Bone Compression Fastener Threads for Multi-Axial Fixation
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Solution Overview
Problem
Traditional fastener thread designs fail to provide sufficient fixation and load sharing in bone-fastener interfaces subjected to multi-axial forces and off-axis loading during the healing process.
Innovation Solution
The development of fastening devices with improved thread designs, featuring a shaft with a proximal and distal shaft portion, and helical threads with varying pitches and undercut surfaces angled towards the ends of the shaft, to enhance bone fixation and load distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional fastener thread designs are used, then the device complexity is low, but the bone fixation strength and load sharing capability are insufficient under multi-axial and off-axis loading conditions
Solution Approach 1:
The patent applies local quality by varying the thread pitch along the length of the fastener shaft. Different sections of the shaft have different pitch values, allowing each local region to be optimized for specific loading conditions. This creates non-uniform stress distribution that enhances overall bone fixation strength while managing the complexity through a systematic variation pattern
Solution Approach 2:
The patent employs asymmetry by introducing undercut surfaces that are angled towards one end of the shaft rather than being symmetrically distributed. This asymmetric feature creates directional load paths that specifically address multi-axial and off-axis loading scenarios, improving fixation strength in critical directions while maintaining manufacturability
2Strength
If traditional uniform pitch threads are used, then the manufacturing process is simple, but the load distribution across the bone-fastener interface is inadequate under multi-axial loading
Solution Approach 1:
The patent implements parameter changes by varying the pitch parameter along the shaft length and changing the geometric parameters of the thread profile through undercut surfaces. These parameter variations optimize load distribution across the bone-fastener interface for multi-axial loading conditions while using standard manufacturing processes to maintain ease of production
3Reliability
If conventional thread designs without undercut surfaces are used, then the device structure is simple, but the fixation stability under off-axis loading conditions deteriorates
Solution Approach 1:
The asymmetric undercut surfaces are strategically positioned and angled to counteract off-axis loading forces. This asymmetric geometry creates mechanical interlocking that resists pull-out and shear forces from multiple directions, significantly improving fixation stability while adding only moderate geometric complexity to the thread design
Data Source
AI summary
A compression fastener may include a shaft and a helical thread disposed about the shaft. The shaft may include a proximal end, a distal end, a proximal shaft portion, and a distal shaft portion. The helical thread may include at least one concave undercut surface and a plurality of pitches that may include at least one first pitch along the proximal shaft portion and at least one second pitch along the distal shaft portion. The at least one concave undercut surface may be angled towards one of the proximal end and the distal end of the shaft, and the at least one first pitch and the at least one second pitch may not be equal to each other.