Variable Stiffness Prosthetic Trunnion Angularity
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Solution Overview
Problem
Modular hip prosthesis designs, while offering customization and stability, suffer from trunnionosis due to wear, corrosion, and fretting at the metal-on-metal modular junctions, leading to increased revision rates and mechanical insufficiency, with the exact cause remaining poorly understood.
Innovation Solution
The use of additive manufacturing techniques, such as 3D printing, to create prosthetic components with variable stiffness profiles that mimic the mechanical properties of bone, including angularity in the trunnion interface and controlled material density to reduce misalignment and fretting, along with multidimensional differential stiffness to alleviate wear patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If modular design is used to enable customization of leg length and offset, then adaptability is improved, but wear and corrosion at the trunnion interface increase
Solution Approach 1:
The patent changes the geometric parameters of the trunnion interface by introducing angularity (non-zero degrees) instead of the conventional zero-degree interface. This angular configuration modifies the mechanical interaction between components, reducing micro-motion and fretting while maintaining the modular design's adaptability for customization.
Solution Approach 2:
The patent introduces asymmetric angular features at the trunnion interface, creating a non-symmetric geometry that provides mechanical advantage in reducing wear and corrosion. The angularity creates a self-aligning mechanism that minimizes harmful micro-motions while preserving the modular assembly's versatility.
2Strength
If metal-on-metal modular junctions are used to achieve structural strength, then strength is improved, but corrosion and fretting damage increase
Solution Approach 1:
The patent modifies the interface geometry parameters by introducing angularity to the trunnion design. This geometric parameter change reduces the contact stress and micro-motion between metal surfaces, thereby decreasing corrosion and fretting damage while maintaining the necessary structural strength through optimized angular configuration.
Solution Approach 2:
The patent converts the potentially harmful micro-motion and fretting at the metal interface into a beneficial self-aligning mechanism. The angularity creates a mechanical guidance system that directs forces more favorably, reducing harmful wear while maintaining strong structural connection between modular components.
3Manufacturing precision
If conventional machining techniques are used to create the trunnion interface, then manufacturing precision is improved, but angularity and misalignment are introduced
Solution Approach 1:
The patent incorporates angularity directly into the design and manufacturing of the trunnion interface, preparing the geometry in advance to prevent misalignment. By pre-configuring the angular features during manufacturing, the design eliminates the need for post-assembly alignment adjustments and reduces operational misalignment.
Data Source
AI summary
A system and method for improving mechanical assemblies, such as prosthetic implants, intended to be installed in living tissue such as bone. Force-imparting devices are adapted and may include angularity, which may be introduced with specialized additive manufacturing, which may impart congruent cross-sections while providing variable stiffness. In some cases, the variable stiffness may be “stretchy” in a longitudinal direction and “rigid” in a radial directional which may provide an assembly bias. Additive manufacturing may allow the material of a prosthesis to be varied (e.g., density/porosity) to create variable stiffness over a length.