Clinically Relevant Biomedical Factors for Design & Development of Practical Upper Limb Exoskeleton Rehabilitation Robots

Abstract

Introduction: There has been rapid growth in both the development and clinical application of rehabilitation robots in the past decade. However, the goal of providing maximal task-specific repetition of the limb movements to facilitate neuroplasticity and functional recovery in neurorehabilitation, which is significantly superior to conventional rehabilitation therapies, has not yet been achieved. The aim of this study is to identify clinically relevant biomedical factors, distinguishable from simple biomechanical factors, for the design and development of practical but simple neurorehabilitation robots, focusing on exoskeleton-type robots.<br/> Methods: A demand survey was performed on 48 potential users with stroke or neuromuscular diseases to identify the patients practical needs, which may serve as a goal for rehabilitation therapy. As spasticity is a common problem when applying rehabilitation robots to patients with central nervous system disorders, biomechanical response to spasticity was evaluated in 20 chronic stroke patients with various grades of spasticity to characterize the spasticity induced resistance and to determine the minimal torque output required for motors in major robot joints. An inertial measurement unit (IMU) sensor based motion capture system was used to determine workspace and range of motion (ROM) for major upper extremity joints in ten healthy subjects, while performing the Action Research Arm Test (ARAT) and top ranked activities of daily living (ADLs) from the demand survey. The same evaluation method was applied to nine stroke patients with Brunnstrom stages ranging from 3 to 6 to identify the characteristics of patient movements and stroke recovery patterns. For user-intent driven control, an image-processing based robot control system was proposed and a prototype for a hand rehabilitation robot was developed. A usability study was performed with physicians, engineers, therapists, and stroke patients to evaluate the robots clinical feasibility.<br/> Results: In the demand survey, handling foods, dressing, and moving close items were highly necessary ADL functions for both exoskeleton and external robot arm types. Stroke patients demonstrated high demand for self-exercise with exoskeleton. The maximal resistance torques caused by low (modified Ashworth scale (MAS) 0, 1), intermediate (MAS 1+), and high (MAS 2 and 3) grade spasticity were 3.68 ± 2.42, 5.94 ± 2.55, and 8.25 ± 3.35 Nm for the elbow flexor (p < 0.001, between each grade) and 4.23 ± 1.75, 5.68 ± 1.96, and 5.44 ± 2.02 Nm for the wrist flexor (p < 0.001, for low versus intermediate, low versus high grade spasticity). In healthy subjects, the size of the workspace during the ARAT tasks was 0.53 m (x-axis, left-right) × 0.92 m (y-axis, front-back) × 0.89 m (z-axis, up-down) for the dominant hand. For ADL tasks, the workspace size was 0.71 m × 0.70 m × 0.86 m for the dominant hand which was significantly larger than the non-dominant hand (p ≤ 0.011). The ROM for major joints of the upper extremity during the ARAT tasks were 109.15 ± 18.82° (elbow flexion / extension), 105.23 ± 15.38° (forearm supination / pronation), 91.99 ± 20.98° (shoulder internal / external rotation), and 82.90 ± 22.52° (wrist dorsiflexion / volarflexion), whereas the corresponding ROM for the dominant side during the ADL tasks were 120.61 ± 23.64°, 128.09 ± 22.04°, 111.56 ± 31.88°, and 113.70 ± 18.26°, respectively. Of the parameters that showed significant differences in values between healthy subjects and patients and also significant correlation with clinical measures, the average amplitude of the forearm supination / pronation angle during the ARAT domain 4 tasks demonstrated the greatest decline in severely impaired patients compared to normal subjects (29.83%) and also largest difference between severely and mildly impaired patients (48.46%). For the usability test for the image processing based user-intent driven hand rehabilitation robot, the participants found the device interesting (5.7 ± 1.2), motivating (5.8 ± 0.9), and as having less possibility of injury or safety issues (6.1 ± 1.1)