Elliptical Bearing Hinge Knee Prosthesis Stress Distribution
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Solution Overview
Problem
Hinge-type knee prostheses have a short service life due to excessive stress on the bearing, which is not effectively distributed to absorb the various stresses during movement, leading to rapid wear and instability.
Innovation Solution
The design incorporates a bearing with an elliptical generatrix oriented along a sagittal axis, maximizing thickness and stress absorption in the flexed position and minimizing wear by distributing stress more evenly throughout the prosthesis, while maintaining a compact size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a hinge-type prosthesis allows lateral movement of the tibia relative to the femur, then patient comfort is improved, but the bearing experiences excessive stress and wears out quickly
Solution Approach 1:
The bearing is designed with an elliptical cross-section rather than a circular one, creating asymmetric geometry that optimizes stress distribution. The major axis of the ellipse is oriented perpendicular to the direction of extension of the anchoring portion, allowing the bearing to better absorb stresses in flexion while maintaining stability in extension.
Solution Approach 2:
The invention changes the geometric parameters of the bearing by using an elliptical generatrix instead of a circular one. This parameter change allows the bearing to have varying thickness in different directions, maximizing thickness and stress absorption capability in the sagittal axis direction while maintaining compact overall dimensions.
2Duration of action of stationary object
If the bearing thickness is increased to absorb more stress, then service life is extended, but the size of the bearing increases
Solution Approach 1:
The elliptical cross-section creates asymmetric thickness distribution, concentrating material where stress is highest (perpendicular to anchoring portion extension) while minimizing material in directions where less support is needed. This asymmetric geometry maximizes stress absorption efficiency per unit volume.
Solution Approach 2:
The invention transitions from a circular cross-section (one-dimensional symmetry) to an elliptical cross-section (two-dimensional asymmetry), utilizing the additional geometric dimension to optimize stress distribution. This dimensional change allows the bearing to achieve better stress absorption without proportional increase in overall size.
Data Source
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AI summary
The prosthesis has a tibial part comprising an anchoring portion to be inserted in a tibia, and a tibial plateau arranged at an end of the portion. An anchoring portion of a femoral part is inserted in a femur. A pivot (28) articulates the femoral part with the tibial part, and is rotatably mounted in a bearing of one of the parts. The bearing has a cylindrical opening with elliptical surface to receive the pivot. The elliptical surface is directed such that a major axis of elliptical section is perpendicular to a direction of extension of the anchoring portion of the tibial part.