Polyaxial Bone Anchor With Expandable Retainer Locking
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Solution Overview
Problem
Traditional bone screws in spinal surgery often face difficulties in positioning and securing longitudinal structures due to fixed heads, making it challenging to achieve desired rotational alignment, especially when rods or connectors need to be inserted into open-ended screws.
Innovation Solution
A polyaxial bone anchor assembly featuring a receiver with a chamber and a shank, along with a retainer that expands to capture the shank upper portion, allowing for adjustable and secure locking with a compression insert, enabling easy insertion and adjustment of rods or connecting members without losing angular relationship.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed head bone screw is used, then the structure is simple and easy to manufacture, but it is difficult to achieve desired rotational alignment when inserting rods or connectors
Solution Approach 1:
The patent applies the dynamics principle by transforming the fixed head structure into a polyaxial mechanism that allows dynamic movement. The receiver can rotate polyaxially relative to the shank, enabling the rod receiver to be favorably positioned for rod insertion while maintaining structural integrity. This dynamic capability resolves the contradiction by providing rotational alignment freedom without requiring complete structural redesign.
Solution Approach 2:
The bone screw is segmented into distinct functional components: a shank with threads for bone engagement, a receiver for rod accommodation, and a polyaxial mechanism connecting them. This segmentation allows each component to be optimized independently - the shank provides anchoring, the receiver provides rod reception, and the polyaxial mechanism provides rotational freedom, thereby achieving ease of operation while managing device complexity.
2Ease of operation
If an open-ended bone screw is used to facilitate rod insertion, then ease of operation improves, but securing and locking the rod becomes more difficult
Solution Approach 1:
The polyaxial mechanism enables dynamic positioning of the receiver during rod insertion, allowing the surgeon to align the rod with the screw axis before securing. After insertion, the mechanism can be locked to provide static, reliable fixation. This transition from dynamic to static state resolves the contradiction between ease of insertion and reliability of securing.
Solution Approach 2:
The open-ended receiver structure performs preliminary action by facilitating easy rod insertion before the locking mechanism is engaged. The receiver's geometry is designed to guide and accommodate the rod during insertion, and only after this preliminary positioning is complete does the locking mechanism engage to provide secure fixation, thereby resolving the contradiction between ease of insertion and reliability of securing.
3Ease of operation
If a polyaxial mechanism is implemented to allow rotational adjustment, then ease of operation for alignment improves, but the device structure becomes more complex
Solution Approach 1:
The polyaxial mechanism implements controlled dynamics, allowing rotational adjustment only during the alignment phase. The mechanism provides degrees of freedom for positioning the receiver at various angles relative to the shank, facilitating ease of operation for angular alignment. The complexity is managed by designing the mechanism to lock into place once the desired position is achieved, transforming the dynamic adjustment capability into a stable, locked configuration.
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 solution provides a secure, adjustable, and user-friendly mechanism for securing rods or connectors, facilitating easier implantation and alignment in spinal surgery by allowing for polyaxial movement and locking, thus enhancing surgical efficiency and stability.
Implementation Method 1
The retainer is in a non-tapered locking engagement with the shank upper portion when the shank is in a locked orientation with respect to the receiver
Data Source
AI summary
A pivotal bone anchor assembly includes a receiver having upright arms defining a receiver channel for receiving an elongate rod, and an axial bore extending downward from the receiver channel to a bottom opening. The upright arms include break-off extensions, outer horizontally extending curvate tool engagement grooves, and side apertures extending inwardly from outer surfaces of the upright arms to deformable crimp wall portions adjacent the axial bore. The assembly also includes a shank having an anchor portion and an integral upper portion that is positionable in the axial bore of the receiver with the shank extending downward through the bottom opening. The assembly further includes an insert with an insert channel positionable within the axial bore and having opposing depressions formed into side surfaces that are configured to cooperate with the crimp wall portions of the receiver to maintain the insert channel in alignment with the receiver channel.