Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-10-11
2003-03-04
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S022240
Reexamination Certificate
active
06527808
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ball-and-socket joints, and, more particularly, to an improved liner forming the socket of an orthopaedic implant utilized to replace (in whole, or in part) a ball-and-socket joint.
2. Description of the Related Art
Orthopaedic implants for the replacement of all, or a portion of, a patient's joint such as, e.g., the ball-and-socket joints of, e.g., the shoulder and hip are commonly used to restore the use of, or increase the use of a joint which has deteriorated due to, e.g., aging, illness, or injury. For the sake of brevity, this document will describe a ball-and-socket joint with reference to the hip joint, however, it will be understood that the disclosure of this document is adaptable to any ball-and-socket joint, including, e.g., the shoulder joint.
Typically, orthopaedic implants for replacing a patient's hip include a femoral component and an acetabular component. The femoral component includes the “ball” of the joint, while the acetabular component includes the “socket”. The femoral component is designed to replace the head and the neck of the femur, while the acetabular component is positioned in the acetabulum and includes an articular region to receive the head of the femoral component and to allow relative movement between the femoral component and the acetabular component. The head of the femoral component is generally spherical, and the articular region of the acetabular component includes a corresponding spherical cavity to accommodate the head of the femoral component and form the desired ball-and-socket joint.
The acetabular component typically includes both a cup and a liner, with the cup being formed from, e.g., stainless steel or titanium and the liner being formed from ultra-high molecular weight polyethylene (UHMWPE). It is further known that the liner can be formed from a plastic other than UHMWPE and can also be formed from metal. The current disclosure is adaptable to the various materials of construction of the acetabular component.
In a known prosthetic hip joint, the liner of the acetabular component forms the articular region thereof. The acetabular cup is affixed to the acetabulum and the liner is thereafter affixed to the shell and receives the femoral head. Known procedures for affixation of the acetabular cup include, e.g., the use of screws to traverse apertures in the acetabular cup, be sunk into the acetabulum, and thereby effect affixation of the acetabular cup to the acetabulum. The liner of the acetabular component typically includes exterior protrusions and/or indentations which mate with indentations and/or protrusions on the interior of the shell to effect affixation of the liner to the shell and form the complete acetabular component.
The acetabular component described above includes a single articulating surface, however, it is known to provide an acetabular component which is not affixed to, but rather is movable within the natural socket of the acetabulum and therefore includes a pair of articulating surfaces (i.e., the head of the femoral component is moveable against the articular region of the acetabular component and also the acetabular component is moveable within the natural socket of the acetabulum). These devices having a pair of articulating surfaces are generally referred to as “bipolar”. The constrained acetabular liner of the current invention is applicable to both of the above-described types of acetabular components.
In one known prior art hip implant, the articular region of the acetabular component is hemispherical, and, therefore, the head of the femoral component is not “constrained” or held in place by the acetabular component. In such arrangements, the muscles, tendons and ligaments of the individual receiving the implant function to hold the femoral component in place within the articular region of the acetabular component.
FIGS. 1 and 2
illustrate prior art acetabular liner
20
including hemispherical articular region
22
. Acetabular liner
20
further includes affixing protrusions
24
to affix acetabular liner
20
to an acetabular cup to form the complete acetabular component, as described above. Since articular region
22
will not hold the head of a femoral component in place, acetabular liners of this type may result in a relatively high incidence of hip dislocation.
Alternatives to hemispherical acetabular liners include so-called “constrained” acetabular liners. Constrained acetabular liners are characterized in that the head of the femoral component is physically restrained by the acetabular liner after being positioned in abutting relationship with the articular region of the acetabular liner. Constrained acetabular liners have a spherical articular region and are generally spherically shaped themselves. The articular region of a constrained acetabular liner is formed in a cavity of the acetabular liner which is larger than a hemisphere, so that the acetabular liner surrounds more than a hemisphere of the femoral head and, therefore, constrains the femoral head from dislocation from the acetabular component.
While constrained acetabular components advantageously decrease the frequency of joint dislocation, they present assembly problems for the surgeons who implant them. Generally, the more constrained (i.e., the more material of the acetabular liner extending beyond a hemisphere) an acetabular component is, the more difficult the ball-and-socket joint is to assemble. With this in mind, many constrained ball-and-socket joints have an assembly force which necessitates assembly of the femoral head into the articular region of the acetabular component prior to implantation (i.e., not during the surgical procedure). This assembly procedure limits the versatility of these components and, specifically, limits a surgeon's ability to choose an alternative prosthesis during a surgical procedure.
With the above problems in mind, constrained acetabular components having an assembly force which is disproportionately lower when compared to the dislocation force of the assembled prosthesis have been developed.
FIGS. 3 and 4
illustrate prior art acetabular liner
30
having spaced cuts
38
extending from beveled rim
42
into articular region
32
. Acetabular liner
30
further includes affixing protrusions
34
analogous to affixing protrusions
24
described above with respect to acetabular liner
20
illustrated in
FIGS. 1 and 2
.
Prior art acetabular liner
30
includes petals
44
formed between adjacent cuts
38
.
FIG. 4
illustrates insertion of femoral component
78
into acetabular liner
30
. As illustrated in
FIG. 4
, petals
44
flex outwardly as femoral head
80
is inserted into acetabular liner
30
.
FIG. 4
illustrates femoral head
80
prior to being fully seated against articular region
32
. As illustrated, in this transitional state, cuts
38
separate to allow petals
44
to flex outwardly, thus increasing the size of the opening in acetabular liner
30
and decreasing the required assembly force to operatively position femoral head
80
in abutting relationship with articular region
32
.
Referring to
FIG. 3
, acetabular liner
30
includes beveled rim
42
adjacent the opening to facilitate positioning and insertion of femoral head
80
. After femoral head
80
is fully seated within acetabular liner
30
, locking ring
36
will be positioned generally about the exterior portion of acetabular liner
30
surrounding beveled rim
42
. When operably positioned about acetabular liner
30
, locking ring
36
prevents outward flexure of petals
44
, thus increasing the dislocation force required to remove femoral head
80
from acetabular liner
30
.
FIGS. 5 and 6
more fully illustrate prior art locking ring
36
. As illustrated, locking ring
36
includes beveled annular surface
46
to facilitate placement of locking ring
36
about acetabular liner
30
. As illustrated in
FIG. 4
, locking ring
36
is placed about femoral neck
82
prior to being operably positioned about acetab
Albertorio Ricardo
Krebs Robert D.
Baker & Daniels
Isabella David J.
Zimmer Technology, Inc.
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