Pivotal Bone Anchor Assembly With Locking Insert for Easier Rod Placement
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Solution Overview
Problem
Existing bone screws with fixed heads make it difficult to position an elongate rod within the receiver, especially in spinal surgery, as the rod must be favorably positioned before insertion, which can be challenging or impossible.
Innovation Solution
A pivotal bone anchor assembly featuring a shank with a head and receiver, a collet insert, and a pressure ring that allows for the shank head to be captured and locked in a desired angular position using the elongate rod, enabling multi-planar pivotability and secure fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed head bone screw is used, then the structure is simple and stable, but it is difficult to position and insert the elongate rod within the receiver
Solution Approach 1:
The receiver head is made movable relative to the shank, allowing it to pivot and rotate in one or more planes. This dynamic capability enables the receiver to be positioned at various angles to facilitate easy insertion of the elongate rod, while a locking mechanism secures the desired position after insertion.
Solution Approach 2:
The bone screw is divided into separate components: a shank and a movable receiver head. The receiver can be independently positioned and locked relative to the shank, allowing flexible rod insertion while maintaining structural integrity through the locking mechanism.
2Adaptability or versatility
If an open-ended bone screw with receiver is used, then the elongate rod can be easily inserted, but the receiver cannot be moved relative to the shank
Solution Approach 1:
The receiver head is designed to be movable relative to the shank, allowing pivoting and rotation in one or more planes. This enables the receiver to be positioned at various angles to facilitate easy insertion of the elongate rod, while a locking mechanism secures the desired position after insertion.
Solution Approach 2:
The receiver is pre-positioned at various angles relative to the shank before rod insertion. This preliminary angular adjustment allows the surgeon to optimally position the receiver to match the desired final configuration, making rod insertion easier while achieving the target adaptability.
3Adaptability or versatility
If a pivotal bone screw with movable receiver is used, then angular adjustment is possible, but the locking mechanism adds complexity
Solution Approach 1:
The receiver head is made movable relative to the shank, allowing it to pivot and rotate in one or more planes. This dynamic capability enables the receiver to be positioned at various angles to facilitate easy insertion of the elongate rod, while a locking mechanism secures the desired position after insertion.
Solution Approach 2:
The locking mechanism is designed to be simple and self-contained, utilizing the existing structural elements of the receiver and shank. The lock may engage with minimal additional components, allowing the system to lock itself into position without requiring complex external locking devices.
Data Source
AI summary
A bone anchor assembly includes a shank having a head portion opposite an anchor portion, and a receiver including an internal cavity for receiving the head portion of the shank, a first channel for receiving a rod, and an axial bore with interference abutment surfaces below an internal thread. The assembly also includes an insert positionable into the axial bore in a first position and having a second channel and opposite lateral abutment surfaces, and an expandable retainer positionable within a lower recess of the internal cavity. After uploading the head portion of the shank into the internal cavity, the insert is downwardly deployable with tooling toward a second position in which the opposite lateral abutment surfaces are forced at least partially below the interference abutment surfaces to inhibit the insert from moving back up within the receiver, and with lower portions of the insert entering into direct compressive overlapping engagement with the retainer to hold down the retainer within the recess of the internal cavity.