Spinal Anchoring Screw Dynamic Rod Locking
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Solution Overview
Problem
Current spinal stabilization systems, even with dynamic rods, experience stress on screw shanks that can lead to screw backout or failure, necessitating a more effective stabilization method that reduces strain and provides additional kinematic options.
Innovation Solution
A dynamic screw system with a bone anchor assembly featuring a pivotable connecting member, adjustable length options, and a locking mechanism to secure the rod within the receiver member, allowing for flexible movement and reduced stress on the screw-bone interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dynamic rods are used to allow limited movement between pedicle screws, then less strain is placed on adjoining vertebrae and stresses on screw shank are decreased, but stresses on the screw shank remain which could potentially result in screw backout or related failures
Solution Approach 1:
A polyaxial receiver member is introduced as an intermediary component between the bone screw and the rod. This receiver member includes a cavity that receives the rod and allows relative movement, acting as a mediator that decouples the direct stress transmission from the screw-bone interface while still providing stabilization.
Solution Approach 2:
The system employs dynamic elements including a flexible rod portion and a polyaxial receiver member that allows the rod to move relative to the bone screw. This dynamic configuration enables the system to adapt to physiological movements while maintaining stabilization, reducing stress concentrations that could lead to screw backout.
2Adaptability or versatility
If traditional PDS stabilization elements are used, then spinal stabilization is achieved, but kinematic options and loading requirements are limited
Solution Approach 1:
The rod is divided into a first portion and a second portion with a flexible portion between them, allowing independent movement and rotation of each segment. The polyaxial receiver member is also segmented with distinct cavities for receiving different rod configurations, providing multiple kinematic options while maintaining manageable complexity through modular design.
Solution Approach 2:
The polyaxial receiver member is designed with universal functionality to accommodate various rod configurations and orientations. The cavity structure allows the rod to be received in multiple positions and orientations, providing adaptability for different surgical scenarios without requiring multiple specialized components.
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 dynamic screw system provides enhanced stability and reduced risk of screw backout by allowing limited movement between vertebrae, accommodating different segmental units and patient sizes, while offering varied kinematic and loading requirements.
Implementation Method 1
the pivotable connection between the elongated connection member and the receiver member is provided by a ball-shaped pivot member on the rod which engages a bearing surface provided within a cavity of the receiver member
Data Source
AI summary
A spine stabilization system includes at least one bone anchor assembly, the bone anchor assembly including a bone engaging member and a receiver member, wherein the receiver member includes a connecting member cavity, and an elongated connecting member inserted into the connecting member cavity and connected to the receiver member, wherein the connecting member comprises locking features configured to secure the connecting member to the receiver member without the use of a fixation screw extending through a top portion of the receiver member.