Spinal Plate Eccentric Recess Compression Locking
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Solution Overview
Problem
Existing spinal plate fixation systems face challenges with screw back-out due to loosening, leading to potential dislodgement and instability, as current back-out prevention mechanisms do not adequately lock screws in their trajectories, and often require complex components that increase the size of the spinal plate and obscure visualization of vertebrae.
Innovation Solution
A spinal plate assembly featuring a plate with an eccentric recess and a cap that rotates to compress the screw head through its center, providing a secure locking mechanism that prevents screw back-out by engaging the screw head within the plate's opening, thereby stabilizing the screw trajectory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple back-out prevention mechanisms are used, then screw dislodgement is prevented, but device complexity increases and visualization of vertebrae is blocked
Solution Approach 1:
The cap integrates multiple functions into a single component: it provides compression locking through rotational engagement, prevents screw back-out through trajectory restriction, and maintains a low profile for vertebrae visualization. This merging eliminates the need for separate locking mechanisms and retaining structures, resolving the contradiction between reliability and device complexity.
Solution Approach 2:
The cap serves multiple purposes simultaneously: it compresses the screw head into the opening for rigid fixation, locks the screw in its trajectory to prevent back-out, and maintains a compact design that does not obstruct visualization. This multi-functionality achieves reliable screw fixation without requiring additional specialized components.
2Reliability
If rigid fixation is achieved through compression locking, then screw back-out is prevented, but the locking mechanism becomes complex
Solution Approach 1:
The cap transitions from a static component to a dynamic locking mechanism through rotational engagement. The cap is rotated relative to the recess to engage compression ramps that compress the screw head into the opening, providing active compression locking rather than passive mechanical constraints. This dynamic approach achieves reliable locking with a simple rotational motion.
Solution Approach 2:
The compression ramps utilize curved surfaces that guide and compress the screw head into the opening through rotational motion. The curved geometry of the ramps transforms rotational movement into compressive force, achieving reliable locking through a simple curved surface interaction rather than complex mechanical linkages.
3Strength
If screw head compression is applied through the center, then rigid fixation is achieved, but the locking mechanism size increases
Solution Approach 1:
The cap is received within the recess of the spinal plate, with the compression ramps nested within the cap structure. The screw head is compressed within the confines of the opening, and the entire locking mechanism is contained within the profile of the spinal plate. This nesting achieves center compression for rigid fixation without increasing the overall assembly size.
Solution Approach 2:
The compression locking is achieved through rotational engagement in a different dimension rather than through increased linear dimensions. The cap rotates relative to the recess to engage the compression ramps, transforming rotational motion into compressive force. This dimensional approach achieves strong fixation without increasing the plate's linear size or profile.
Data Source
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AI summary
A spinal plate assembly includes a screw (400), spinal plate (100) and cap (500). A head of the screw includes a portion of a first sphere that has a first center and a portion of a second sphere that has a second center approximately concentric with the first center. A body of the screw extends from the first sphere. The spinal plate includes an opening through the spinal plate and an associated recess in the spinal plate that is eccentric with the opening. The cap includes an alignment opening and is configured to be rotationally engaged in the recess between a first rotational configuration and a second rotational configuration. In the first rotational configuration, the body threads into a vertebra in a selected trajectory through the alignment opening and the opening in the spinal plate and the head engages at least a portion of the opening in the selected trajectory. In the second rotational configuration, the cap compresses the second sphere into the first sphere approximately through its center such that the head is compressed into the engaged portion of the opening.