Self-locking Bone Screw with Expandable Petals for Vertebral Settlement Control
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Solution Overview
Problem
Existing spinal fixation plate systems limit the control over vertebral settlement and screw translation, requiring multiple plate configurations and potentially impacting adjacent discs, which complicates surgical procedures and may lead to inadequate bone growth or stress shielding.
Innovation Solution
A self-locking bone screw system with elongated slots and interchangeable screw head configurations, allowing for customizable screw translation and resistance, enabling controlled vertebral settlement and stress distribution without the need for multiple plate designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If predefined hole and slot configurations are used in fixation plates, then screw translation and vertebral settlement are controlled, but the surgeon has very few options for controlling settlement at specific segments
Solution Approach 1:
The screw head is designed with expandable petals that can transition between expanded and retracted states, allowing the screw to dynamically change from a locked (fixed) state to an unlocked (translatable) state. This dynamic mechanism enables a single plate configuration to provide multiple settlement control options by simply changing the screw head state, eliminating the need for multiple predefined plate configurations.
Solution Approach 2:
The invention changes the parameter of screw head geometry through the expandable petals mechanism. By expanding or retracting the petals, the effective diameter and shape of the screw head changes, allowing it to either engage with or slide within the slot. This parameter change enables the same screw to provide different levels of translation resistance without requiring different plate designs.
2Stability of the object's composition
If circular holes are used to rigidly fix the plate to vertebrae, then screw translation is prevented, but settlement of adjacent segments cannot be controlled
Solution Approach 1:
The invention applies different functional qualities to different parts of the screw system. The screw shaft provides stable fixation to the vertebra, while the expandable petals on the screw head provide localized adaptability within the slot. This allows the plate to be rigidly fixed at some locations while allowing controlled settlement at others, by simply changing the petal state of individual screws.
Solution Approach 2:
The expandable petals transform the static screw head into a dynamic component that can change its engagement state with the slot. When expanded, the petals provide rigid fixation similar to circular holes; when retracted, they allow translation similar to slots. This dynamic capability resolves the contradiction between stable fixation and settlement control.
3Adaptability or versatility
If slots are used to allow screw translation, then vertebral settlement is permitted, but screw backout cannot be prevented
Solution Approach 1:
The expandable petals create a dynamic locking mechanism that engages with the slot walls during translation but can also prevent backout. When the screw is driven forward, the petals expand to engage the slot; when translation is complete, the petals maintain engagement to prevent the screw from backing out, while still allowing forward movement if needed.
Solution Approach 2:
The expandable petals act as an intermediary between the screw shaft and the slot. They provide the interface that allows translation in one direction while preventing movement in the opposite direction, effectively mediating between the need for screw mobility and the need for secure retention.
4Adaptability or versatility
If multiple plate configurations with different hole and slot arrangements are used, then control over settlement at different segments is improved, but the number of plate designs required increases
Solution Approach 1:
The expandable petal mechanism gives the screw head multiple functions: it can provide rigid fixation, allow controlled translation, and prevent backout, all within a single screw design. This universality means that a single plate configuration can be used for all segments, and the desired settlement control is achieved by adjusting the screw head state rather than selecting different plate designs.
Solution Approach 2:
Instead of having different plate configurations to control settlement, the invention inverts the approach by having a single plate configuration with screws that can change their own behavior. The settlement control is achieved by inverting the screw head state (expanded vs. retracted) rather than by inverting the plate design.
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 allows for precise control of vertebral settlement and screw translation at each segment, reducing the need for multiple plate configurations and minimizing impact on adjacent discs, while promoting bone growth and maintaining constant load on graft material.
Implementation Method 1
The spring is moveable in the recess between a first operative position, in which the shoulder on the spring abuts the lip in the passage to expand the petals radially outwardly
Implementation Method 2
The spring is moveable in the recess between a first operative position, in which the shoulder on the spring abuts the lip in the passage to expand the petals radially outwardly and lock them in the radially expanded position
Implementation Method 3
The at least one deformable extension engages the seat section in the chamber and creates a spring bias that holds the shoulder in abutment with the lip
Data Source
Figure 1
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Figure 4~5
AI summary
A fixation plate system includes a plate with elongated slots, and first and second anchors for attaching the plate to vertebrae. The first and second anchors have different head configurations that are selected by the surgeon to control how settlement occurs at each fused segment. The head of the first fastener is insertable in any of the slots and resists translation. The head of the second fastener is insertable in any of the slots in free sliding engagement to allow translation of the head in that slot. In one method of use, the surgeon selects a segment where settling needs to be limited, and uses the first fastener to fix the plate near the segment and limit settling at that segment. The first and second fasteners have a built-in spring that assists in securing the fasteners in the plate.