Gradient Bone Screw Shaft Elasticity
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Solution Overview
Problem
Existing bone screws with integrally formed metal materials lack relative micro-motion and external buffer force, leading to potential joint dislocation or incomplete bone repositioning after surgery, especially in Asian populations with different body types and trauma causes.
Innovation Solution
A bone screw design where the shaft portion has a smaller Young's modulus than the front and rear portions, allowing for moderate elasticity and integral fixation, with the shaft portion being fixedly joined to both ends, enabling buffering of receiving forces and simplifying surgical procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the bone screw is made with the same metal material throughout (front portion, shaft portion, and rear portion), then the manufacturing process is simple and the structure is strong, but it fails to provide relative micro-motion and external buffer force between the two bones
Solution Approach 1:
The patent applies local quality by making the shaft portion have a different material composition than the front and rear portions. Specifically, the shaft portion contains a lower proportion of alloying elements (such as aluminum, vanadium, and titanium) compared to the front and rear portions, creating a gradient structure. This allows the shaft to have different mechanical properties (lower Young's modulus for elasticity) while the threaded portions maintain high strength for bone fixation.
2Strength
If the shaft portion is made with the same Young's modulus as the front and rear portions, then the bone screw has high structural strength, but it cannot provide moderate elasticity to buffer receiving forces
Solution Approach 1:
The patent changes the material parameters (chemical composition and Young's modulus) along the length of the bone screw. The shaft portion has a lower Young's modulus (30-100 GPa) compared to the front and rear portions (100-120 GPa), creating a gradient structure. This parameter variation allows the shaft to be elastic and absorb forces, while the threaded portions remain strong for secure fixation.
3Adaptability or versatility
If surgical sutures are used to connect the front portion and rear portion (as in U.S. Pat. No. 7,625,395), then some flexibility is provided, but the surgery process becomes complicated and requires a large wound
Solution Approach 1:
The patent merges the shaft portion with the front and rear portions through fixed connection structures (such as interference fits, keyways, or welding) to create a single integral bone screw. This eliminates the need for separate surgical sutures and complex assembly procedures, while the gradient material structure internally provides the necessary flexibility and force buffering capability.
4Strength
If the bone screw uses high-strength metal material throughout, then the fixation strength is high, but it increases the loosening probability when subjected to large receiving forces
Solution Approach 1:
The patent applies local quality by creating a gradient material structure where the shaft portion has different compositional and mechanical properties than the threaded portions. The shaft contains lower proportions of alloying elements, giving it lower strength but higher elasticity. This allows the shaft to absorb and buffer receiving forces through elastic deformation, protecting the threaded portions from excessive loads that would cause loosening.
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 bone screw effectively reduces the force on bones, lowers loosening probability, and facilitates minimally invasive surgery by providing moderate elasticity and integral fixation, thereby improving surgical efficiency and patient recovery.
Implementation Method 1
The Young's modulus of the shaft portion is smaller than that of the front portion and that of the rear portion, thereby providing the bone screw with moderate elasticity
Data Source
AI summary
A bone screw includes a front portion, a rear portion, and a shaft portion. The shaft portion is fixedly joined to the front portion and the rear portion, so as to form an integral bone screw. The Young's modulus of the shaft portion is smaller than that of the front portion and that of the rear portion.