Prosthetic Joint Stem with Localized Roughness for Bone Fixation
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Solution Overview
Problem
Conventional artificial joints with roughened surfaces via thermal spraying face issues with stress concentration at the edge portions, leading to potential breakage and reduced bone fixation ability, necessitating body weight limitations and limited applications.
Innovation Solution
An artificial joint with a stem portion featuring a distal end and a proximal end, where the proximal end-side roughened surface has a higher surface roughness and larger cross-sectional area than the distal end-side, with a sloped surface and varying surface roughness to alleviate stress concentration and enhance fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface of the stem portion is roughened by thermal spraying to improve bone fixation, then the ability to fix to bone is improved, but stress concentration occurs at the edge portion leading to breakage
Solution Approach 1:
The patent applies different surface roughness levels to different regions of the stem portion. The proximal end-side portion has a roughened surface with higher surface roughness for bone fixation, while the distal end-side portion has a smoother surface with lower surface roughness to reduce stress concentration. This local differentiation resolves the contradiction by optimizing each region for its specific function.
Solution Approach 2:
The stem portion is divided into distinct segments: a proximal end-side portion with roughened surface for fixation and a distal end-side portion with smoother surface for stress distribution. This segmentation allows each portion to be optimized independently, with the roughened portion providing bone fixation and the smoother portion preventing stress concentration.
2Strength
If the edge portion of the roughened surface is placed out of the position subject to greatest load to prevent breakage, then fatigue strength is improved, but the roughened area becomes insufficient reducing bone fixation ability
Solution Approach 1:
Instead of uniformly smooth or uniformly rough surfaces, the patent creates a localized roughened area at the proximal end-side portion while maintaining a smoother distal end-side portion. This allows the roughened area to be positioned optimally for bone fixation while the smoother distal portion handles stress concentration, resolving the contradiction between fixation ability and fatigue strength.
3Reliability
If thermal spraying is used to roughen the surface, then bone fixation is improved, but the thickness of the thermal sprayed part increases causing stress concentration
Solution Approach 1:
The patent applies thermal spraying selectively only to the proximal end-side portion to create a roughened surface for bone fixation, while leaving the distal end-side portion smooth. This localized application prevents excessive thickness accumulation in stress-prone areas while maintaining adequate roughness in the fixation-critical proximal region.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design improves fatigue strength and bone fixation ability without the need for edge portion displacement or body weight limitations, ensuring effective integration with the bone.
Implementation Method 1
thermal spraying, which involves forming a coating layer by spraying molten particles of titanium or the like onto a substrate such as a metal substrate or a ceramic substrate
Implementation Method 2
the artificial joint and the bone are fixed together because of the bone and the roughened surface portion fixed together by frictional resistance
Implementation Method 3
after surgery, new bone grows into the spaces in the roughened surface portion as time passes, thereby fixing the artificial joint firmly to the bone
Data Source
AI summary
Provided is an artificial joint that can improve fatigue strength while achieving the ability to fix to a bone. An artificial joint 1 includes a stem portion 2. The stem portion 2 has a distal end for insertion into a bone and a proximal end opposite the distal end and includes a roughened surface portion 4 which is provided in a proximal end-side portion, which has a rougher surface than a distal end-side portion, and which is larger in cross-sectional area than the distal end-side portion. The roughened surface portion 4 includes a distal end-side edge section 7 and a proximal end-side section 7, the distal end-side edge section 7 including a distal end-side edge portion of the roughened surface portion 4, the proximal end-side section 7 being configured as a section closer to the proximal end than the distal end-side edge section 7 is to the proximal end. The distal end-side edge section 7 has a surface roughness Ra1 lower than a surface roughness Ra2, Ra3 of the proximal end-side section.