Three-Strut Parallel Orthopedic Fixator for Fracture Reduction
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Solution Overview
Problem
Existing orthopedic external fixators face limitations in adjustable degrees of freedom, weight, manufacturing complexity, and interference with fluoroscopic imaging, particularly when attempting to reduce spatial fracture deformities.
Innovation Solution
A six-degree-of-freedom parallel external fixator comprising three struts and two fixation rings, with freely connectable struts featuring guide rails, lead screws, and spherical hinges, allowing for precise adjustment and reduced weight, minimizing interference with imaging and bone pin fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If six struts are used with circumferential symmetric configuration to achieve six DoFs, then fracture reduction capability is improved, but device weight increases and interferes with fluoroscopic imaging
Solution Approach 1:
The fixator is segmented into only three essential struts rather than six, with each strut equipped with independent driving joints that provide six degrees of freedom collectively. This segmentation reduces redundant components and overall weight while maintaining full fracture reduction capability through the coordinated action of the three struts.
Solution Approach 2:
The patent adopts an asymmetric three-strut configuration rather than the traditional symmetric six-strut arrangement. The struts are positioned at non-uniform intervals around the fixation rings, breaking the circumferential symmetry to minimize interference with fluoroscopic imaging while still achieving complete six-DoF adjustment capability through the driving joints on each strut.
2Ease of operation
If worm-and-gear kinematic pairs are used in each strut, then driving capability is improved, but manufacturing complexity and weight increase
Solution Approach 1:
The patent replaces the complex worm-and-gear mechanical system with a simpler direct driving mechanism using lead screws and sliding blocks. This substitution eliminates the need for intricate gear tooth edges and worm gears, significantly reducing manufacturing complexity and weight while maintaining effective driving capability through the lead screw-threaded hole connection that provides both actuation and positioning functions.
Solution Approach 2:
The invention changes the fundamental parameters of the driving mechanism from high-ratio gear transmission to direct lead screw translation. This parameter change simplifies the kinematic chain, reduces the number of moving parts, and eliminates complex manufacturing requirements for gear teeth while preserving the ability to provide controlled driving motion for fracture reduction.
3Manufacturing precision
If six struts are used to achieve six DoFs, then fracture reduction accuracy is improved, but interference with bone pin fixation and fluoroscopic imaging increases
Solution Approach 1:
The fixator structure is segmented into three struts with driving joints distributed along each strut, concentrating the six degrees of freedom in localized joints rather than requiring six separate struts. This segmentation reduces the overall spatial footprint and minimizes interference with bone pin fixation and fluoroscopic imaging while maintaining fracture reduction accuracy through the distributed driving capability.
Solution Approach 2:
The patent distributes the six degrees of freedom across three struts by adding driving capability in the longitudinal dimension of each strut through lead screws. This dimensional reorganization allows the system to achieve six-DoF accuracy with fewer struts, reducing radial interference with imaging and fixation while maintaining full adjustment capability through longitudinal translation of the driving joints.
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 solution enables effective six-DoF fracture reduction with a lighter weight, improved manufacturing simplicity, and reduced interference with fluoroscopic imaging, enhancing adjustment accuracy and practicality.
Implementation Method 1
a lead screw is provided in the first sliding groove of the guide rail, two ends of the lead screw are rotatably connected with connecting holes in lugs on two sides of the guide rail respectively, the lead screw is in threaded connection with the slider
Implementation Method 2
the head part of the first rotary connecting rod is rotatably connected with the slider through a first pin shaft, the first rotary connecting rod and the slider form a first revolute pair
Implementation Method 3
the other end of the sliding sleeve is rotatably connected with one end of a universal hinge with a cross shaft component through a second revolute pair such that one end of the universal hinge has one rotational DoF relative to the sliding sleeve; the universal hinge contains a cross shaft component such that the two ends of the universal hinge have two rotational DoFs therebetween
Data Source
AI summary
A freely-connectable three-strut parallel orthopedic external fixator including two fixation rings and three struts, connecting holes are circumferentially and uniformly distributed on the ring surfaces of each fixation ring, each strut is provided with two driving translational pairs, a revolute pair and a spherical pair. Two fixation rings are respectively fixedly connected with the bone segments of the fracture site by using medical metal bone pins; adjusting the driving translational pairs of the six struts can achieve six DoF relative movement of the two fixation rings, thereby achieving fracture reduction. The external fixator of the present invention realizes free connection between the two fixation rings, which facilitates fixator installment; number of struts is less than the existing external fixators.