Prosthetic Disc Compressible Core Torque Transmission
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Solution Overview
Problem
Current prosthetic intervertebral discs, such as ball-and-socket and elastic rubber types, either fail to mimic the natural disc's torque transmission or suffer from high stiffness and interface issues leading to adjacent disc degeneration and mechanical failure.
Innovation Solution
A prosthetic intervertebral disc assembly featuring a compressible core that interlocks with end plates via protrusions, providing torque transmission and incorporating stress members for affixation to vertebral bone, designed to mimic the biomechanical properties of natural discs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If ball-and-socket type artificial discs are used to allow free rotation between adjacent vertebrae, then spinal flexion is enabled, but the disc structure causes high vertical stiffness leading to adjacent disc degeneration
Solution Approach 1:
The patent changes the physical parameters of the disc core from a rigid spherical ball to a compressible elastomeric material with viscoelastic properties. This allows the disc to exhibit low vertical stiffness for shock absorption while maintaining rotational capability, directly resolving the contradiction between enabling spinal flexion and reducing vertical stiffness that causes adjacent disc degeneration
Solution Approach 2:
The patent employs composite construction with an elastomeric polymer core embedded between metal end plates. The elastomeric material provides compressibility and torque transmission, while the metal plates provide structural support and attachment points. This composite approach enables the disc to simultaneously achieve low vertical stiffness and adequate mechanical strength, resolving the contradiction between flexibility and structural integrity
2Strength
If elastomeric polymer body is bonded to metal plates through rough porous interface to absorb compressive shocks, then vertical load bearing is improved, but the interface is subject to peeling or severance
Solution Approach 1:
The patent replaces the mechanical bonding interface (rough porous surface bonding) with a mechanical interlocking system featuring protrusions from the elastomeric core that extend into openings in the end plates. This substitution eliminates the peeling and severance issues of bonded interfaces while maintaining strong load transfer, resolving the contradiction between compressive strength and interface reliability
Solution Approach 2:
The patent divides the interface connection into discrete mechanical elements (protrusions and openings) rather than relying on a continuous bonded interface. This segmentation allows for controlled stress distribution and prevents the propagation of interface failures, thereby improving both load bearing capacity and interface durability
3Reliability
If spinal fusion is performed to remove the damaged disc and secure vertebrae, then short-term results are excellent, but long-term studies show degenerative changes in adjacent mobile segments
Solution Approach 1:
The patent creates a dynamic prosthetic disc that can compress, extend, and rotate, mimicking the natural disc's motion capabilities. This dynamic behavior allows the prosthesis to absorb loads and transmit torques in a physiologically appropriate manner, preventing the excessive motion and stress that cause adjacent disc degeneration after fusion, thereby improving long-term adjacent disc health while maintaining short-term stability
4Ease of operation
If ball-and-socket disc allows free rotation between adjacent vertebrae, then spinal mobility is maintained, but the disc does not share any of the load placed on the spine
Solution Approach 1:
The patent changes the mechanical parameters of the disc core to exhibit viscoelastic properties with shear modulus and bulk modulus characteristics that enable both rotational motion and load sharing. The elastomeric material's ability to undergo shear deformation allows torque transmission, while its compressibility enables vertical load bearing, resolving the contradiction between maintaining mobility and achieving load sharing
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 transmits torque and absorbs compressive loads, reducing the risk of adjacent disc degeneration and mechanical failure, while providing a biologically similar range of motion and shock absorption.
Implementation Method 1
a compressible core member situated between the two end plates. The compressible core member interacts, directly or indirectly, with the end plates
Implementation Method 2
The protrusions extend into openings in the end plates or in intermediate members, such as springs, forming part of the endplates
Data Source
AI summary
This description deals with a medical device, specifically a prosthetic intervertebral disc having a compressible core that is mechanically interactive with the prosthetic disc's end plates thereby providing excellent torque or twisting transmission between the end plates.