Defining the design requirements for an assistive powered hand exoskeleton

Background

How many motions have you made with your hands in the last 5 minutes without realizing it?  Do you have to think about reaching for that mug of coffee or glass of wine?  Most of us are fortunate to have full motion in our hands but this is not the case for everyone.  Every year, 15 million people worldwide suffer from a stroke, which often leads to partial upper limb paralysis. In addition, spinal cord injury and multiple neurological disorders can cause reduced hand function.  Thankfully, technology has improved to allow creation of a “hand exoskeleton”, which aids movement of the hand and digits, but it is important to consider the needs of the patient when designing these exoskeletons. In this preprint, Boser et. al. describe interviews with both clinicians and patients who have restricted hand movement to determine how to optimize development of hand exoskeletons.

 

Key findings

The study recruited clinicians and patients, through the Glenrose Rehabilitation Hospital in Canada, to participate in interviews and hand motion characterization.   The interviews focused on what the participants considered critical in a hand exoskeleton design, starting with the activities they predicted the exoskeleton being most useful. The clinicians felt that one of the most important aspects was being able to get the thumb into opposition, an impression shared by one patient. However, the most common activities desired by the patients were day to day actions, including writing/typing, carrying objects and preparation/consumption of food and drink. However, both the clinicians and patients did not envision the device being put on and removed multiple times throughout the day.  This is an important point for development, as the device would need to be waterproof and slight enough to fit under outer clothing, such as a coat.   Nevertheless, the ability to be able to remove the device independently was critical for the patients.  Questions regarding the size of the device elicited a range of responses, possibly due to the size and age of the individual, but most agreed that the device could not exceed 5 x 5 x 3 cm and it could weigh between 200 – 500g. Interestingly, noise was not a restrictive factor, although the patients did note that one of the motors was too loud to be used in public.

Although the clinicians and patients agreed on most points, their opinions differed regarding the best method for controlling the device.  Electromyography (EMG) uses tiny electrodes to detect nerve signals which can then be translated in motion, but the clinicians were concerned that using EMG to control the exoskeleton could be difficult to learn and result in unwanted movements.  Therefore, they suggested that using EMG in association with a button mechanism could be a potential solution.  However, the patients did not like the idea of a button-control mechanism and one stated they would not use the device if that was the case.

In addition to interviews, the study also assessed the range of motion and grip force of the restricted hand in three of the patients.  This showed that each participant had different hand characteristics, which indicates that there will not be a ‘one size fits all’ exoskeleton.  Every device would need to be tailored to the needs of the individual in order to most completely aid the patient and to prevent injury.

 

What I like about this preprint

As scientists, I often find we tend to consider the immediate question that we want to answer and not the bigger picture.  Yet it is essential to value the input of the patient, who is, after all, the end user. This study emphasized the importance of this as, although the patients and clinicians agreed on most points, they differed in the best way to control the device.  In terms of the hand exoskeleton, a failure to comprehend the aversions of the patient could lead to dissatisfaction of the device and result in the device being unwearable.

 

Questions for the authors

Have you had contact with developers of hand exoskeletons to put your results into practice?

Are there any ethical considerations for designing exoskeletons, e.g. could they be used for non-medical purposes?

 

References

https://www.world-stroke.org/component/content/article/16-forpatients/84-facts-and-figures-about-stroke

https://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/electromyography_92,p07656

 

 

 

doi: https://doi.org/10.1242/prelights.7092

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