Cannulated Bone Screw Guide Wire Strength Optimization
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Solution Overview
Problem
Small cannulated bone screws face issues with weak guide wires causing inaccuracies in implantation, low bending and torsional strength, and compromised pull-out resistance due to small cannula sizes, leading to screw breakage and difficulties in surgical procedures.
Innovation Solution
The development of small cannulated bone screws with optimized cannula size and thread purchase, allowing the use of larger guide wires while maintaining high strength, and featuring a combination of enhanced bending and torsional strength, and improved pull-out resistance, with a focus on maximizing cannula size without sacrificing strength characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the cannula size is increased to allow larger guide wires, then the bending and torsional strength of the screw decreases
Solution Approach 1:
The screw is made from a high-strength alloy material that combines nickel, titanium, and other elements in specific proportions. This composite alloy provides both the necessary mechanical strength and the ductility required to support larger cannula sizes without compromising overall screw strength
Solution Approach 2:
The patent optimizes the wall thickness parameter of the cannulated screw to achieve the right balance between cannula size and strength. By carefully controlling the wall thickness within specific ranges, the screw can accommodate larger guide wires while maintaining sufficient bending and torsional strength
2Strength
If the thread major diameter is increased to improve pull-out resistance, then the cannula size decreases
Solution Approach 1:
The screw features varied thread characteristics along its length, with different thread depths and pitch patterns in different zones. This allows the threads to maximize pull-out resistance in the bone while maintaining adequate cannula size in the shaft portion, as each region is optimized for its specific function
Solution Approach 2:
The patent addresses the trade-off by moving the optimization focus to the material composition dimension rather than purely geometric dimensions. The high-strength alloy allows the screw to achieve both large cannula size and adequate thread major diameter simultaneously by utilizing the enhanced material properties
3Volume of moving object
If the screw size is reduced for smaller implant sites, then the guide wire becomes too thin and flimsy
Solution Approach 1:
The high-strength alloy material enables the screw to maintain adequate structural integrity even with reduced overall size. This allows the cannula to remain sufficiently large for stable guide wire passage while the screw dimensions are minimized for smaller implant sites
Solution Approach 2:
The patent maintains the cannula-to-major-diameter ratio within optimized ranges even as overall screw size is reduced. This proportional scaling ensures that smaller screws still accommodate guide wires of adequate thickness and stability
Data Source
AI summary
A small cannulated bone screw is provided having an optimized combination of strength, cannula size and thread depth. A set of such strong and small size screws is also provided where the smallest sizes can have one performance ratio emphasized over another, and the larger sizes can have the emphasis reversed. In particular, the smallest screws optimize the combination of their strength and cannula size with the larger screws optimizing the combination of their strength and thread depth. In any event, each of the screws in the set has an optimized combination of strength, cannula size and thread depth throughout the full range of screw sizes in the set, e.g. 3.0 mm to 7.5 mm major diameters.