Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1998-02-17
2000-09-19
Willse, David H.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 18, A61F 238, A61F 230
Patent
active
061205435
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns an artificial joint, particularly an endoprosthesis for replacement of natural joints, consisting of at least two artificial joint parts, each with curved articulation surface, on which the joint parts articulate relative to one another.
Such an artificial joint is known from German Patent Application No. P 4202717.9. Here, the joint surfaces have planes vertical with respect to one another, a longitudinal plane and a transverse plane, different circular section contours, wherein the curvature ratios of the articulation surfaces in each of the planes are convex-convex, convex-concave, or concave-concave, and the joint geometry of the articulation surfaces with respect to one another, in each of the two planes, is determined by a joint chain with two joint axes (dimeric joint chain), which pass through the rotation centers of the articulation surface of the individual section contours. Since the articulation surfaces of this artificial joint are shaped convex-concave, concave-concave, or convex-convex, punctiform force transfer areas are formed, wherein increased surface pressing on the articulation surfaces arises, which can lead to material wear. In this way, the service life of these artificial joints can be shortened. In order to attain an improvement in force transfer between the articulation surfaces of the joint parts, the proposal is made that, in the known joint, a pressure distribution element be placed between these articulation surfaces, with which a better and more uniform force distribution is attained. These pressure distribution elements, however, increase the number of the required joint parts of the artificial joint.
The goal of the present invention is to create an artificial joint in which the punctiform force transfer areas are avoided and in which the incorporation of pressure distribution elements is not required, and which, at the same time, makes possible an optimal adaptation to the realities of the human body in use as an endoprosthesis for a natural human joint.
In accordance with the invention, this is attained with an artificial joint which consists of at least two artificial joint parts with curved articulation surfaces, wherein on each of the articulation surfaces, a contact line shaped as an arc of a circle is formed, which, in each case, is a section of a contact circle, lying in a plane with a center M, wherein the articulation surfaces are arranged as a pair with respect to one another in such a way that the contact lines can roll onto one another and axes running vertical to the plane and through the center of the contact circles intersect in an intersection point S, whereby ruled surfaces which are formed from a large number of straight pathlines of contact are found at one side of the contact lines, whereby the pathlines of contact lie on the momentary connecting lines of the momentary contact points, momentarily appearing during the rolling movement, with the momentary intersection points, which are produced by a swiveling movement of the contact lines at an angular velocity .OMEGA. around a common tangent of the contact lines through the momentary contact points. In accordance with the invention, therefore, a spatial gear system is formed. Here, a contact line is assigned to the individual joint surface of each joint part (limb), wherein these contact lines always touch and have a common contact tangent. During the articulation of the joint parts, the slope of the contact lines lying on the contact circles can be changed with respect to one another, wherein they carry out a rotation around the joint contact tangent moving in the contact point, so that then the contact circle axes exhibit a varying spherical arrangement with respect to one another. Since, in accordance with the invention, in the area of the ruled surfaces, straight pathlines of contact are present between the articulating ruled surfaces, wherein these pathlines of contact emanate from the contact point of the contact lines, an area of direct force transfer arises next to
REFERENCES:
patent: 3748662 (1973-07-01), Helfet
patent: 3798679 (1974-03-01), Ewald
patent: 4242759 (1981-01-01), White
patent: 5330533 (1994-07-01), Walker
patent: 5556432 (1996-09-01), Kubein-Meesenburg
Kubein-Meesenburg Dieter
Nagerl Hans
Joachim Theusner
Willse David H.
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