Intervertebral Endoprosthesis with Segmented Resilient Insert
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Solution Overview
Problem
Existing intervertebral endoprostheses often lack adequate compliance, fail to replicate the non-linear force versus displacement and damping characteristics of a natural disc, and do not allow for the full range-of-motion or sufficient stability, leading to undesirable wear and instability.
Innovation Solution
An intervertebral endoprosthesis with first and second base members and a resilient insert, featuring a core connected to the base members via coupling members that allow independent movement, and a polymer or metal construction to mimic the mechanical properties of a natural disc, including a spherical core and cup-shaped recesses for freedom-of-motion, and a press-fit stem design for stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid metal centerbody is used in the endoprosthesis, then structural strength is improved, but compliance and ability to replicate non-linear force versus displacement characteristics deteriorate
Solution Approach 1:
The centerbody is divided into multiple segments or struts that can independently deform, allowing the structure to exhibit non-linear force versus displacement characteristics while maintaining overall structural strength. This segmentation enables the prosthesis to replicate the compliance behavior of natural discs through controlled deformation of individual elements.
Solution Approach 2:
The material properties or geometric parameters of the centerbody elements are designed to change under different loading conditions, enabling non-linear mechanical response. This may include using materials with non-linear stress-strain characteristics or designing structures where stiffness varies with compression level, thereby achieving both strength and compliance.
2Stability of the object's composition
If the endoprosthesis structure is made more constrained to improve stability, then stability is improved, but range-of-motion available from a natural disc deteriorates
Solution Approach 1:
The endoprosthesis incorporates dynamic elements that allow controlled movement and adaptation to physiological loads. The base members and centerbody are designed to move relative to each other in a controlled manner, providing stability under load while preserving the range of motion necessary for natural disc function. This dynamic design enables the prosthesis to transition between constrained and mobile states as needed.
3Reliability
If sliding surfaces are made more durable to reduce wear, then wear resistance is improved, but compliance and natural movement characteristics deteriorate
Solution Approach 1:
The resilient insert acts as an intermediary element between the base members, providing a compliant interface that reduces direct sliding contact between metal surfaces. This intermediary layer absorbs wear and deformation, protecting the sliding surfaces while maintaining the compliance and natural movement characteristics of the disc space.
4Adaptability or versatility
If the endoprosthesis is designed to replicate natural disc characteristics, then compliance is improved, but stability and constraint deteriorate
Solution Approach 1:
The division of the centerbody into multiple struts or segments provides both compliance through individual element deformation and stability through the collective behavior of all elements. Each segment can deform independently to maintain compliance, while the overall structure remains stable due to the distributed load-bearing capacity of multiple elements working together.
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 provides improved compliance, non-linear force versus deflection characteristics, and stability, allowing for the same range-of-motion as a natural disc, reducing wear and enhancing the durability of the prosthesis.
Implementation Method 1
a resilient insert disposed between said base members, said insert comprising an outer shell defining an interior chamber, said outer shell disposed in contacting engagement with said second surface of each of said first and second base members
Implementation Method 2
The core of the resilient insert has an outer surface, that may be spherical, and the head of each coupling member may include a generally cup-shaped recess that cooperates with the outer surface of the core to permit freedom-of-motion of a respective one of the coupling members in all directions
Implementation Method 3
a press-fit stem design for stability
Data Source
Figure 1~2
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Figure 5~6
AI summary
An intervertebral endoprosthesis for insertion into the intervertebral space between two adjacent vertebrae (V1,V2) is provided that includes first (12) and second (14) base members, each having a first surface configured to engage one of the vertebrae and a second opposite surface and a resilient insert (16) disposed between the base members. The insert includes an outer shell (60) defining an interior chamber (62) and is disposed in contacting engagement with the second surface of each of the base members. The resilient insert further includes a core (64) disposed within the chamber and connected to the outer shell. The intervertebral endoprosthesis further includes first (18a) and second (18b) coupling members, each of the coupling members extending between the core of the resilient insert and one of the base members. The first and second coupling members independently couple the first and second base members to the resilient insert, wherein the first and second base members are movable independently of one another and the adjacent vertebrae are movable independently of one another when the intervertebral endoprosthesis is inserted into the disc space.