Variable Fastener Cam Mechanism for Spinal Plate Subsidence
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Solution Overview
Problem
Current surgical plate systems for treating back pain due to intervertebral disc degeneration or misalignment lack adequate screw-plate interfaces to accommodate subsidence, as they do not allow sufficient angulation or angular movement of screws relative to the plate, leading to inadequate stabilization and increased risk of graft displacement.
Innovation Solution
A surgical plate system with variable fasteners that can change their diameter to fit through holes in the plate, allowing for inward flexing during insertion and locking in place to prevent backout, while allowing articulation to accommodate subsidence, and a method for installing these fasteners using a specialized instrument to ensure secure fixation and dynamic adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If current plate systems use fixed screw-plate interfaces, then structural simplicity is maintained, but the system cannot accommodate subsidence and angular movement of screws relative to the plate
Solution Approach 1:
The fastener incorporates a cam mechanism that transitions from a locked state to an unlocked state, enabling the head to rotate relative to the plate body. This dynamic feature allows the screw-plate interface to adapt to subsidence while maintaining structural integrity during insertion and fixation.
Solution Approach 2:
The fastener is divided into distinct functional components: a head portion that interfaces with the plate, a cam mechanism for locking/unlocking, and a threaded shaft for bone engagement. This segmentation allows each component to perform its specific function independently, achieving adaptability without excessive overall complexity.
2Reliability
If the fastener head is designed to prevent backout by locking mechanism, then fixation reliability is improved, but the fastener cannot articulate to accommodate subsidence
Solution Approach 1:
The cam mechanism provides a dynamic locking system that can transition between locked and unlocked states. When locked, it prevents backout with high reliability; when unlocked, it allows the head to rotate and articulate to accommodate subsidence, thus resolving the contradiction between fixation reliability and adaptability.
Solution Approach 2:
The system changes the rotational parameter of the fastener head relative to the plate body. The cam mechanism controls this parameter, allowing the head to maintain a fixed angular position when locked (for reliability) or to change its angular position when unlocked (for adaptability to subsidence).
3Ease of operation
If the fastener allows inward flexing for insertion through the plate hole, then ease of installation is improved, but the fastener may back out after insertion
Solution Approach 1:
The fastener is designed to be inserted in a preliminary unlocked state where the head can flex inward to pass through the plate hole. After insertion, the cam mechanism is engaged to lock the head in place, preventing backout. This preliminary action sequence resolves the contradiction between ease of installation and prevention of backout.
Solution Approach 2:
The cam mechanism provides a dynamic state change from unlocked (during insertion for ease of operation) to locked (after insertion for reliability). This dynamic transition allows the fastener to flex inward during installation while preventing backout once secured.
4Stability of the object's composition
If the fastener head is compressed against inner side walls to prevent articulation, then stability is improved, but the fastener cannot dynamically accommodate subsidence
Solution Approach 1:
The cam mechanism enables a dynamic transition between two stable states: locked (where the head is compressed against inner side walls for stability) and unlocked (where the head can rotate to accommodate subsidence). This dynamic capability resolves the contradiction between stability and adaptability.
Solution Approach 2:
The system controls the rotational parameter of the fastener head. When the cam is locked, the rotational parameter is fixed, providing stability. When the cam is unlocked, the rotational parameter can change to accommodate subsidence, thus resolving the contradiction between stability and dynamic adjustment capability.
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 provides enhanced biomechanical stability, reduces graft displacement, and maintains alignment, thereby reducing the need for external bracing and minimizing pseudoarthrosis by allowing for dynamic adjustment to accommodate subsidence and load-sharing with the spine.
Implementation Method 1
the head, in a first configuration allows inward flexing to reduce a diameter of the head to allow the head to pass through an entrance opening of the through hole
Implementation Method 2
The variable fastener may include a variable cam that interacts with a protrusion on an inner surface of the head
Data Source
AI summary
A surgical plate system, components and methods of using are described. A surgical plate system includes a plate having an anterior surface, a posterior surface, a longitudinal axis, a transverse axis and a through hole passing through the anterior and posterior surfaces. A variable fastener is configured and dimensioned to connect to the plate, the variable fastener having a head and a shaft extending distally from the head. The head is configured to assume different proximal end diameters. The head, in a first configuration allows inward flexing to reduce a diameter of the head to allow the head to pass through an entrance opening of the through hole. In a second configuration, the head is prevented from flexing inwardly thereby preventing the head from backing out of the entrance opening, while allowing articulation of the head, within the through hole, relative to the plate.