Polyaxial Bone Screw Extension for Vertebral Repositioning
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Solution Overview
Problem
Current spinal fixation devices face challenges in safely and effectively repositioning vertebrae, particularly in conditions like spondylolisthesis, due to limitations in controlled force application and maintaining physiological disc space height during reduction procedures.
Innovation Solution
The device employs a polyaxial bone screw system with a screw extension and a moveable rod that transmits force to prevent screw movement, and a fixation device with articulated bone screws connected by a cross strut, allowing for controlled repositioning and stabilization of vertebrae using a pivoted lever and tightening mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a polyaxial bone screw system is used for repositioning vertebrae, then the flexibility and adaptability of screw orientation are improved, but the control over force application and screw movement prevention becomes insufficient
Solution Approach 1:
A dedicated extension component is introduced as an intermediary between the polyaxial bone screw and the repositioning force application system. This extension includes a longitudinal sleeve and moveable rod that transmits force to prevent screw movement during repositioning, providing reliable control while maintaining the screw's polyaxial orientation flexibility
Solution Approach 2:
The bone screw system is segmented into distinct functional components: the polyaxial bone screw for orientation flexibility, the longitudinal sleeve and moveable rod for force transmission, and the contact surface for preventing screw movement. This segmentation allows each component to optimize its specific function while working together as an integrated system
2Ease of operation
If articulated bone screws connected by cross strut are used, then the controlled repositioning capability is improved, but the device complexity increases
Solution Approach 1:
The extension components (longitudinal sleeve, moveable rod, contact surface) are nested within or integrated with the bone screw structure. The moveable rod extends from within the longitudinal sleeve, and the contact surface is disposed on the end of the rod, creating a compact nested arrangement that reduces overall device complexity while maintaining controlled repositioning capability
3Manufacturing precision
If force is applied to prevent polyaxial rotation during repositioning, then the repositioning precision is improved, but the distraction of disc space increases
Solution Approach 1:
The extension acts as an intermediary that transmits repositioning forces directly to the vertebral body through the bone screw, preventing polyaxial rotation and improving repositioning precision. The design ensures that forces are applied in a controlled manner that minimizes distraction of the disc space between vertebrae
Data Source
AI summary
A device for repairing a bone disorder using a polyaxial screw. The device has a pivoted lever mounted rotatably to an extension of a bone screw and which extends essentially at right angles to the longitudinal direction of the extension to which it is mounted and is in contact with a stop on the other extension associated with the vertebral body to be repositioned. The extension that acts on the polyaxial bone screw comprises a longitudinal sleeve, a rod, preferably threaded, extending from within the sleeve and moveable within the sleeve, and a contact surface disposed on the end of the threaded rod which is configured to transmit a force against the bone screw to prevent polyaxial movement of the polyaxial bone screw for as long as the force is transmitted.