External Fixator Strut Quick-Release Locking Against Mode Slips
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Solution Overview
Problem
Existing telescopic struts for external fixators face challenges in reliably switching between rapid and gradual length adjustment modes, with previous solutions being either expensive to manufacture or prone to unintentional mode transitions under load, which can compromise patient safety.
Innovation Solution
A telescopic strut design featuring a hollow outer tube and inner tube with texturized surfaces, a rotatable adjustment knob, and a quick-release mechanism that uses a spring and detents to securely lock or unlock the adjustment mode, preventing unintentional transitions and ensuring stability under load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a quick-release mechanism is used to enable rapid length adjustment during assembly, then the time necessary for strut setup is reduced, but the mechanism becomes prone to unintentional mode transitions during the correction phase
Solution Approach 1:
A compression member acts as an intermediary element that mediates between the first and second adjustment knobs. This compression member provides a mechanical link that ensures reliable engagement and disengagement between the texturized surfaces, preventing unintentional mode transitions while maintaining quick-release functionality. The compression member translates rotational motion into linear compression, providing a controlled mechanism for mode switching.
Solution Approach 2:
The texturized surfaces on the adjustment knobs and compression member are designed to self-eng age and self-disengage based on rotational position. The interlocking texturized profiles automatically lock into engagement when properly aligned, providing passive reliability without requiring additional active components or complex control systems. The mechanism serves itself through geometric constraints.
2Device complexity
If compression is used to maintain engagement between adjustment components, then the mechanism remains simple in structure, but the engagement becomes unreliable under load
Solution Approach 1:
The adjustment mechanism is segmented into distinct functional zones: texturized engagement surfaces for mode locking, a compression member for force transmission, and detent features for positional stability. This segmentation allows each component to perform its specific function reliably, with the texturized surfaces handling engagement and the detent handling positional retention, preventing unintentional transitions.
Solution Approach 2:
The texturized surfaces utilize curved or rounded profiles rather than sharp edges, allowing for smoother engagement and disengagement. The curved surfaces of the compression member and adjustment knobs provide gradual load transfer and reduce stress concentration, improving reliability under cyclic loading while maintaining a simple overall structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a robust, cost-effective mechanism that reliably switches between rapid and gradual length adjustment modes, reducing the risk of unintentional transitions and enhancing patient safety by maintaining strut stability during bone deformity correction.
Implementation Method 1
a spring configured to bias the quick-release pin into the detents
Implementation Method 2
The inner tube has a plurality of texturized surfaces... the texturized surfaces of the inner tube engages the texturized surfaces of the interior surface of the adjustment knob
Data Source
AI summary
An adjustable length strut for use in an external fixation system may include an outer tube, an inner tube within the outer tube, and a first adjustment knob. A plurality of texturized surfaces may extend in the length direction of the inner tube, each of the plurality of texturized surfaces of the inner tube being spaced apart from each other in the circumferential direction of the inner tube. Each circumferentially adjacent pair of texturized surfaces of the inner tube is separated by a non-texturized surface. The first adjustment knob may also include texturized surfaces separated by non-texturized surfaces, and may be rotatable relative to the outer tube and the inner tube between a locked condition and an unlocked condition. In the locked condition, the texturized surfaces engage each other, to prevent translation of the inner tube relative to the outer tube.