CA2125393A1

CA2125393A1 - Artificial joint

Info

Publication number: CA2125393A1
Application number: CA002125393A
Authority: CA
Inventors: Dietmar Kubein-Meesenburg; Hans Nagerl
Original assignee: Individual
Current assignee: KUBEIN MEESENBURG DIETMAR
Priority date: 1991-12-11
Filing date: 1992-12-08
Publication date: 1993-06-24
Also published as: EP0617597A1; WO1993011722A1; DE59208205D1; EP0617597B1; ATE149819T1; RU94030380A; DE4140838C1; AU3086092A; JPH07501730A; BR9206920A

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.

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 2~2~;393 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.

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

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 :: .. :

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 ; -~

~12~393 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.

Claims

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.

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.