Development and results of body-powered upper-limb prosthesis for children using rotational opposition mechanisms of 2 degrees of freedom

Abstract

This study describes the development of a body-powered upper-limb prosthesis for children with congenital digit defects that realizes pinching motions using their own residual digits and joints. Existing digit prostheses assume that the thumb remains intact. If there is no thumb, a conventional upper-limb prosthesis cannot sufficiently restore grasping function. The developed body-powered upper-limb prosthesis was designed to mechanically convert the flexion and rotation power of the residual digits into the power of the opposing prosthetic digit. This conversion enabled the reconstruction of opposing pinching motions at the fingertip. Consequently, this design enhanced the function of the residual digit in the absence of the thumb. In this study, we developed a body-powered upper-limb prosthesis applicable to a single residual digit or two parallel digits. The digit prosthesis, which includes the thumb, was designed to synchronize its movement with the motion of the metacarpophalangeal (MP) joint of the residual digit. The prosthesis joints enable two degree-of-freedom (DOF) motions: flexion/extension and adduction/abduction. The digit opposing the thumb can be selected through this joint by the adduction and abduction rotation movements of the residual digit. The mechanism performance was evaluated using tensile tests, which confirmed that the force applied to the residual digit was linearly transmitted and exerted as a pinch force on the prosthesis. This feature allows for a more intuitive use by the user. The evaluation of its application in children with congenital digit defects revealed that expanding the palm allows the user to throw and catch a ball and use scissors in daily life.

Keywords

• body-powered upper-limb prosthesis
• congenital digit defect
• rotational opposition mechanisms