Intervertebral Implant Undercut Threads for Multi-Axial Fixation
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Solution Overview
Problem
Traditional bone fixation fasteners fail to provide sufficient fixation under multi-axial forces and off-axis loading scenarios, leading to loosening over time.
Innovation Solution
Bone fixation devices with improved thread and compression designs, featuring helical threads with concave undercut surfaces and varying diameters, are used to stabilize the bone/fastener interface, enhancing fixation and load sharing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional bone fastener thread designs are used, then the device complexity is low, but the fixation strength is insufficient under multi-axial forces and off-axis loading
Solution Approach 1:
The thread design is segmented into multiple functional zones: a first portion with a first pitch for initial engagement and compression, and a second portion with a second pitch for enhanced load distribution. This segmentation allows each zone to perform its specific function optimally, improving overall fixation strength under complex loading conditions while maintaining a relatively simple overall structure.
Solution Approach 2:
Different portions of the thread are given different local qualities through varying pitch values. The first portion has a coarser pitch for aggressive bone engagement and compression, while the second portion has a finer pitch for load distribution and stability. This local differentiation optimizes performance for specific loading scenarios without requiring complete redesign of the entire thread structure.
2Strength
If traditional compression designs are used, then the manufacturing process is simple, but the load sharing capability at the bone/fastener interface is insufficient
Solution Approach 1:
The compression capability is enhanced by changing geometric parameters of the fastener, specifically the pitch values of different thread portions. By optimizing the pitch ratios and thread geometry, the device achieves improved load sharing capability at the bone/fastener interface. These parameter changes can be implemented through standard manufacturing processes without requiring complex tooling or assembly steps.
3Reliability
If uniform thread pitch is used throughout the fastener, then the device complexity is low, but the ability to resist multi-axial forces is insufficient
Solution Approach 1:
The thread is divided into segments with different pitch characteristics. The first portion with its distinct pitch handles axial loading and initial bone engagement, while the second portion with its different pitch addresses multi-axial forces and off-axis loading. This segmentation provides targeted performance for different loading scenarios without requiring overly complex variable pitch patterns throughout the entire thread length.
Data Source
AI summary
An intervertebral implant may include a shaft having a proximal end, a distal end, a longitudinal axis, a minor diameter, and a helical thread disposed about the shaft along the longitudinal axis between the proximal end and the distal end of the shaft. The helical thread may include a major diameter and a concave undercut surface angled towards one of the proximal end and the distal end of the shaft. The intervertebral implant may be implanted within an intervertebral space between a superior vertebral body and an inferior vertebral body. A ratio of the major diameter to the minor diameter may be less than 1.50. The concave undercut surface may engage the superior vertebral body and the inferior vertebral body and may be shaped to resist at least one force transmitted between the superior vertebral body and the inferior vertebral body to stabilize the intervertebral space.