Development of an Efficient Soft Hand Orthosis Optimized for Patients Post-Stroke

Abstract

Most of the patients post-stroke experience clenched hand deformity due to hypertonic flexor muscles caused by spasticity and weakness of extensor muscles. Since recovery of the motor function through rehabilitation has a limit, more than half of patients in the chronic stage still could not use their affected hand in activities of daily living(ADL), requiring assistance. Many orthoses have developed for assistance. Passive devices mainly focus on passively assisting hand opening by placing springs along dorsal side which are connected to fingertips and does not assist grasping. Active devices assist flexion and extension by using cable actuated by motors, but they tend to have large actuating module limiting the portability. In this study, we developed a 3D printed soft hand orthosis that passively assist opening by placing structure on the palmer aspect and actively assist closing by applying twisted string actuation that allow enlarged force with compact design. We optimized the thickness profile of the orthosis based on the patient’s metacarpophalangeal and proximal interphalangeal joint stiffness to open the hand and to minimize the actuation force for conducting pinching. The proposed orthosis is expected to help the patients to conduct bimanual activities in daily living.