Conductive Set Screw With Insulating Body For Implantable Leads
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Solution Overview
Problem
Existing lead retention assemblies for implantable medical devices face issues with electrical isolation and secure retention, as nonconductive plastic set screws can strip easily, compromising the electrical insulation and lead retention, and grommets are prone to tearing.
Innovation Solution
A lead retention assembly using a conductive set screw that is electrically isolated from the device's electronics, combined with a nonconductive member and a lead engagement feature, which moves to secure the lead without direct contact, reducing the risk of stripping and eliminating the need for grommets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nonconductive plastic set screw is used to prevent pocket stimulation, then electrical isolation is improved, but the set screw may strip more easily
Solution Approach 1:
The set screw is constructed as a composite structure with a nonconductive plastic body for electrical isolation and a conductive metal insert (such as a stainless steel or titanium rod) embedded within it. This metal insert provides the necessary mechanical strength and stripping resistance while the plastic exterior maintains electrical isolation from tissue, effectively combining the benefits of both materials.
Solution Approach 2:
The set screw has different material properties at different locations: the exterior surface is made of nonconductive plastic for electrical isolation, while the interior core contains a conductive metal element for mechanical strength. This local differentiation of material properties allows each region of the set screw to perform its specific function optimally.
2Reliability
If a grommet is used to electrically isolate the set screw from tissue, then pocket stimulation is prevented, but the grommet may tear during screw tightening
Solution Approach 1:
The grommet component is completely removed from the assembly. Instead of using a separate grommet to provide electrical isolation, the set screw itself is designed with an integrated nonconductive plastic body that inherently provides electrical isolation without requiring any additional isolating components.
Solution Approach 2:
The electrical isolation function, previously performed by a separate grommet, is merged into the set screw structure itself. The nonconductive plastic body of the set screw combines the fastening function and the electrical isolation function into a single integrated component, eliminating the need for separate isolation elements.
3Strength
If a metallic set screw is used for secure retention, then stripping resistance is improved, but pocket stimulation occurs due to electrical contact with tissue
Solution Approach 1:
The set screw combines nonconductive plastic material for electrical isolation with a conductive metal insert for mechanical strength. This composite construction allows the metallic core to provide stripping resistance while the plastic exterior prevents electrical contact between the metal and tissue, thereby preventing pocket stimulation.
Solution Approach 2:
The nonconductive plastic body acts as an intermediary layer between the conductive metal insert and the surrounding tissue. This intermediate plastic layer electrically isolates the metallic core from tissue contact, preventing harmful electrical stimulation while allowing the metal to provide structural integrity.
Data Source
Figure 1
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AI summary
A lead retention assembly for an implantable medical device includes (i) a conductive set screw and (ii) a housing defining an opening for receiving at least a portion of the set screw. The assembly further includes a block disposed within the housing. The block defines a lead receiving bore and a second bore extending generally perpendicular to and intersecting with the lead receiving bore. The assembly further includes a conductive lead engagement member having a lead engagement feature. The lead engagement feature is disposed within and movable within the second bore such that advancement of the set screw causes the lead engagement feature to move within the second bore towards the lead receiving bore. The set screw is electrically isolated from the conductive lead engagement member.