Pivoting Bone Anchor Positioner for Secure Snap-on Retainer Alignment
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Solution Overview
Problem
Current bone anchor systems face challenges in ensuring secure and reliable snap-on connections, particularly with pivoting retainers that can become misaligned, leading to difficulties in maintaining the shank within the receiver assembly during spinal surgeries, which complicates the procedure and increases inventory costs due to the need for various sizes and configurations.
Innovation Solution
A bone anchor assembly featuring a shank with a capture structure and a multi-purpose positioner that aligns and stabilizes the pivoting retainer within the receiver, preventing it from returning to the expansion chamber after snapping onto the shank, ensuring secure locking and alignment, and allowing for both mono-planar and multi-planar motions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a pivoting retainer is used to allow multi-planar motion of the shank, then the adaptability of the bone anchor system is improved, but the reliability of the snap-on connection deteriorates due to misalignment and unintended disengagement
Solution Approach 1:
A positioner component is introduced as an intermediary element between the retainer and the receiver. The positioner maintains proper alignment of the retainer during the snap-on process and prevents unintended disengagement, thereby resolving the contradiction between allowing pivoting motion and ensuring reliable connection.
Solution Approach 2:
The positioner is pre-installed in the receiver before the retainer is snapped on. This preliminary positioning ensures that the retainer is correctly aligned with the shank capture structure before engagement, preventing misalignment issues that would compromise connection reliability.
2Device complexity
If a universal capture structure is used to work with multiple receiver configurations, then the device complexity is reduced, but the manufacturing precision requirements increase to ensure proper alignment across different configurations
Solution Approach 1:
The capture structure is designed with universal geometric features (such as spherical or conical surfaces) that can interface with multiple different receiver configurations. This universal design reduces the number of specialized components needed while maintaining proper alignment through standardized geometric relationships.
Data Source
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AI summary
In a pivotal bone anchor assembly (1001) for securing an elongate rod (1022) to a bone, the pivotal bone anchor assembly comprising a bone anchor (1004) and a receiver assembly (B20) having a capture portion (1008), a receiver (1010), a retainer (1012), a positioner (1009, and a pressure insert (1014), the bone anchor comprises a capture portion (1008) including an upper partial spherical surface (1046) with a tool engaging structure (1049) formed therein, a lower partial spherical surface (1034), and a capture recess formed between the upper partial spherical surface (1046, 7046) and the lower partial spherical surface (1034) and comprising a recessed outward-facing interface surface (1038) extending between an upper ledge surface (1043) and a lower ledge surface (1036). Upon insertion of the capture portion (1008) of the bone anchor into an internal cavity (1091) of the receiver through a bottom opening (1136), the retainer and positioner are configured to expand together within an upper expansion chamber (95) around the upper partial spherical surface of the bone anchor, after which the retainer is released from the positioner to snap into the capture recess to capture and hold the capture portion within the internal cavity.