Coordination of Reaching and Grasping in Prosthetic and Normal Limbs

Abstract

An experienced user of a body powered voluntary-close upper extremity prosthesis was studied while tending to the task of grasping a vertical cylindrical object. Trials of repeated grasps were carried out under three different speeds of action. Similar trials were run using the subject’s normal right hand. Findings for the normal hand are consistent with previous studies by Fraser & Wing (1981) and Wing & Fraser (1983) in that the thumb tended to deviate significantly less from a straight line trajectory to the target than did the index finger. In the prosthetic hand, the moveable “thumb” maintained a straight line course toward the target while the fixed portion of the prehensor was moved normal to the trajectory in a manner which accounted for change in the aperture. Maximum aperture was greatest for the fast grasp in both prosthetic and normal hands. Other findings show significantly greater variability in most measures of the normal hand grasp compared to the prosthetic grasp. In general, the findings suggest multiple, but less variable, temporal patterns of coordination between transport and manipulation in the prosthetic compared to the normal hand.