Polyaxial Screw Friction Device Axial Pre-positioning
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Solution Overview
Problem
Polyaxial screws with free rotational movement of the mechanically threaded anchoring part relative to the threaded bone anchoring part complicate the assembly of spinal devices, as they cannot be accurately positioned or maintained in a determined axial plane, leading to assembly complications during the placement of connecting connectors and rods.
Innovation Solution
A polyaxial screw design incorporating a friction device, such as a helical spring, and retaining means, including two half-shells, ensures axial pre-positioning and immobilization of the mechanically threaded anchoring part relative to the threaded bone anchoring part, allowing for freedom of movement in vertical translation and angular pivoting, while preventing separation and ensuring precise positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the mechanically threaded anchoring part is made free in rotation around the threaded bone anchoring part, then the polyaxial screw achieves adaptability for different positioning angles, but the assembly complexity increases and positioning precision deteriorates
Solution Approach 1:
The friction device is pre-configured between the threaded bone anchoring part and the mechanically threaded anchoring part to provide preliminary axial pre-positioning. This preliminary action establishes a determined axial plane before the surgeon positions the connecting connector and rod, eliminating the need for complex real-time adjustments during assembly.
Solution Approach 2:
The friction device acts as an intermediary element between the threaded bone anchoring part and the mechanically threaded anchoring part. It mediates the interaction by providing friction-based retention that maintains the anchoring parts in a determined angular position while still allowing the necessary polyaxial movement for positioning.
2Adaptability or versatility
If the mechanically threaded anchoring part is free in rotation, then the polyaxial screw achieves versatility in orientation, but the positioning precision and assembly ease deteriorate
Solution Approach 1:
The friction device provides preliminary axial pre-positioning that establishes a determined axial plane before final assembly. This preliminary positioning action ensures that the mechanically threaded anchoring part is held in a specific angular position relative to the threaded bone anchoring part, enabling precise positioning while maintaining orientation versatility.
3Adaptability or versatility
If the mechanically threaded anchoring part can pivot freely, then the polyaxial screw achieves adaptability for anatomical variations, but the assembly process becomes more difficult
Solution Approach 1:
The friction device performs preliminary axial pre-positioning that establishes a determined axial plane before the surgeon positions the connecting connector and rod. This preliminary action simplifies the assembly process by eliminating the need for the surgeon to manually maintain complex angular positions, while still allowing the necessary pivoting for anatomical adaptability.
Solution Approach 2:
The friction device serves as an intermediary that facilitates the assembly process by automatically maintaining the mechanically threaded anchoring part in a determined angular position. This intermediary function reduces the operational complexity for the surgeon while preserving the anatomical adaptability needed for different patient geometries.
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 enables precise axial pre-positioning and immobilization of the mechanically threaded anchoring part, simplifying the assembly of spinal fixation devices by maintaining the anchoring parts together during assembly and allowing for secure attachment without compromising the mechanical thread's freedom of movement.
Implementation Method 1
a helical wire in the form of a spring positioned inside a housing provided in the head of the threaded bone anchoring part and on which comes support the spherical external profile head of the mechanically threaded anchor part
Data Source
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AI summary
The invention relates to a polyaxial screw having a mechanical thread, comprising a friction means (12) arranged between the head (3) of the bone-anchoring threaded portion (2) and the head (9) of the anchoring portion having the mechanical thread (4), as well as a retaining means (13, 18) for ensuring that the anchoring portions (2, 4) cannot be separated from one another while guaranteeing the freedom of vertical translatable and angularly pivotable movement of the anchoring portion having the mechanical thread (4) relative to said bone-anchoring threaded portion (2) in order to be capable of axially prepositioning said mechanical anchoring portion (4), prior to immobilising same, relative to the axial anchoring position of the bone-anchoring threaded portion (2).