Design Criteria for Hand Exoskeletons: Measurement of Forces Needed to Assist Finger Extension in Traumatic Brain Injury Patients

The development of powered hand orthoses and exoskeletons for treatment of chronic motor deficits due to stroke, traumatic brain injury, and cerebral palsy has been widely explored by the robotics engineering community. The conditions arising from these disorders take several forms and clinical descriptions of the various deficits are at times difficult to interpret for those with limited interaction with patients. With devices commonly designed and evaluated on their ability to aid hand closure, well-known extension deficits that are present among these patients typically receive only secondary consideration by robotic approaches. Quantitative characterization of these extension deficits in a manner that is easily translated into engineering design criteria would greatly benefit device design and evaluation. Here, we measure the externally applied torques required to assist extension of the index finger and thumb of three patients with increased flexor tone in the hand. The average torque required to fully extend a subject's index finger MCP joint ranged from 0.22 - 0.75 N·m and the thumb's MCP from 0.29 - 1.35 N·m. The highest torques were recorded when subjects were asked to volitionally extend their fingers, causing an increase in flexor tone requiring more assistance to overcome than when they were relaxed.