Pivotal Bone Anchor Assembly With Cutout-Based Shank Angulation
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Solution Overview
Problem
Existing bone anchors, particularly open-ended polyaxial screws, face difficulties in securely attaching longitudinal connecting members due to the high forces required to maneuver closure structures, especially in cases of spinal misalignments and irregularities, making initial placement of rods or connectors challenging.
Innovation Solution
A multi-start closure mechanism with helically wound guide and advancement features, featuring dual or more helical forms that engage simultaneously with the implant arms, allowing the closure to rotate and advance axially, reducing the force needed for secure attachment of rods or connectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single-start helical closure structure is used, then the closure can be rotated and advanced, but high forces are required to maneuver the closure and secure the rod, especially in cases of spinal misalignments
Solution Approach 1:
The closure structure is divided into multiple independent helical forms (dual-start or multi-start) that can engage and advance separately. Each helical form acts as an independent advancement mechanism, distributing the force requirement across multiple engagement points rather than relying on a single helical thread, thereby reducing the force needed to maneuver the closure while maintaining secure attachment
2Reliability
If the closure structure is designed to securely capture the rod, then reliable attachment is achieved, but the complexity of the closure mechanism increases
Solution Approach 1:
Multiple helical forms are combined into a single integrated closure structure that rotates as one unit while engaging multiple advancement features simultaneously. This merging approach maintains attachment reliability through multiple engagement points while avoiding the complexity of multiple separate closure mechanisms, as all helical forms are formed as one piece and rotate together
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 multi-start closure mechanism simplifies the attachment process by distributing the force requirement, making it easier to align and secure rods or connectors within the bone anchor, even in challenging surgical conditions.
Implementation Method 1
A multi-start closure mechanism with helically wound guide and advancement features, featuring dual or more helical forms that engage simultaneously with the implant arms, allowing the closure to rotate and advance axially
Data Source
AI summary
A pivotal bone anchor assembly includes a receiver having a first channel for receiving a rod and a central bore with a seating surface adjacent a bottom opening with a first cut-out portion. The assembly also includes a bone anchor having an upper end portion pivotably engageable with the seating surface, an anchor portion opposite the upper end portion, and a neck extending between the upper end and anchor portions. The assembly further includes an insert positionable in the central bore with a second channel alignable with the first channel, a concave lower surface engageable with the upper end portion of the bone anchor, and a second cut-out portion alignable with the first cut-out portion. The neck and at least a portion of the upper end portion of the bone anchor are positionable into the first cut-out portion and the second cut-out portion, respectively, to provide for increased pivotal angulation of the bone anchor with respect to the receiver in the direction of the cut-out portions.