Uniplanar Spinal Screw With Compressive Locking Mechanism
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Solution Overview
Problem
Conventional polyaxial screw systems in spinal stabilization procedures face challenges in accurate placement due to excessive motion, requiring precise positioning and often compromising stability during the connection of a rod to a bone screw, necessitating a system that limits motion and provides superior fixation in bony elements.
Innovation Solution
A uniplanar screw system with a housing, seating element, and cap design that compresses the rod to lock the fastener in place, allowing motion only in one plane until the cap and set screw secure the elongate rod, providing a stable and accurate fixation mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a polyaxial screw system is used to allow full range of motion during placement, then the screw can be positioned at various angles, but the excessive motion makes it difficult to place correctly within the bony elements and compromises positioning accuracy
Solution Approach 1:
The coupling element transitions from a dynamic state allowing uniplanar motion during insertion to a static locked state after rod insertion. The system provides angular adjustment during placement through controlled motion in one plane, then secures the position to maintain positioning accuracy.
Solution Approach 2:
The system separates the insertion phase (allowing motion for adaptability) from the fixation phase (locking for precision). The coupling element is designed as a distinct component that mediates between the screw and rod, enabling sequential fulfillment of adaptability and precision requirements.
2Stability of the object's composition
If a cap is used to compress the rod onto the coupling element to lock the angle, then the angle between bone screw and coupling element is fixed, but the system requires additional components and assembly steps
Solution Approach 1:
The cap integrates multiple functions: it compresses the rod onto the coupling element, locks the angular position, and secures the assembly together. By combining these functions into a single component, the system achieves angular stability without proportionally increasing complexity.
Solution Approach 2:
The compression mechanism uses the rod itself as part of the locking mechanism. When the rod is inserted and compressed by the cap, it actively participates in securing the angular position rather than requiring a separate locking mechanism.
3Measurement precision
If a uniplanar screw system is used to limit motion during placement, then positioning accuracy is improved, but the system must still allow controlled motion in one plane during insertion
Solution Approach 1:
The coupling element provides controlled dynamics during insertion, allowing motion only in the plane necessary for rod alignment. This limited freedom of motion simplifies the insertion process compared to completely rigid systems while maintaining positioning accuracy better than polyaxial systems.
Data Source
AI summary
A spinal stabilization system for surgical implantation in the spine having a bone fastener. The bone fastener is provided with a head portion and a shaft portion. A housing is also provided with a recess defined by sidewalls and an opening for receiving the head portion of the bone fastener. A seating element is disposed within the housing and positioned over the head portion of the bone fastener. An elongate rod is positioned on the seating element within the recess of the housing. The system also includes a cap capable of engaging with a top portion of the housing and capturing the elongate rod within the recess of the housing when the cap is rotated. The bone fastener articulates in a single plane with respect to the housing and the seat element.