Exoskeleton Robotics in Stroke Rehabilitation

Raymond TONG Kai-Yu, Chairman - Department of Biomedical Engineering, The Chinese University of Hong KongProfessor Raymond Kai-yu Tong has made great strides in developing a wide range of rehabilitation devices.

Background of Stroke Rehabilitation
The high prevalence of stroke puts growing pressure on the global healthcare system. Every year more than 15 million people have a stroke accident. The mortality rate of stroke decreased in the past two decades thanks to the technological advancement in medicine, but the absolute number of stroke survivors increased 84 percent, with a 33 million global stroke count in 2010. In 2017, India had a stroke incidence rate of up to 152 in every 100,000 persons per year, double the figures from a few decades ago. Every three out of four stroke cases occur in people aged 65 years or older. A higher burden of stroke is expected in the future because of population ageing. The disability rate tends to be high among the elderly because of the high morbidity rate caused by cerebrovascular disorders stroke, arthropathy, dementia and other senile diseases.

Long term disability is a major burden for stroke survivors. About 90 percent of stroke survivors will have different levels of muscle weakness and spasticity on one side of the body. These motor impairments have significant impact on their activity in daily living (ADL). On discharge from hospital, more than 60 percent of subacute stroke patients still cannot walk independently, whereas 20 percent remain non-ambulatory, and about 85 percent have impaired motor function in hands and arms. Many stroke survivors are dependent on care givers short handed with heavy workloads to provide manual assistance in selfcare and mobility. Healthcare professionals are looking for advanced technologies to facilitate stroke rehabilitation.

The Added Value of Exoskeleton Robots
Exoskeleton robots are wearable devices that can be equipped in parallel to the user’s limb to augment human performance, or to amplify residual joint movement of the impaired limb using powered actuators. These robots can be used to facilitate ADL of stroke patients as assistive devices, as well as therapeutic devices being used in combination with conventional physiotherapy. The application of robotic devices has several benefits that could lead to added value in stroke rehabilitation:

1.Repetitive & Assistive: The repeatable robotic output can increase training intensity and dosage without requiring more physical effort from the therapists.
2.Programmable and Customizable: Therapists can adjust the level of assistance andpowered assistance profile to customize it to the needs of individual patients.
3.Multi sensory: Integrated sensors and control algorithms can identify movement patterns and classify user intention, which enables active voluntary assistance.
4.Therapeutic Effect: Synchronized with residual joint movement with afferent sensory feedback that enhances Experience driven neuroplasticity for motor relearning.
5.Instrumentation: The computer can evaluate and report patients’performance and therapeutic progression using quantitative and objective measurements.

As a wearable device for assistive and rehabilitative purposes, device weight and portability are some of the important design considerations in exoskeleton robots

The R&D and Global Market forExoskeleton Robots
The research & development of rehabilitation oriented exoskeleton robots began proliferating about two decades ago, and has been growing exponentially from 2010 onwards. Over 300 studies related to wearable healthcare technology have been published in 2016 alone. Literature review up to now counted a non exhaustive list of at least 52 different versions of exoskeleton robots designed for upper limb assistance on shoulder, elbow, wrist, hand and more than 18 exoskeleton robots designed for lower limb assistance on hip, knee and ankle.

Translation of robotic research into clinical application requires investigators to follow evidence-based research practices. Large scale randomized controlled trials(RCT)have been conducted to evaluate the safety and effectiveness of robotic devices in stroke rehabilitation. Some notable examples of exoskeleton robots being tested in RCT are MIT Manus an end effect or type of upper limb trainer, and Lokomat a treadmill based body weight support gait trainer. The results of these clinical trials demonstrate the efficacy of exoskeleton robotics in stroke rehabilitation, including the significant improvements in hand and wrist motor recovery, and gait independency.

The global market for wearable devices has been evolving rapidly in recent years. Many exoskeleton robots have been commercialized into the market in the healthcare sector. The projected size of this global market is anticipated to increase significantly from $105.27 million in 2015 to $17.8 billion in 2021. With this trend, we can be confident that exoskeleton robotics will play a big role in the market for rehabilitation.

Current Trend of Exoskeleton Robotic Design
As a wearable device for assistive and rehabilitative purposes, device weight and portability are some of the important design considerations in exoskeleton robots. By today’s standards, stroke patients are unlikely to be willing to wear a heavy and bulky metal suit made up of a rigid metal frame for mobility and ADL unless they are the Iron Man. The large inertia from a heavy exoskeleton would increase energy expenditure and impede body joint movement.

Although rigid bodied exoskeletons are simple and robust, the robots actually transfer force/torque by bypassing the body joint they are assisting. Long term use of the rigid device may do more harm than good as the users may become dependent on the system. Therefore, the control system design tends to use an assist as needed approach, which provides power just sufficient to assist patients’ residual joint movement to encourage active participation.

Recently, researches on soft robotics have begun to gain popularity. The actuators of soft robots are often light weight and flexible, which would be ideal for exoskeleton at distal joints such as ankle and hand as they often require more rigorous movement and carry a larger moment of inertia. Many research groups use different kinds of power transmission systems, like Bowen cables and pneumatic and hydraulic actuators, to transfer power without the need of a rigid mounting frame. More research & development of soft exoskeleton robots is expected in the rehabilitation field as these designs could address many functional requirements of wearable devices, like the device weight and user compliance.