Cervical Plate Screw Locking via Cam Dynamics
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Solution Overview
Problem
Spinal fixation devices face issues such as screw loosening due to unwanted rotation and axial movement, leading to instability and complications in bone fusion and stabilization procedures.
Innovation Solution
A cervical plate fusion system with a resilient retaining member that includes projections fitting within cavities in the plate, preventing screw backout by deflecting and snapping back to intercept the screw, and a toothed wheel mechanism that allows clockwise rotation while preventing counter-rotation, ensuring secure fixation without the need for welding or additional fixtures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional fixation devices are used, then bone alignment and stabilization can be achieved, but screw loosening occurs due to unwanted rotation and axial movement under repetitive loading
Solution Approach 1:
The patent employs a dynamic locking mechanism where the screw head includes a cam surface that interacts with a cam follower on the plate. As the screw is tightened, the cam surface converts rotational motion into lateral movement of the cam follower, which then engages with a retention feature to prevent backout. This dynamic mechanism actively prevents screw loosening under repetitive loading rather than relying on static friction alone.
Solution Approach 2:
The patent introduces a cam follower as an intermediary element between the screw head and the plate. This cam follower translates the cam surface geometry into a locking action that prevents both rotation and axial movement. The intermediary mechanism ensures that the screw remains securely fixed by converting simple screw tightening into a positive mechanical lock.
2Ease of operation
If fixation devices are subjected to repetitive loads from patient movements, then normal physiological function is maintained, but screw loosening and device instability occur
Solution Approach 1:
The dynamic cam-based locking mechanism is designed to maintain its locking force under varying load conditions. The cam surface geometry ensures that as loads are applied during patient movement, the cam follower remains engaged with the retention feature, preventing screw backout. The mechanism adapts to loading conditions while maintaining fixation stability.
Solution Approach 2:
The patent implements preliminary anti-action by designing the cam mechanism to preemptively counteract the loosening forces that occur during patient movement. The cam follower is positioned and shaped to engage the retention feature before significant loosening can occur, preventing the harmful effect of screw backout before it compromises device longevity.
3Reliability
If robust fixation systems are implemented to prevent screw loosening, then fixation reliability improves, but device complexity increases
Solution Approach 1:
The patent merges the locking function directly into the screw-plate interface by integrating the cam surface on the screw head with the cam follower and retention feature on the plate. This integration eliminates the need for separate locking mechanisms or additional fixtures, achieving robust fixation while minimizing device complexity. The locking action is inherent to the basic screw tightening operation.
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 system effectively prevents screw loosening and instability, enhancing the longevity and success of bone fusion by providing robust fixation and reducing the risk of complications associated with spinal fixation devices.
Implementation Method 1
a resilient retaining member that includes projections fitting within cavities in the plate, preventing screw backout by deflecting and snapping back to intercept the screw
Implementation Method 2
a toothed wheel mechanism that allows clockwise rotation while preventing counter-rotation
Data Source
AI summary
An embodiment of the invention provides for a system, such as a cervical plate fusion system, that has mechanisms for preventing bone anchors (e.g., screws, pins, and the like) from backing out of the plate. The system prevents both counter-rotation of the screw and axial backing out of the screw. Other embodiments are described herein.