The biomechanics of control in upper-extremity prostheses.

1 Professor of Engineering, University of California, Los Angeles; member, Advisory Committee on Artificial Limbs, National Research Council, and of the Technical Committee on Prosthetics, ACAL, NRC. In the rehabilitation of the upper-extremity amputee, structural replacement by prosthetic arm and hand is an obvious requirement, and it poses a comparatively easy task; functional replacement by remote control and by substitute mechanical apparatus is more elusive and hence infinitely harder. For the purposes of functional utility, remaining movements of upper arm, shoulder, and torso must be harnessed, and use must be made of a variety of mechanical devices which amplify remaining resources by alternators, springs, locks, and switching arrangements. The facility of control attained through this apparatus is the key to its ultimate value. The future of upper-extremity prosthetics depends upon an ever-increasing understanding of the mechanics of the human body by all who minister to the amputee—prosthetist, surgeon, and therapist alike. It must always be stressed that the final goal is an amputee who can function. Too often there is a tendency to put undue faith in the marvels of mechanism alone, when in fact it is the man-machine combination that determines performance. It is in this broad frame of reference that the biomechanical basis of upper-extremity control must be approached.