of the reinforcing component. The first peripheral region is
cooperable with said first component and the second peripheral
region is cooperable with the second component.
[0021] According to another embodiment of the present invention,
there is provided a knee prosthesis including a femoral component
for attachment to a femur and a tibial tray for attachment to a
tibia. The knee prosthesis also includes a bearing component
positionable between the femoral component and the tibial tray for
cooperation with the femoral component and the tibial tray. The
bearing component includes a reinforcing component with a first end
and a second end. The bearing component also includes a polymeric
material. The polymeric material surrounds at least 99% of the
surface area of the reinforcing component and is and molded to the
reinforcing component, so that the material may be sterilized by a
predominately surface sterilizing technology. The bearing component
defines a first peripheral region and a second peripheral region.
The first peripheral region is adjacent to the first end of the
reinforcing component and the second peripheral region is adjacent
to the second end of the reinforcing component. The first
peripheral region is cooperable with the femoral component and the
second peripheral region is cooperable with the tibial tray.
[0022] According to yet another embodiment of the present
invention, there is provided a bearing component. The bearing
component is for use in knee joint arthroplasty. The bearing
component is positionable between a femoral component and a tibial
tray for cooperation with the femoral component and said tibial
tray, the bearing component including a reinforcing component
having a first end and a second end. The bearing component also
includes a polymeric material surrounding at least 99% of the
surface area of the reinforcing component, so that the material may
be sterilized by a predominately surface sterilizing technology.
The bearing component defines a first peripheral region and a
second peripheral region. The first peripheral region is adjacent
the first end of the reinforcing component and the second
peripheral region is adjacent the second end of the reinforcing
component. The first peripheral region is cooperable with the
femoral component and the second peripheral region is cooperable
with the tibial tray.
[0023] According to another embodiment of the present invention,
there is provided a method of manufacturing a polymeric bearing
component for use in joint arthroplasty and for cooperation with a
first joint component and a second joint component. The method
includes the steps of providing a reinforcing support having a
first end and a second end thereof and providing a molding die
adapted for manufacturing the bearing component for use in joint
arthroplasty and having a first mold portion and a second mold
portion. The first mold portion is adapted to provide a first
surface to cooperate with the first joint component and the second
mold portion and is adapted to provide a second surface to
cooperate with the second joint component. The method also includes
the steps of providing a positioning member for cooperation with
the reinforcing support and molding die and positioning the support
in a desired position within the molding die. One of the first end
and at the second end is located in the first mold portion. The
method further includes the steps of maintaining the position of
the support with the positioning member in intimate contact with
the support and adding moldable polymeric material into the molding
die. The method also includes the steps of substantially
surrounding the support with the moldable material, heating and
pressurizing the mold, and permitting the moldable material to cool
to form the bearing component and during the cooling and forming of
the moldable material, removing the positioning member from the
support while maintaining a lower amount of one of heat and
pressure on the mold and allowing the polymeric material to replace
the space occupied by the positioning member The method also
includes the step of removing the component from the molding
die.
[0024] If a total knee prosthesis requires removal from the patient
and replacement with a new prosthesis, such replacement prosthesis
typically engages further into the medullary canals of the femur
and tibia. Such prostheses are called revision prosthesis. During
the prosthesis replacement, cruciate ligaments are much more often
sacrificed than in an initial or primary total knee arthroplasty.
Currently, no revision tibial bearing inserts with rotational
features include a spine which centerline is not aligned with the
center of the distal stem portion of the insert which rotationally
engages the tibial tray.
[0025] Attempts have been made to reinforce polyethylene bearings.
One such attempt is that as shown in U.S. Pat. No. 5,989,472 Ashby
et al, incorporated herein by reference. The polyethylene bearing
in Ashby includes a reinforcement feature for bone attachment. The
reinforcement feature is to assist in eliminating motion between
the polyethylene and the metal backing.
[0026] Another attempt at reinforcing a polyethylene bearing is
described in U.S. Pat. No. 4,997,445 to Hodoreck incorporated
herein by reference. This patent describes a metal backed
prosthesis implant with enhanced bonding of polyethylene to the
metal base.
[0027] Other technical advantages of the present invention will be
readily apparent to one skilled in the art from the following
figures, descriptions and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
description taken in connection with the accompanying drawings, in
which:
[0029] FIG. 1 is a perspective view of the knee system including
the bearing component of the present invention showing the femoral
component and the tibial tray component with the tibial bearing
showing the knee system in extension;
[0030] FIG. 2 is an elevation view from the anterior of FIG. 1;
[0031] FIG. 3 is a side view of the assembly shown in FIGS. 1 and
2;
[0032] FIG. 4 is an exploded side view showing the plastic bearing
component partially removed from the tibial tray or plateau;
[0033] FIG. 5 is an elevation view from the posterior of FIG.
1;
[0034] FIG. 6 is an exploded elevation view from the anterior
showing the plastic bearing component partially removed from the
tibial tray or plateau;
[0035] FIG. 7 is an exploded perspective view showing the plastic
bearing component partially removed from the tibial tray or
plateau;
[0036] FIG. 8 is a fully exploded side view showing the plastic
bearing component removed from the tibial;
[0037] FIG. 9 is a fully exploded elevation view from the anterior
showing the plastic bearing component removed from the tibial;
[0038] FIG. 10 is a plan view of a reinforcing rod for use with the
bearing component for an embodiment of the prosthesis of the
present invention;
[0039] FIG. 10A is a view of the reinforcing rod of FIG. 10 along
the line 10A-10A in the direction of the arrows;
[0040] FIG. 11 is a plan view of the reinforcing rod of FIG. 10
located in a molding die for use in manufacturing the bearing
component for the prosthesis of the present invention;
[0041] FIG. 12 is a plan view of the reinforcing rod of FIG. 10
located in a molding die shown partially in cross section for use
in manufacturing the bearing component for the prosthesis of the
present invention showing the molding die in greater detail;
[0042] FIG. 13 is a bottom view of the molding die of FIG. 12;
[0043] FIG. 14 is a plan view of the bearing component made from
the reinforcing rod of FIG. 10 utilizing the molding die of FIG.
12;
[0044] FIG. 15 is a plan view of a reinforcing rod for use with the
bearing component for another embodiment of the prosthesis of the
present invention;
[0045] FIG. 15A is a view of the reinforcing rod of FIG. 10 along
the line 15A-15A in the direction of the arrows;
[0046] FIG. 16 is a plan view of the reinforcing rod of FIG. 15
located in a molding die for use in manufacturing the bearing
component for the prosthesis of the present invention;
[0047] FIG. 17 is a plan view of the reinforcing rod of FIG. 15
located in a molding die shown partially in cross section for use
in manufacturing the bearing component for the prosthesis of the
present invention showing the molding die in greater detail;
[0048] FIG. 18 is a bottom view of the molding die of FIG. 16;
[0049] FIG. 19 is a plan view of the bearing component made from
the reinforcing rod of FIG. 15 utilizing the molding die of FIG.
16;
[0050] FIG. 20 is a process flow chart for a method of
manufacturing the prosthesis component of FIG. 21;
[0051] FIG. 21 is a side view of the assembly shown in FIGS. 1 and
2 showing the assembly in flexion;
[0052] FIG. 22 is a perspective view of the knee system of FIG. 1
including the bearing component of the present invention showing
the femoral component and the tibial component with the tibial
bearing showing the knee system in flexion;
[0053] FIG. 23 is an elevation view from the anterior side of the
assembly shown in FIGS. 1 and 2 showing the assembly in flexion;
and
[0054] FIG. 24 is an elevation view from the posterior side of the
assembly shown in FIGS. 1 and 2 showing the assembly in
flexion.
DETAILED DESCRIPTION OF THE INVENTION
[0055] Embodiments of the present invention and the advantages
thereof are best understood by referring to the following
descriptions and drawings, wherein like numerals are used for like
and corresponding parts of the drawings.
[0056] According to the present invention and referring now to FIG.
8, a joint prosthesis in the form of knee prosthesis 10 as shown.
The knee prosthesis 10 includes a femoral component or first joint
component 12 for attachment to femur or first long bone 14. The
prosthesis 10 further includes a tibial tray or second joint
component 16 for attachment to tibia or second long bone 20. The
femoral component 12 and the tibial component 16 are shown in
greater detail in FIGS. 1-9 and 21-24. The femoral component 12 and
the tibial component 16 are made of any suitable durable material
which are biologically compatible with the human anatomy. The
femoral component 12 and the tibial component 16 may, for example,
be made of a metal alloy, for example, cobalt-chromium-molybdenu-
m, a titanium and its alloys, or be made of stainless steel.
[0057] The knee prosthesis 10 further includes a bearing component
222. The bearing component 222 is positionable between the femoral
component 12 and the tibial tray 16. The bearing component 222
cooperates with the femoral component 12 and the tibial tray 16 to
provide for the kinematics of the knee prosthesis.
[0058] The prosthesis, as shown in FIGS. 1-9 and 21-24, are
commonly referred to as a mobile bearing prosthesis or a mobile
bearing knee. Such mobile bearing knees have been provided by DePuy
Orthopaedics, Inc. under the trade name LCS since about 1977.
Mobile bearing knees of this type are different than fixed bearing
knees in that the tibial component 20 and the bearing component 222
may be physically separated from each other. The bearing component
is also allowed to have rotational freedom about the tibial tray
component. The use of mobile bearing knees may require that the
patient have satisfactory cruciate collateral ligaments and tendons
necessary to maintain the proper relationship of the femoral
component to the bearing component. In those cases where the
cruciate ligaments are either severely damaged or have been
sacrificed or removed during a knee surgery, provisions must be
made within the prosthesis to constrain the femoral component with
respect to the tibial tray.
[0059] Referring now to FIGS. 21 and 22, one solution to
restraining the femoral component 12 with respect to the tibial
tray 16 is by the use of a mechanism in the form of a spine 24
located on the bearing component 222 which mates with cam 26
located on femoral component 12. As shown in FIGS. 21 and 22, to
provide medial/lateral support for the knee prosthesis 10
preferably the femoral component 12 includes femoral face 30 which
cooperate with spine faces 32 on the spine 24. The spine faces 32
define a spine width SW which is related to the femoral width CW
defined by femoral faces 32. The relation behind SW & CW define
the level of constraint in the prosthesis in the medial-lateral
direction.
[0060] Referring now to FIG. 8, to provide anterior support the
spine 24 includes a cam cooperating face 34 with which the spine
cooperating face 35 of the cam 26 cooperates (see FIG. 21). It
should be appreciated that for patients in which the posterior
cruciate is severely damaged or missing the forces on the spine 24
both anterior/posterior and medial/lateral can be quite severe.
[0061] Preferably, and as shown in FIG. 8, the bearing component
222 is made of a polymeric material, for example, polyethylene.
Preferably, the bearing component 222 is made of UHMWPE. The
bearing component 222 may be further processed to improve the wear
properties of contact surface 40 of the bearing component. The
contact surface 40 is the surface that is in contact with the
laterally spaced condylar outer periphery 42 of the femoral
component 12. Methods of improving the wear properties of UHMWPE
include a process known as Gamma Vacuum Foil (GVF) as disclosed in
U.S. Pat. No. 5,577,368 to Hamilton, et al, and a process known as
the Marathon.RTM. process as disclosed in U.S. Pat. No. 6,017,975
and U.S. Pat. No. 6,242,507 to Saum et al and in U.S. Pat. No.
6,228,900 to McKellop et al. These patents are incorporated herein
by reference.
[0062] Referring again to FIG. 8 and according to the present
invention, the bearing component 222 of the prosthesis 10 includes
a first component or reinforcing component 236. The reinforcing
component 236 serves to strengthen the bearing component 222 so
that the spine 24 may withstand the forces that are present in the
spine of the knee prosthesis 10 when the posterior cruciate and
collateral ligaments cannot support the knee properly.
[0063] Since the bearing component 222 is preferably made of a
polymer and since the reinforcing component 236 is to strengthen
the bearing component 222, the reinforcing component 236 is
preferably made of a higher strength material than polymer,
preferably a material with a higher modulus of elasticity. For
example, the reinforcing component 236 may be made of a metal that
is a material compatible with the human anatomy, for example,
stainless steel, a titanium and its alloys or a
cobalt-chromium-molybdenum alloy.
[0064] Applicants have found that desired kinematics of the knee
during a full range of motion may require that an optimum design of
the components that comprise a knee prosthesis, for example, those
of FIG. 8, may include a tibial tray 16 having a central pivot axis
44 which is not coincident with center line 46 of the spine 24 of
the bearing component 222. Since the prosthesis 10 including the
bearing component 222 will be implanted into the human body, it is
essential that the prosthesis 10 including the bearing component
222, be sterilized. Several effective methods of sterilization are
possible for the prosthesis 10 including the bearing component
222.
[0065] For example, the bearing component 222 may alternatively be
sterilized by subjecting the bearing component 222 to gamma
irradiation. The subjection of the bearing component 222 to gamma
irradiation may lead to the presence of free radicals within the
polymer or polyethylene with which the bearing component 222 is
typically manufactured. The presence of free radicals within the
bearing component 222 may lead to early degradation of the bearing
component 222 through an oxidation process.
[0066] To minimize the negative effect of the free radicals
generated from gamma sterilization, the bearing component 222
preferably is barrier packaged in vacuum or inert gas to keep the
oxygen out and also to trap hydrogen gas inside the package. Such
treatment precludes early oxidation of the bearing material and
sufficient sterilization for the bearing component 222.
[0067] According to the present invention, a preferred method of
sterilization is gas plasma sterilization. Gas plasma sterilization
is predominantly a surface sterilizing technology. Gas plasma
sterilization has limited ability to sterilize internal surfaces
which have limited exposure to the outer surfaces of the
component.
[0068] Therefore, and according to the present invention, there is
the need for a bearing component designed to be amenable to gas
plasma sterilization and yet have the reinforced spine necessary
for use of a constrained mobile bearing knee prosthesis for use
with patients having compromised or sacrificed cruciate
ligaments.
[0069] According to the present invention and now referring to
FIGS. 15 through 19, an embodiment of the present invention is
shown as bearing component 222.
[0070] Referring now to FIG. 19, the bearing component 222 of the
present invention is shown in greater detail. The bearing component
222 is a component that may be molded as a net shaped molding
including a reinforcing component or reinforcing rod 236 to provide
sufficient strength for the spine 224 and the distal stem. The
reinforcing rod includes a first end 286 and an opposed second end
294. The bearing component 222 is designed to not include bearing
component openings in the polyethylene portion of the bearing
component to expose the reinforcing rod to atmosphere. The
technology that permits this configuration will be described in
greater detail herein.
[0071] By providing the bearing component 222 with no external
exposure to the reinforcing rod, the bearing component 222 may be
gas plasma sterilized. By gas plasma sterilizing the bearing
component 222, the bearing component 222 may be sterilized without
providing free radicals which could lead to oxidative degradation
of the bearing material.
[0072] Referring now to FIG. 19 and according to the present
invention, the bearing component 222 of the prosthesis 10 includes
the reinforcing component 236 which is designed to accommodate the
fact that centerline 44 of the central pivot stem of the tibial
tray 16 (see FIG. 8) and is offset from centerline 46 of the spine
24.
[0073] Thus, as shown in FIG. 19, the reinforcing component 236 is
designed with a first centerline 250 which is not coincident with
second centerline 252. As shown in FIGS. 8 and 10, the first
centerline 250 of the reinforcing component 236 is coincident with
central pivot stem centerline 44 of tibial tray 16. Similarly the
second centerline 252 of the reinforcing component 236 is
coincident with the centerline 46 of the spine 24.
[0074] Continuing to refer to FIG. 19, the reinforcing component
236 includes a first portion 254 which defines the first centerline
250 thereof. The reinforcing component 236 further includes a
second portion 256 thereof which-defines-the second centerline 252
thereof. The first centerline 250 and the second centerline 252 are
non-coincidental.
[0075] As shown in FIG. 19, the first centerline 250 may be
parallel and spaced from the second centerline 252. It should be
appreciated, however, that the first centerline 250 and the second
centerline 252 may, in fact, be skewed or converging or diverging.
As shown in FIG. 19, however, the first centerline 250 and the
second centerline 252 are separated and offset a distance COO which
is similar to the offset SOO between the centerline of 46 of spine
24 and the centerline 44 of the tibial tray 16 (see FIG. 8).
[0076] As shown in FIG. 19, the reinforcing component 236 includes
a connecting portion 260 positioned between first portion 254 and
second portion 256. The connecting portion 260 may have any
suitable shape but preferably for strength and simplicity the
connecting portion 260 is an arcuate portion. In such a
configuration, the shape of the connecting portion 260 is defined
by a pair of radii, RR1 and RR2 which may, for example, be
similar.
[0077] While it should be appreciated that the reinforcing
component 236 may have any suitable shape capable of providing for
support with a pair of offset centerlines, it should be appreciated
that for simplicity, and as shown in FIG. 15A, the reinforcing
component 236 may have a uniform cross section. For example, the
cross section of the reinforcing component may be square,
triangular, hexagonal or as shown in FIG. 15A, may be circular. A
circular cross section may provide for optimum bending strength in
a variety of directions for a given weight or size of the
reinforcing component 236.
[0078] The reinforcing component 236 may be hollow or as shown in
FIG. 18, may be made of a generally solid material. Due to space
constraints, the reinforcing component 236 may be solid as shown in
FIG. 18.
[0079] As can be readably apparent by FIGS. 15 and 19, in
particular, the bearing component 222 including the reinforcing
component 236 may be made by a number of methods but cannot simply
and easily be made by first making the bearing component 222 and
then preparing an opening or conduit for installing the reinforcing
component 236 therein. Therefore, typical methods of providing a
reinforcing rod to a bearing component 222 in the form of drilling
a hole in the bearing component 222 and inserting a straight
cylindrical rod therein is not possible.
[0080] Referring now to FIG. 19, the reinforcing component or
reinforcing rod 236 is shown in greater detail. The bearing
component 222 includes the reinforcing rod 236 which is placed into
a mold and the polymeric material is molded around the reinforcing
rod 236. Thus, the bearing component 222 requires that the mold
provide provisions for the proper placement of the reinforcing rod
236 within the molding die. Therefore, and as shown in FIG. 19, the
reinforcing rod 236 includes an orientation and location feature
202 which provides both orientation and location. The location and
orientation feature 202, as shown in FIG. 15, include a first
recess or through hole 204 and a second recess or through hole
206.
[0081] Preferably, the first recess 204 and the second recess 206
are small. The first recess and second recess 204 and 206 in the
reinforcing rod 236 are preferably both located on the same portion
of the rod. By placing the recesses on the same portion, for
example second portion 256, the recesses may be both positioned in
the base or bottom mold 266 of the die 262 (see FIG. 17) to assist
in the proper operation of the invention. The value of having the
recesses on the same end of the rod will be described in greater
detail herein.
[0082] Referring now to FIG. 17, a molding die 262 is shown for
molding the bearing component 222. Molding die 262 is utilized in
the direct compression molding process. The bearing component 222
is molded in the molding die 262 in reverse or upside down order to
provide for the positioning of the recesses 204 and 206 in the base
or bottom mold 266.
[0083] The advantage of positioning the location and orientation
features 202 in the base or bottom mold 266 will be described in
greater detail later.
[0084] As shown in FIG. 17, the molding die 262 includes base or
bottom mold 266. The bottom mold 266 is utilized to form bottom
bearing surface 280 and rotating shaft or second peripheral region
282 of the bearing component 222. Extending upwardly from the
bottom mold 266 is the body or side mold 272. The side mold 272 is
utilized to form curved profile 274 of the bearing component 222.
Slidably positioned within the side mold 272 is plunger or top mold
270. The plunger or top mold 270 is utilized to form articular
surface or first peripheral region 271 of the bearing component
222. The molds 270, 272 and 266 serve to provide an inner forming
surface 264 which conforms to the outer periphery of the bearing
component 222 with provisions for accommodating the shrinkage
dimensions that are well known in the art.
[0085] The inner forming surface 264 defines an internal cavity
208.
[0086] The reinforcing rod 236 needs to be properly positioned
within the cavity 208 of the molding die 262. Preferably, thus, the
molding die 262 includes a positioner 284 for proper repositioning
of the reinforcing rod 236 within the cavity 208 of the molding die
262. For example and as shown in FIG. 17, the positioner 284 is in
the form of a first pin 290 and a second pin 292. The pins 290 and
292 cooperate with first recess 204 and second recess 206 of the
reinforcing rod 236 (see FIG. 19).
[0087] Preferably, and according to the present invention, the pins
290 and 292 have a very small dimension with respect to the
reinforcing rod 236. For example, if, as shown in FIG. 17, the pins
290 and 292 are cylindrical, the pins 290 and 292 may have a
diameter D which is much smaller than diameter DD of the second
portion 256 of the reinforcing rod 236. For example for a
reinforcing rod 236 having a diameter DD of, for example,
approximately 10 millimeters. The corresponding diameter D of the
pins 290 and 292 may be, for example, 0.5 to 2.0 millimeters.
[0088] It is preferred to have the pins 290 and 292 made of
materials that have a high melting point in order to resist the
heat and pressure experienced in the mold during the molding
process. Pins may be made of metals, ceramics or pyrolytic carbons.
The molding process for the molding die 262 to mold the bearing
component 222 as shown in FIG. 17 includes first separating the top
mold 270 from the bottom mold 266 and adding powder 207 similar to
powder 112 of the process as described for the molding die 62 of
FIG. 12. After the required powder 207 is added, the top mold 270
is placed within the side mold 272 and lowered in the direction of
the bottom mold 266 until the molds 266, 270 and 272 forming
surface 264 correspond to the periphery of the bearing component
222.
[0089] Towards the end of the compression molding cycle when the
UHMWPE material has almost assumed full density and completely
fills the mold the pins 290 and 292 are withdrawn from the cavity
preferably in a direction normal to the centerlines 250 and 252 of
the reinforcing rod 236. For example, as shown in FIG. 17, the
first pin moves from a position as shown in solid to the position
shown in phantom. As the first pin 290 and second pin 292 are
retracted to the position in phantom, a small pin cavity 238 is
left behind where the pin 290 was withdrawn from. Since the
compression cycle has not ended, the melted polymer still under
pressure quickly fills the pin cavity 238 thereby eliminating the
pin cavity 238.
[0090] Since the powder 207 within the mold cavity 208 has obtained
a high viscosity at the point in the compression molding cycle when
the UHMWPE material has assumed full density and completely fills
the mold, the reinforcing rod 236 remains in its previous position
even after the pins 290 and 292 have been fully retracted and no
longer support the rod 236.
[0091] Preferably, and as shown in FIG. 17, the pins 290 and 292
are preferably spaced apart along second centerline 250 a distance
P of, for example, twice the distance DD of the diameter of the rod
236. The larger the dimension P, the greater the stability and
accuracy of the positioning of the rod 236 within the molding die
262.
[0092] Preferably, and as shown in FIG. 17, the pins 290 and 292
are positioned perpendicularly to the second centerline 250 and
preferably at an angle with respect to each other, preferably at 90
degrees or perpendicular to each other. Such positioning optimizes
the effectiveness of the pins 290 and 292 to properly position the
reinforcing rod 236 in more than 3 degrees of freedom. After
appropriate cooling, the plunger or top mold 270 is opened and the
completed bearing component 222 is removed from the molding die
262.
[0093] It should be appreciated that other approaches may be taken
to position the reinforcing rod 236 within the molding die 262 and
yet provide for a complete encapsulation of the reinforcing rod
with the polyethylene. For example, the pins 290 and 292 may be
made of a polyethylene identical to that of the powder 207. The
pins 290 and 292 may then be left fully extended and not retracted.
The pins 290 and 292 then would melt and form with the powder 207,
and yet have sufficient strength early on in the forming process to
properly locate the rod 236 within the molding die 262 until the
polyethylene becomes sufficiently viscous to support the rod.
[0094] Other approaches for properly supporting the rod yet
allowing for complete encapsulation of polyethylene around the rod
236 may fall within the scope of the present invention.
[0095] According to the present invention and now referring to
FIGS. 10 through 14, another embodiment of the present invention is
shown as bearing component 22.
[0096] Referring to FIG. 8 it should be appreciated that the
bearing component 22 of FIG. 10 may be substituted for the bearing
component 222 for the prosthesis 10. The bearing component 22 is
made of similar materials and has similar strength and load
carrying capacity of bearing component 222 as well as similar
contour dimensions such that bearing component 22 can readily
replace bearing component 222 in the prosthesis 10.
[0097] Referring now to FIG. 10 an alternate embodiment of the
bearing component of the present invention is shown as the bearing
component 22 which may alternatively be used in prosthesis 10.
Bearing component 22 includes the reinforcing component 36 which is
designed to accommodate the fact that centerline 44 of the central
pivot stem of the tibial tray 16 is offset from centerline 46 of
the spine 24 (see FIG. 8). Thus as shown in FIG. 10, the
reinforcing component 36 is designed with a first centerline 50
which is not coincident with second centerline 52. As shown in
FIGS. 8 and 10, the first centerline 50 of the reinforcing
component 36 is coincident with central pivot stem centerline 44 of
tibial tray 16. Similarly the second centerline 52 of the
reinforcing component 36 is coincident with the centerline 46 of
the spine 24.
[0098] Continuing to refer to FIG. 10, the reinforcing component 36
includes a first portion 54 which defines the first centerline 50
thereof. The reinforcing component 36 further includes a second
portion 56 thereof which defines the second centerline 52 thereof.
The first centerline 50 and the second centerline 52 are
non-coincidental.
[0099] As shown in FIG. 10, the first centerline 50 may be parallel
and spaced from the second centerline 52. It should be appreciated,
however, that the first centerline 50 and the second centerline 52
may, in fact, be skewed or converging or diverging. As shown in
FIG. 10, however, the first centerline 50 and the second centerline
52 are separated and offset a distance CO which is similar to the
offset SO between the centerline of 46 of spine 24 and the
centerline 44 of the tibial tray 16 (see FIG. 8).
[0100] As shown in FIG. 10, the reinforcing component 36 includes a
connecting portion 60 positioned between first portion 54 and
second portion 56. The connecting portion 60 may have any suitable
shape but preferably for strength and simplicity the connecting
portion 60 is an arcuate portion. In such a configuration, the
shape of the connecting portion 60 is defined by a pair of radii,
R1 and R2 which may, for example, be similar.
[0101] While it should be appreciated that the reinforcing
component 36 may have any suitable shape capable of providing for
support with a pair of offset centerlines, it should be appreciated
that for simplicity, and as shown in FIG. 10A, the reinforcing
component 36 may have a uniform cross section. For example, the
cross section of the reinforcing component may be square,
triangular, hexagonal or as shown in FIG. 10A may be circular. A
circular cross section may provide for optimum bending strength in
a variety of directions for a given weight or size of the
reinforcing component 36.
[0102] The reinforcing component 36 may be hollow, or as shown in
FIG. 10A may be made of a generally solid material. Due to space
constraints the reinforcing component 36 may be solid as shown in
FIG. 10A.
[0103] As can be readably apparent by the FIGS. 8 and 10, in
particular, the bearing component 22, including the reinforcing
component 36, may be made by a number of methods but cannot simply
and easily be made by first making the bearing component 22 and
then preparing an opening or conduit for installing the reinforcing
component 36 therein. Therefore, typical methods of providing a
reinforcing rod to a bearing component 22 in the form of drilling a
hole in the bearing component 22 and inserting a straight
cylindrical rod therein is not possible.
[0104] Therefore, referring to FIGS. 11, 12 and 13, the bearing
component 22 is preferably made by a molding process for example a
compression molding process or any molding process by which the
polymeric material may be processed.
[0105] Referring to FIGS. 11, 12 and 13, the bearing component 22
is preferably made in molding die 62. While the bearing component
22 may be manufactured utilizing any suitable molding technique
preferably and as shown in FIG. 12, the molding die 62 is for use
with direct compression molding. Plastic powder is placed into the
molding die 62, the die is closed and pressure is applied to
compress, heat, and cause flow of the plastic to be conformed to
the cavity shape.
[0106] The molding die 62 is made in a shape including an inner
forming surface 64 which is made in the shape of the final finished
bearing component 22. Preferably, the inner forming surface 64 is
sized to allow for appropriate shrinking dimensions as is known in
the art.
[0107] The molding die is made in several pieces. Typically, a base
or bottom mold 66 is utilized to form articular surface 70 of the
bearing component 22. The molding die 62 also includes a body or
side mold 72. The body 72 is utilized to form the curved lateral
surfaces 74 of the bearing component 22. Also the molding die 62
further includes a plunger assembly 76. The plunger assembly 76 is
utilized to form bottom bearing surface 80 and the rotating shaft
82. One mold may be used to obtain varying thickness of the bearing
component 22.
[0108] In order to manufacture the bearing component 22 according
to the present invention, the molding die 62 is modified to support
reinforcing component 36 in the form of, for example, a reinforcing
rod.
[0109] Preferably, and as shown in FIG. 12, reinforcing rod or
component 36 is position spaced from the inner forming surface 64.
Preferably, and as shown in FIG. 12, the reinforcing rod 36 is kept
spaced from the inner forming surface 64 by use of a support
feature 84 as initially designed to provide the offset between the
spine and distal stem of the bearing component 22. The support
feature 84 is utilized to space, support or position the
reinforcing rod 36 within the molding die 62. The positioner or
support feature 84 may support or secure the reinforcing component
36 at any suitable position on the reinforcing component 36. For
simplicity, and as shown in FIG. 12, the positioner 84 may be
located on first end 86 of the reinforcing rod 36.
[0110] The positioner 84 may include a sole positioning member
which interacts with first end 86 of the reinforcing rod 36. If the
positioner is located only on one end and the rod is held at that
one end, that portion of the die including the positioner either at
the base or bottom mold 66 or the plunger or top mold 76 must
provide rigid temporary attachment of the reinforcing rod 36 to the
positioner 84.
[0111] While the present invention may be practiced utilizing a
sole positioner located on one end of the reinforcing rod 36 such a
configuration may have some problems in that the tolerance between
the positioner and the reinforcing rod may be such that the
accuracy of the position of the reinforcing rod 36 within the
molding die 62 may not be sufficiently accurate resulting in the
misposition of the reinforcing rod 36 within the finished
reinforcing component 36. Misposition may occur either in the
anterior-posterior or medial-lateral direction. Additionally, the
reinforcing pin 36 may be rotationally mispositioned with respect
to the superior spine and distal stem.
[0112] Preferably, and as shown in FIG. 12, the positioner 84 is in
the form of a first positioner 90 located at the first end 86 of
the reinforcing rod 36 and a second positioner 92 located at second
end 94 of the reinforcing rod 36. If the reinforcing rod 36 is held
at both the first end 86 and the second end 94 of the rod 36, then
one end, for example, end 86 must be a rigid temporary attachment
and the other end, for example, second end 94 or second positioner
92 must be a sliding temporary attachment. A sliding temporary
attachment is necessary as the two ends of the molding die approach
and separate from each other during each molding cycle.
Additionally, the sliding temporary attachment may provide for
rotational alignment to obtain the optimal position of the
reinforcing component 36 in the spine by allowing equal polymeric
material around the reinforcing component 36.
[0113] To improve the accuracy of the positioning of the
reinforcing rod 36 within the molding die 62, optionally, the
molding die may include an orientation feature 100 to optimally
angularly orient the reinforcing rod 36 with respect to the inner
forming surface 64 and eventually the reinforcing component 36. The
orientation feature 100 may, for example, be included with the
positioners 90 and 92 and may, as shown in FIG. 12, be in the form
of flat 102 located on the second positioner 92. As shown in FIG.
12, the orientation feature 100 is in the form of six equally
spaced flats, three of which are shown. Therefore the positioner 84
and the orientation features are in the form of a hexagonal rod. An
additional flat may help better fine tune the position of the
reinforcing element with respect to the mold components.
[0114] Referring again to FIG. 10, preferably, and as shown in FIG.
10, the reinforcing rod 36 includes positioning features in the
form of, for example, first recess 104 which is located on first
end 86 of the rod 36 and second recess 106 which is located on
second end 94 of the rod 36. The first recess 104 matingly receives
the first positioner 90 while the second recess 106 receives the
second positioner 92 (see FIG. 11). Preferably, and as shown in
FIG. 10, the second recess 106 includes a recess flat 110 which
mate with flat 102 on second positioner 92.
[0115] Referring now to FIG. 14, the bearing component 22 is shown
having been molded on the molding die 62 (see FIG. 12). In order
that the first positioner 90 and the second positioner 92 may be
removed from the cavity 114 and from the bearing component 22 when
it is removed from the cavity 114 of the molding die 62, the
bearing component 22 includes a first bearing component opening 120
located in line and above the first recess 104 of the reinforcing
rod 36. Likewise, the bearing component 22 further includes a
second bearing component opening 122 extending outwardly from the
second recess 106 of the reinforcing rod 36. The first bearing
component 120 and the second bearing component opening 122 provide
for access to the reinforcing rod 36 from the outside of the
bearing component 22.
[0116] Referring again to FIG. 12, plastic powder 112 is added in
the proper amount into cavity 114 of the molding die 62. The
molding die 62 is closed by the positioning of the plunger assembly
or top mold 76 over the body or side mold 72 of the molding die
62.
[0117] The bearing component 22 is fully formed by subjecting the
molding die 62 to the well known conditions of pressure and
temperature required to consolidate the powder 112. After
appropriate cooling, the molding die 62 is opened by the removal of
the plunger assembly or top mold 76 from the body or side mold 72.
The bearing component 22 including the reinforcing rod 36 is then
removed from the cavity 114 of the molding die 62. After proper
cleaning an additional reinforcement rod and additional powder 112
is added to the cavity 114 and the process is repeated in order to
obtain a second bearing component.
[0118] Referring now to FIG. 14, the bearing component 22 of the
present invention includes first bearing component opening 120 and
second bearing component opening 122 which expose the bearing
component 22 to access the reinforcing rod 36. The reinforcing rod
thus has internal surfaces which have limited exposure or
connection to the outside surfaces of the bearing component 22.
[0119] Therefore, because the reinforcing rod, 36 is exposed to the
surface of the component via the holes 120 and 122 through which it
was inserted or by the method of holding the post using the mold
which holds the post during the molding process, the bearing
component 22 is not amenable to sterilization by techniques which
are predominantly surface sterilizing technology, for example, gas
plasma sterilization.
[0120] In order to utilize the bearing component 22 with gas plasma
sterilization, steps can be taken to fill the holes 120 and 122
with polyethylene plugs or the positioners 90 and 92 can be made of
polyethylene and not retracted once the bearing 22 is removed from
the die 62 (see FIG. 12).
[0121] Referring now to FIG. 20, a process for molding a bearing
component with a reinforcing rod is described more fully. First
step 120 of the process described in FIG. 20 is the step of
providing a component of a durable material. The durable material
may, for example, be in the form of cobalt chrome alloy, stainless
steel or titanium and its alloys. The component may be in the form
of, for example, an elongated member, for example, a rod. The rod
as described in the present invention is in the form of a bent rod
or a rod having two substantially linear portions with the portions
being skewed or non-linear with respect to each other.
[0122] Second step 122 of the process, as described in FIG. 20, is
the step of providing a molding die adapted for manufacturing a
component for use in total joint arthroplasty.
[0123] Third step 124 in the process is the step of placing the
reinforcing component into the molding die in the desired position.
Fourth step 126 of the process is placing moldable material powder
into the molding die. Fifth step 130 in the process for making a
bearing component is the step of substantially surrounding the
component with moldable material. Sixth step 131 of the process is
the step of heating and pressurizing the mold, thus the moldable
material. Seventh step 132 of the process is the step of permitting
the moldable material to cool to form the component and the eighth
step 134 of the process is the step of removing the component from
the molding die.
[0124] By utilizing the non-linear reinforcement component of the
present invention, a knee may be provided with improved load
carrying capacity in the anterior-posterior and medial-lateral
directions for the spine and cam mechanism in situations in which
the center line of the insert which engages the tibial tray and the
superior spine portion which engage the cam of the femoral
component are not in the same plane. In such situations where these
planes are different, the kinematics of the knee may be
improved.
[0125] By providing a tibial bearing insert with an insert that has
most of its entire periphery encapsulated in polyethylene, a tibial
bearing insert can be made that has improved strength and can be
gas plasma sterilized.
[0126] By providing a non-linear re-inforcing component to the
tibial bearing insert, the non-linear support rod may be properly
positioned within the tibial bearing insert to optimize the load
transfer mechanism through the spine.
[0127] By providing a tibial bearing insert including a nonlinear
support including an orientation feature, the support rod may be
adjusted with respect to the tibial bearing insert during the
manufacturing of the tibial bearing insert.
[0128] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions, and alterations can be made therein without
departing from the spirit and scope of the present invention as
defined by the appended claims.
* * * * *