Decoupled Rod Reducer for Spinal Fusion

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Solution Overview

Problem

Existing rod reducers in spinal fusion surgery often experience set screw binding, cross threading, and unwanted force due to applying reduction load directly to the set screw, leading to inefficiencies and additional steps in aligning male and female threads.

Innovation Solution

A rod reducer design with decoupled shafts, where a ram applies the reduction load to the fixation rod independently of a driver shaft, allowing the set screw to be secured and advanced after the rod is reduced below the start of the female threads, preventing binding and additional steps.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the rod reducer applies reduction load directly to the set screw, then the rod reduction function is achieved, but set screw binding and cross threading occur

Engineering Contradiction:

Improverod reduction reliabilityVSAvoidset screw binding and cross threading

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The device is divided into two independent functional components: a driver shaft that rotates the set screw and a ram that applies reduction load to the rod. This segmentation separates the rotational function from the linear reduction function, preventing the set screw from bearing both torsional and axial loads simultaneously, thereby eliminating binding and cross threading issues

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The ram acts as an intermediary component that applies reduction force directly to the rod through a separate load path. This intermediary mechanism transfers the reduction load away from the set screw, allowing the set screw to rotate freely without binding while the rod undergoes reduction

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If counter clockwise rotation is used to align threads, then thread alignment is achieved, but thread deformation and cross threading occur due to load on female threads

Engineering Contradiction:

Improvethread alignment precisionVSAvoidfemale thread integrity

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The set screw is pre-loaded axially by the driver shaft before rotation begins. This preliminary axial pre-loading ensures proper thread engagement and alignment is maintained throughout the rotation process, preventing thread deformation and cross threading while achieving precise thread alignment

Inventive Principle:

Principle #10Preliminary action

3Productivity

If the set screw is pushed into the rod during reduction, then rod reduction occurs, but additional counter clockwise rotation steps are required

Engineering Contradiction:

Improverod reduction efficiencyVSAvoidadditional rotation steps

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The driver shaft and ram operate in a coordinated continuous sequence: the driver shaft continuously rotates the set screw while the ram continuously applies reduction force. This continuous coordinated action eliminates the need for intermittent stopping and additional rotation steps, maintaining productivity while reducing time loss

Inventive Principle:

Principle #20Continuity of useful action

Data Source

PatentUS20200093521A1Rod reducer

Publication Date: 2020.03.26 ASTURA MEDICAL INC

AI summary

A rod reducer designed to deliver a set screw by way of a decoupled ram and driver shaft. The driver shaft secures and delivers the set screw while the ram applies the load to the rod for reduction. By separating the ram and driver, the rod is reduced down below the start of the female threads, allowing for the set screw to be started by the driver, avoiding binding and additional steps.