Bone Screw Inserter Locking Mechanism for Stylet Control

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Solution Overview

Problem

Conventional bone screw insertion methods face challenges such as obstruction of the visual field by pre-assembled screw heads, difficulty in maintaining screw connection during insertion, and inaccurate depth control, particularly in minimally invasive procedures like transforaminal lumbar interbody fusion (TLIF).

Innovation Solution

The development of a screw inserter instrument with a driver shaft and a retaining sleeve, featuring a locking mechanism that allows for controlled rotation and detachment of the sleeve from the screw, and a stop sleeve for depth control, ensuring precise insertion and maintaining screw alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a sleeve is threaded into the polyaxial head or collet to retain the screw, then the screw can be held securely, but the sleeve unthreads from the screw during driving, causing delays and requiring reengagement

Engineering Contradiction:

Improvescrew retentionVSAvoidreengagement delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The instrument employs a dynamic locking mechanism that transitions between locked and unlocked states. During stylet advancement, the locking mechanism engages to prevent screw rotation. During screw driving, it unlocks to allow rotation while maintaining screw retention, eliminating the need for reengagement and resolving the time loss issue.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

A locking mechanism acts as an intermediary between the handle and driver shaft. This intermediary component controls the relative rotation between these parts, enabling the handle to remain stationary during stylet advancement while allowing driver shaft rotation during screw insertion, thus maintaining reliable screw retention without time loss.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the user holds the handle stationary to prevent screw rotation during stylet advancement, then the screw remains secured, but this interferes with stylet advancement and retraction

Engineering Contradiction:

Improvescrew securityVSAvoidstylet manipulation

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The locking mechanism dynamically changes state based on operational phase. It is locked during stylet advancement to secure the screw, then unlocks during screw driving to allow rotation. This dynamic behavior resolves the contradiction by providing screw security when needed without interfering with stylet manipulation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The locking mechanism is engaged in advance during stylet advancement to prevent screw rotation. This preliminary locking action ensures screw security is established before the conflicting operations occur, allowing smooth stylet manipulation without compromising screw security.

Inventive Principle:

Principle #10Preliminary action

3Productivity

If the screw is driven into bone without precise depth control, then insertion is simple, but overinsertion or underinsertion occurs, compromising proper attachment

Engineering Contradiction:

Improveinsertion speedVSAvoidinsertion depth accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The instrument incorporates tactile feedback through the handle and driver shaft connection. As the screw approaches the correct insertion depth, the user can feel resistance or engagement cues that indicate proper depth has been reached. This feedback mechanism enables precise depth control while maintaining efficient insertion speed.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces visual depth assessment with a mechanical feedback system. Instead of relying on visual confirmation (which is difficult in minimally invasive procedures), the instrument provides tactile mechanical feedback through the driver shaft and handle connection, enabling precise depth control without compromising insertion speed.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS20250302517A1Screw inserter instruments and methods

Publication Date: 2025.10.02 MEDOS INT SARL

AI summary

Screw inserter instruments and methods for implanting a bone screw are disclosed herein. In one exemplary embodiment, a screw inserter instrument can include a screw drive assembly having a first handle and a driver shaft coupled to the first handle, and a stylet assembly having a second handle and a stylet extending through the driver shaft. The first handle can have a locked configuration, in which the first handle and the driver shaft are coupled such that the first handle can maintain the driver shaft in a fixed position while the second handle is rotated relative to the first handle, and an unlocked configuration, in which the first handle and the driver shaft can rotate simultaneously in a first direction and the first handle can rotate independent of the driver shaft in a second opposite direction.