Dual-Helical Bone Fastener Threads for Off-Axis Load Fixation
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Solution Overview
Problem
Traditional fastener thread designs fail to provide sufficient fixation and load sharing under multi-axial and off-axis loading conditions in surgical procedures, leading to loosening of fasteners implanted in bone and other tissues.
Innovation Solution
The development of fastening devices with improved thread designs, including dual helical threads with specific undercut and convex surfaces, chevron, and crescent shapes, which provide enhanced bone fixation and load sharing by creating interlocking spaces with bone tissue, and manufacturing methods that allow for varied thread configurations and orientations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional fastener thread designs are used, then the device complexity is low, but the fixation strength and reliability under multi-axial loading conditions are insufficient
Solution Approach 1:
The thread design is segmented into multiple distinct surfaces (first undercut surface, second undercut surface, third undercut surface, fourth open surface) with different orientations and functions. Each surface is optimized to resist specific loading directions, allowing the fastener to handle multi-axial forces through distributed resistance rather than a single monolithic thread structure.
Solution Approach 2:
The thread geometry employs asymmetric surface orientations where the first and third undercut surfaces are angled toward the distal end while the second and fourth surfaces are angled toward the proximal end. This asymmetric configuration creates directional load resistance that adapts to off-axis loading scenarios, improving fixation strength without requiring symmetric reinforcement in all directions.
2Reliability
If traditional thread designs are used, then the manufacturing process is simple, but the fastener loosens over time under off-axis loading
Solution Approach 1:
Different portions of the thread structure are given specialized local qualities - the undercut surfaces are optimized for load bearing in specific directions, while the open surfaces facilitate bone ingrowth and tissue integration. This localized optimization of functional properties ensures that each part of the thread contributes to preventing loosening under the specific loading conditions it encounters.
Solution Approach 2:
The helical thread geometry introduces curvature and three-dimensional complexity to the otherwise linear fastener shaft. The spiral configuration of multiple undercut surfaces wrapped around the shaft creates a geometry that naturally resists rotational and off-axis forces, improving reliability while the curvature distributes stress more evenly throughout the thread structure.
3Strength
If simple thread designs are used, then the manufacturing precision requirements are low, but the load sharing capability between bone and fastener is insufficient
Solution Approach 1:
The thread design transitions from simple linear threading to a multi-surfaced helical structure that utilizes three-dimensional space more effectively. By wrapping multiple undercut surfaces in a helical pattern around the shaft, the design creates additional load-bearing pathways in multiple dimensions, enhancing load sharing capacity between the fastener and bone tissue.
Solution Approach 2:
The multiple undercut surfaces are nested within the helical thread structure, with each surface positioned at different angular and axial locations. This nested arrangement allows the fastener to engage bone tissue through multiple overlapping contact zones, distributing the load across nested regions rather than relying on a single thread engagement point.
Data Source
AI summary
A fastener with improved threading for resisting multi-axial forces and off-axis loading scenarios is provided. The fastener may include a shaft and a plurality of helical threads disposed about the shaft. The plurality of helical threads may include a first helical thread and a second helical thread adjacent the first helical thread. The first helical thread may include a first concave undercut surface and a first convex undercut surface. The second helical thread may include a second concave undercut surface and a second convex undercut surface. When the fastener is viewed in section along a plane intersecting a longitudinal axis of the shaft, the first concave undercut surface and the second convex undercut surface may be oriented toward the proximal end of the shaft, and the first convex undercut surface and the second concave undercut surface may be oriented toward the distal end of the shaft.