Concave Rod Coupling for PEEK Rod Pressure Distribution
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Solution Overview
Problem
Existing bone screw systems deform non-titanium rods like PEEK due to high pressure points of contact, reducing mechanical strength.
Innovation Solution
Incorporating a saddle insert or concave portion into the screw or locking cap to increase surface area contact with the rod, reducing pressure points and preventing deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a flat surface coupling member and locking cap are used to secure the rod, then the rod is firmly secured, but the contact area is small causing high pressure points that plastically deform non-titanium rods like PEEK
Solution Approach 1:
The locking cap incorporates a concave curved surface that conforms to the cylindrical shape of the rod, replacing the traditional flat contact surface. This curvature increases the contact area from a line or point contact to a surface contact, distributing the clamping force evenly across the rod surface and preventing localized high pressure points that cause plastic deformation in PEEK rods
Solution Approach 2:
The invention changes the geometric parameters of the locking cap by introducing a concave portion with specific radius of curvature that matches the rod diameter. This parameter modification transforms the contact geometry from flat to curved, enabling increased contact area and reduced pressure density while maintaining the same clamping force
2Ease of manufacture
If existing screw systems with flat contact surfaces are used, then assembly is simple, but non-titanium rods experience plastic deformation reducing their mechanical strength
Solution Approach 1:
The locking cap is designed with a concave curved surface that matches the rod's cylindrical geometry, transforming point or line contact into surface contact. This increases the contact area to distribute clamping forces evenly, preventing plastic deformation in PEEK rods while maintaining assembly simplicity through the single-piece cap design
3Force
If high clamping force is applied to secure the rod, then the rod is firmly held in place, but the pressure deforms notched-sensitive materials like PEEK
Solution Approach 1:
The concave curved surface of the locking cap distributes the clamping force over a larger contact area on the rod surface. This geometric modification reduces the pressure concentration (force per unit area) while maintaining the same total clamping force, preventing plastic deformation in pressure-sensitive PEEK materials
Solution Approach 2:
By changing the contact surface geometry from flat to curved with a specific radius of curvature, the invention modifies the pressure distribution parameters. The curved surface increases the contact area, thereby reducing the pressure concentration for a given clamping force and preventing material deformation
Data Source
AI summary
Provided are rod coupler devices, systems, kits and methods, which include at least one saddle having a concave configuration that either abuts a bone fastener and/or a locking cap and is shaped so as to contact the rod in two or more lines of contact, which reduces pressure on the rod, and therefore permits use of a rod having various materials, such as PEEK, without significant deformation of the rod. Also provided is the saddle itself and integrated locking caps that include a saddle, the locking cap and a set screw. Also provided are elongate rods having advantageous shapes, configurations, and/or compositions for rod coupler devices, systems and methods. Further provided are screw and cap devices and systems that themselves include a concave configuration so as to contact a rod in two or more lines of contact, which reduces pressure on the rod.