Multi-thread Bone Screw Segmented Shank Design
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Solution Overview
Problem
Existing bone screws face challenges in effectively engaging both cancellous and cortical bone regions due to a single constant pitch threading, which compromises stability and purchase in each bone type, requiring additional turns for full engagement.
Innovation Solution
A bone screw design featuring multiple threaded sections with a first section for cancellous bone and a second section with a finer thread pattern for cortical bone, allowing for improved anchoring in both bone types without requiring additional turns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single constant pitch threading is used in bone screws, then the threading can engage cancellous bone effectively, but the purchase and stability in cortical bone are compromised
Solution Approach 1:
The threaded shank is divided into multiple threaded sections, each with different thread patterns optimized for specific bone types. The first threaded section has a first thread pattern for cancellous bone, while the second threaded section has a second thread pattern for cortical bone, allowing each section to independently optimize engagement with its target bone type.
Solution Approach 2:
Different portions of the threaded shank are given different thread characteristics tailored to local bone type requirements. The distal portion features a thread pattern with larger pitch and deeper thread depth for cancellous bone, while the proximal portion features a thread pattern with smaller pitch and shallower thread depth for cortical bone.
2Strength
If finer pitched threads are used to increase stability in cortical bone, then cortical engagement is improved, but purchase in cancellous bone decreases and additional turns are required
Solution Approach 1:
The threaded shank is segmented into distinct threaded sections with different pitch characteristics. The first threaded section uses a coarser pitch for efficient cancellous bone engagement, while the second threaded section uses a finer pitch for strong cortical bone fixation, eliminating the need to compromise either function.
Solution Approach 2:
Each threaded section is designed with sufficient length to achieve its specific function independently. The first threaded section provides adequate cancellous bone purchase with its coarser pitch, while the second threaded section provides adequate cortical bone fixation with its finer pitch, ensuring both functions are fully achieved without requiring excessive turns.
3Ease of manufacture
If a single thread pattern is used for all bone regions, then the screw design is simple, but it cannot optimize engagement in both cancellous and cortical bone simultaneously
Solution Approach 1:
The threaded shank is divided into multiple threaded sections, each with thread patterns optimized for specific bone types. This segmentation allows each section to independently optimize engagement with its target bone type, significantly improving overall bone engagement reliability despite increased manufacturing complexity.
Solution Approach 2:
Different portions of the threaded shank are given different thread characteristics tailored to local bone type requirements. The distal portion features a thread pattern optimized for cancellous bone, while the proximal portion features a thread pattern optimized for cortical bone, ensuring reliable engagement in both bone types.
Data Source
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AI summary
A bone screw (10) comprising a threaded shank (52) including a distal end portion (50a) and a proximal end portion (50b), and defining a first threaded section (60) extending from the distal end portion (50a) toward the proximal end portion (50b) and adapted for anchoring in cancellous bone, and a second threaded section (62) extending contiguously from the first threaded section (60) toward the proximal end portion (50b) and adapted for engagement in cortical bone, with the second threaded section (62) having a finer thread pattern relative to the first threaded section (60). In one embodiment, the first threaded section (60) includes a first helical threading (64) defining a single lead thread pattern for anchoring in cancellous bone, and the second threaded section (62) includes a second helical threading (66) interleaved with the first threading (64) to define a duel lead thread pattern for engagement in cortical bone. In a further embodiment, the bone screw (10) includes a head portion (54) extending from the threaded shank (52) and configured for coupling to a spinal implant.