Spinal Screw Anchor With Overlapping Divisions
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Solution Overview
Problem
Conventional screw fixation methods often lead to screw loosening over time, especially in patients with severe osteoporosis, resulting in adjacent segment degeneration and the need for reoperation, which imposes a significant physical and economic burden.
Innovation Solution
A screw anchor assembly with anchor threads and a receiving part that expands to increase contact area and pull-out strength, featuring a plurality of divisions with overlapping parts and a stopper part to enhance fixation, using materials like PMMA, calcium phosphate, or PEEK for secure integration with the vertebra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional screw fixation is used, then the procedure is simple and quick, but screw loosening occurs over time leading to reoperation
Solution Approach 1:
The screw anchor is divided into multiple divisions (first division, second division, third division) along its length, with each division having overlapping parts that create expansion zones. This segmentation allows the anchor to expand progressively within the bone cavity, increasing contact area and fixation stability without requiring a completely different device design.
Solution Approach 2:
The screw is inserted into the screw anchor, creating a nested structure where the screw resides within the expanded anchor. This nested configuration allows the screw to benefit from the expanded anchor's increased contact area while maintaining the simplicity of the overall fixation system.
2Strength
If a larger screw is inserted to prevent loosening, then pull-out strength increases, but the risk of bone damage and adjacent segment degeneration increases
Solution Approach 1:
Instead of increasing screw size in one dimension, the invention expands the screw anchor in radial dimensions within the bone cavity. The overlapping parts between divisions create expansion zones that increase contact area with the bone wall, achieving higher pull-out strength through dimensional expansion rather than size increase.
Solution Approach 2:
The screw anchor's physical parameters change during insertion and expansion. The overlapping parts are designed to separate and expand the anchor radially, changing its diameter and contact area parameters. This parameter change allows the same screw size to achieve higher pull-out strength through increased contact area rather than increased size.
3Reliability
If screw fixation is performed in osteoporotic bone, then initial fixation is achieved, but bone resorption around the screw occurs over time causing loosening
Solution Approach 1:
The screw anchor is inserted and expanded into the bone cavity before the screw is fully secured. This preliminary expansion creates a stable, enlarged contact area with the bone that prevents subsequent loosening even as bone resorption occurs. The overlapping parts are designed to expand the anchor in advance, creating a durable fixation foundation.
Solution Approach 2:
The screw anchor acts as an intermediary between the screw and the bone. It transfers and distributes the mechanical loads from the screw across a larger bone contact area, reducing stress concentration that would otherwise lead to bone resorption and loosening in osteoporotic patients.
4Strength
If the screw anchor is made with complex division structure to increase contact area, then fixation strength improves, but manufacturing complexity increases
Solution Approach 1:
The anchor is segmented into divisions with overlapping parts, but these can be manufactured as a single integrated component using modern additive manufacturing or precision forming techniques. The segmentation design allows for modular assembly or monolithic fabrication, balancing structural complexity with manufacturing feasibility.
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 screw anchor assembly provides secure screw fixation, reducing the rate of reoperation and associated burdens by increasing the contact area and pull-out strength, thereby stabilizing the spine effectively.
Implementation Method 1
the receiving part being expanded during screw coupling with the screw
Implementation Method 2
screw having screw threads in a lengthwise direction, and a screw anchor which is inserted into a predefined position of spine, and has anchor threads on an inner surface defining a receiving part into which the screw is inserted
Implementation Method 3
the screw anchor includes a plurality of divisions formed along a lengthwise direction, and has overlapping parts between adjacent divisions in the plurality of divisions
Data Source
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AI summary
A screw anchor assembly is a screw anchor assembly used in spinal screw fixation, and includes a screw having screw threads in a lengthwise direction, and a screw anchor which is inserted into a predefined position of spine, and has anchor threads on an inner surface defining a receiving part into which the screw is inserted, the receiving part being expanded during screw coupling with the screw, wherein the screw anchor includes a plurality of divisions formed along a lengthwise direction, and has overlapping parts between adjacent divisions in the plurality of divisions.