CERAMIC SANDWICH INSERT FOR AN ARTIFICIAL HIP JOINT

INSERTION EN SANDWICH EN CERAMIQUE POUR ROTULE ARTIFICIELLE

English Abstract

The invention relates to a sandwich insert, comprising an inner ceramic
sliding cup (1) that is surrounded by a plastic cover (2), for inserting into
an outer, metal cup of an artificial hip joint. According to the invention,
the sliding cup (1) has a stud (3) on the outer end facing towards the
opening, in order to increase its resistance to impact while using minimal
construction space.

French Abstract

La présente invention concerne une insertion en sandwich comprenant une surface convexe de glissement interne (1) en céramique entourée d'une gaine synthétique (2), destinée à être mise en place dans une surface convexe métallique externe d'une rotule artificielle. Pour une meilleure résistance au pliage et un encombrement réduit, la surface convexe de glissement (1) de l'invention présente un tenon (3) à son extrémité externe voisine de l'ouverture.

Claims

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Claims
1. Sandwich insert having an inner ceramic sliding cup
(1), which is surrounded by a plastics cover (2), for
insertion into an outer metal shell of an artificial
hip joint, characterized in that the sliding cup (1)
has a stud (3) at its outer end that is remote from the
opening.
2. Sandwich insert according to claim 1, characterized
in that the stud (3 ) is arranged on the central axis
(4) of the sliding cup (1).
3. Sandwich insert according to claim 1 or 2,
characterized in that the stud (3) has an axial length
of 1 - 8 mm, preferably approximately 2 mm.
4. Sandwich insert according to one of claims 1 to 3,
characterized in that the stud (3) is arranged in the
plastics cover (2) by means of a fit.
5. Sandwich insert according to one of claims 1 to 4,
characterized in that the stud (3) projects into the
plastics cover (2) or projects completely through it.
6. Sandwich insert according to one of claims 1 to 4,
characterized in that the stud (3) is surrounded at
least in part by the plastics cover (2).
7.. Sandwich insert according to one of claims 1 to 6,
characterized in that the cross section of the stud (3)
forms an n-sided body, preferably with n = 2, 4, 5 or
6.
8. Sandwich insert according to one of claims 1 to, 6,

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characterized in that the cross section of the stud (3)
forms a polygon.
9. Sandwich insert according to one of claims l to 6,
characterized in that the cross section of the stud (3)
is oval.
10. Sandwich insert according to one of claims l to 9,
characterized in that the sliding cup (1) is of a
spherical or a stepped structural form on its outside.
11. Sandwich insert according no one of claims 1 to
10, characterized in that the plastics cover (2)
embraces the sliding cup (1) at its open end.
12. Sandwich insert according to one of claims 1 to
11, characterized in that the sliding cup (1) is
pressed into the plastics cover (2).

Description

CA 02378135 2002-O1-14
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Ceramic sandwich insert for an,artificial hip joint
The invention relates to a sandwich insert having an
inn~r ceramic sliding cup, which is surround~d.by a
plastics cover, far insertion into an, outer metal shell
of an artificial hip joint:
An artificial hip joint as a rule consists of a eliding
cup which is inserted into an outer metal shell either
directly or by way of a plaatics cover:. This metal
shell is implanted in the pelvic bone: The combination
of sliding cup and plastics cover is termed a sandwich
insert.
25 A shaft, on which there is arranged a ball head that
articulates in the sliding shell; is implanted in the
femur.
2n the case of artificial hip joints. it is possible
that the ball-head shaft will strike against the
acetabulum time and time again. If zhe impact forces
are sufficiently great, this can result in the
mechanical acetabulum=composite breaking up. In
particular, sandwich socket systems are at risk here,
since the polyethylene (PE) that is predominantly used
can only put up insufficient resistance against these
forces of impact .
Sandwich inserts sre produced in verious ways.
In one system, the ceramic sliding cup or the insert
respectively has plastics material injection-moulded
around it, with recesses being arranged on the sliding
shelf: What is disadvantageous about this is the fact
that the polyethylene (PE)-properties that result when
the same is heated are inferior. Furthermore, there is

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a thermal shock for the ceramic sliding cup. In
addition to..the outlay on injection-moulding on account
of the injecting mould and the handling of the hot
portions, the large amount of construction space that
is required is disadvantageous.
In the case of an alternative. system, the sliding shell
is anchored by a conical clamp in the plastics cover,
with there being to some extent; instanced of low __
l0 resistance of the composite component. The
disadvantage here as well is the large amount of
construction apace that is required.
The process of pressing the. eliding cup into the
plastics cover in the warm state is also preferably
employed. sn this connection, however, there :occur to
some extent instances of composite component strength
that are too low. Moreover, narrow tolerances must be
observed on account of the press-connection.
The underlying objaet of the invention.is to improve a
sandwich insert in accordance.with the preamble of
claim Z in such away that a high level of resistance
to sudden change is achieved with a small amount of
construction space being required.
In accordance with the invention this object is
achieved by the sliding cup having,a stud at its outer
eud that. is remote from the opening, whereby the
resistance to .sudden chang~ is substantially increa9ed,
With a small amount of construction space being
required, since the stud necessitates almost no
increase in construction space.
Advantageously, the stud is arranged on the c~ntral
axis or the axis of rotation ~of the sliding cup and has

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an axial length of l - 8 mm, preferably approximately 2
mm. This length suffices in order to increase the
resistance to sudden change. However, other lengths
can also be used.
In a.preferred embodiment, the stud:is arranged in the
plastics coves by_means of a fit. This can be an
interference fit, a transition fit or a close clearance
fit, dep~nding on the desired resistance-conf guration.
zo
The stud can.project completely through the plastics
cover; project into it or ~lse be surrounded at least
in part by the plastics cover. It is preferably even
completely surrounded by the plastics cover.
15.
The cross section of the stud forms an n-sided body
with n = 2, 4, 5 or 6. Alternatively, the cross
section of the-stud can even form a polygon or be oval.
20 The sl;;iding shell is preferably of a spherical or a
stepped structural foam on its outside. Spherical
structural forms require a very small amount of
__ construction space.
25 In an advantageous embodiment, the plastics cover
embraces the sliding shell at its open. end.
The sandwich insert is preferably produced by pressing
the sliding shell into the plastics cover.
Further features of the invention follow from the
figures which are described in the following and in
which
Figure 1 shows a sandwich insert in accordance with
the invention in a spherical structural fore;
~:~y:.

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Figure 2 shows a sandwich insert in accordance with
the invention in a stepped structural form;
and
Figure 3 shows advantageous configurations of the
cross sections of the stud.
Figure 1 shows a sandwich insert having a sliding cup 1
of spherical structural form. During productioy; this
sliding shell 1 is pressed into the plastics cover 2:
The.plastics cover 2 preferably c.onsiste of
polyethylene (PE).. The upper edge of the sliding shell _..
ie constructed so as to be flush with the upper edge of
the plastics cover 2. In order to increase the
resistance to sudden change, that is, also to anchor
the sliding cup 1 in the plastics cover 2 in a better ~~ --_
way, a stud 3 is. arranged at the end of the sliding
shell that is remote~from the opening on the axis of
rotation or central axis 4. This stud 3 projects into
the plastics cover 2 in this embodiment.
Figure'2 shows an alternative embodiment with a stepped
structural form for the sliding cup 1 on. the outside
thereof. Here, as well, a stud 3 is arranged on the
central axis 4 and is completely surrounded here by the
plastics cover 2. The axial length of the stud 3 is
then approximately 2 mm.
In view of thg fact that the sliding shell 1 is pressed
into the plastics cover 2 during production; the stud 3
is inserted in the plastics cover 2 by means of a fit.
At its open end the plastica cover 2 embraces the
sliding cup l, thereby improving the securement. The
collar 5 of the plastics cover 2 that rests on the
upper side of the..sliding cup l covers almost half of _

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the upper edge.
Figure 3, by way of cross sections, shows the various
configurations of the stud 3. In each case a cross
section of the stud 3 is shown ~t right angle9 to the
central.axis 4.
Figure 3a shows.an oval cross section for .the purpose
of increasing the resistance to rotation;.Figure 3b
to shows a two sided bodyr arid Figure 3c shows a polygonal
cross section. The latter has the advantage of being
able to be produced by turning with a comparatively
high level of removal of plastic9 material.
Figure 3d shows a four sided or a square.stud 3; arid
Figure 3e shows a five sided body as.a stud 3. .
Advantageously, also possible is a,six sided body for
the stud.

Representative Drawing