Composite Spinal Fixation Rod for MRI Compatibility and Fragment Containment
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Solution Overview
Problem
Metal fixture rods for spinal fixation are susceptible to magnetization interference in MRI imaging, leading to image disturbance, and lack sufficient rigidity and durability, with exposed fibers posing safety risks during breakage.
Innovation Solution
A fixture rod comprising a core member made of fiber-reinforced resin with a high-elongation metal yarn or fiber member as a reinforcing element, embedded within a coating resin layer, providing enhanced rigidity and durability while minimizing fragment dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal fixture rod is used, then fixing force and strength are improved, but magnetization occurs in MRI magnetic field causing image disturbance
Solution Approach 1:
The harmful magnetic properties are extracted by removing metal from the fixture rod body. The patent uses a non-magnetic polymer core instead of metal, eliminating the magnetization problem while maintaining structural integrity through alternative reinforcement methods.
Solution Approach 2:
The patent employs composite materials consisting of polymer core with embedded high-elongation metal yarn or fiber. This composite structure provides the necessary strength and rigidity while the polymer matrix prevents magnetization interference, as the metal reinforcement is contained and does not exhibit bulk magnetic properties.
2Object-affected harmful factors
If polymer rod without metal reinforcement is used, then MRI compatibility is improved, but rigidity and strength are insufficient
Solution Approach 1:
The patent creates a composite structure where high-elongation metal yarn or fiber is embedded within the polymer core. This combination provides the necessary rigidity and strength through the reinforcement elements while the polymer matrix maintains MRI compatibility by preventing bulk magnetization.
Solution Approach 2:
The patent applies local reinforcement by embedding metal yarn or fiber only in specific regions where strength is needed, rather than using metal throughout the entire rod. This localized approach provides structural support while minimizing magnetic interference.
3Ease of manufacture
If fiber density is lowered in polymer rod, then manufacturing is simplified, but safety is compromised due to exposed spinate fibers at breakage
Solution Approach 1:
The patent embeds high-elongation metal yarn or fiber within the polymer core to prevent fiber exposure during breakage. This reinforcement acts as a safety mechanism that contains the spinate fibers, preventing them from exposing outward even when the rod fails, thereby maintaining safety while allowing manufacturing flexibility.
4Strength
If metal yarn or fiber with low elongation is used, then strength is improved, but damage occurs during fixation and fragment dispersion increases at breakage
Solution Approach 1:
The patent specifically selects metal yarn or fiber with high elongation properties (elongation greater than the reinforcing fiber of the fiber-reinforced resin). This parameter change allows the reinforcement to stretch and absorb energy during fixation and breakage, reducing fragment dispersion while maintaining necessary strength.
Data Source
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AI summary
A rod for intra-spinal fixture that reduces damage at the time of fixing with a screw, has high rigidity and high durability against a deformation load, and significantly reduces a discretization risk of fragments even at the time of breakage, is provided. A fixture rod according to one embodiment of the present invention comprises a core member containing a fiber-reinforced resin, and a coating resin layer that coats the core member. A reinforcing member is provided inside the core member along a longitudinal direction of the core member.