Bone Screw with Ceramic Outer Layer for MRI Safety
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Solution Overview
Problem
Magnetic resonance imaging (MRI) scans cause significant heating in metallic implants like bone screws due to radiofrequency-induced heating, which can lead to increased tissue temperature, exacerbated by the properties and dimensions of these implants.
Innovation Solution
A fastener design featuring a metallic shaft with a ceramic or polyether ether ketone (PEEK) outer layer that limits electromagnetic field effects, including a cannulated sleeve to enclose the shaft and prevent radiofrequency exposure, thereby reducing temperature increases during MRI scans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metallic implant is used for bone fixation, then mechanical strength and fixation reliability are improved, but RF-induced heating during MRI scans increases
Solution Approach 1:
The implant combines a metallic core (titanium alloy or stainless steel) with a non-conductive outer layer (PEEK or ceramic coating). This composite structure maintains mechanical strength through the metallic core while the non-conductive outer layer prevents RF-induced heating by blocking electromagnetic field penetration, thus resolving the contradiction between strength and temperature control.
Solution Approach 2:
The non-conductive coating is applied selectively on the outer surface of the metallic implant, creating different functional zones: the metallic core provides structural strength while the coated surface provides RF shielding. This local differentiation allows the implant to simultaneously achieve mechanical integrity and thermal safety during MRI procedures.
2Reliability
If the length of the metallic implant is increased, then fixation stability is improved, but RF-induced heating probability increases
Solution Approach 1:
The full-length non-conductive coating on the extended implant structure prevents RF field interaction along the entire length of the implant. This allows the implant to be longer for improved fixation stability without proportionally increasing heating risk, as the non-conductive material prevents eddy current formation throughout the extended surface area.
3Temperature
If a non-conductive coating is applied on the metallic shaft, then RF-induced heating is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent specifies optimal coating thickness parameters (0.002-0.006 inches) that balance RF shielding effectiveness with manufacturing feasibility. By defining specific thickness ranges, the patent simplifies the manufacturing process while ensuring adequate protection against RF-induced heating, thus resolving the contradiction between temperature control and manufacturing complexity.
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 use of a ceramic or PEEK outer layer significantly attenuates RF-induced heating in metallic implants, minimizing temperature rises in both the implants and surrounding tissue during MRI procedures.
Implementation Method 1
an outer layer disposed on an outer surface of the shaft, the outer layer being configured to limit the effect of an electromagnetic field on the metallic shaft
Implementation Method 2
the outer layer is further configured to prevent radiofrequency exposure to the fastener from heating the metallic shaft
Data Source
AI summary
The present disclosure is directed towards a fastener for implanting into a bone, the fastener comprising a metallic shaft and an outer layer. The outer layer is disposed on an outer surface of the shaft, the outer layer being configured to limit the effect of an electromagnetic field on the metallic shaft, wherein the outer layer includes a threaded portion along its length.