Self-Retaining Screw Inserter with Active Reverse-Collet Retainer
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Solution Overview
Problem
Existing self-retaining screw inserters for spinal fixation devices often fail due to excessive torque, as they rely on springs or morse tapers that can deform or break during the insertion of set screws in orthopedic surgery.
Innovation Solution
A self-retaining screw inserter featuring an active reverse-collet retainer with radially outward-moving fingers, allowing for secure retention and release of set screws, which is designed to withstand excessive torque without failing, utilizing an outer shaft with a distal tip and an inner shaft with a push rod for controlled engagement and disengagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If springs or morse tapers are used to retain the set screw on the inserter, then the set screw can be retained during insertion, but the springs or morse tapers can deform or break when the inserter experiences excessive torque
Solution Approach 1:
The patent inverts the traditional spring-based retention mechanism by using a reverse-collet design where the fingers move radially outward to engage the set screw instead of inward. This inversion allows the structure to withstand excessive torque without deforming or breaking, as the outward-moving fingers create a more robust engagement that resists rotational forces better than conventional spring mechanisms.
Solution Approach 2:
The reverse-collet retainer employs a dynamic mechanism where the fingers can move radially outward during engagement and then lock into position. This dynamic capability allows the retainer to adapt to the insertion process while maintaining strength under torque, as the movable fingers can accommodate slight variations in positioning while providing consistent retention force throughout the procedure.
2Reliability
If the inserter is designed to withstand excessive torque, then reliability is improved, but the complexity of the retention mechanism increases
Solution Approach 1:
The retainer is segmented into multiple fingers that can move independently radially outward. This segmentation allows each finger to engage the set screw at different points, distributing the torque load across multiple contact points rather than a single complex joint. The segmented design achieves high reliability under torque while maintaining relatively simple individual finger structures.
Solution Approach 2:
The reverse-collet retainer features a nested structure where the fingers are contained within the outer shaft and can move within a defined space. The push rod is nested within the outer shaft to actuate the fingers. This nesting approach allows the complex retention mechanism to be compact and integrated within the inserter body, reducing overall device complexity while maintaining the ability to withstand excessive torque.
Data Source
AI summary
A self retaining screw inserter for inserting, positioning and removing a set screw of a spinal fixation system, includes an active reverse-collet retainer. The active reverse-collet retainer has fingers configured to move outward to engage and retain a set screw. When engaged, the fingers flare outward to engage the set screw.