Resilient Contact Pin for Spinal Screw Positioning
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Solution Overview
Problem
Multi-axial screw assemblies used in spinal corrections lack sufficient friction between components, causing the receiver portion to potentially flop freely relative to the screw portion, necessitating a mechanism to maintain the angular/pivotal position during attachment of spinal rods.
Innovation Solution
A bone fastener assembly incorporating a contact pin that is resiliently biased, positioned between the receiver and screw components, providing friction to stabilize the angular/pivotal position of the screw and receiver, and further secured by an expansion ring and crown, ensuring fixed attachment of the spinal rod.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the receiver portion is made angularly positionable relative to the screw portion, then the adaptability of the fastener assembly is improved, but the stability of the components relative to each other deteriorates
Solution Approach 1:
The contact pin is designed as a resilient component that can deflect and return to its original position. During assembly, the contact pin deflects to allow the receiver to be positioned at different angles relative to the screw. Once positioned, the contact pin's resiliency provides continuous frictional contact that stabilizes the receiver at the selected angle, thus resolving the contradiction between adaptability and stability.
Solution Approach 2:
The contact pin changes its physical state from a flexible assembly aid to a rigid stabilizing element. During assembly, the contact pin is flexible to allow positioning. After assembly, the contact pin maintains a resilient state that provides friction to hold the receiver firmly at the selected angular position, thus enabling both angular adjustability and positional stability.
2Stability of the object's composition
If friction between components is increased to prevent free movement, then the stability of the angular position is improved, but the ease of operation deteriorates
Solution Approach 1:
The contact pin's resiliency allows it to dynamically adapt to assembly forces. During assembly, the contact pin can deflect to accommodate positioning adjustments, making assembly easy. Once positioned, the same resiliency creates friction that stabilizes the angular position. This dynamic behavior resolves the contradiction between ease of operation and position stability.
3Stability of the object's composition
If a contact pin is added to provide friction between components, then the stability of the angular position is improved, but the device complexity increases
Solution Approach 1:
The contact pin serves as an intermediary element between the receiver and the screw assembly. It provides the necessary friction to stabilize the angular position without requiring direct complex mechanisms between the receiver and screw. The contact pin's simple resilient design allows it to mediate the interaction, providing stability while adding minimal complexity to the overall assembly.
Solution Approach 2:
The contact pin performs multiple functions: it acts as a friction element to stabilize the angular position, serves as a positioning aid during assembly, and provides structural support within the receiver cavity. By consolidating these functions into a single simple component, the contact pin improves stability without proportionally increasing device complexity.
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 contact pin and expansion ring system effectively maintains the selected angular/pivotal position of the screw and receiver, preventing movement and ensuring secure attachment of the spinal rod to the bone, facilitating stable spinal construct alignment.
Implementation Method 1
there is a need for a contact pin portion receivable within the receiver portion that can provide enough friction between the components so that the receiver portion can be adjusted to approximately the final position and the components will stay in that position
Implementation Method 2
a contact pin having a first end, a second end, and a length between the first end and the second end, the contact pin being resiliently biased in a first configuration
Data Source
AI summary
A bone fastener assembly including a bone screw, a receiver, a crown, a seat, and a contact pin is provided. The contact pin is formed as a leaf spring resiliently biased in a first position that affords generation of spring force via deformation thereof, and the contact pin acts as a tensioner to ultimately press against a head portion of the screw to aid movement prevention of the head portion relative to the receiver.