Hip Prosthesis Stem Fatigue Resistance via Lateral Machining

Solution Overview

Problem

Hip prostheses, particularly medium and long stems, face challenges in withstanding fatigue tests due to weakness in the lateral part where fibers are extended under stress, leading to potential cracking and breakage, and existing solutions do not adequately address this issue.

Innovation Solution

A hip prosthesis stem with a lateral surface designed using additive manufacturing and a machining allowance, followed by Hot Isostatic Pressing and mechanical machining to reduce porosity and enhance fatigue resistance, combined with a relief pattern for osseointegration and shot peening to increase hardness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the stem is made with additive manufacturing technology, then manufacturing flexibility and customization are improved, but the lateral part becomes weak and prone to cracking under fatigue loads

Engineering Contradiction:

Improvemanufacturing flexibilityVSAvoidfatigue resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies local quality by providing a machining allowance specifically at the lateral surface of the stem, while other surfaces may have different surface characteristics. This localized approach allows the lateral surface to be free from printing defects through machining, while maintaining the additive manufacturing benefits for the rest of the structure. The machining allowance is removed to create a smooth, crack-free lateral surface that can withstand fatigue loads.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent applies preliminary action by incorporating a machining allowance during the additive manufacturing process itself, before the final finishing operations. This preliminary consideration ensures that the lateral surface is prepared for subsequent machining operations that will eliminate porosity and prevent crack formation, thereby ensuring fatigue resistance from the outset.

Inventive Principle:

Principle #10Preliminary action

2Device complexity

If the lateral surface is left as-printed from additive manufacturing, then manufacturing complexity is reduced, but cracks can form during fatigue tests leading to stem breakage

Engineering Contradiction:

Improvesurface processing complexityVSAvoidresistance to cracking

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The patent applies local quality by providing a machining allowance specifically at the lateral surface of the stem, while other surfaces may have different surface characteristics. This localized approach allows the lateral surface to be free from printing defects through machining, while maintaining the additive manufacturing benefits for the rest of the structure. The machining allowance is removed to create a smooth, crack-free lateral surface that can withstand fatigue loads.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent applies preliminary action by incorporating a machining allowance during the additive manufacturing process itself, before the final finishing operations. This preliminary consideration ensures that the lateral surface is prepared for subsequent machining operations that will eliminate porosity and prevent crack formation, thereby ensuring fatigue resistance from the outset.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If medium or long stems are used to reach the medullary canal, then stability is improved, but difficulty in insertion and positioning increases

Engineering Contradiction:

Improveimplant stabilityVSAvoidinsertion difficulty

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent applies dynamics by designing the stem with a flexible or adaptable geometry that can navigate the curved medullary canal. The additive manufacturing technology enables complex, non-linear stem shapes that can conform to the anatomical variations of the femoral canal, allowing the stem to be inserted more easily while maintaining stability at the target location.

Inventive Principle:

Principle #15Dynamics

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 stem effectively withstands fatigue tests with heavier loads, preventing crack formation and ensuring stability, making it suitable for medium and long sizes while being reliable, cost-effective, and easy to implement.

Implementation Method 1

The anterior surface 5, the posterior surface 6 and the medial surface 7 are made at least partially with a porous structure with undercuts

Methodology Applied

Scientific EffectOsteointegration:

Implementation Method 2

followed by Hot Isostatic Pressing and mechanical machining to reduce porosity

Methodology Applied

Scientific EffectHot Isostatic Pressing: Hot Isostatic Pressing

Implementation Method 3

combined with a relief pattern for osseointegration and shot peening to increase hardness

Methodology Applied

Scientific EffectShot peening: Shot Peening

Data Source

PatentEP3876872B1Method of manufacturing a stem for a hip prosthesis, with fixed or modular neck

Publication Date: 2023.09.20 ADLER ORTHO SRL

Figure 1
Figure 2
Figure 3

AI summary

A stem (1) for a hip prosthesis, with fixed or modular neck, which comprises a stem body which is divided into a proximal region (2) and a distal region (3), the body of the stem forming an anterior wall (5), a posterior wall (6), a medial wall (7) and a lateral wall (8); the anterior wall, the posterior wall and the medial wall are provided at least partially with a porous structure with undercuts, the lateral wall (8) being provided with a machining allowance.