Polyaxial Screw Assembly Friction Fit for Stable Receiver Alignment
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Solution Overview
Problem
Existing spinal fixation systems face challenges in aligning and securing receivers to bone screws due to gravity-induced drooping and slipping, requiring complex repositioning and specialized tools for assembly, limiting surgical flexibility and efficiency.
Innovation Solution
A friction-fit mechanism between a receiver and a bone screw is implemented, utilizing resilient tabs and a tapered recess to stabilize the receiver's orientation before locking, allowing modular assembly and alignment, facilitated by a pressure insert that flexes to create a spring force for secure engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If receivers are oriented in alignment for connecting rod insertion, then the connecting rod can be positioned through each receiver, but gravity causes the receivers to droop or slip out of alignment requiring repositioning and reorienting multiple times
Solution Approach 1:
The receiver assembly incorporates a friction-fit mechanism with resilient tabs and tapered recesses that automatically maintains alignment between the receiver and bone screw head during implantation. This preliminary alignment stabilization eliminates the need for repeated repositioning and reorienting operations, directly resolving the time loss issue while maintaining ease of operation.
2Ease of operation
If preassembled receiver and fastener assemblies are used, then assembly by the physician is simplified, but the surgeon is limited based on the variety of selections available at the time of surgery
Solution Approach 1:
The receiver assembly is divided into separable components (receiver body, fastener, resilient tabs, tapered recesses) that can be independently selected and assembled. This segmentation allows the surgeon to choose from multiple preassembled options with different characteristics while maintaining the ability to customize the assembly, thus preserving both ease of operation and adaptability.
Solution Approach 2:
The friction-fit mechanism provides dynamic adjustment capability during implantation, allowing the receiver to maintain optimal alignment through elastic deformation of the resilient tabs. This dynamic feature enables the system to adapt to varying surgical conditions while maintaining assembly simplicity.
3Reliability
If specialized tools and trained technicians are used for assembly, then the assembly process is reliable, but the procedure becomes more complex and less flexible
Solution Approach 1:
The receiver assembly incorporates a self-aligning friction-fit mechanism where the resilient tabs automatically engage with the tapered recesses to maintain proper orientation. This self-service alignment feature eliminates the need for specialized alignment tools and trained technicians, reducing assembly complexity while maintaining reliability through the inherent mechanical design.
4Manufacturing precision
If the friction-fit mechanism is implemented with resilient tabs and tapered recesses, then receiver alignment is stabilized during implantation, but the device structure becomes more complex
Solution Approach 1:
The friction-fit mechanism utilizes elastic deformation parameters of the resilient tabs interacting with the tapered recesses to achieve precise alignment. By leveraging material elasticity and geometric parameters, the system achieves high manufacturing precision without requiring complex active control systems, thus minimizing the increase in device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The friction-fit mechanism stabilizes receiver alignment during implantation, enabling efficient and flexible assembly of spinal fixation systems, allowing for pre-surgical selection and alignment adjustments before final locking, reducing assembly complexity and improving surgical precision.
Implementation Method 1
The resilient tabs may engage a ramped or sloped surface of a tapered recess in the receiver body, such that longitudinal movement of the pressure insert is translated into compressing or flexing the resilient tabs inward
Implementation Method 2
The frictional force may be facilitated by one or more resilient tabs of the pressure insert which are configured to flex or deflect in response to longitudinal movement of the pressure insert relative to the receiver
Implementation Method 3
a frictional force may be applied between a screw head and a retention ring, and another frictional force may be applied between the screw head and a pressure insert. The frictional force and contact maintains and stabilizes an orientation of a receiver relative to the screw head
Data Source
AI summary
Implantable devices and assemblies are described that provide a friction fit between a receiver and a fastener, such as a bone screw. The friction is created between a screw head, a retention ring, and a pressure insert, stabilizing the receiver's orientation before locking with a set screw. This mechanism facilitates manual alignment of the receiver in a way that retains the orientation of the receiver after it has been moved and oriented at a desired setting. The devices and assemblies allow for modular assembly before or during spinal fixation procedures, accommodating various screw characteristics. The frictional force may be facilitated by resilient tabs on the pressure insert, which engage a recess and/or a ridge in the receiver. This engagement translates into a downward spring force of the pressure insert on the head of the bone screw, which helps provide the friction between the head of the bone screw and the receiver assembly.