Anterior Cervical Plate Retention Ring and Locking Pin Mechanism
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing anterior cervical plates face issues with bone screws loosening or backing out due to anatomical forces and degeneration of vertebral bone quality, leading to instability and increased pain, particularly due to the proximity of the implant site to sensitive tissues like the esophagus.
Innovation Solution
A bone plate design featuring retention rings with deflectable tabs and a locking pin mechanism that securely fastens bone screws, preventing them from backing out by deflecting inwardly to cover the screw head and locking into place with a camming surface, providing audible and tactile feedback for proper seating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If bone screws are used to fasten the plate to the spine, then the plate can be securely attached to vertebral bodies, but the screws may vibrate, toggle out of position, or back out due to anatomical forces and bone quality degeneration
Solution Approach 1:
A retention ring is introduced as an intermediary component between the bone screw and the plate. The retention ring includes a retention flange that extends radially inwardly to contact and prevent backing out of the bone screw head, while the ring itself is received within the plate's through hole. This intermediary structure transfers the retention function from the screw-threaded connection to a mechanical barrier that actively prevents screw migration.
Solution Approach 2:
The retention flange is designed to proactively prevent screw backing out before it can occur. By positioning the flange to extend radially inwardly and contact the screw head, the structure creates a preliminary mechanical barrier that counteracts the forces that would otherwise cause the screw to vibrate, toggle, or back out during normal physiological loading.
2Reliability
If retention structures are added to prevent screw backing out, then screw retention is improved, but the plate bulk and complexity increase
Solution Approach 1:
The retention ring is nested within the existing through hole of the plate, utilizing the available space within the plate structure rather than adding external components. The ring fits inside the through hole aperture, and the retention flange extends inwardly into the hole to contact the screw head, creating a compact nested arrangement that prevents screw backing out without significantly increasing the overall plate footprint or external complexity.
Solution Approach 2:
The retention function is segmented into a separate retention ring component that can be independently manufactured and assembled into the plate. This modular approach allows the retention mechanism to be optimized separately from the plate structure itself, and enables the ring to be inserted through the existing aperture without requiring complex integrated designs.
3Object-affected harmful factors
If the plate is made low profile to avoid impinging on esophagus and sensitive tissue, then patient safety is improved, but the space for retention structures is reduced
Solution Approach 1:
The retention ring is nested within the existing through hole of the plate, utilizing the available space within the plate structure rather than adding external components. The ring fits inside the through hole aperture, and the retention flange extends inwardly into the hole to contact the screw head, creating a compact nested arrangement that prevents screw backing out without significantly increasing the overall plate footprint or external complexity.
Solution Approach 2:
The retention flange extends radially inwardly into the through hole, utilizing the radial dimension rather than increasing the plate's external footprint. By directing the retention structure inwardly along the screw insertion path, the design maintains a low external profile to avoid tissue impingement while still providing effective retention through the radial extension of the flange into the hole.
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 secures bone screws, reducing the risk of loosening and migration, enhancing stability and reducing pain by maintaining screw retention without adding bulk to the plate, allowing for easier implantation and bone growth promotion.
Implementation Method 1
The retention flange is resiliently deflectable and is deflectable radially inwardly to a deflected position in which the retention flange covers at least a portion of the bone screw
Implementation Method 2
The locking pin has at least one blocking surface and at least one camming surface. The locking pin is movable to selectively position the blocking surface and camming surface adjacent to the retention flange
Data Source
AI summary
An anterior cervical plate system is provided. The cervical plate includes a retention ring with a deflectable flange that is upwardly spaced from the top surface of the ring and configured to prevent an inserted bone fastener from backing out of the plate. The plate includes a locking pin having a camming surface and a blocking surface. When the camming surface is moved into position adjacent to the flange, the flange is free to flex out of the way of a bone screw being inserted into or removed from the plate. When the blocking surface is positioned adjacent to the flange, outward deflection of the flange is prevented to retain the bone screw inside the plate. The locking pin is rotated through a camming surface to bring a blocking surface against the flange deflecting the flange onto the head of the bone screw.