Intervertebral Disc Prosthesis Spherical Element Shear Stress

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Solution Overview

Problem

Existing intervertebral disc prostheses face issues with resistance over time due to wear and shearing from complex and repeated movements of the vertebrae, which are not accurately replicated by current designs.

Innovation Solution

A lumbar disc prosthesis featuring a spherical flexible element surrounded by a free space, with rounded contact zones and guided movement, allowing only compression without shear stress, thus preventing damage from walls or edges during deformation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a flexible element is used in existing intervertebral disc prostheses to allow complex vertebral movements, then the prosthesis can replicate natural disc movements, but the flexible element suffers from wear and shearing over time due to repeated complex movements

Engineering Contradiction:

Improveability to replicate natural disc movementsVSAvoidresistance over time

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The flexible element is segmented into a spherical ball that can be independently compressed, allowing complex movements to be decomposed into simple compression cycles that the ball can withstand without wear or shearing

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The flexible element is designed as a spherical ball with rounded contact zones, eliminating sharp edges and corners that cause stress concentration and shearing, allowing the element to withstand repeated compressive loads without degradation

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Stability of the object's composition

If the flexible element is constrained by walls or sharp edges during deformation, then the structure provides guidance and stability, but the flexible element is at risk of damage from contact with walls or edges during deformation

Engineering Contradiction:

Improvestructural guidanceVSAvoiddamage from walls or edges

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

All contact surfaces are designed with rounded geometries - the flexible element is a sphere, contact zones are rounded faces, and guide surfaces are curved - eliminating sharp edges and corners that cause stress concentration and potential damage during deformation

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

Rounded contact zones act as intermediaries between the flexible element and the rigid structure, distributing contact stresses and preventing direct contact between the flexible element and potentially damaging sharp edges or walls

Inventive Principle:

Principle #24Intermediary (Mediator)

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 prosthesis maintains long-term resistance to complex vertebral movements while faithfully replicating natural disc movements with a simple design, eliminating shear stress and ensuring durability.

Implementation Method 1

this flexible element comprises, on two opposite sides, two zones of contact with these parts and allows, by its elastic deformation, movements towards/away from said parts

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 2

said rounded faces are intended to come into contact with the corresponding contact zones of the flexible element

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentEP2716262B1Intervertebral disc prosthesis

Publication Date: 2015.05.13 MEDICREA INT SA

Figure 1~2
Figure 3~4
Figure 5

AI summary

The prosthesis i.e. lumbar prosthesis, has two shells (5, 6) extending mainly in a plane, and a flexible element i.e. spherical ball (7), that is interposed between the two shells. The flexible element is arranged with two contact zones on two opposed sides of the shells. Each of the shells is arranged with a face having a round form. The faces are formed by cups arranged as hollow spheres in the center of the shells. The shells form a free space (28) surrounding a periphery unit of the flexible element arranged outside of the contact zones.