Modular Tulip Assembly Locking Mechanism for Bone Screws
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Solution Overview
Problem
Current modular head tulip assemblies for bone anchor screws lack a secure and intuitive method for attaching to pedicle screws already threaded into bone, making it difficult for surgeons to ensure proper and secure connections without clear visibility, which can lead to loosening or weakened screw-bone interfaces.
Innovation Solution
A modular tulip assembly with a saddle and tulip design featuring a locking projection and external locking groove, allowing the saddle to be pre-loaded in an unlocked state and easily moved to a locked position using a tool, ensuring secure attachment to the bone screw head and enabling easy removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the tulip assembly is pushed onto the bone screw head without a clear path of vision, then the assembly can be placed onto the screw, but the surgeon cannot verify if the connection is properly secured
Solution Approach 1:
A tool with a threaded portion is introduced as an intermediary to engage with the threaded bore of the tulip assembly. This tool serves as a mediator between the surgeon and the assembly, allowing the surgeon to rotate the tool to move the saddle to different positions (unlocked, locked, re-locked) while providing tactile feedback about the connection status through resistance changes, thereby compensating for the lack of visual verification during implantation
2Reliability
If the saddle is moved to a locked position to secure the assembly, then the connection is tightened, but the only way to verify security requires an upward pulling test which may loosen or weaken the screw-bone interface
Solution Approach 1:
The system provides tactile feedback through the tool engagement with the threaded bore. When the saddle is moved to the locked position, the tool encounters increased resistance as the locking projection engages with the locking groove. This feedback mechanism allows the surgeon to verify the locked state without needing to perform an upward pulling test, eliminating the risk of loosening the screw-bone interface during verification
Solution Approach 2:
The locking mechanism is designed to be self-verifying through the tool engagement. The threaded interaction between the tool and the tulip's threaded bore automatically provides feedback about the saddle's position and locking status. The system serves itself by using the tool's rotation to both move the saddle and provide verification through tactile resistance, eliminating the need for separate verification tests
3Adaptability or versatility
If the saddle is designed with arcuate fingers to flex over the screw head, then the assembly can accommodate the head geometry, but the complexity of the locking mechanism increases
Solution Approach 1:
The saddle is segmented into multiple arcuate fingers that can independently flex and engage with the screw head. This segmentation allows each finger to adapt to the head geometry while maintaining overall structural integrity. The locking projection is separated from the fingers, allowing independent movement and locking of the saddle body without affecting the fingers' ability to conform to the screw head shape
Solution Approach 2:
The arcuate fingers are designed with dynamic flexibility, allowing them to bend and flex outwardly during assembly to accommodate the screw head geometry, then return to their original position to provide a secure locked state. This dynamic behavior enables the same structure to serve both adaptation and locking functions without requiring separate mechanisms, thereby managing complexity through functional integration
Data Source
AI summary
A modular tulip assembly has a rod receiving tulip and a saddle. The saddle is interlockingly held inside a distal portion of the tulip. The saddle has an external locking groove or recess. The tulip has a locking projection. The locking projection is positioned into the external locking groove or recess and holds the saddle in a pre-loaded unlocked state ready to be pushed onto a head of an implanted bone screw. Upon receiving the head of the bone screw, the saddle can be moved distally relative to the tulip to a locked state by moving the locking groove or recess distally past the locking projection to where the proximal end of the saddle is past abutting the locking projection.