Variable Flank Bone Screw Segmented Threading Design
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Solution Overview
Problem
Conventional bone screws with constant pitch threading are not suitable for engaging different bone regions, such as cancellous and cortical bone, and lack sufficient support and stability when driven into bone.
Innovation Solution
A bone screw with a threaded shank featuring a first and second helical threading section, where the first section engages cancellous bone with a larger volume and crest width, and the second section engages cortical bone with a smaller volume and crest width, providing secure anchoring through compression of bone material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single constant pitch threading is used in bone screws, then the manufacturing is simple and consistent, but the screw cannot effectively engage different bone regions (cancellous and cortical bone) and lacks sufficient support and stability
Solution Approach 1:
The bone screw threading is divided into multiple distinct sections: a first threading section with a first pitch optimized for cancellous bone engagement, and a second threading section with a second pitch optimized for cortical bone engagement. Each section can be independently designed and manufactured, allowing the screw to adapt to different bone densities along its length while maintaining manufacturing feasibility through modular thread design.
Solution Approach 2:
Different portions of the bone screw threading are given different local characteristics - the first threading section has specific pitch and flank angle properties suited for cancellous bone, while the second threading section has different properties suited for cortical bone. This local differentiation allows each section to optimize its engagement with the specific bone type it encounters, improving overall adaptability without requiring a completely complex redesign of the entire screw.
2Strength
If the thread volume and crest width are increased for better bone purchase, then the anchoring in cancellous bone is improved, but the screw becomes less effective in denser cortical bone regions
Solution Approach 1:
The threading is segmented into sections with different volumes and crest widths. The first threading section has larger volume and crest width characteristics that provide strong anchoring in softer cancellous bone, while the second threading section has reduced volume and crest width that are better suited for denser cortical bone. This segmentation allows the screw to achieve optimal bone purchase in each bone type without compromising performance in either region.
Solution Approach 2:
The patent varies key threading parameters including volume, crest width, and pitch along the length of the screw shaft. By changing these parameters from the first threading section to the second threading section, the screw adapts its mechanical characteristics to match the varying density of bone tissue, achieving effective engagement in both cancellous and cortical bone without the trade-offs of a uniform design.
Data Source
AI summary
A bone screw comprising a threaded shank having a longitudinal axis and including a first helical threading extending along a first length of the threaded shank portion and a second helical threading extending from a location proximately adjacent the first helical threading and along a second length of the threaded shank portion. The first helical threading defines a first volume between adjacent thread turns along the first length, and the second helical threading defines a second volume between adjacent thread turns along the second length, with the first volume being different from the second volume.