ARTIFICIAL JOINT

ARTICULATION ARTIFICIELLE

English Abstract

ABSTRACT OF THE DISCLOSURE


An artificial joint for the replacement, in
particular, of human joints, consisting of at least
two joint sections (21,22) with spherical functional
surfaces moving in relation to each other, wherein the
relation to one another of the curvature of the
functional surfaces (23,24) featuring a circular
section contour are convex-convex, convex-concave or
concave-concave, and the geometry of the joint is
determined by means of a joint line with two joint
axes progressing through the centers of rotation M1,M2
of the functional surfaces with the radii R1,R2, where
R1 is the radius of the circular section contour of
the functional surface with the midpoint M1 and R2 is
the radius of the circular section contour of the
functional surface with the midpoint M2, and where a
pressure distribution body (25), the slide faces
(26,27) of which feature a curvature adapted to
correspond to the functional surfaces, is arranged

between and supported by the two functional surfaces
(23,24) of the joint sections (21,22), where the slide
faces (26,27) of the pressure distribution body (25)
are approximately the same size.

Claims

6
CLAIMS:


1. An artificial joint for the replacement, in
particular, of human joints, consisting of at least
two joint sections (21,22) with spherical functional
surfaces moving in relation to each other, wherein the
relations to one another of the curvature of the
functional surfaces (23,24) featuring a circular
section contour are convex-convex, convex-concave or
concave-concave, and the geometry of the joint is
determined by means of a line of joints with two joint
axes running through the centers of rotation M1,M2 of
the functional surfaces with the radii R1,R2, where R1
is the radius of the circular section contour of the
functional surface with the midpoint M1 and R2 is the
radius of the circular section contour of the
functional surface with the midpoint M2, and where a
pressure distribution body (25), the slide faces
(26,27) of which feature a curvature adapted to
correspond to the functional surfaces, is arranged

between and supported by the two functional surfaces
(23,24) of the joint sections (21,22), characterized
in that the slide faces (26,27) of the pressure
distribution body (25) are approximately the same
size.


2. A joint as in Claim 1, characterized in
that the slide faces (26,27) are polished to a mirror
finish.


3. A joint as in Claim 2, characterized in
that the functional surfaces (23,24) of the joint
sections (21,22) are of a convex configuration and
their centers of rotation M1,M2 lie within the
associated joint section (21,22) and their joint axis
path possesses a radius R = R1 + R2 + D.

7
4. A joint as in Claim 2, characterized in
that each respective functional surface (24) of a
joint section (22) is of a convex configuration and
the other functional surface (23) of the joint section
(21) of a concave configuration and their centers of
rotation M1,M2 lie within the joint section with the
convex functional surface and their joint axis path
possesses a radius R = R2 - R1 - D, where R2 is
greater than the sum of R1 and D, such that this
bestows a stable, folding, dimeric chain.

5. A joint as in Claim 2, characterized in
that the two functional surfaces are of a concave
configuration and their centers of rotation M1,M2 lie
within the pressure distribution body and their path
of the joint axis possesses the radius R = R2 + R1 -
D.

6. A joint as in Claim 2, characterized in
that one functional surface of a joint section is of a
convex configuration and the other functional surface
(23) of the joint section of a concave configuration
and the center of rotation M1 of the joint section
with the convex functional surface lies within the
latter and the center of rotation M2 of the joint
section with the concave functional surface lies
within the pressure distribution body and their path
of the joint axis possesses a radius R = R2 - R1 + D.

7. A joint as in Claim 4, characterized in
that the minimal thickness D of the pressure
distribution body (25) amounts to less/equal 50% of
the smaller radius R1.

Description

212~93




Artificial Joint




The present invention pertains to an artificial joint for
the replacement, in particular, of human joints, consisting of at
least two joint sections with spherical functional surfaces
moving in relationship with each other, where the relationships
between the curvatures of the functional surfaces featuring a .-
circular sectional contour are convex-convex, convex-concave or
concave-concave, and the geometry of the joint is determined by
means of a line of ~oints with two joint :
axes progressing through thè centers of rotation Ml, M2 of the
function surfaces with the radii R~, R2, where R~ is the radius of
the circular sectional contour of the functional surface with
midpoint M~, and Rt is the radius of the circular sectional ~:
contour of the functional surface with midpoint M2, and where a
pressure distribution body, the slide faces of which feature a
curvature

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adapted to correspond to the functional surfaces, is arranged
between and is supported by the two functional surfaces of the
joint sections.
A joint of this type is known from the German Patent
Application P 3,908,958.4. Here, arranged between the two joint
sections is a pressure distribution body, whose slide faces are
supported by the functional surfaces and feature a curvature
adapted to correspond to that of the functional surfaces. It has
proven to be necessary for the functional capability of this
joint that the pressure distribution body remain freely mobile.
The underlying purpose of the invention is to improve the
present known joint in such a manner that free mobility of the
pressure distribution body is bestowed at all stress points.
This is achieved in accordance with the invention in that the
slide faces of the pressure distribution body are configured to
be of substantially the same size, i.e., both surfaces of the
pressure distribution body contacting the two joint sections are
of the same size. This causes an equal amount of compressive
stress to occur at both sides of the pressure distribution body.
A deviation to the extent of 5-10~ between the two slide faces of
the pressure distribution body, nevertheless, lies within the
scope of the patent invention.
It is advantageous if, in addition, the slide faces are as
frictionless as possible. This is achieved as claimed in the
invention by the means that the slide faces, in particular, are
polished to a mirror finish.
It is also advantageous, according to the invention, if the
radii of the functional surfaces featuring a circular section -~
contour are equal, or if they feature only a slight difference.




'~,,,' - , ~: : :,.,. :

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This makes achieving uniformity of the slide faces of the
pressure distribution body possible in that only a special
configuration of its edge lip is necessary to bring about the
e~uality in area. It can also be advantageous if the minimum
thickness of the pressure distribution body for a configuration
of the functional surfaces of the two joint sections in the
convex-concave configuration, which minimum thickness is
present on the connecting line of the two centers of rotation,
is small in comparison to the two radii of the functional
surfaces, and indeed, preferably, if the minimum thickness of the
pressure distribution body is less than or equal to 50% of the
smaller radius of the two functional surfaces. It can also be
advantageous in the invention if the radius R of tl:e folding
dimeric chain amounts to approximately 2.5-6 mm. This
dimensioning of the radius R is recommended for the reason that
the method securely ensures that the friction between the bodies
sliding against each other is overcome.
The invention is more closely explained with the aid of the
embodiment example represented in the enclosed drawings.
As may be seen from the enclosed figure, a joint in
accordance to the invention is composed of a joint section (21)
and a joint section (22). The two joint sections (21,22) possess
different spherical curvatures. The joint body (21) features a
concave functional surface (23) and the joint body (22) a convex
functional surface (24).
A pressure distribution body (25) is arranged between the
joint sections (21,22). This pressure distribution body (25)
possesses slide faces (26,27). The joint section (22) possesses




:: .. :

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the center of rotation Ml and the circular sectional contour of
the functional surface (24) of the joint section (22) possesses
the radius Rl. The joint section (21) possesses a center of
rotation M2 and its concave functional surface (23) features the
radius R2 in its circular section contour. Here, the centers of
rotation are arranged within the joint section with the convex
functional surface (24). The radius R of the path of the joint
axis is yielded from the relationship
R = R2 - Rl - D
Here, D is the thickness of the pressure distribution body (25)
on the connecting line of the centers of rotation M~ and M2. The
radius R2 is proportioned in a manner such that R is a positive
size, such that M2 is displaced in the direction of the joint
section (22) with reference to M~. Here, a stable position is
yielded under compressive stress of the mutually sliding bodies.
The slide faces (26,27) are configured to be of essentially
the same size, such that the static friction forces are also
equally great at the two sliding faces. It is recommended that
this be achieved in that the two radii R~ and R2 of the functional ..
surfaces (23,24) not be differentiated too sharply, such that the .
equality of the areas can be achieved by means of the
configuration of the edge lips. A deviation of 5-10% of the area
sizes of the two slide faces can, nevertheless, be permitted, :~
without this substantially impairing the desired effect.
The present configuration causes the minimum thickness D of
the pressure distribution body to be small in comparison to the ; -~

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radii of the functional surfaces and, indeed, D is to be a
maximum of approximately SO% of the smaller of the two radii R~,
2~
In addition, the slide faces (25,26) are procured in such a
fashion that their surfaces are practically frictionless. This
can be achieved by the means that the slide faces are polished to
a mirror finish.

Representative Drawing