Hip Joint Stem Surface Roughness Zones
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Solution Overview
Problem
Existing artificial hip joint stems face challenges with poor insertability and risk of premature fixation to the femoral bone, leading to issues like thigh pain and stress shielding due to increased surface roughness for bonding, which complicates stem insertion and bone integration.
Innovation Solution
The artificial hip joint stem is designed with a proximal rough surface (Ra 10-80 µm), an intermediate smooth satin surface (Ra 0.1-1.0 µm), and a distal shiny surface (Ra < 0.1 µm) to enhance insertability and prevent fixation, reducing friction and bone ongrowth, while maintaining fixability at the proximal part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the surface roughness (Ra) of the stem is increased to improve bonding strength between the stem and the bone, then the bonding strength is improved, but the friction against the bone increases, resulting in poor insertability of the stem
Solution Approach 1:
The stem surface is divided into three distinct regions with different roughness characteristics: proximal rough surface (Ra 10-80 μm) for bone bonding, intermediate smooth satin surface (Ra 0.1-1.0 μm) for reduced friction during insertion, and distal shiny surface (Ra < 0.1 μm) for preventing premature fixation. This local differentiation allows each region to perform its specific function optimally without compromising the others.
2Strength
If the surface roughness (Ra) of the stem is increased to improve bonding strength, then bone ongrowth occurs on the surface of the stem, but the distal part of the stem becomes apt to be fixed to the femoral bone, causing thigh pain and stress shielding
Solution Approach 1:
Different surface roughness zones are applied to different anatomical regions of the stem: the proximal rough surface promotes bone ongrowth where fixation is desired, while the distal shiny surface prevents bone ongrowth where fixation would cause harm. This spatial differentiation of surface properties eliminates the harmful effects of premature distal fixation while maintaining beneficial proximal bone integration.
Solution Approach 2:
The stem surface is segmented into three distinct roughness zones along its length, allowing independent control of bone interaction characteristics at each segment. This segmentation enables the proximal segment to provide stable fixation through bone ongrowth while the distal segment remains free of harmful fixation, thus preventing thigh pain and stress shielding.
3Strength
If the surface roughness (Ra) is increased to roughen the surface of the stem, then bonding strength between the stem and the bone is improved, but the distal part of the stem contacts with soft tissue and cancellous bone, resulting in poor insertability
Solution Approach 1:
The stem surface is differentiated into three roughness zones: proximal rough surface (Ra 10-80 μm) for bone bonding, intermediate smooth satin surface (Ra 0.1-1.0 μm) for facilitating insertion by reducing friction, and distal shiny surface (Ra < 0.1 μm) for preventing soft tissue and cancellous bone contact. This local quality differentiation allows the intermediate and distal regions to provide smooth insertion while the proximal region maintains strong bone bonding capability.
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
This configuration improves stem insertability, reduces the risk of premature fixation and associated pain and stress shielding, while facilitating bone integration and rotary resistance, making it suitable for bone preservation type stems.
Implementation Method 1
an increase in the surface roughness (Ra) of the stem increases friction against the bone
Implementation Method 2
a smooth satin surface located at the stem intermediate part and having a surface roughness (Ra) of 0.1-1.0 μm
Implementation Method 3
a shiny surface located at the stem distal part and having a surface roughness (Ra) of less than 0.1 μm
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An artificial hip joint stem of the present invention includes a stem body divided into a stem proximal part, a stem distal part, and a stem intermediate part located between the stem proximal part and the stem distal part. The stem body includes a rough surface located at the stem proximal part and having a surface roughness (Ra) of 10-80 µm, a smooth satin surface located at the stem intermediate part and having a surface roughness (Ra) of 0.1-1.0 µm, and a shiny surface located at the stem distal part and having a surface roughness (Ra) of less than 0.1 µm. The present invention also provides an artificial hip joint including the artificial hip joint stem.