Wrist-Driven Flexor Hinge Orthosis Using Inversion and Segmentation
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Solution Overview
Problem
Current flexor hinge orthoses for individuals with tetraplegic spinal cord injury are complex, bulky, and require extensive technical support, with limited understanding of their biomechanical properties due to outdated studies and lack of biomechanical analysis.
Innovation Solution
A wrist-driven flexor hinge orthosis with a mechanical operating model that includes a forearm frame, rotatable frames for the wrist and palmar, an actuating lever, and a torsion spring to enhance hand function by converting wrist extension into finger flexion, providing a three-point prehension grasp.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a wrist-driven flexor hinge orthosis is used to restore hand function in tetraplegic SCI patients, then functional tenodesis grasp is achieved, but the device complexity and bulkiness increase
Solution Approach 1:
The orthosis is divided into three main components (finger, palmar, and forearm sections) that are hinged at anatomical axes. Each section can be independently adjusted and fitted, allowing the complex function to be distributed across modular segments rather than a single monolithic structure.
Solution Approach 2:
The orthosis inverts the natural muscle action by using wrist extension (by paralyzed or weak extensors) to create finger flexion through the tenodesis effect. Instead of directly activating flexor muscles, the system uses the opposing wrist extensor action to passively close the fingers, achieving grasp function through reverse biomechanics.
2Reliability
If external power sources like CO2 gas or electric motors are used to activate the orthosis, then grasp function is restored, but the device becomes bulkier and requires more technical support
Solution Approach 1:
The orthosis utilizes the patient's own residual wrist extensor muscles as the power source. By harnessing the active wrist extension capability that remains in C6-C7 tetraplegic patients, the system eliminates the need for external power sources like CO2 tanks or electric motors, making the device self-powered and significantly reducing its complexity.
3Reliability
If the orthosis uses a two-hinge parallelogram system to convert wrist extension to finger flexion, then three-point prehension is achieved, but torque transfer efficiency is reduced
Solution Approach 1:
The orthosis employs a dynamic two-hinge parallelogram mechanism that allows the finger section to move through a controlled arc of motion. The system dynamically adjusts the mechanical advantage throughout the range of motion, optimizing torque transfer at different positions rather than using a fixed rigid linkage, thereby improving overall efficiency while maintaining the three-point prehension function.
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
Significantly increases pinch force and correlates with wrist extensor strength, while improving biomechanical understanding and efficiency of hand function, particularly for those with cervical 6 or 7 tetraplegia, despite potential inefficiencies in torque transfer.
Implementation Method 1
an operating lever connected to the second frame to be rotatable about a third rotation axis that extends in a second lateral direction
Data Source
AI summary
A flexor hinge orthosis comprises a forearm frame; a first frame connected to the forearm frame to be rotatable about a first rotation axis that extends in a lateral direction; a second frame configured to be fixed to a palmar of a user and connected to the second frame to be rotatable about a second rotation axis that extends in an upward-and-downward direction; a thumb frame; an operating lever; an actuating lever; an actuating rod; and a finger frame.