Polyaxial Screw Spherical Head Prevents Collar Flaring
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Solution Overview
Problem
Conventional polyaxial screw systems with U-shaped collars are prone to failure due to outward flaring and are limited to use with stabilizing rods, making them unsuitable for applications with plates or other non-rod stabilizing structures.
Innovation Solution
A polyaxial screw system comprising an elongated screw, a collet, a drive body, a compression cap, and a stabilizing structure that includes a rod clamp or plate, allowing for secure attachment of a stabilizing rod or plate between the screws, with a design that prevents outward flaring and enables versatile use with various stabilizing structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a U-shaped collar is used to secure the stabilizing rod, then the rod can be fixed between polyaxial screws, but the collar may outwardly flare and fail when the set screw is threaded into the U-shaped slot
Solution Approach 1:
The invention extracts the problematic U-shaped collar from the system and replaces it with a spherical head on the screw that directly receives the stabilizing rod. This eliminates the weak collar component that was prone to flaring and failure, while maintaining the rod securing function through the spherical receptacle design.
Solution Approach 2:
Instead of using a collar that flares outward under screw tension, the invention inverts the design by having the spherical head contain the rod endpoint within a spherical receptacle. The rod endpoint bears against the interior surface of the receptacle, creating an inward-directed force that prevents flaring and enhances reliability.
2Adaptability or versatility
If a U-shaped collar with set screw is used, then the stabilizing rod can be secured, but the screw can only be used with stabilizing rods and not with plates or other non-rod stabilizing structures
Solution Approach 1:
The spherical head with spherical receptacle design serves multiple functions: it can receive and secure stabilizing rods through the receptacle, and it can also accommodate plates and other non-rod stabilizing structures by attaching them to the spherical head surface. This universal design eliminates the need for specialized collar configurations for different stabilizing structure types.
Solution Approach 2:
The invention removes the specialized U-shaped collar configuration that limited compatibility to rod-only applications. By replacing it with a versatile spherical head design, the system can accommodate various stabilizing structures including rods, plates, and other configurations without requiring complex specialized components.
3Adaptability or versatility
If a conventional polyaxial screw with U-shaped collar is used, then the screw can be positioned in vertebrae, but the specialized collar configuration limits its use to direct rod attachment only
Solution Approach 1:
The spherical head design provides universal compatibility with multiple stabilizing structure types. Surgeons can attach stabilizing rods, plates, or other structures to the spherical head using appropriate connectors, providing operational flexibility without requiring different screw designs for different applications.
Solution Approach 2:
Instead of designing specialized collars for each stabilizing structure type, the invention inverts the approach by creating a universal spherical receptacle that can accommodate various structure types through standardized connection methods, simplifying the installation process and increasing flexibility.
Data Source
AI summary
A method for mounting a polyaxial screw into a bone includes rotating a drive cap so that a screw mounted to the drive cap is screwed into a bone, the drive cap having a socket in which a portion of the screw is pivotably disposed, at least a portion of a collet being disposed within the socket between the screw and the drive cap. A stabilizing structure and a fastener are positioned onto a shaft projecting from the drive cap. The fastener is advanced along the shaft so as to push a portion of a compression cap against the collet which in turn wedges the collet within the socket of the drive cap and causes the collet to bias against a portion of the screw, thereby locking the position of the screw, the collet, and the drive cap relative to each other.