The Effect of the Poly-Articulated Prosthetic Hand on Shoulder and Trunk Compensatory Movements during Manipulation and Grasp Tasks

Conventional myoelectric prosthetic hands only offer a basic tri-digital pinch. Transradial amputees need to compensate for this lack of function with altered kinematics at the shoulder and trunk that might expose them to an increased risk of musculoskeletal injuries. A poly-articulated prosthetic hand may reduce the physical compensatory movements and close the gap between the sound and the prosthetic side. Six male transradial amputees completed four standardized reach-and-grasp activities with their tri-digital, poly-articulated and sound side hands. Trunk, shoulder girdle, scapula and humerus kinematics were measured with an optoelectronic system. Differences between hands were analyzed in terms of the amplitude of motion, the duration of the altered kinematics over the motion cycle, peak-to-peak amplitude and time to complete the activity. An overall score was defined, which assigned three points when the kinematics of a joint angle was altered for over 41% of the motion cycle, two points between 11 divided by 40% and one point between 1 divided by 10%; thus, a lower score indicates less variation from normal kinematics. Despite no changes in times, tri-digital vs. sound hand scored 93 points, tri-digital vs. poly-articulated hands scored 49 and poly-articulated vs. sound hand scored 28, supporting the hypotheses of the poly-articulated hand positively affects shoulder and trunk kinematics.