Aspheric Hip Bearing Spindle Torus Clearance Control
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Solution Overview
Problem
Existing joint prostheses face challenges in minimizing clearance between the ball and cup components, as manufacturing tolerances and acetabular cup deformation during implantation can lead to interference and wear, with previous solutions failing to provide optimal results by either increasing clearance too much, resulting in significant wear or not adequately addressing deformations near the equatorial lip.
Innovation Solution
A prosthetic ball and cup joint system is designed with a spindle torus configuration, featuring a concave articulation surface defined by one radius of curvature and a convex surface with a cap portion and toroidal portion, where the differences in radii are less than 0.05 millimeters, and the circular origin of the toroidal portion is located on a plane perpendicular to the axis, providing controlled clearance and reduced likelihood of interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diametral clearance is reduced to minimize wear, then wear is reduced, but interference and deformation occur during implantation
Solution Approach 1:
The acetabular cup is designed with non-uniform clearance distribution, providing small clearance (15-30 microns) in the conformal region for wear reduction, while providing larger clearance in the peripheral region to prevent interference during implantation. This local differentiation resolves the contradiction by optimizing clearance for its specific functional requirement in each zone.
Solution Approach 2:
The articulation surface is divided into two distinct regions: a conformal region with small clearance and a peripheral region with larger clearance. This segmentation allows each region to be optimized independently - the conformal region minimizes wear while the peripheral region prevents interference during cup insertion.
2Object-affected harmful factors
If clearance is increased to prevent interference during implantation, then interference is reduced, but wear increases significantly
Solution Approach 1:
Instead of uniformly increasing clearance throughout the entire articulation surface, the patent applies larger clearance only to the peripheral region where interference occurs during implantation, while maintaining small clearance in the conformal region where wear is the primary concern. This localized approach prevents interference without compromising wear resistance.
3Ease of manufacture
If spherical cup and head arrangement is used, then manufacturing is simplified, but clearance reduction near the pole also reduces clearance near the equatorial lip causing interference
Solution Approach 1:
The patent introduces asymmetry in the clearance distribution by designing the acetabular cup with different clearance characteristics in different regions. The conformal region has small clearance optimized for wear, while the peripheral region has larger clearance to prevent interference during implantation. This asymmetric clearance distribution resolves the limitation of spherical geometry.
Data Source
AI summary
In one embodiment a method of implanting a prosthetic includes implanting a first member including a concave articulation surface portion defined by a first radius of curvature in a first bone, implanting in a second bone a second member including a first convex articulation surface portion defined by a second radius of curvature and a second convex articulation surface defined by a third radius of curvature, wherein the second convex articulation surface is defined by the lemon portion of a spindle torus and each of the second radius of curvature and the third radius of curvature has a length that is different from the length of the first radius of curvature by less than 0.05 millimeters and wherein the origin of the second radius of curvature is not coincident with the origin of the third radius of curvature, and bringing the first member into slidable contact with the second member.