Bone Attachment Assembly With Three-Point Rod Retention
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Solution Overview
Problem
Existing bone attachment assemblies, particularly monoaxial and uniplanar screws, face issues with rod slippage due to rigid structures that constrain mobility and lack of adjustability, leading to increased risk of disengagement under load.
Innovation Solution
A bone attachment assembly with a three-point fixation mechanism using a rod carrier and set screw configuration that allows adjustable rod positioning and secure retention through a first and second raised portion and a pointed tip of the set screw, enhancing frictional hold and preventing slippage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a rigid structure is used to secure the rod in monoaxial bone screws, then the rod is held firmly in place, but the rod mobility is constrained and slippage risk increases under load
Solution Approach 1:
The attachment head incorporates a movable rod carrier that can pivot relative to the attachment head body, allowing the rod to be positioned at multiple angles (e.g., 0°, 45°, 90°) before final securing. This dynamic adjustment capability resolves the contradiction by providing both positioning flexibility and secure retention through the same mechanism.
Solution Approach 2:
The system changes the angular parameter of rod positioning from fixed (90° only) to variable (multiple angles), allowing adaptation to different surgical requirements while maintaining secure retention through the set screw mechanism that can lock at any selected angle.
2Adaptability or versatility
If a polyaxial screw design is used to provide rod adjustability, then rod positioning flexibility is improved, but the screw size and bulk increase
Solution Approach 1:
The polyaxial functionality is segmented into two separate components: the attachment head (fixed to bone) and the movable rod carrier (attached to rod). This segmentation allows the adjustability mechanism to be distributed across components rather than requiring a single bulky polyaxial screw body, reducing overall implant size while maintaining positioning flexibility.
Solution Approach 2:
The rod carrier acts as an intermediary component between the attachment head and the rod, providing the swiveling and positioning adjustment functionality. This intermediary mechanism achieves polyaxial adjustability without requiring the entire screw assembly to be bulky, as only the carrier portion needs the swiveling capability.
3Device complexity
If the rod is secured at a fixed angle in monoaxial screws, then the structure is simple, but the rod cannot be adjusted to accommodate variations in screw placement and alignment
Solution Approach 1:
The rod carrier is designed to pivot dynamically within the attachment head, transitioning from a fixed-angle constraint to a multi-angle adjustment capability. This dynamic mechanism maintains relative simplicity compared to full polyaxial screws while providing the necessary alignment adaptability for varying screw placement scenarios.
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 three-point fixation mechanism provides enhanced stability and resistance to rod slippage, allowing for adjustable alignment and secure attachment of connecting rods under load, reducing the risk of disengagement during spinal fusion surgeries.
Implementation Method 1
enhancing frictional hold and preventing slippage
Data Source
AI summary
A bone attachment assembly may include an attachment head, a set screw configured to attach to the attachment head, and a rod surface with a first raised portion and a second raised portion that define a lowered portion positioned between the first raised portion and the second raised portion. The first raised portion, the second raised portion, and the set screw may be configured to directly contact a rod in order to retain the rod within the attachment head.