Development of a Low Cost, High Function 3D Printed Hand Prosthesis Using the Wrist Extension as Activator

Abstract

Objective: The authors have developed a prosthesis for hand amputees or malformations that can be activeted mecanically through the moviment of the wrist using the wrist tenodesis pattern and not the the wrist flexion - finger flexion model available. The majority of models for this level of amputation available for free download on the internet, are activated by the the flexion of the wrist, not respecting the physiological and natural sinergical movement of extension of the wrist and flexion of fingers. Method: The 3D prosthesis device is composed by a forearm suport, a hand component with the metacarpals and carpals and four or five fingers, depending on the level of deformity or amputation, polyester lines flex the fingers and elastic bands extend the fingers on a return force and an adjustable traction of the lines that flex the fingers. Results: The invertion of the moving pattern was possible thanks to a mechanism composed by two concentric arcs at the axis of the wrist joint, where one is positioned at the hand and the other on the forearm support. Through a rolling part attached to the hand arc, the finger flexion lines are pulled by the extension of the wrist. The curve ratio of the arcs was projected to use only 20º of extension to produce a displacement of up to 30mm of the flexion lines in relation to the forearm support. This displacement may vary, according to the need, to finger sizes and force needed to perform the activities. Conclusion: Prosthesis prototyped on 3D printers are becoming very known world wide. The possibility of having a low cost device that can improve function and is not meant to substitute the limb, but better, improve the possibilities of action and interaction with the ambient.