U.S. patent application number 09/414431 was filed with the patent office on 2001-11-01 for acetabular bearing assembly for total hip joints.
This patent application is currently assigned to Walter G. Hanchuk. Invention is credited to Burstein, Albert, Mauldin, C. Michael, Miller, Gary J..
Application Number | 20010037156 09/414431 |
Document ID | / |
Family ID | 23641423 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010037156 |
Kind Code |
A1 |
Burstein, Albert ; et
al. |
November 1, 2001 |
ACETABULAR BEARING ASSEMBLY FOR TOTAL HIP JOINTS
Abstract
A modular acetabular bearing assembly which minimizes or
eliminates the production of wear debris resulting from relative
motion at the interface between the acetabular shell and bearing
insert portions of the modular acetabular bearing assembly. The
modular acetabular bearing assembly includes an acetabular shell
and composite bearing insert. The composite bearing insert includes
an endoskeleton and a polymer layer which is preferably molded into
and locked within the endoskeleton. The endoskeleton is configured
to be locked within the acetabular shell. As such, the modular
acetabular bearing assembly, and its method of manufacture,
eliminate all contact between any polymer surface on the composite
bearing insert and any metal surface on the acetabular shell. The
modularity of the assembly facilitates the interchangeability of
various composite bearing inserts within an acetabular shell which
is fixed to the acetabulum of a patient. This provides for various
advantages, including the ability to use a central screw to fix the
acetabular shell to a patient.
Inventors: |
Burstein, Albert; (Sarasota,
FL) ; Mauldin, C. Michael; (Lake City, FL) ;
Miller, Gary J.; (Gainesville, FL) |
Correspondence
Address: |
MORGAN & FINNEGAN LLP
345 PARK AVENUE
NEW YORK
NY
10154
|
Assignee: |
Walter G. Hanchuk
|
Family ID: |
23641423 |
Appl. No.: |
09/414431 |
Filed: |
October 7, 1999 |
Current U.S.
Class: |
623/22.28 |
Current CPC
Class: |
A61F 2230/0017 20130101;
A61F 2002/30448 20130101; A61F 2002/30492 20130101; A61F 2250/0018
20130101; A61F 2220/005 20130101; A61F 2002/3448 20130101; A61F
2310/00029 20130101; A61F 2002/30787 20130101; A61F 2002/30426
20130101; A61F 2002/30973 20130101; A61F 2002/30957 20130101; A61F
2310/00179 20130101; A61F 2002/30143 20130101; A61F 2002/30337
20130101; A61F 2220/0025 20130101; A61F 2002/30378 20130101; A61F
2002/30367 20130101; A61F 2002/3403 20130101; A61F 2002/30495
20130101; A61F 2310/00023 20130101; A61F 2002/30332 20130101; A61F
2002/30507 20130101; A61F 2002/30405 20130101; A61F 2002/30604
20130101; A61F 2002/3054 20130101; A61F 2310/00017 20130101; A61F
2002/30355 20130101; A61F 2002/3401 20130101; A61F 2002/30685
20130101; A61F 2002/30014 20130101; A61F 2/30771 20130101; A61F
2002/3414 20130101; A61F 2220/0033 20130101; A61F 2/34
20130101 |
Class at
Publication: |
623/22.28 |
International
Class: |
A61F 002/32 |
Claims
What is claimed is:
1. An acetabular bearing assembly, comprising: an acetabular shell
having (a) an outer convex surface for fixation to a surgically
prepared acetabulum and (b) an inner concave surface; a bearing
insert, comprising a polymer layer and a metal layer, the polymer
layer forming a concave bearing surface shaped to receive a ball
end of a stem, the metal layer forming a convex surface interlocked
with the concave surface of the acetabular shell, wherein said
polymer bearing layer and said metal layer are interlocked to
minimize relative movement therebetween.
2. The acetabular bearing assembly of claim 1 wherein said polymer
layer and said metal layer are interlocked through a plurality of
interlocking dovetails.
3. The acetabular bearing assembly of claim 1 wherein said polymer
layer is a compression molded layer interlocked with said metal
layer.
4. The acetabular bearing assembly of claim 1 wherein said bearing
insert contacts said inner concave surface of said acetabular shell
only through metal to metal contact.
5. The acetabular bearing assembly of claim 1 wherein said metal
layer forms a metal endoskeletal portion of said bearing
insert.
6. The acetabular bearing assembly of claim 1 wherein said
acetabular shell and said bearing insert are interlocked through a
locking taper on said acetabular shell and a locking taper on said
bearing insert.
7. The acetabular bearing assembly of claim 1 wherein said
acetabular shell and said bearing insert are interlocked through a
locking arrangement selected from the group consisting of a taper
lock, a screw fastener, a pin fastener, a locking bayonet and a
snap ring.
8. The acetabular bearing assembly of claim 1 wherein said
acetabular shell contains a hole which receives a portion of said
endoskeleton to prevent relative rotation therebetween.
9. The acetabular bearing assembly of claim 8 wherein said hole has
an oval or polygonal shape.
10. The acetabular bearing assembly of claim 1 wherein said polymer
layer comprises polyethylene.
11. The acetabular bearing assembly of claim 1 wherein said
acetabular shell is made of a material selected from the group
consisting of titanium, titanium alloy, cobalt-chrome alloy, a low
corrosion iron alloy, and ceramic.
12. The acetabular bearing assembly of claim 1 wherein said outer
convex surface of said acetabular shell is configured for fixation
to an acetabulum through a technique selected from the group
consisting of biological fixation, mechanical fixation and grouting
fixation.
13. An acetabular bearing assembly comprising: an acetabular metal
shell; a metal endoskeleton disposed within and interlocked with
said acetabular metal shell; and a polymer layer disposed within
and interlocked with said metal endoskeleton, said polymer layer
having an internal bearing surface shaped to receive a ball end of
a stem.
14. The acetabular bearing assembly of claim 13 wherein said
acetabular metal shell is made of a material selected from the
group consisting of titanium, titanium alloy, cobalt-chrome alloy,
and a low corrosion iron alloy, and ceramic.
15. The acetabular bearing assembly of claim 13 wherein said
polymer layer comprises polyethylene.
16. The acetabular bearing assembly of claim 13 wherein said metal
acetabular shell and said metal endoskeleton are interlocked
through a locking arrangement selected from the group consisting of
a taper lock, a screw fastener, a pin fastener, a locking bayonet
and a snap ring.
17. A method of constructing an acetabular bearing assembly
comprising: constructing a metal endoskeleton with a first locking
mechanism and a second locking mechanism, said first locking
mechanism disposed on a concave portion of said metal endoskeleton
and said second locking mechanism supplied on a convex portion of
said metal endoskeleton; filling at least a portion of said metal
endoskeleton with polyethylene powder; and molding said
polyethylene powder within said metal endoskeleton to form and lock
a polyethylene layer within said metal endoskeleton.
18. The method of claim 17 further comprising locking said metal
endoskeleton to an acetabular shell.
19. The method of claim 17 wherein said first locking mechanism is
selected from the group consisting of a plurality of interlocking
dovetails, beaded surfaces, undercut surfaces, and chemically
bonding surfaces.
20. The method of claim 17 wherein said second locking mechanism is
selected from the group consisting of an external thread and a
locking taper.
21. A method of constructing an acetabular bearing assembly
comprising: constructing a metal endoskeleton with at least one
tapered hole extending at least partly though said metal
endoskeleton; filling at least a portion of said metal endoskeleton
with polyethylene powder such that said polyethylene powder fills
at least a portion of said tapered hole; and molding said
polyethylene powder within said metal endoskeleton and said tapered
hole to form and lock a polyethylene layer within said metal
endoskeleton.
22. The method of claim 21 wherein said tapered hole extends
through said metal endoskeleton.
23. A modular acetabular bearing assembly comprising: acetabular
shell means for attachment to the acetabulum of a patient; and
composite bearing means for receiving a ball of a femoral stem and
for attachment to said acetabular shell means such that said
acetabular shell means and said composite bearing means are
attached through metal to metal contact, wherein said composite
bearing means comprises (1) endoskeleton means for attachment to
said acetabular shell means; and (2) polymer insert means for
attachment to said endoskeleton means and for receiving said ball
of said femoral stem.
24. The modular acetabular bearing assembly of claim 23 further
comprising interlocking means for interlocking said acetabular
shell means to said composite bearing means to prevent relative
movement therebetween.
25. The modular acetabular bearing assembly of claim 23 further
comprising interlocking means for interlocking said polymer layer
means into said endoskeleton means.
26. The modular acetabular bearing assembly of claim 23 wherein
said assembly has polymer-metal interfaces only between said
endoskelton means and said polymer layer means.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to medical devices
and, more particularly, to an acetabular bearing assembly of a
total hip joint prosthesis for minimizing or eliminating the
production of wear debris resulting from relative motion at the
interface between the acetabular shell and polymer bearing insert
portions of a modular acetabular bearing assembly.
BACKGROUND OF THE INVENTION
[0002] Hip surgery for the replacement and repair of hip joints has
become relatively commonplace in recent years. Prosthetic hip joint
devices are available from a variety of manufacturers. Such hip
prosthetic systems, when properly installed, approximate a
patient's natural hip movement.
[0003] Typical hip joint prostheses contain a femoral component and
an acetabular component. The femoral component has an
intramedullary portion which is fixed to the femur of a patient.
The femoral component also has an attached ball portion which
allows articulation, restricts dislocation or subluxation, and
transfers loads to the acetabular component. The acetabular
component may be unitary, including a concave bearing surface to
articulate with the ball, and a fixation surface for attachment to
the acetabulum. Acetabular components may be of modular
construction, including a bearing insert portion and an acetabular
shell portion which receives the bearing insert and is affixed to
the acetabulum of a patient.
[0004] Currently available modular acetabular components use a
polymeric material for the bearing insert. Such currently available
modular acetabular components suffer from a tendency toward
relative motion between the bearing insert and the acetabular shell
portion. Such relative motion can cause wear and the generation of
small particles from the polymeric bearing insert. Such wear can
lead to failure of the hip joint prosthesis and lysis of the
surrounding bone.
[0005] Various attempts to solve this problem include elaborate and
often costly locking systems to minimize relative motion at the
interface between the bearing insert and the metal acetabular shell
portion. In addition, such attempts at solving this problem have
often not been modular and therefore have lost the advantages of
modularity, including the possibility of using screws to fix the
metal acetabular shell portion to the acetabulum.
[0006] Accordingly, there is a need for a modular acetabular
bearing assembly which either minimizes or eliminates the
production of wear debris resulting from relative motion at the
interface between the polymer bearing insert and metal acetabular
shell portions of hip joint prostheses.
SUMMARY OF THE INVENTION
[0007] The present invention fulfills the aforementioned need by
providing an acetabular bearing assembly for a total hip joint
which either minimizes or eliminates the production of wear debris
that results from relative motion at the interface between the
polymer bearing insert portion and metal acetabular shell portions
of a total hip joint prosthesis.
[0008] In one embodiment of the present invention, an acetabular
bearing assembly is provided, which includes (1) an acetabular
shell having an outer convex surface for fixation to a surgically
prepared acetabulum and an inner concave surface, and (2) a
composite bearing insert having a polymer layer and a metal layer,
wherein the polymer layer forms a concave bearing surface shaped to
receive a ball-end of a stem, and wherein the metal layer forms a
convex surface to interlock with the concave surface of the
acetabular shell. The composite bearing insert is constructed so
that the metal layer and the polymer layer are interlocked to
minimize relative movement therebetween. The acetabular bearing
assembly may be configured such that the composite bearing insert
contacts the acetabular shell only through metal-to-metal contact.
In one embodiment of the invention, the composite bearing insert
and metal acetabular shell are interlocked through a plurality of
interlocking dovetails. In various other embodiments of the
invention, the acetabular shell and composite bearing insert are
interlocked through a locking arrangement selected from the group
consisting of: a locking taper, a screw fastener, a pin fastener, a
locking bayonet and a snap ring.
[0009] The present invention also includes a technique for
constructing acetabular bearing assemblies. In one embodiment of
the present invention, the method includes (1) constructing a metal
layer in the form of a metal endoskeleton with a first locking
mechanism and a second locking mechanism, wherein the first locking
mechanism is disclosed on a concave portion of the metal
endoskeleton and the second locking mechanism is supplied on a
convex portion of the metal endoskeleton, (2) filling at least a
portion of the metal endoskeleton with a polymeric powder, (3)
molding the polymeric powder upon and within the metal endoskeleton
to form and lock the polymeric bearing layer to the metal
endoskeleton, and (4) locking the metal endoskeleton to an
acetabular shell. In various embodiments of the invention, the
locking mechanisms between the endoskeleton and the acetabular
shell may include a locking taper or threaded surface.
[0010] The details of the various embodiments of the present
invention are set forth in the accompanying drawings and
description below. Numerous additional features and advantages will
become apparent from a review of the following details of various
embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a cross-sectional view of an acetabular bearing
assembly for total hip joints in accordance with one embodiment of
the present invention.
[0012] FIG. 2 is a top view of a metal endoskeleton having a
plurality of radial blind dovetail dovetail holes in accordance
with another embodiment of the present invention.
[0013] FIG. 3 is a cross-section of the endoskeleton shell of FIG.
2 along lines 3-3.
[0014] FIG. 4 is a cross-sectional view of an alternate embodiment
of a composite bearing assembly in accordance with another
embodiment of the present invention.
[0015] FIG. 5 is a cross-sectional view of a composite bearing
insert in accordance with another embodiment of the present
invention.
[0016] FIG. 6 is a top view of an alternate embodiment of an
acetabular bearing assembly in accordance with another embodiment
of the present invention.
[0017] FIG. 7 is a cross-sectional view of the embodiment to FIG. 6
along lines 7-7.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE PRESENT
INVENTION
[0018] With reference to the drawings, various embodiments of the
present invention will now be shown and described. The leading
numeral of each reference numeral indicate the first drawing in
which that reference numeral is introduced. The trailing two
numerals of each reference number are consistently used throughout
the drawings to designate counterpart or like elements.
[0019] With reference to FIG. 1, a cross-sectional view of an
acetabular bearing assembly in accordance with one embodiment of
the present invention is shown. In general, the acetabular bearing
assembly 100 of the present invention consists of two elements: an
acetabular shell portion 120 and a composite bearing insert 130,
each of which will now be described in greater detail below.
[0020] The acetabular shell portion 120 is preferably made of a
suitable, bio-compatible material that allows the outer convex
surface 122 to be fixed to a surgically-prepared acetabulum. The
acetabular shell 120 may be fixed to the acetabulum by various
techniques including biological fixation, mechanical fixation, or
grouting fixation. The acetabular shell 120 has an inner concave
surface 124 configured to receive the composite bearing insert 130
therewithin. The acetabular shell 120 of the embodiment of FIG. 1
further includes a threaded portion 126 to lock the acetabular
shell 120 to the composite bearing insert 130.
[0021] The acetabular shell 120 may be made of biocompatible metal,
such as titanium or titanium alloy, cobalt-chrome alloy, or a
suitable low corrosion iron alloy. In the alternative, the
acetabular shell 120 may be made of ceramic, or a composite
material of suitable strength and stiffness.
[0022] The second component of the acetabular bearing assembly 100
is a composite bearing insert 130 made of the endoskeleton 140 and
the polymer layer 160. As such, the bearing insert is a composite
structure of a polymer and a stiffer, stronger material such as a
bio-compatible metal, including titanium or titanium alloy,
cobalt-chrome alloy or a suitable low corrosion iron alloy. The
polymer layer 160 forms a concave bearing surface 164 which
receives the ball-end of a stem in the cavity 170. The endoskeleton
140 of the composite bearing insert 130 is received by, and locked
into, the concave surface 124 of the acetabular shell portion
120.
[0023] In one embodiment of the present invention, the polymer
layer 160 is attached to the endoskeleton 140 by means of an
interlocking structure such as dovetails or tapered holes 162. In
the alternative, mechanical, chemical or adhesive bonding may be
used to interlock the endoskeleton 140 and the polymer layer 160.
This interlocking structure eliminates meaningful relative motion
between the two portions of the composite bearing insert, thus
minimizing or eliminating the production of wear debris that
results from relative motion at the interface between the
endoskeleton 140 and the polymer layer 160.
[0024] The endoskeleton 140 of the composite bearing insert is
received by, and locked into, the concave surface 124 of the
acetabular shell portion 120. Preferably, the composite bearing
insert 130 may be shaped so that its outer convex surface 141
contacts the inner concave surface 124 of the acetabular shell 120
only by metal-to-metal contact. As such, the present invention
minimizes the generation of wear debris by eliminating contact
between any polymer surface on the composite bearing insert 130 and
any metal surface on the acetabular shell 120. In addition, the
shell/endoskeleton interface may be configured to have on the
non-tapered portion of the interface an appropriate small clearance
between the acetabular shell 120 and endoskeleton 140 along curved
portions of the shell 120 and endoskeleton 140.
[0025] The present invention further provides a suitable locking
mechanism between the composite bearing insert 130 and the
acetabular shell 120. This may be accomplished through a number of
techniques including screws or pin fasteners, locking bayonets,
taper locking surfaces or snap rings. With reference to FIG. 1, the
threaded portion 126 of the acetabular shell 120 and the threaded
portion 142 of the endoskeleton 140 form a threaded interface to
interlock the composite bearing insert 130 and the acetabular shell
120. The threaded interface may be further treated with a polymer
locking surface and augmented by locking pins to prevent back out
of the threads.
[0026] With reference to FIGS. 2 and 3, an alternate embodiment of
the endoskeleton 240 is shown. The endoskeleton 240 has a plurality
of blind radial dovetail holes 260. These radial tapered holes 260
may extend through the endoskeleton 240. As such, a polymer layer
may be molded within the endoskeleton 240 such that the polymer
extends into holes 260, thereby locking the polymer bearing layer
to the endoskeleton 240.
[0027] With reference to FIG. 4, an acetabular bearing assembly 400
may include an acetabular shell 420 which is interconnected to the
composite bearing insert 430 through a locking or morse taper 436.
The locking taper 436 includes a taper element 426 on the concave
side 424 of the acetabular shell portion 420 and a taper element
442 on the convex surface 441 of the endoskeletal portion 440. Such
a tapered locking mechanism offers the advantages of an unlimited
number of positions of rotational engagement, while transmitting
both axial and torsion loads with minimum relative motion at the
locking interfaces. The remaining elements of the embodiment of
FIG. 4 are similar to the corresponding elements of the embodiment
of FIG. 1: a convex outer surface 422, a polymer bearing layer 460,
several dovetails 462 and a bearing surface 464.
[0028] With reference to FIG. 5, another embodiment to the present
invention is shown. The composite bearing insert 530 contains an
interlocking interface formed between the endoskeleton 540 and the
polymer bearing layer 560. In this embodiment, the endoskeleton 540
includes several undercuts or stump projections 562 which project
into the polymer layer 560. As such, the endoskeleton 540 includes
a beaded surface containing the undercuts or stump projections
562.
[0029] With reference to FIGS. 6 and 7, another embodiment to the
present invention is shown in which a multifaceted structure 610 is
used to prevent rotation between the acetabular shell 720 and
endoskeleton 740. Although a hexagonal shape 610 is shown, it is to
be understood that other polygonal shapes or an oval shape may be
used to prevent relative rotation between the acetabular shell 720
and the endoskeleton 740.
[0030] In the embodiment of FIGS. 6 and 7, the acetabular shell 720
and endoskeleton 740 may be configured so that a portion of the
shell/endoskeleton interface is spherical. In addition, a snap ring
locking device 765 may be used to interlock the endoskeleton 740
and acetabular shell 720. Moreover, the polymer bearing layer 760
may have a plurality of lip extensions over the edge or face of the
endoskeleton or acetabular shell to provide an asymmetric face.
[0031] The remaining elements of this acetabular bearing assembly
600 may be similar to the structures found in the embodiments of
FIG. 1-5.
Method of Manufacture
[0032] In manufacturing the composite bearing insert element of the
present invention, one method includes attaching the polymer
bearing layer of the insert to the metal endoskeleton by molding,
such as by compression molding. Preferably, the polymer material
used is ultra-high molecular weight polyethylene.
[0033] In implementing this method, the metal endoskeleton portion
of the composite bearing insert may be suitably shaped or surfaced
to securely interlock with, or bond to, the polymer bearing layer.
As previously discussed, one locking technique involves providing
wedge-shaped mating surfaces at the endoskeleton/polymer layer
junction so as to mechanically lock the two portions by the action
of the shrinking of the polymer about the endoskeleton at the time
of molding. This locking technique could involve the formation of
dovetails, such as the dovetails 162 shown in FIG. 1. Another
technique would involve the formation of tapered holes in the
endoskeleton, such as the tapered holes 260 shown in FIGS. 2 and 3.
These techniques effectively interlock the endoskeleton and polymer
bearing layer, thereby preventing relative movement therebetween.
Locking of the polymer layer to the endoskeleton may also be
accomplished by coating the concave surface of the endoskeleton
with a beaded metal layer, a coated undercut surface layer produced
by plasma spraying or electrical surface undercutting.
[0034] By the aforementioned detailed description and the attached
drawings, a number of embodiments of the present invention have
been shown and described. It is to be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, it is to be understood that
the invention is not to be limited by the illustrated and described
embodiments, but by the scope of the appended claims.
* * * * *