Intervertebral Disc Replacement With Variable Spring Constant Columns
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Solution Overview
Problem
Current intervertebral disc replacements often reduce compressive support, overload adjacent facet joints, and generate excessive wear particles, leading to premature arthritic changes and surgical complications.
Innovation Solution
A three-layer intervertebral disc replacement with compressible column springs having varying spring constants, arranged in concentric rings and designed to mimic the biomechanical properties of a natural disc, including compressive, extension, and rotational behavior, using materials like titanium and nitinol, and manufactured using 3D printing for patient-specific customization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If existing intervertebral disc replacements are used, then spinal motion is maintained, but compressive support is reduced and facet joints are overloaded
Solution Approach 1:
The patent applies local quality by varying the spring constant of different column springs based on their position within the disc replacement. Outer column springs have different spring constants than inner column springs, allowing each region to provide appropriate local support characteristics. This ensures proper load distribution to facet joints while maintaining overall compressive support, resolving the contradiction between force support and joint overload prevention.
Solution Approach 2:
The patent implements parameter changes by adjusting the spring constant parameter of individual column springs based on their spatial location. The spring constant varies as a function of radial position from the center of the disc, with outer springs having different stiffness characteristics than inner springs. This parameter variation optimizes both compressive support and facet joint load distribution simultaneously.
2Ease of operation
If existing intervertebral disc replacements are used, then spinal motion is maintained, but excessive wear particles are generated
Solution Approach 1:
The patent replaces traditional mechanical bearing surfaces that generate wear particles with a spring-based mechanical system. The column springs absorb and dissipate loads through elastic deformation rather than through sliding or rolling contact between hard surfaces. This substitution eliminates the wear particle generation mechanism while preserving spinal motion capabilities.
Solution Approach 2:
The patent changes the mechanical parameters of the disc replacement by using compliant spring elements instead of rigid bearing surfaces. The spring constant and material properties are selected to provide appropriate compliance that reduces stress concentrations and minimizes wear, while still allowing necessary spinal motion in compression, extension, flexion, and rotation.
3Force
If column springs with varying spring constants are used, then compressive support and load distribution are improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by assigning different spring constants to column springs based on their radial position. This creates a graduated structure where outer springs differ from inner springs, optimizing load distribution without requiring complete customization of each individual spring. The pattern-based approach reduces complexity compared to fully customized designs.
Solution Approach 2:
The patent achieves universality by using a family of column springs that follow a common design pattern with varying spring constants. Rather than designing unique springs for each position, the system uses a standardized approach where springs are differentiated only by their spring constant parameter based on location. This multi-functional design allows the same basic spring structure to serve different roles throughout the disc.
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 enhanced compressive and shear stress dampening, reduces the incidence of facet and adjacent level disc disease, minimizes wear debris, and allows for precise customization to maintain spinal motion and load distribution, thereby reducing surgical complications and improving long-term outcomes.
Implementation Method 1
the second layer comprising a plurality of compressible column springs... Each of the plurality of compressible column springs includes a plurality of stacked coils
Implementation Method 2
Each of the plurality of compressible column springs includes a plurality of stacked coils, and each of the plurality of stacked coils has a spring constant (K)
Data Source
AI summary
According to some embodiments of the invention, an intervertebral disc replacement includes a first layer having a lower surface for contacting a first vertebral bone, a second layer coupled to the first layer, the second layer comprising a plurality of compressible column springs, and a third layer coupled to the second layer, the third layer having an upper surface for contacting a second vertebral bone. Each of the plurality of compressible column springs comprises a plurality of stacked coils, and each of the plurality of stacked coils has a spring constant (K). At least one of the plurality of compressible column springs includes a first coil having a first spring constant and a second coil comprising a second spring constant, wherein the first spring constant is different from the second spring constant.