  We propose a dual-cable method of stabilizing the thumb in the context of a
hand orthosis designed for individuals with upper extremity hemiparesis after
stroke. This cable network adds opposition/reposition capabilities to the
thumb, and increases the likelihood of forming a hand pose that can
successfully manipulate objects. In addition to a passive-thumb version (where
both cables are of fixed length), our approach also allows for a
single-actuator active-thumb version (where the extension cable is actuated
while the abductor remains passive), which allows a range of motion intended to
facilitate creating and maintaining grasps. We performed experiments with five
chronic stroke survivors consisting of unimanual resistive-pull tasks and
bimanual twisting tasks with simulated real-world objects; these explored the
effects of thumb assistance on grasp stability and functional range of motion.
Our results show that both active- and passive-thumb versions achieved similar
performance in terms of improving grasp force generation over a no-device
baseline, but active thumb stabilization enabled users to maintain grasps for
longer durations.
