Polyaxial Screw Insert Segmentation for Iliosacral Fixation
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Solution Overview
Problem
Current spinal fixation systems, particularly for iliosacral constructs, require stronger and more rigid screw and rod constructs to manage large deformity corrections, but existing polyaxial screws often lack the necessary strength and stability, especially when larger diameters are needed to accommodate anatomical variations.
Innovation Solution
A polyaxial screw system comprising a housing, a bone screw member with a threaded shaft, a wedge member, and an insert member that allows the screw to be positioned at multiple angles up to 80 degrees, with a set screw securing a rod within the housing, and an insert member made of two pieces to accommodate larger shank diameters without disassembly, providing enhanced stability and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If larger diameter screws are used to improve strength for deformity corrections, then screw strength increases, but screw head size must increase which complicates the polyaxial mechanism design
Solution Approach 1:
The insert member is divided into two separate halves that can be independently positioned and secured to the housing. This segmentation allows the insert to accommodate larger screw shank diameters without requiring a correspondingly larger housing opening, thereby maintaining screw head size compatibility with existing polyaxial mechanisms while providing the necessary strength for deformity corrections
Solution Approach 2:
The two-piece insert member is nested within the housing structure, with each insert half fitting around portions of the screw shank. This nesting arrangement allows the insert to provide internal support and locking functionality without increasing the external dimensions of the screw head or housing, thus resolving the contradiction between strength requirements and mechanism complexity
2Adaptability or versatility
If larger diameter screws are used to accommodate anatomical variations, then anatomical adaptability improves, but the polyaxial screw design becomes more complex
Solution Approach 1:
The insert member is designed with adjustable parameters including the size and positioning of openings in each insert half, allowing the same basic two-piece insert structure to accommodate various screw shank diameters. This parameter adjustability provides anatomical versatility without requiring fundamentally different design approaches for different size requirements
Solution Approach 2:
By segmenting the insert into two independent halves, the design can be adapted to different anatomical requirements by modifying the dimensions and configuration of each half separately, while maintaining the overall simplicity of the polyaxial mechanism
3Ease of manufacture
If a single-piece insert is used, then manufacturing is simpler, but larger shank diameters cannot be accommodated without disassembly
Solution Approach 1:
The insert is divided into two halves that can be separately manufactured using standard manufacturing processes, then assembled around the screw shank. This segmentation enables the accommodation of larger shank diameters without requiring complex disassembly procedures, as the two halves can be positioned and secured independently
Solution Approach 2:
While the insert is divided into two halves for manufacturing and assembly purposes, these halves are merged together through securing mechanisms (such as welding, bonding, or mechanical fastening) to form a unified structure that provides continuous support around the screw shank, maintaining structural integrity while enabling larger diameter accommodation
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 system enables cost-effective, rigid, and stable spinal fixation capable of managing significant deformity corrections by allowing for larger shank diameters and secure rod positioning, enhancing the strength and stability of the screw and rod construct, particularly at the iliosacral junction.
Implementation Method 1
The head includes surface texture that frictionally engages with the wedge member such that a user applied force is necessary to reposition the bone screw member relative to the wedge member
Data Source
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AI summary
Provided is an iliosacral polyaxial screw system. A multiple part insert member is provided to secure the screw to the housing of the assembly to accommodate screws in which the shank diameter of the screw is greater than the bottom opening of the screw housing or greater than the opening of a ring member designed to capture the head of the screw in the housing.