A comparison of the grip force distribution in natural hands and in prosthetic hands.
PURPOSE: The aim of this study is to analyse the grip force distribution for different prosthetic hand designs and the human hand fulfilling a functional task. METHOD: A cylindrical object is held with a power grasp and the contact forces are measured at 20 defined positions. The distributions of contact forces in standard electric prostheses, in a experimental prosthesis with an adaptive grasp, and in human hands as a reference are analysed and compared. Additionally, the joint torques are calculated and compared. RESULTS: Contact forces of up to 24.7 N are applied by the middle and distal phalanges of the index finger, middle finger, and thumb of standard prosthetic hands, whereas forces of up to 3.8 N are measured for human hands. The maximum contact forces measured in a prosthetic hand with an adaptive grasp are 4.7 N. The joint torques of human hands and the adaptive prosthesis are comparable. CONCLUSIONS: The analysis of grip force distribution is proposed as an additional parameter to rate the performance of different prosthetic hand designs.