RF Shielded External Fixation Bone Anchors
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Solution Overview
Problem
Conventional external bone fixation systems can induce electrical current and heat in patients when exposed to MRI magnetic fields due to their conductive materials, causing discomfort and tissue damage.
Innovation Solution
The external fixation system incorporates a layer of electrically insulative material, such as polyimide tape, applied to the shafts of Schanz screws to prevent current flow and heat buildup during MRI procedures, while maintaining the same dimensions and structural integrity as existing systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional conductive materials (stainless steel, titanium) are used for external fixation systems, then structural strength and thermal conductivity are improved, but radiofrequency heating and tissue damage occur during MRI procedures
Solution Approach 1:
An electrically insulative material is introduced as an intermediary layer between the conductive Schanz screw and the surrounding environment. This insulative layer blocks the flow of induced electrical currents during MRI procedures while allowing the conductive screw to maintain its structural strength and thermal conductivity properties for normal fixation functions.
Solution Approach 2:
The external fixation system transitions from homogeneous conductive materials to a composite structure combining conductive materials (for strength and thermal management) with electrically insulative materials (for RF shielding). This composite approach allows simultaneous optimization of mechanical properties and electromagnetic compatibility.
2Object-affected harmful factors
If electrically insulative material is added to Schanz screws for MRI safety, then radiofrequency heating is prevented, but device complexity and manufacturing cost increase
Solution Approach 1:
A thin film or coating of electrically insulative material is applied to the surface of the Schanz screw. This thin-layer approach provides effective RF shielding without significantly increasing the overall device complexity, volume, or weight, maintaining the simplicity of the external fixation system while achieving MRI safety.
3Object-affected harmful factors
If the core size is reduced to accommodate insulative sheath, then MRI safety is improved, but manufacturing cost and complexity increase due to higher modulus carbon fiber requirements
Solution Approach 1:
Electrically insulative material is applied locally to specific portions of the Schanz screw where current flow and RF heating are most problematic, rather than requiring complete redesign of the entire screw structure. This localized approach maintains manufacturing simplicity while achieving effective RF shielding at critical interfaces.
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 insulative material effectively shields the bone anchors from radiofrequency heating, preventing significant temperature increases and ensuring patient safety during MRI imaging.
Implementation Method 1
At least the first Schanz screw can include a layer of electrically insulative material that is attached to at least a portion of the first external surface and is not attached to the first threaded region
Implementation Method 2
The insulative material effectively shields the bone anchors from radiofrequency heating, preventing significant temperature increases and ensuring patient safety during MRI imaging
Data Source
AI summary
An electrical insulator is applied to a bone anchor, for instance of a bone implant, such as an external fixation frame, so as to prevent undesirable temperature increases in the bone anchor and surrounding anatomical tissue when subjected magnetic resonance imaging.