Background
An upper limb amputee currently has two choices for a body-powered prosthesis, a Voluntary Opening (VO) or Voluntary Closing (VC) hand prosthesis. Which type is best, depends on the task and the individual. Currently, there are no good options for VO and VC in one design.
Objectives
To design a proof-of-principle of a hand prosthesis and to validate the feasibility of the prosthesis. The hand prosthesis must have two different modes, the VO mode and the VC mode. Changing between these modes can be done without using the other hand..
Methods
First, a list of requirements and wishes was made, where cable forces are important because too much cable force can cause discomfort, fatigue or make the prosthesis difficult to control.
A new design was created and a prototype was built for user testing. SHAP was used as the outcome measure.
Results
The prototype allowed the user to change between VO and VC and SHAP showed promising Linear Index of Functionality (LIF) values. The calculated cable forces were mostly within the requirements. However, because the prototype of this design was produced with an FDM-printer, not all the tests could be done and the calculated forces could not be verified.
Conclusions
A prototype of a hybrid hand prosthesis with VO and VC modes showed promise, with positive test results. However, limitations in the prototype's construction hindered some tests. The calculated cable forces mostly met requirements, except for a slightly high pinch grip force. Further development is needed, and there are material and design recommendations. This concept demonstrates feasibility but requires more work to become a functional hand prosthesis.