Pivotal Bone Anchor Assembly With Collet Locking for Rod Positioning
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Solution Overview
Problem
Existing bone screws with fixed heads make it difficult to position an elongate rod within the receiver head, especially in spinal surgery, as they require precise alignment which can be challenging or impossible to achieve.
Innovation Solution
A pivotal bone anchor assembly featuring a shank with a head, a 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 collet insert and pressure ring, enabling multi-planar pivotability and secure fixation of an elongate rod.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed head bone screw is used, then the structure is simple and reliable, but the rod cannot be easily positioned within the receiver head
Solution Approach 1:
The bone screw head is made dynamically adjustable through a polyaxial mechanism that allows the rod receiver to pivot and rotate relative to the shank in one or more planes. This enables the receiver to be positioned at various angles during insertion and then locked into a fixed position once the rod is properly seated, combining the ease of positioning with final structural stability
2Ease of operation
If an open-ended polyaxial bone screw is used, then the rod can be easily positioned, but the device complexity increases
Solution Approach 1:
The bone screw is divided into distinct functional segments: a shank for bone anchoring, a rod receiver for rod accommodation, and a polyaxial mechanism with movable and fixed components. This segmentation allows each part to perform its specific function independently, enabling easy rod positioning while maintaining overall structural reliability
Solution Approach 2:
The polyaxial mechanism employs nested components where a movable receiver portion is positioned within a fixed receiver portion. The movable portion can pivot and rotate independently before being locked into place, providing adjustable positioning capabilities without significantly increasing the overall device footprint or complexity
Data Source
AI summary
A method of assembling a pivotal bone anchor assembly includes loading an insert into a central bore of a receiver, with the receiver having the central bore extending upward from a bottom opening to and through a first channel for receiving a rod, and the insert having an upper portion defining a second channel, opposite lateral protrusions extending outwardly in a direction transverse to the second channel, a lower collet portion, and a center opening. The method also includes positioning the insert into the central bore with the opposite lateral protrusions located adjacent to and above interference abutment surfaces formed into the central bore, and positioning a load ring within the center opening of the insert. The method further includes uploading a shank head into the central bore of the receiver through the bottom opening, capturing the shank head within the lower collet portion of the insert, and then forcibly downward displacing the insert within the central bore with the tooling so as to move the opposite lateral protrusions below the interference abutment surfaces.