Adjustable Stiffness External Fixator for Bone Healing
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Solution Overview
Problem
Conventional external fixators face challenges in modulating stiffness to match the different biological phases of bone healing, leading to uncertain and uneven bone healing progress, increased infection risk due to pin placement through soft tissue, and high production costs, making them unsuitable for developing countries.
Innovation Solution
An external fixator with a clamshell frame design allowing bone pins to be inserted parallel or at an angle, with adjustable stiffness achieved by locking varying numbers of pins, using a high-performance, fiber-reinforced polymer frame and shims to modulate stiffness according to the healing phases, reducing production costs and infection risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional external fixators use multiple parallel bone pins, then the construct stability is improved, but the stiffness modulation capability deteriorates
Solution Approach 1:
The fixator system segments the stabilization function by allowing selective locking of individual bone pins or pin groups. The frame includes multiple clamping positions that can be independently secured, enabling the user to lock only the necessary pins for initial stability while leaving others unlocked for future stiffness modulation as bone healing progresses.
Solution Approach 2:
The fixator implements dynamic stiffness modulation through a time-dependent locking mechanism. Initially, only essential pins are locked to provide minimal stability, allowing physiological movement beneficial for early healing. As healing progresses, additional pins are locked to increase stiffness, adapting the construct to the evolving mechanical needs of the healing bone.
2Reliability
If bone pins are inserted through soft tissue to achieve fixation, then the fixation capability is improved, but the infection risk increases
Solution Approach 1:
The invention extracts the essential fixation function from traditional pin-through-skin methodology. By using percutaneous pin insertion with external clamping, the system removes pins from direct contact with skin and soft tissue, eliminating the primary infection pathway while maintaining adequate fixation capability through the external frame structure.
Solution Approach 2:
The external frame acts as an intermediary structure that provides fixation without requiring pins to traverse soft tissue. The frame clamps bones externally or through minimal incisions, mediating the fixation function while avoiding the soft tissue penetration that creates infection risk in conventional fixators.
3Adaptability or versatility
If conventional external fixators are designed with complex stiffness modulation mechanisms, then the adaptability to healing phases is improved, but the device complexity and production cost increase
Solution Approach 1:
The frame is segmented into multiple identical bar sections with standardized clamping positions. This modular segmentation allows stiffness modulation through simple selective locking of predefined positions rather than complex adjustable mechanisms, reducing device complexity while maintaining adaptability to different healing phases.
Solution Approach 2:
The system achieves stiffness modulation by changing the discrete parameter of locked pin positions rather than through continuous adjustment mechanisms. The frame provides multiple predetermined clamping positions along the bars, and stiffness is modulated by selecting which positions to lock, simplifying the device while enabling adaptation to healing progression.
4Strength
If all bone pins are locked simultaneously in conventional fixators, then the construct stiffness is maximized, but the ability to match different healing phases deteriorates
Solution Approach 1:
The fixator implements dynamic stiffness adjustment by allowing progressive locking of pins over time. Initially, only essential pins are locked to provide minimal stability that allows physiological movement beneficial for early healing. As healing progresses, additional pins are locked to increase stiffness, dynamically adapting to the evolving mechanical needs of the healing bone.
Solution Approach 2:
The frame is pre-configured with multiple clamping positions along the bars, preparing the system for progressive stiffness modulation. The predetermined positions allow users to lock pins in a staged manner, with preliminary locking of essential pins followed by additional locks as healing progresses, eliminating the need for complex real-time adjustment mechanisms.
Data Source
AI summary
The invention relates to an external fixator device and the method of its use in treating bone fractures and in orthopedic interventions, such as corrective osteotomies.