Total Disc Replacement Device Stress Shielding
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Solution Overview
Problem
Total disc replacement devices face challenges with high compression stresses at the interface between apposition plates and joint components due to press-fitting, leading to potential damage and wear, particularly with ceramic materials, which can result in sharp edges and stress shielding issues.
Innovation Solution
A total disc replacement device design featuring a central axis with first and second apposition plates, joint components, and intermediate means that allow for a clearance-free connection with stress shielding, reducing compression stress through the use of elastic or deformable intermediate means, such as polymeric rings or spring-like elements, to absorb and distribute stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If press-fitting is used to assemble inlays into bone contact plates, then a clearance-free connection is achieved, but high compression forces are generated that can damage ceramic portions and create sharp fragments
Solution Approach 1:
A press-fit ring is introduced as an intermediary component between the inlay and the bone contact plate. This ring absorbs the compression forces during assembly through elastic or plastic deformation, preventing direct transmission of high stresses to the ceramic inlay and avoiding fragment creation while maintaining the clearance-free connection.
Solution Approach 2:
The press-fit ring is designed beforehand to provide stress shielding during the assembly process. By selecting materials with appropriate elastic or plastic properties, the ring is pre-configured to deform and cushion the compression forces before they reach the inlay, preventing damage in advance.
2Reliability
If ceramic materials are used for inlays, then wear debris is minimized and biocompatibility is improved, but the materials are brittle and susceptible to damage during press-fitting
Solution Approach 1:
The press-fit ring serves as a protective intermediary that shields the brittle ceramic inlay from compression stresses during assembly. The ring's elastic or plastic deformation capacity allows it to absorb assembly forces while the ceramic inlay maintains its wear-resistant and biocompatible properties.
Solution Approach 2:
The device employs a composite structure combining the press-fit ring (made from elastic or plastic materials) with the ceramic inlay. This composite approach allows each material to contribute its advantageous properties: the ring provides stress absorption and the ceramic provides wear resistance and biocompatibility.
3Volume of moving object
If the device is designed to be relatively small for intervertebral implantation, then anatomical fit is improved, but the use of thick wall design for ceramic protection is prevented
Solution Approach 1:
The press-fit ring acts as a protective intermediary that compensates for the reduced wall thickness of the ceramic inlay. By absorbing compression forces during assembly, the ring provides stress shielding that allows the use of thinner ceramic walls in the compact device design, maintaining both small size and adequate protection.
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 solution effectively reduces compressive stress on components during assembly and implantation, minimizing the risk of damage and wear, while maintaining a secure connection between apposition plates and joint components, ensuring biocompatibility and stability.
Implementation Method 1
the intermediate means can be disposed at least between the first apposition plate and the first joint component in such manner that the first joint component is not freely moveable transversely to the central axis with respect to the first apposition plate under load-free conditions, but a limited movement of the first joint component relative to the first apposition plate transversal to the central axis is allowed under load
Implementation Method 2
the invention is provided with a stress shielding capacity in order to reduce the compression stress in the concerned interface
Data Source
AI summary
The total disc replacement device (1) comprising a central axis (2), a first and a second apposition plate (3; 5), a first and a second joint component (4; 6) being mutually arranged in a ball joint like manner and being located between said first and second apposition plates (3; 5) and intermediate means (7) being disposed at least between the first apposition plate (3) and the first joint component (4) in such manner that, the first joint component (4) is not freely moveable transversely to the central axis (2) with respect to the first apposition plate (3) under load-free conditions, but a limited movement of the first joint component (4) relative to the first apposition plate (3) transversal to the central axis (2) is allowed under load.