Quantifying loss of independent joint control in acute stroke with a robotic evaluation of reaching workspace

Early recovery after stroke is significant for slow emergence of volitional movement. Initial movements are constrained by stereotypical co-activation of muscle groups such as shoulder abductors and distal limb flexors resulting in the loss of independent joint control. The objective of this study was to utilize new quantitative methods to evaluate the emergence and progression of the loss of independent joint control in the acute phase of recovery from stroke. Fifteen participants have been followed a maximum range of 2 to 32 weeks post-stroke. Participants underwent weekly and monthly robotic evaluations of horizontal plane reaching workspace as a function of abduction loading (0%-200% of limb weight). The magnitude of loss of independent joint control, indicated by the rate of work area reduction as a function of abduction loading, was evident even as early as 2 weeks post-stroke. Group analysis indicated that individuals with mild stroke show immediate presence of the impairment with an exponential rate of recovery over time while individuals with severe stroke show persistent impairment. Early detection and quantification of reaching impairments, such as the loss of independent joint control, will allow clinicians to more efficiently identify patients who would benefit from impairment-based targeted interventions. For example, patients with severe loss of independent joint control will likely benefit from early administration of an intervention attempting to reduce abnormal shoulder abductor/distal limb flexor co-activations during reaching. The field of rehabilitation robotics has demonstrated such interventions to be promising in the chronic severe stroke population.