Translating Polyaxial Screw Yoke Mechanism
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Solution Overview
Problem
Current spinal fixation systems face challenges in accommodating varying spine angulations and curvatures, leading to rod bending and increased complexity and cost, particularly in polyaxial bone anchoring systems.
Innovation Solution
A polyaxial bone anchor comprising a bone screw, collar, ball insert, slider, and yoke, which allows for translational and polyaxial movement, enabling the yoke to translate 90 degrees out of phase with the rod slot, providing flexibility in anchor placement and reducing rod bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a polyaxial bone anchor system is used to accommodate varying spine angulations and curvatures, then the adaptability to different spinal configurations is improved, but the device complexity and cost increase
Solution Approach 1:
The bone anchor is divided into separate functional components: a bone screw for vertebral engagement, a collar for positioning, a ball insert for polyaxial movement, a slider for translation, and a yoke for rod connection. This segmentation allows each component to perform its specific function independently, reducing overall system complexity while maintaining adaptability to various spinal configurations.
Solution Approach 2:
The invention incorporates dynamic movement capabilities through the ball insert that enables polyaxial swiveling and the slider that provides translational movement. These dynamic elements allow the anchor to adapt to different spine angulations and curvatures without requiring a complex multi-component system, as the movement is integrated into the anchor structure itself.
2Adaptability or versatility
If a polyaxial bone anchor system is used to accommodate varying spine angulations and curvatures, then the adaptability to different spinal configurations is improved, but the cost increases
Solution Approach 1:
By segmenting the anchor into standardized components (bone screw, collar, ball insert, slider, yoke), each part can be manufactured independently using conventional processes and then assembled. This modular approach reduces manufacturing complexity and cost compared to creating a single integrated polyaxial system, while still providing the necessary adaptability.
Solution Approach 2:
The ball insert and slider mechanism provides self-aligning and self-adjusting capabilities through their geometric designs. The ball insert automatically orients itself within the socket, and the slider translates the yoke in a controlled manner, reducing the need for complex external alignment tools or procedures, thereby lowering overall system cost.
3Reliability
If standard polyaxial screw systems are used, then the ability to engage vertebrae is improved, but rod bending and stress risers increase
Solution Approach 1:
The slider mechanism provides dynamic translation of the yoke relative to the bone screw, allowing the rod to be inserted at an optimal angle without requiring excessive bending. This dynamic adjustment capability maintains reliable vertebral engagement while reducing rod bending and associated stress risers.
Solution Approach 2:
The invention adds a translational degree of freedom through the slider mechanism, moving beyond the traditional single polyaxial rotation dimension. This additional dimension of movement allows the yoke to be positioned optimally in three-dimensional space, reducing the need to bend the rod and thereby improving rod strength and reducing stress concentration.
4Adaptability or versatility
If polyaxial movement is added to the bone anchor, then the flexibility of accommodating spine angulations is improved, but the device complexity increases
Solution Approach 1:
The polyaxial movement is segmented into two independent functional elements: the ball insert for rotational movement and the slider for translational movement. This segmentation allows each element to handle a specific degree of freedom, achieving enhanced flexibility while keeping the complexity of individual components manageable and the assembly straightforward.
Data Source
AI summary
A translating polyaxial bone anchor for anchoring a connecting rod to a spinal vertebra comprises a fastener having a bone engaging portion and a head, the head defining a socket. An insert is captively retained in the socket and configured for swiveling polyaxial movement therein. The insert includes an elongate connecting element defining an axis, the connecting element projecting outwardly from and through the socket. A yoke having at one end a rod receiving channel for receiving a connecting rod is coupled to the fastener by a coupling member. The coupling member couples the yoke to the insert connecting element for joint polyaxial movement relative to the fastener and for translational movement of the yoke in a direction transverse to the axis of the connecting member. A fastening element is supported by the yoke for securing the connecting rod between the fastening element and the coupling member.