Uniplanar Screw Spinal Stabilization Rod Placement
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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 vertical solid member, such as a rod, to a bone screw.
Innovation Solution
A uniplanar screw system with a housing, seating element, and cap design that allows for uniplanar motion until the cap and set screw compress the rod, securely locking the fastener in position, providing superior fixation and reducing the complexity of the surgical procedure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a polyaxial screw system is used to allow full range of motion for rod connection, then adaptability in rod placement is improved, but placement accuracy and stability are compromised due to excessive motion during screw positioning
Solution Approach 1:
The invention implements a dynamic motion control mechanism where the screw head is initially free to move axially within the housing during insertion, then transitions to a locked position after rod attachment. The set screw mechanism enables the system to switch from a mobile state (allowing adaptability) to a fixed state (ensuring placement accuracy), resolving the contradiction between range of motion and placement precision
Solution Approach 2:
The screw system is divided into functional segments: the screw shaft for bone engagement, the head portion with controlled motion, the housing with recess for rod reception, and the set screw for locking. This segmentation allows each component to perform its specific function - the head provides adaptability during insertion while the housing and set screw ensure precise final positioning and stability
2Ease of operation
If a polyaxial screw system with full range of motion is used, then ease of rod connection is improved, but stability and fixation strength are reduced due to difficulty in correct placement
Solution Approach 1:
The housing is pre-configured with a recess that guides and receives the rod in the correct orientation before final locking occurs. The set screw mechanism is pre-positioned to engage with the rod, ensuring that stability is established as part of the connection process rather than requiring separate positioning steps, thus maintaining both ease of operation and fixation reliability
3Adaptability or versatility
If a conventional polyaxial screw system is used, then adaptability in connecting rod at various angles is improved, but device complexity increases due to additional components like caps and multiple locking mechanisms
Solution Approach 1:
The invention merges the angular adjustment function and the locking function into a single integrated mechanism. The housing with its recess structure combines the angular positioning capability with the rod retention function, while the set screw simultaneously secures both the rod and the angular position. This eliminates the need for separate caps and multiple locking mechanisms found in conventional systems, reducing overall device complexity while maintaining adaptability
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.