Pedicle Screw Rod System with Degradable Stoppers for Dynamic Fixation
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Solution Overview
Problem
Current pedicle screw-rod systems lack the ability to gradually transition from rigid fixation to non-rigid fixation, leading to issues such as stress shielding, disuse osteoporosis, and the need for frequent surgical interventions to remove internal fixtures.
Innovation Solution
A pedicle screw-rod system that utilizes a degradable stopper made of biomaterials like magnesium metal/polylactic acid composite, allowing the system to transition from rigid to non-rigid fixation as the stopper degrades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rigid fixation is used with static pedicle screws, then fracture healing and intervertebral bony fusion are promoted, but stress shielding occurs leading to disuse osteoporosis of the spine
Solution Approach 1:
The patent employs a dynamic pedicle screw system where the screw body can rotate relative to the screw seat within a controlled angle range (0-2 times the design angle). This dynamic capability allows the fixation system to transition from rigid to non-rigid fixation over time, promoting bone healing initially while gradually allowing physiological movement to prevent stress shielding and disuse osteoporosis.
Solution Approach 2:
The patent changes the fixation parameter from static rigid fixation to dynamic fixation with variable movement amplitude. The dynamic screw allows the fixed segment to perform flexion-extension activities with controlled amplitude (0-2*∠), transforming the fixation state to prevent both excessive rigidity and complete instability.
2Reliability
If long-term rigid fixation is used, then fracture healing is maintained, but protection failure phenomena such as fatigue fracture or loosening of the internal fixture occur
Solution Approach 1:
The dynamic pedicle screw system transitions from rigid to non-rigid fixation, allowing the fixed segment to perform appropriate flexion-extension activities. This dynamic capability reduces stress concentration on the internal fixture, preventing fatigue fracture and loosening while maintaining fixation stability throughout the healing process.
3Adaptability or versatility
If dynamic screw with hinged connection is used, then flexion-extension activities are enabled, but the coaxial relationship between screw seat and screw body is destroyed causing excessive movement amplitude
Solution Approach 1:
The patent employs preliminary action by pre-setting the screw body and screw seat in a coaxial relationship before implantation. The dynamic connection mechanism is designed to maintain this coaxial alignment during flexion-extension movements, ensuring that the screw body and screw seat move synchronously within the controlled angle range without destroying their coaxial relationship.
Solution Approach 2:
The patent implements a dynamic connection between screw body and screw seat that allows controlled movement while maintaining coaxial relationship. The design ensures synchronous movement of screw body and screw seat during flexion-extension, limiting the movement amplitude to 0-2 times the design angle rather than allowing uncontrolled excessive movement.
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 achieves the goal of initial rigid fixation followed by non-rigid fixation, reducing the risk of stress shielding and osteoporosis, while also allowing for flexible adjustment of fixation strength based on the degradation rate of the stopper.
Implementation Method 1
A pedicle screw-rod system capable of gradually changing from rigid fixation to non-rigid fixation includes a pedicle screw, a connecting rod, and a screw plug. The screw body and the screw seat of the pedicle screw are flexibly connected by a flexible connecting part, and the flexible connecting part is also connected to a degradable stopper for preventing flexible parts from swinging each other. With gradual degradation of the degradable stopper, a fixation manner of the pedicle screw-rod system will be gradually converted from initial rigid fixation into non-rigid fixation.
Data Source
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AI summary
A pedicle screw-rod system capable of gradually changing from rigid fixation to non-rigid fixation is provided. The system includes a pedicle screw, a connecting rod (2), and a screw plug (1). The connecting rod (2) is used for connecting in series the pedicle screw fixed to adjacent vertebrae on the same side of a spine, and the screw plug (1) is used for locking the connecting rod (2) on the pedicle screw intersecting therewith. At least one of two structural members of the pedicle screw or the connecting rod (2) is connected by a flexible connecting part, and the flexible connecting part is also connected to degradable stoppers (3, 22, 3a, 3b, 3c, 3d) for preventing flexible parts from swinging with each other; and with gradual degradation of the degradable stoppers (3, 22, 3a, 3b, 3c, 3d), a fixation manner of the pedicle screw-rod system will be gradually converted from initial rigid fixation into non-rigid fixation. The system has a low notch, prevents disengagement of threads, can be opened in a neutral position, and can be randomly selected to perform, according to an intraoperative situation, one of the three fixation manners of rigid fixation, flexible fixation, or first rigid fixation and then automatic flexible fixation.