A Novel Robotic Technique for Evaluating Thumb Proprioception Predicts Hand Function After Stroke

The thumb has been called a "hallmark of humanity", and yet, in stroke rehabilitation, there are few studies that have examined thumb function and even fewer that have focused specifically on thumb sensory function. Here we describe a novel robotic technique to assess thumb proprioception and apply it to quantify the relationship between thumb proprioception and hand function after stroke. Based on a video game, "SomatoCircleJump" challenges participants to "jump" to radial targets presented on a screen as their thumb rotates around a circle, driven by a robot. Proprioceptive ability is quantified by radial jump error. We evaluated 35 individuals in the chronic phase post-stroke as part of a randomized controlled trial of robotic finger training. Compared to an agematched control group, people with stroke had significantly increased jump error ($\mathrm{p}<\text{0. 0 0 1}$). Thumb proprioception ability predicted hand function, as measured by the Box and Block Test score ($\rho=-0.44, \mathrm{p}=0.01$) and the Nine-Hole Peg Test time ($\rho= 0.49, \mathrm{p}=0.006$). Jump error was also correlated with an independent robotic measure of finger proprioception ($\rho=0.54, \mathrm{p}=0.003$). These results validate a novel robotic method to quantify thumb proprioception and indicate thumb proprioception deficits are common after stroke, co-occur with finger proprioception deficits, and relate to functional hand ability.