Use of a Novel Robotic Interface to Study Finger Motor Control E. G. CRUZ 1,2 and D. G. KAMPER 2,3 1 Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA; 2 Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA; and 3 Department of Biomedical Engineering, Illinois Institute of Technology, 314 Wishnick Hall, Chicago, IL 60616, USA (Received 22 May 2009; accepted 14 November 2009; published online 25 November 2009) Abstract—Stroke is the leading cause of permanent adult disability in the U.S., frequently resulting in chronic motor impairments. Rehabilitation of the upper limb, particularly the hand, is especially important as arm and hand deficits post-stroke limit the performance of activities of daily living and, subsequently, functional independence. Hand rehabili- tation is challenging due to the complexity of motor control of the hand. New instrumentation is needed to facilitate examination of the hand. Thus, a novel actuated exoskeleton for the index finger, the FingerBot, was developed to permit the study of finger kinetics and kinematics under a variety of conditions. Two such novel environments, one applying a spring-like extension torque proportional to angular dis- placement at each finger joint and another applying a constant extension torque at each joint, were compared in 10 stroke survivors with the FingerBot. Subjects attempted to reach targets located throughout the finger workspace. The constant extension torque assistance resulted in a greater workspace area (p < 0.02) and a larger active range of motion for the metacarpophalangeal joint (p < 0.01) than the spring-like assistance. Additionally, accuracy in terms of reaching the target was greater with the constant extension assistance as compared to no assistance. The FingerBot can be a valuable tool in assessing various hand rehabilitation paradigms following stroke. Keywords—Stroke, Hand rehabilitation, Motor control. INTRODUCTION Motor control of the hand is a complicated task. For the index finger alone, tendons from seven different muscles insert on the three phalanges. Each of these tendons crosses more than one joint, thereby influenc- ing joint torque production at multiple joints. Even relatively simple movements of the finger require coordinated activity from a number of muscles. 8 Thus, the study of motor control of the hand can be complex, especially following neuromuscular injury such as stroke. Of the roughly 425,000 individuals who survive a stroke in a given year, 21 50% will have some form of chronic impairment, 25 typically involving weakness of the hand. 21,27 The limited finger extension associated with hemiparesis greatly reduces the function of the hand in activities of daily living. 28 While a number of factors have been examined for contributions to impairment following stroke, 4,18,20 the mechanisms of this impairment have not been fully elucidated. Addi- tionally, the effects of different rehabilitation strategies, such as error augmentation, 19 guided-force training, 10 and passive assistance, 22 are not well understood. Instrumentation permitting quantified assessment of rehabilitation paradigms and of finger motor control under a variety of imposed conditions would thus be beneficial. Indeed, use of robots in the study of the upper extremity has greatly contributed to knowledge of motor control of the arm, both in stroke surviors 19 and in individuals without neurological impairment. 26 For simplicity, the apparatus could be designed to examine a single finger, with the assumption that results obtained for this digit would be representative of those expected in the other fingers due to the extensive neurophysiological coupling that exists across the digits. 14 The index finger is the most likely choice for the representative digit due to: its functional importance as the primary finger involved in tip and lateral grasps; its greater voluntary individuation of movement in comparison with its other fingers 14 ; and its accessibility. This system would necessarily require the ability to provide independent control or pertur- bations of each of the three finger joints. A number of devices have been developed which can actuate the digits of the hand. These devices include both commercial products, such as the CyberGrasp TM (VRLOGIC GmbH, Dieburg, Germany) and Amadeo Ò (Tyromotion GmbH, Graz, Germany), and research systems, such as the Rutgers Hand Master II, 9 HWARD, 24 a haptic interface, 16 and a cable-driven exoskeleton. 29 As these devices were developed with other criteria in mind, however, they do not provide Address correspondence to D. G. Kamper, Department of Bio- medical Engineering, Illinois Institute of Technology, 314 Wishnick Hall, Chicago, IL 60616, USA. Electronic mail: kamper@iit.edu Annals of Biomedical Engineering, Vol. 38, No. 2, February 2010 (Ó 2010) pp. 259–268 DOI: 10.1007/s10439-009-9845-4 0090-6964/10/0200-0259/0 Ó 2009 Biomedical Engineering Society 259