Actuated Thumb Exoskeleton with Variable Axes of Rotation For Stroke Rehabilitation

Abstract

Chronic hand impairment is very common amongst stroke survivors. More specifically, movement of the thumb is highly restricted causing a major decrease in the functionality of the entire hand. The non-orthogonal, non-intersecting joint axes of the thumb and the many actuating muscles involved make it very difficult to understand the thumb, let alone provide techniques for rehabilitation. Thus, an exoskeleton that incorporates
the 5 anatomical Degrees of Freedom (DOF) of the thumb, both for actuation and measuring, was created in order to better understand motor control of the thumb, both in neurologically intact individuals and in stroke survivors. A mounting bracket was developed to affix the exoskeleton to a forearm brace. The exoskeleton was then tested to determine if it restricted movement. The movement space of the thumb was tracked both with
the thumb connected to the exoskeleton and for the free thumb using a Digital Motion Analysis System (DMAS). Neurologically intact subjects were able to cover an average of 72% of their normal thumb working space while wearing the exoskeleton. Most of the restriction occurred in the upper region of the workspace. Thus, the device seems to allow considerable freedom of movement of the thumb, particularly in the region of the workspace used for everyday tasks. Subjects remarked that thumb movement felt quite natural. Further research using this exoskeleton can be done to better understand the impairments that occur in the thumb and thus provide better insight into rehabilitation methods. For example, the use of a system including motors and flexible shafts to drive the joints of the exoskeleton which in turn drives the joints of the thumb might provide a successful mode of rehabilitation.