Artificial joint, particularly an artificial hip joint
AssigneeSulzer Orthopaedie AG
InventorManfred Semlitsch
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Abstract
With the invention, a geometry is described which makes it possible to use similar, wear-resistant, metallic materials such as PROTASUL 21 WF for a bearing shell (1) and a joint ball (2) in a spherical bearing without micro-weldings and without excessive wear arising, while other properties such as toughness, stability of shape and elasticity can be exploited for the function. Micro-weldings of the similar metallic materials are largely prevented by a suitable relationship between the average radii R.sub.m, r.sub.m of the bearing surfaces A and B as well as of the permissible deviations (12, 13) in shape and of the permissible roughness of the bearing surfaces.
Claims14
Artificial joint, comprising a bearing shell which has a concave spherical surface A with a center M.sub.s, and a joint ball which has a convex spherical surface B with a center M.sub.K, which is rotationally symmetrically arranged with respect to a mounting axis D in the direction of a neck of an artificial joint shaft connected with the joint ball, the bearing shell and the joint ball comprising a wear-resistant metallic material;
- the surface A having an average radius R.sub.m and the surface B having an average radius r.sub.m, with their difference amounting to 35 .mu.m<R.sub.M -r.sub.m <85 .mu.m;
- wherein the shape error of the surface A amounts to less than .+-.7.5 .mu.m over an angle 90.degree.>.alpha.<180.degree.;
- wherein the shape error of the surface B amounts to less than .+-.2 .mu.m over an angle .beta.>140.degree.;
- wherein the joint ball is continued outside the area B by a set-back surface C which has a distance to the center M.sub.K which is less than that of surface B, while a roughness of the surface A corresponds to a value R.sub.a <0.08 .mu.m and a roughness of the surface B corresponds to a value R.sub.a <0.08 .mu.m.
Method for the manufacture of an artificial joint including a bearing shell which has a concave spherical surface A with a center M.sub.s, and a joint ball which has a convex spherical surface B with a center M.sub.K, which is rotationally symmetrically arranged with respect to a mounting axis D in the direction of a neck of an artificial joint shaft connected with the joint ball, the bearing shell and the joint ball comprising a wear-resistant metallic material;
- the surface A having an average radius R.sub.m and the surface B having an average radius r.sub.m, with their difference amounting to 35 .mu.m<R.sub.m -r.sub.m <85 .mu.m;
- wherein the shape error of the surface A amounts to less than .+-.7.5 .mu.m over an angle 90.degree.<.alpha.<180.degree.;
- wherein the shape error of the surface B amounts to less than .+-.2 .mu.m over an angle .beta.>140.degree.;
- and wherein the joint ball is continued outside the area B by a set-back surface C which has a distance to the center M.sub.K which is less than that of surface B, while a roughness of the surface A corresponds to a value R.sub.a <0.08 .mu.m and a roughness of the surface B corresponds to a value R.sub.a <0.08 .mu.m, the method comprising the steps of mounting the bearing shell as a workpiece in the form of a pre-turned shell which is undersize in the area of the bearing surface A with a polar axis of the bearing shell being aligned with an axis of rotation of a machine-tool spindle;
- or mounting the pre-turned joint ball as a workpiece with its mounting axis D aligned with an axis of rotation of a machine-tool spindle and is oversize in the area of the bearing surface B;
- pressing during the rotation of the workpiece a circular edge of the front side of a circularly cylindrical abrasion body, which is rotatingly mounted with its cylinder axis along an axis of rotation of a tool spindle, against the bearing surface of the workpiece while adding abrasive means, the axis of rotation of the tool spindle intersecting the axis of rotation of the workpiece spindle at a point of intersection and at a deflection angle (.gamma.,.delta.)<90.degree.;
- and exerting contact pressure by advancing the tool spindle in the direction of its axis of rotation.
Dependencies are inferred from the claim text.