Spinal Bone Anchors With Offset Cord Receivers to Reduce Migration
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Solution Overview
Problem
Current spinal tethering systems face issues such as screw migration, stress concentration on flexible cords, construct failure, and overcorrection during spinal deformity correction procedures, along with difficulties in implantation and construct strengthening.
Innovation Solution
The development of improved bone anchors with modular designs, offset cord receivers, and enhanced cord clamping mechanisms that include connectors, set screws, and extending staples to secure and distribute tension evenly across multiple implant levels, reducing screw migration and stress on cords.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional bone anchors with central cord receivers are used, then the implantation is simple, but screw migration occurs and construct strength is reduced
Solution Approach 1:
The bone anchor is divided into multiple functional components: a staple portion for bone engagement, a cord receiver portion for cord attachment, and a connector for tension distribution. This segmentation allows each component to perform its specific function optimally, preventing screw migration while maintaining construct strength.
Solution Approach 2:
The cord receiver is offset from the central axis of the bone anchor, creating an eccentric configuration. This dimensional change allows the cord to be positioned laterally, distributing forces away from the screw axis and preventing screw migration while maintaining overall construct integrity.
2Reliability
If cord tension is applied at a single point, then the cord clamping is simple, but stress concentration occurs on the flexible cord
Solution Approach 1:
The cord clamping function is segmented into multiple clamping points along the cord length, rather than a single clamping point. This distributes the clamping force and reduces stress concentration at any single location, preventing cord breakage while maintaining secure attachment.
Solution Approach 2:
The connector extends the cord receiver laterally offset from the bone anchor axis, creating an eccentric cord path. This geometric configuration distributes tensile forces across multiple anchor points and reduces stress concentration on the cord by changing the force distribution geometry.
3Ease of operation
If fixed cord clamping is used, then the implantation is straightforward, but overcorrection cannot be prevented
Solution Approach 1:
The connector allows for dynamic adjustment of cord tension and positioning after implantation. The modular design enables surgeons to adjust the cord receiver position and tensioning characteristics, providing controlled correction while preventing overcorrection through adjustable mechanical constraints.
4Reliability
If modular bone anchors with offset cord receivers are used, then screw migration is reduced and cord clamping is enhanced, but implantation difficulty increases
Solution Approach 1:
The staple and cord receiver portions are merged into a single integrated bone anchor assembly, combining the functions of bone engagement and cord attachment in one implant. This reduces the number of separate components to be implanted while maintaining the benefits of offset cord reception and modular design.
Data Source
AI summary
A bone anchor and system for applying tension via a tether or cord between bone anchors is provided. An illustrative bone anchor includes a screw having a head and a shank, where the shank defines a screw axis. The bone anchor further includes a connector attachable to the head of the screw, where the connector is configured to receive and secure a cord to the bone anchor.