Polyaxial Screw Locking Insert Axial Load Distribution
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Solution Overview
Problem
Current polyaxial screws for surgical implantation face challenges in easy implantation, high component complexity, uneven force distribution, and increased manufacturing and assembly costs due to eccentric positioning of springs and multiple elements, leading to potential malfunctions and safety concerns.
Innovation Solution
A polyaxial screw design featuring a central body with U-shaped notches and a locking insert that applies direct axial load to the spherical portion, reducing the number of components and eliminating eccentricity, with a simplified structure that allows for easier assembly and alignment using a screwdriver, and a pre-assembly method involving axial preload and deformation to secure the locking insert.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple elements and eccentric springs are used in the polyaxial screw design, then the locking mechanism can be achieved, but the device complexity increases and manufacturing costs increase
Solution Approach 1:
The patent combines multiple functions into a single integrated locking insert that eliminates the need for separate springs and multiple locking components. The locking insert directly engages with the spherical portion through axial loading, merging the locking, springing, and force distribution functions into one element, thereby reducing device complexity while maintaining reliability.
Solution Approach 2:
The patent removes the eccentric springs and multiple intermediate elements from the design, extracting only the essential locking function. The locking insert directly applies axial load to the spherical portion without requiring auxiliary spring mechanisms, simplifying the overall structure while achieving the same locking effect.
2Reliability
If multiple elements and eccentric springs are used in the polyaxial screw design, then the locking mechanism can be achieved, but manufacturing and assembly costs increase
Solution Approach 1:
By merging multiple components into a single locking insert, the patent reduces the number of manufacturing steps, material inventories, and quality control checkpoints. The simplified structure requires fewer machining operations and assembly steps, directly lowering manufacturing and assembly costs while maintaining the locking mechanism's reliability.
Solution Approach 2:
The patent extracts unnecessary intermediate components (eccentric springs, multiple locking elements) that contribute to manufacturing complexity and cost. The direct axial loading mechanism requires fewer precision-machined parts and less complex assembly procedures, reducing both manufacturing and assembly expenses.
3Force
If eccentric springs are used in the polyaxial screw design, then the locking force can be applied, but uneven force distribution occurs leading to potential malfunctions
Solution Approach 1:
The patent eliminates the eccentric (asymmetric) spring positioning that causes uneven force distribution. The locking insert applies axial load symmetrically along the central axis of the spherical portion, ensuring uniform force distribution across the contact surface and preventing malfunctions related to asymmetric loading.
Solution Approach 2:
The patent changes the loading parameter from eccentric spring force to direct axial compression. This parameter change ensures that the locking force is applied uniformly along the central axis, eliminating the uneven force distribution caused by eccentric spring positioning and improving reliability.
4Reliability
If a complex multi-element design is used in the polyaxial screw, then the locking function can be achieved, but the ease of implantation decreases
Solution Approach 1:
The patent removes complex multi-element components and eccentric spring mechanisms that complicate the implantation procedure. The simplified locking insert with direct axial loading can be implanted more quickly and easily, reducing surgical time and technical difficulty while maintaining the locking function's reliability.
Solution Approach 2:
By merging multiple components into a single locking insert, the patent simplifies the implantation procedure. The integrated design requires fewer assembly steps during surgery and reduces the skill level needed for proper implantation, thereby improving ease of operation while preserving the locking function.
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 design enhances ease of implantation, reduces the risk of malfunctions, lowers manufacturing costs, and simplifies assembly, while ensuring reliable locking and alignment of the polyaxial screw components during surgical procedures.
Implementation Method 1
there is a perimetral groove (33) having a helical conformation... which impose to the elastic portion (30.1) of said insert a behaviour of an elastic means, when the insert (30) is subjected to a compressive axial force
Implementation Method 2
an elastic portion (30.1) of said insert, which is in contact with at least an upper part of the spherical head (22)... capable of applying a distributed compression load axially onto said spherical head (22)
Data Source
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AI summary
A polyaxial screw for surgical implant comprising an axially hollow central body; an anchoring element having an anchoring portion and a coupling portion, said anchoring portion projecting from said central body and said coupling portion being received inside the axial cavity of said central body; an insert axially received inside said axial cavity of the central body and an attachment element suitable to couple internally to said central body, characterised in that said insert has an elastic portion able to apply to at least a portion of the anchoring element a distributed compression load the resultant force of which being directed along the central axis X.