Cannula Stylet Lock Arm for Secure Insertion and Torque Removal
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Solution Overview
Problem
Existing access cannula assemblies face challenges with lock mechanisms that fail to securely hold the stylet during insertion into bone, particularly under uneven axial and rotational forces, leading to unintended disengagement and difficulty in withdrawing the stylet due to interference fits and small handle sizes.
Innovation Solution
A lock assembly with a radially extending arm that flexes to engage with complementary features on the cannula handle, allowing for secure attachment and easy disengagement, featuring angled segments and tabs that prevent unintended rotation and facilitate torque application for stylet removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lock assembly with interference fit is used to hold the stylet to the cannula, then the stylet is securely held during insertion, but the stylet becomes difficult to withdraw due to the tight interference fit
Solution Approach 1:
The lock assembly transitions from a static interference fit to a dynamic system where the arm can flex between engaged and disengaged states. The flexible arm allows the lock to adapt to forces during insertion while enabling easy release when force is applied to the release feature.
Solution Approach 2:
The physical state of the arm changes from rigidly engaged to flexed/disengaged. By changing the position and flexibility parameters of the arm, the system transitions between a tight holding state during insertion and an easy release state for withdrawal.
2Volume of moving object
If the stylet handle is made small to fit within the cannula handle, then the assembly is more compact, but it becomes difficult to apply sufficient torque for stylet removal
Solution Approach 1:
The solution moves from a one-dimensional size constraint to a two-dimensional solution by adding the radially extending arm that projects outward from the stylet handle. This allows the user to apply torque at a greater radial distance while the stylet handle itself remains compact for fitting within the cannula handle.
3Reliability
If the lock assembly uses tabs and slots for engagement, then the stylet is held securely against axial and rotational forces, but unintended disengagement can occur under uneven forces
Solution Approach 1:
The lock assembly combines multiple engagement mechanisms: the flexible arm provides continuous contact pressure, tabs engage with slots for positive mechanical locking, and the overall structure distributes forces across multiple contact points. This composite approach creates a more robust connection that resists unintended disengagement.
4Productivity
If the stylet tip extends distally forward of the cannula end, then the stylet can effectively drill into bone, but the stylet is more susceptible to retracting into the cannula bore under resistive forces
Solution Approach 1:
The lock assembly is engaged before insertion to pre-establish the positional relationship between stylet and cannula. This preliminary locking action prevents the stylet from retracting during the insertion process, maintaining the distal extension configuration needed for effective bone penetration.
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 lock assembly ensures the stylet and cannula remain aligned during insertion, preventing disengagement and allowing for quick and efficient withdrawal of the stylet, even when embedded in bone, by applying sufficient torque without dislodging the cannula.
Implementation Method 1
An arm extends radially outwardly from the stylet handle. The arm is flexibly attached to the stylet handle and can be flexed relative to the rest of the stylet handle.
Data Source
AI summary
A cannula assembly including a cannula and a stylet that is removably fitted in the cannula. A lock selectively holds the stylet to the cannula so the stylet rotates in unison with the cannula. The lock is configured so that the force applied to release the lock results in the subsequent rotation of the stylet relative to the cannula. Methods of disengaging a lock assembly releasably coupling a stylet handle secured to a stylet and a cannula handle secured to a cannula are also provided.