Bone Fastener Thread Profile for Load Sharing Without Bone Blowout
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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 potential loosening of fasteners implanted in bone and other tissues.
Innovation Solution
The development of fastening devices with improved thread designs, including a shaft with a helical thread featuring angled undercut surfaces and a polyaxial head, which allows for secure attachment and distribution of forces across the bone-fastener interface, enhancing fixation and load sharing.
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 thread design incorporates varying root radii at different locations along the fastener length, with larger root radii at the distal end and smaller root radii at the proximal end. This local variation optimizes stress distribution and load sharing at different positions, enhancing bone fixation strength without requiring complete redesign of the entire thread structure
Solution Approach 2:
The thread profile features asymmetric geometry with different forward and reverse thread angles, as well as non-uniform root radii distribution along the length. This asymmetric design allows the fastener to better handle multi-axial and off-axis loading conditions by distributing forces more effectively across the bone-fastener interface
2Reliability
If traditional thread designs are used, then the manufacturing process is simple, but the fastener loosens over time under multi-axial forces and off-axis loading
Solution Approach 1:
The thread design incorporates specific geometric parameters including thread pitch, root radii variations, and angle specifications that are optimized for long-term fixation reliability. These parameter changes enhance the fastener's ability to resist loosening under multi-axial forces while maintaining manufacturability through precise control of key dimensions
3Strength
If the shaft minor diameter is increased to improve bone fixation, then the load sharing capability improves, but the risk of bone blowout increases
Solution Approach 1:
The shaft features a constant minor diameter in the distal portion that matches the bone hole diameter, preventing blowout at the critical insertion point, while the thread root radii and profile variations in other regions provide enhanced load sharing capability without increasing the problematic shaft diameter
Data Source
AI summary
A method of preventing bone blowout may include forming a hole in a bone, the hole having a bone hole diameter, and inserting a bone fastener into the hole. The bone fastener may include a shaft having a minor diameter and a helical thread. The helical thread may be disposed about the shaft and may include a first undercut surface and a second undercut surface. The first undercut surface may be angled toward one of the proximal end and the distal end of the shaft, and the second undercut surface may be angled toward the other one of the proximal end and the distal end of the shaft. The minor diameter of the shaft may not be greater than 5% larger the bone hole diameter.