Self-Tapping Bone Screw Shank Design for Reduced Insertion Force
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Solution Overview
Problem
Self-tapping bone screws often require significant screwing-in forces due to the elastic nature of bone material, which can be problematic, especially in small areas like the face or skull, where the force required increases with screwing depth.
Innovation Solution
A self-tapping bone screw design featuring a screw shank with a cutting portion, intermediate portion, and head portion, where the core diameter transitions from larger in the cutting area to smaller in the intermediate area, with a constant outer diameter and a thread that extends continuously or in separate sections, reducing the bearing surface and penetration depth of thread teeth, thereby reducing screwing forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a self-tapping bone screw is used to cut through bone material, then the screw can be inserted without pre-tapping, but the screwing-in forces become considerable and increase with screwing depth
Solution Approach 1:
The patent applies local quality by varying the core diameter along the length of the screw shank. The cutting portion has a larger core diameter to reduce cutting resistance and screwing-in forces, while the intermediate portion has a smaller core diameter to maintain secure fit and stability. This spatial variation in geometric properties allows the screw to optimize performance at different locations along its length.
Solution Approach 2:
The screw shank is segmented into distinct portions (cutting portion and intermediate portion) with different geometric characteristics. This segmentation allows each portion to perform its specific function optimally - the cutting portion reduces insertion forces while the intermediate portion ensures secure anchoring.
2Manufacturing precision
If the core diameter is reduced in the intermediate area to increase fit security, then the screw fits more precisely in the bone, but the screwing-in forces increase due to greater bone material resistance
Solution Approach 1:
The patent resolves this contradiction by applying local quality - different sections of the screw shank have different core diameters optimized for their specific functions. The cutting portion has larger core diameter to minimize cutting resistance, while the intermediate portion has smaller core diameter for precise fit, with a transition area connecting them.
3Strength
If the screwing depth is increased in small areas like face or skull, then the anchoring strength improves, but the screwing-in forces increase considerably
Solution Approach 1:
The patent addresses this contradiction by varying the core diameter along the screw shank length. The cutting portion with larger core diameter reduces cutting resistance during insertion, enabling deeper screwing in small bone areas without excessive forces. The intermediate portion maintains secure anchoring with its smaller core diameter that fits precisely into the created thread.
Data Source
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AI summary
The screw has a screw shank with a front tip (104) e.g. centring tip, a cutting region (106), an intermediate region (108) and a rear head region. A trapezoidal thread (322) extends in a threaded region of the screw shank over a transition region and includes mutually adjoining parts of the cutting region and the intermediate region. An outside diameter and a root diameter of the screw shank defined by the thread. The root diameter in the cutting region is greater than the root diameter in the intermediate region and the outside diameter is constant in the transition region. An independent claim is also included for a method for manufacturing a self-tapping bone screw.