A 2-Axis Robotic Mirror Therapy System to Enhance Proprioception and Functional Recovery of Hemiplegic Arms in Patients with Stroke

Abstract

Introduction: Mirror therapy has been performed as an effective occupational therapy in a clinical setting for functional recovery of a hemiplegic arm after stroke. It is conducted by eliciting a visual illusion through the use of a mirror as if the hemiplegic arm is moving in real-time while moving the healthy arm. It can facilitate brain neuroplasticity through activation of the sensorimotor cortex. However, conventional mirror therapy has a critical limitation in that the hemiplegic arm is not actually moving. Methods: We developed a real-time 2-axis mirror robot system as a simple add-on module for conventional mirror therapy using a closed feedback mechanism, which allows for real-time movement of the hemiplegic arm. This is the first attempt that combined a robot with a real mirror for facilitation of proprioception followed by motor recovery. We used three attitude and heading reference system sensors, two brushless DC motors for elbow and wrist joints, and exoskeletal frames. Results: Motion synchronicity between the motors in the hemiplegic arm and the AHRS sensors in the healthy arm was validated. A study with six healthy subjects showed that robotic mirror therapy was safe and feasible. We further selected useful tasks for activities of daily living training through feedback from six rehabilitation doctors. Two chronic stroke patients showed improvement in the Fugl-Meyer assessment scale and elbow flexor spasticity, proprioception and hemispatial neglect after a 2-week application of the mirror robot system. The enhancement of proprioceptive input can be explained by the functional MRI results. The results revealed that both the lower part of the superior parietal lobule and the premotor cortex (PMC) were activated during the passive range of motion (ROM) exercise, whereas the PMC was mainly activated during the active ROM exercise. Conclusions: Robotic mirror therapy could enhance proprioceptive stimulus to the sensory cortex, which is considered to be very important in neuroplasticity and functional recovery of hemiplegic arms. The mirror robot system presented in this study can be easily developed and utilized effectively to advance occupational therapy.