Bone Screw Ultrasonic Cement Augmentation
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Solution Overview
Problem
Existing bone fracture fixation systems using bone screws with flow cavities for cement augmentation suffer from unreliable and uneven cement distribution due to variable manual pressure application.
Innovation Solution
A bone screw design with a dual-diameter axial bore and transverse passageways, combined with a polymer pin and metal insert, where the polymer pin is pressurized and vibrated to fluidize and distribute cement evenly within the bone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If manual compression force is applied to jet fixation cement into the bone screw, then the cement can be introduced into the bone, but the pressure varies and results in unreliable and uneven cement distribution
Solution Approach 1:
The patent replaces manual mechanical compression with ultrasonic vibration. The ultrasonic device generates high-frequency vibrations that fluidize the cement and facilitate its introduction into the bone screw through the axial bore, eliminating the need for manual compression while ensuring uniform pressure distribution and consistent cement placement.
Solution Approach 2:
The patent changes the physical state of the cement from a semi-solid paste to a fluidized state through ultrasonic vibration. This parameter change allows the cement to be introduced more reliably and evenly into the bone screw, as the vibration reduces viscosity and creates consistent flow characteristics.
2Device complexity
If a single-diameter axial bore is used in the bone screw, then the structure is simple, but the cement distribution is unreliable and uneven
Solution Approach 1:
The patent segments the axial bore into two distinct diameter portions: a first bore portion with a larger diameter and a second bore portion with a smaller diameter. This segmentation creates a stepped configuration that facilitates uniform cement distribution by controlling the flow path and pressure distribution throughout the cement introduction process.
Solution Approach 2:
The patent applies local quality by creating different bore diameters at different locations along the axial bore. The larger first bore portion allows for initial cement intake, while the smaller second bore portion ensures controlled delivery into the bone, improving reliability without significantly increasing overall device complexity.
3Device complexity
If polymer pin is inserted without metal insert support, then the insertion is simpler, but the polymer pin cannot be effectively pressurized and vibrated to fluidize
Solution Approach 1:
The patent introduces a metal insert as an intermediary component between the polymer pin and the bone screw. The metal insert serves as a support structure that enables effective pressurization and vibration of the polymer pin, facilitating fluidization while maintaining a relatively simple overall insertion assembly.
Solution Approach 2:
The patent combines polymer and metal materials in a composite insertion assembly. The polymer pin provides the material for bone augmentation, while the metal insert provides structural support for pressurization and vibration, creating a synergistic composite system that achieves both material delivery and fluidization.
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
Ensures reliable and even augmentation of the bone screw within the bone, improving the consistency and effectiveness of the fixation process.
Implementation Method 1
pressuring and vibrating the polymer pin, wherein the polymer pin is supported by the metal insert which is in turn supported by a step in the diameter in the through bore, resulting in the polymer pin being fluidized at its tip
Data Source
AI summary
A device and method for fixation of bone fractures has a bone screw comprising a shank with a threaded end portion, on the outer surface. The screw has a through bore with two bore portions differing in diameter. A step in the diameter is formed between these bore portions and is located within the end of the screw having the thread. This step in diameter can support a metal insert which in turn supports a polymer pin when the latter if pressurized with a sonotrode in the bone screw. Together with an applied ultrasonic vibration the pressure fluidizes the polymer pin and presses the material through holes configured in the wall of the bone screw and into surrounding bone.