Dynamic Disc Assembly With Fresnel Surfaces
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Solution Overview
Problem
Existing artificial disc designs suffer from limited range of motion, high wear rates, and excessive stress on facet joints due to non-anatomical movement, leading to audible clunking sounds and reduced implant longevity.
Innovation Solution
A dynamic disc assembly featuring annular and linear Fresnel-shaped surfaces with coupling cords and elastomeric ROM control dampers, designed to match anatomical motion, providing controlled range of motion and reducing wear through bone growth promoting textures and low profile height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If prior art artificial disc designs use elastomers and mechanical springs to provide motion, then motion preservation is achieved, but the range of motion is limited and non-anatomical, causing excessive stress on facet joints
Solution Approach 1:
The core incorporates Fresnel-shaped surfaces with specific curvatures that guide anatomical motion patterns. The superior surface has a first curvature radius in the anterior-posterior direction and a second curvature radius in the lateral direction, while the inferior surface has corresponding curvature radii, creating a spherical-like articulation that matches natural disc kinematics and prevents non-anatomical movement
Solution Approach 2:
The patent specifies precise parameter ranges for the core surfaces including curvature radii (first curvature radius: 15-30mm, second curvature radius: 8-15mm), surface area (100-200mm²), and height (5-15mm). These controlled parameters ensure anatomical range of motion while limiting excessive movement that would stress facet joints
2Shape
If prior art artificial discs have a larger height to contour the lens shaped disc, then anatomical alignment is improved, but the implant profile is bulky and the range of motion is limited
Solution Approach 1:
The core uses different curvature radii for different regions and directions: the superior surface has a first curvature radius (15-30mm) in the anterior-posterior direction and a second curvature radius (8-15mm) in the lateral direction, while the inferior surface has corresponding curvature radii. This localized variation in geometric properties achieves anatomical alignment without requiring uniform increases in overall disc height
3Device complexity
If prior art artificial discs use small articulating surfaces, then device complexity is reduced, but wear rates increase due to high contact stress
Solution Approach 1:
The Fresnel-shaped surfaces with specific curvature radii create a spherical-like articulation that distributes contact stress across a larger effective area (100-200mm²). This curved surface geometry reduces point contact stress and prevents high wear rates while maintaining a relatively simple overall device structure
4Adaptability or versatility
If prior art artificial discs use elastomeric nuclei to provide motion, then motion preservation is achieved, but elastomer degradation occurs under high sustained loads, reducing implant longevity
Solution Approach 1:
The core is made of a polymeric material with specific mechanical properties (compressive modulus: 10-50MPa, tensile strength: 5-20MPa, elongation at break: 100-300%). This composite polymeric structure provides the necessary motion preservation while resisting degradation under sustained loads, combining the benefits of elastomeric motion with improved durability
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 dynamic disc assembly achieves anatomically correct range of motion, reduces wear, and prevents excessive stress on facet joints, enhancing implant longevity and compatibility with vertebral bodies.
Implementation Method 1
The core has a first inferior surface being an annular Fresnel lens shaped surface configured to articulate about a complimentary Fresnel lens shaped surface of the interior surface of the inferior end plate
Implementation Method 2
The core has a second superior surface having a linear Fresnel like shape configured to articulate in an anterior and posterior position, but not a lateral position (flexion and distraction)
Implementation Method 3
Each of the coupling cords includes a plurality of elastomeric ROM control dampers
Implementation Method 4
providing controlled range of motion and reducing wear through bone growth promoting textures
Data Source
AI summary
A dynamic disc assembly has a superior end plate, an inferior end plate, and a core. The core has surfaces of an annular Fresnel shape and a linear Fresnel-like shape combined to control the dynamic range of motion (ROM) movement arranged to match anatomical ROM. The core is interposed between and held against interior surfaces of the superior end plate and the inferior end plate. The assembly further has a pair of coupling cords, one coupling cord at each lateral end of the superior and inferior end plates wherein each lateral end of each end plate has one or more cord connections attached and affixed to the coupling cord to form and retain the dynamic disc assembly.