Spherical Bone Fastener Assembly for Spinal Fixation
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Solution Overview
Problem
Existing bone fastener assemblies for spinal fixation face challenges in secure attachment due to rigidity issues and misalignment, leading to potential stress on vertebrae and loosening of screws over time, especially when trying to maintain desired spatial relationships among vertebrae.
Innovation Solution
A bone fastener assembly comprising a bone fastener with an adjusting member and a securing fastener, allowing for universal movement and secure attachment to an appliance, featuring a spherical recess and complementary surface for alignment and a cone-shaped opening to accommodate adjustments, ensuring firm fixation while minimizing stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If rigid bone fasteners and coupling members are used to achieve stable fixation, then fixation stability is improved, but the ability to accommodate misalignment and vertebral displacement deteriorates
Solution Approach 1:
The coupling member incorporates a spherical interface that allows dynamic adjustment and movement between the bone fastener and the rod/plate. This spherical joint enables the system to adapt to misalignment and vertebral displacement while maintaining secure fixation, resolving the contradiction between rigidity for stability and flexibility for adaptability.
Solution Approach 2:
The coupling member changes the mechanical parameters of the connection by introducing a spherical bearing surface that permits rotation and angular adjustment. This parameter change allows the system to accommodate varying degrees of misalignment while maintaining stable fixation forces.
2Reliability
If the rod or plate is bent to align with bone fasteners, then connection security is improved, but the risk of creating stresses that cause fracture or loosening increases
Solution Approach 1:
Instead of bending the rod or plate to achieve alignment, the spherical coupling member provides dynamic alignment capability. This allows the rod/plate to maintain its original shape and avoid stress concentration, while still achieving secure connection to the bone fasteners through the adjustable spherical interface.
Solution Approach 2:
The coupling member acts as an intermediary between the rod/plate and the bone fastener, providing the alignment function that would otherwise require bending the rod/plate. This intermediary absorbs the misalignment through its spherical joint, preventing harmful stresses in the rod/plate while ensuring secure connection.
3Stability of the object's composition
If precise alignment of the rod or plate with all bone fasteners is required, then fixation stability is improved, but installation difficulty increases
Solution Approach 1:
The spherical coupling member provides dynamic alignment capability during installation, allowing the rod/plate to be positioned without precise pre-alignment. The spherical joint automatically accommodates angular differences and positional variations, making installation easier while maintaining fixation stability once assembled.
Solution Approach 2:
The spherical interface is pre-configured to accommodate a range of alignment variations, eliminating the need for precise pre-alignment of the rod/plate with all bone fasteners during installation. This preliminary design feature simplifies the installation process while ensuring stable fixation.
Data Source
AI summary
An assembly, comprising a bone fastener, an adjusting member and a securing fastener for fastening an appliance to a bone body so that a plurality of the bone fastener assemblies and the appliance constitute an apparatus that retain a plurality of bone bodies. Each fastener has an attaching portion for attaching the bone fastener to a bone body, a supporting portion for supporting the adjusting member for universal movement relative to the supporting portion, and a securing portion for securing the bone fastener to the fastener. The fastener has a first end that passes through an aperture in the appliance and an opening in the adjusting member and is secured to the securing portion of the bone fastener. A second end of the fastener has a bearing surface that adjustably bears against the appliance in opposition to an engaging surface of the adjusting member that engages the appliance.