Polyaxial Screw Fixation via Segmented Stem and Head Assembly
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Solution Overview
Problem
Existing surgical implant fixation systems face limitations in minimizing dimensions for minimally invasive surgery, require complex assembly procedures, and suffer from unstable fixation due to imperfect couplings and punctiform contact surfaces, leading to relative movements and wear.
Innovation Solution
A device with a central body featuring a truncated cone shape and lying-down C-shaped slot allows the polyaxial screw head and neck to pass through, using an insert with a retaining area and connection pin for stable locking, enabling reduced dimensions and simplified assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the stem of the polyaxial screw is made to pass through the tulip for assembly, then the device can be assembled, but the minimum inner diameter of the tulip is limited to the outer diameter of the screw stem, increasing the overall size
Solution Approach 1:
The polyaxial screw is divided into two separate components: the screw stem and the screw head. The stem is inserted through the tulip first, then the head is coupled to the stem outside the tulip, eliminating the need for the head to pass through the tulip and reducing the required inner diameter of the tulip.
Solution Approach 2:
The assembly process transitions from a single linear path (head passing through tulip) to a two-stage process involving axial insertion of the stem followed by radial/coupling attachment of the head to the stem, effectively using multiple dimensions for assembly.
2Ease of operation
If the tulip inner diameter is increased to accommodate the screw head, then the screw can be assembled, but the device dimensions increase which is not suitable for minimally invasive surgery
Solution Approach 1:
By segmenting the screw into stem and head components that are assembled in two stages, the tulip only needs to accommodate the stem during insertion, maintaining a small diameter suitable for minimally invasive surgery while still enabling complete screw assembly.
3Reliability
If a blocking element is used to prevent the screw from coming out, then axial movement is prevented, but the assembly procedure becomes more complex
Solution Approach 1:
The retention function is merged with the coupling mechanism between the screw head and stem. The coupling elements serve dual purposes: assembling the screw components and preventing the screw from disassembling or coming out, eliminating the need for separate blocking elements.
4Volume of moving object
If the screw head and stem are coupled outside the tulip, then the tulip dimensions are reduced, but the coupling procedure requires additional steps
Solution Approach 1:
The screw stem is inserted through the tulip and positioned in advance, preparing the assembly path. This preliminary action allows the head to be coupled to the stem in a subsequent step without requiring the tulip to be larger or the assembly to be more complex.
Data Source
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AI summary
A device is for fixing surgical implants in place. The device may include a central body having an axially hollow upper zone, and an axially hollow lower zone. The upper and lower zones may form a single body being open at the bottom and at the top. A central through cavity may extend inside the upper and lower zones. The upper zone may have two portions projecting axially from the upper zone, divided from each other by two through U-shaped slots and forming, in conjunction with part of the central cavity, a channel for housing a connection rod. The lower zone may include a slot for the lateral access to the central cavity of an anchoring device. The slot may be in a conformation such as to permit the lateral insertion of the anchoring device inside the central cavity.