Cervical Pop Rivet Locking Mechanism for Screw Back-out Prevention
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Solution Overview
Problem
Conventional bone fixation devices for stabilizing the cervical spine face challenges in preventing screw back-out, which can lead to irritation or piercing of the esophagus, causing pain, infection, or death, due to their design that does not adequately account for the proximity to the esophagus and other connective tissue.
Innovation Solution
An orthopedic bone fixation device featuring a bone plate with varying diameter thru-bores and a screw assembly that includes a pull-lock pin and expandable ring, which increases frictional force to resist pull forces greater than the yield or fracture force of the pin, preventing screw back-out while maintaining a low profile to avoid tissue irritation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional screws are used to secure the plate to the cervical spine, then the plate can be firmly secured to stabilize bone segments, but the screws may back out and irritate or pierce the esophagus due to the proximity of the plate to the esophagus
Solution Approach 1:
The patent applies preliminary anti-action by incorporating an anti-backout mechanism that proactively prevents screw backout before it can occur. The pop-rivet mechanism is pre-configured to engage with the bone plate and screw, creating a mechanical interlock that opposes any backward motion of the screw. This preliminary protective structure ensures that even if forces attempt to back out the screw, the mechanism is already in place to prevent contact with the esophagus.
Solution Approach 2:
The patent uses an intermediary mechanism (the pop-rivet and expandable ring system) between the screw and the bone plate to prevent direct harmful contact. When the screw is inserted, the pop-rivet engages with the expandable ring, creating an intermediate locking structure that mediates the connection between the screw and the plate, preventing the screw from backing out and contacting the esophagus.
2Reliability
If the plate is designed to lie near and posterior to the esophagus for cervical spine stabilization, then the plate can effectively secure and stabilize the cervical vertebrae, but any protrusion or screw backout can cause tissue irritation or piercing
Solution Approach 1:
The anti-backout mechanism is pre-installed on the screw before insertion, creating a preliminary protective structure that prevents any backward motion. This ensures that during cervical spine stabilization, even if forces attempt to back out the screw, the mechanism is already in place to prevent contact with the esophagus or other connective tissues.
Solution Approach 2:
The pop-rivet and expandable ring system serves as an intermediary between the screw and the bone plate, creating a mechanical barrier that prevents direct contact between the screw and surrounding tissues. This intermediary structure allows the plate to be positioned close to the esophagus for effective stabilization while preventing harmful contact.
3Reliability
If the screw assembly is designed with an expandable ring and pin mechanism to prevent backout, then screw backout is prevented, but the assembly complexity increases
Solution Approach 1:
The screw assembly is segmented into distinct functional components: the screw itself, the pop-rivet mechanism, and the expandable ring. This segmentation allows each component to perform its specific function independently while working together as a system. The pop-rivet is a separate element that engages with the expandable ring, creating a modular anti-backout mechanism that can be manufactured and assembled separately, reducing overall complexity.
Solution Approach 2:
The expandable ring mechanism is designed to be self-actuating through the insertion process itself. As the screw is inserted into the bone plate, the pop-rivet automatically engages with the expandable ring, and the mechanical properties of the materials cause the ring to expand and lock into position without requiring additional actuators or complex control systems. This self-service approach reduces device complexity while maintaining reliability.
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 effectively prevents screw back-out and reduces the risk of tissue irritation, allowing for secure stabilization of bone segments with a minimized profile, enhancing patient comfort and safety by eliminating protrusions and minimizing the risk of swallowing difficulties.
Implementation Method 1
The frictional force exerted by the increasing diameter of the pin is increased as the pin is pulled from the bore, until the frictional force resists a pull force greater than a yield or fracture force of the pin.
Data Source
AI summary
An orthopedic device includes an implant member with a thru-bore having an entry diameter, an intermediate diameter, and an exit diameter. According to one embodiment the intermediate diameter of the thru-bore is larger than both the entry diameter and the exit diameter. Additionally, the orthopedic device includes a screw assembly configured to be coupled to the thru-bore, including a thread portion and a selectively expandable head portion. The selectively expandable head portion includes both an expandable ring and a pull-lock pin configured to selectively expand the expandable ring as the pull-lock pin is pulled from said screw assembly.