Double-threaded bone screw with varying thread profiles
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Solution Overview
Problem
Existing bone screws face challenges in securely attaching prostheses or implants due to the varying strengths between cortical and spongy bone tissues, as they do not effectively engage and stabilize across the different bone components.
Innovation Solution
A discontinuously double-threaded bone screw design featuring a cylindro-conical core with varying anchoring portions, including conical and cylindrical threads of different pitches and lengths, to accommodate the different hardnesses and strengths of bone tissue, ensuring engagement and stability in both cortical and spongy bone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single-threaded or uniformly double-threaded bone screw is used, then the screw structure is simple, but the mechanical hold in bone tissue is insufficient due to varying bone density
Solution Approach 1:
The patent applies local quality by varying the thread profile along the length of the anchoring body. The first anchoring portion (proximal) has a first thread profile optimized for cortical bone engagement, while the second anchoring portion (distal) has a second thread profile optimized for spongy bone engagement. This local differentiation allows each portion to optimally engage the specific bone type it encounters, thereby improving overall mechanical hold without requiring a completely complex redesign of the entire screw.
Solution Approach 2:
The anchoring body is segmented into at least two distinct anchoring portions with different thread profiles. The first anchoring portion includes threads with a first profile (e.g., deeper, more aggressive threads) for cortical bone, while the second anchoring portion includes threads with a second profile (e.g., shallower, more distributed threads) for spongy bone. This segmentation allows each portion to be optimized for its specific function, improving mechanical hold while maintaining manageable complexity through modular design.
2Adaptability or versatility
If the thread profile is uniform throughout the anchoring body, then the manufacturing process is simple, but the engagement with different bone components (cortical and spongy) is not optimized
Solution Approach 1:
The patent implements local quality by providing different thread profiles at different locations along the anchoring body. The first anchoring portion has threads with a first profile characterized by specific pitch, depth, and shape optimized for cortical bone engagement, while the second anchoring portion has threads with a second profile optimized for spongy bone engagement. This local differentiation enhances adaptability to different bone components while the profiles remain regular enough to be manufactured using standard threading processes.
Solution Approach 2:
The patent applies parameter changes by varying key thread parameters (pitch, depth, shape, orientation) between the first and second anchoring portions. For example, the first threads may have a larger pitch and deeper profile for cortical bone, while the second threads have a smaller pitch and shallower profile for spongy bone. These parameter variations improve engagement with different bone components while still allowing manufacture through conventional machining or forming processes.
3Strength
If the screw engages deeply in cortical bone, then the initial fixation is strong, but the penetration into spongy bone is insufficient for long-term stability
Solution Approach 1:
The anchoring body is segmented into a first anchoring portion for cortical bone engagement and a second anchoring portion for spongy bone engagement. The first portion, located proximally, has thread profiles optimized for strong initial fixation in cortical bone. The second portion, located distally, extends deeper into the spongy bone with profiles optimized for long-term stability. This segmentation allows the screw to achieve both strong initial fixation and deep penetration for long-term stability.
Solution Approach 2:
The patent addresses the depth issue by adding a longitudinal dimension to the thread profile variation. Instead of uniform threads throughout, the thread profiles change along the length of the anchoring body. The first anchoring portion engages cortical bone at a shallower depth with aggressive threads, while the second anchoring portion extends deeper into spongy bone with modified thread profiles, thereby achieving both initial fixation strength and long-term stability through extended effective anchoring length.
Data Source
AI summary
A discontinuously double-threaded bone screw includes a drive head and anchoring body consisting of a cylindro-conical core over which extend at least two cylindro-conical threads, the anchoring body including anchoring portions of different profiles, ensuring an anchoring corresponding to different bone hardnesses and strengths, the anchoring body including, below the drive head, a first anchoring portion with a conical core and two threads with cylindrical profile and identical pitch, a second anchoring portion with a cylindrical core and a single cylindrical thread over ¼ turn, a third anchoring portion with a cylindrical core and two threads with cylindrical profile over ½ turn, a fourth anchoring portion including a cylindrical core and a single thread with cylindrical profile n turn based on total length of the bone screw, and a fifth anchoring portion including a conical core and two threads with conical profile forming the tip of the bone screw.