Grasping after trans-radial amputation: Comparison of kinematics between amputated limbs equipped with myoelectric prosthesis and healthy limb

Abstract

After upper limb amputation, myoelectric prosthesis does not allow total functional recovery: grasping is executed with compensation motions. The objective of this study is to compare grasping's kinematics between prosthetic and healthy upper limb for myoelectric trans-radial prosthesis users. This prospective study includes 10 trans-radial amputees (9 traumatic, 1 agenesis) using a myoelectric prosthesis. The kinematics of the trunk and upper limb were quantified during a mono-manual grasping task successively with each upper limb. The task was to grasp and lift one of three objects (mug, cylinder, cone) placed on a table at a close or far distance (60 and 80% of arm length). Motion was measured at 30 Hz with Polhemus Fastrak sensors placed on the ipsilateral acromion, the forearm and the hand (or prosthesis). A geometrical model was used to compute shoulder elevation and elbow flexion-extension angles as well as the elbow 3D position. The amounts of displacements and rotations were calculated during two phases: reach-to-grasp and lift. Both sides were compared. The initial velocity of reaching (peak velocity and duration of acceleration) was similar on both sides. On the amputated side, the duration of reach-to-grasp was significantly prolonged with a more curved and less smooth trajectory. The amount of elbow extension during reach-to-grasp was smaller on the amputated side for the far target but greater for the close target. The contribution of the trunk for reaching was greater on the amputated side, particularly for far targets. During lifting, the elbow had a tendency to flex on the amputated side, with a smaller shoulder elevation than on the control side. There were some differences between objects (i.e. the mug was grasped at lower height after a shorter hand displacement). After trans-radial amputation, grasping phases are disturbed for time of realization and trajectories, in particular because of shoulder and elbow compensations on the amputated side. Such kinematic bases could allow to evaluate the influence on grasping of medical technologies (active pronation and supination, wrist flexion-extension, poly-digital hands…) and effects of rehabilitation on compensation motions.