Abstract
Recently, extratheses, aka Supernumerary Robotic Limbs (SRLs), are emerging as a new trend in the field of assistive and rehabilitation devices. We proposed the SoftHand X, a system composed of an anthropomorphic soft hand extrathesis, with a gravity support boom and a control interface for the patient. In preliminary tests, the system exhibited a positive outlook toward assisting impaired people during daily life activities and fighting learned-non-use of the impaired arm. However, similar to many robot-aided therapies, the use of the system may induce side effects that can be detrimental and worsen patients' conditions. One of the most common is the onset of alternative grasping strategies and compensatory movements, which clinicians absolutely need to counter in physical therapy. Before embarking in systematic experimentation with the SoftHand X on patients, it is essential that the system is demonstrated not to lead to an increase of compensation habits. This paper provides a detailed description of the compensatory movements performed by healthy subjects using the SoftHand X. Eleven right-handed healthy subjects were involved within an experimental protocol in which kinematic data of the upper body and EMG signals of the arm were acquired. Each subject executed tasks with and without the robotic system, considering this last situation as reference of optimal behavior. A comparison between two different configurations of the robotic hand was performed to understand if this aspect may affect the compensatory movements. Results demonstrated that the use of the apparatus reduces the range of motion of the wrist, elbow and shoulder, while it increases the range of the trunk and head movements. On the other hand, EMG analysis indicated that muscle activation was very similar among all the conditions. Results obtained suggest that the system may be used as assistive device without causing an over-use of the arm joints, and opens the way to clinical trials with patients.
Highlights
One of the main symptoms of neuro-muscular diseases consists of partial or total loss of motor functions, such as walking or manipulating objects (Wade, 1992; Mozaffarian et al, 2015)
Considering the upper extremities, the functional reduction of the hand-arm may drastically compromise the independence of the subject, hampering the ability in performing many Activities of Daily Living (ADL) (Mondiale de la Santé and Organization, 2001)
From other assistive robotic systems (Wu et al, 2013; Nordin et al, 2014; Grimm et al, 2016), where variations on movement patterns are mainly due to the subject’s impairments, in supernumerary robotic hand such alteration can be introduced by the encumbrance of the additional robotic hand itself
Summary
One of the main symptoms of neuro-muscular diseases consists of partial or total loss of motor functions, such as walking or manipulating objects (Wade, 1992; Mozaffarian et al, 2015). Developed to improve the user’s ergonomics and capacity in industrial applications (Llorens-Bonilla et al, 2012; Parietti and Asada, 2017; Ciullo et al, 2018a), they consist of additional artificial limbs that can perform tasks in close coordination with the subject wearing them Their clinical use was pioneered by Hussain et al (2016) where an additional robotic finger (the Sixth finger) was used for compensating hand missing abilities in chronic stroke subjects. Some discussions and analysis have been already proposed to evaluate compensatory movements in post-stroke subjects (Cirstea and Levin, 2000; Roby-Brami et al, 2003; Michaelsen et al, 2004) These compensatory strategies most prominently involve the use of the trunk, the shoulder or proximal residual muscles capabilities to perform the requested tasks (Metzger et al, 2012; Hussaini et al, 2017). This study has been extended including transhumeral prosthesis and body-powered devices users (Metzger et al, 2012) confirming the presence of compensatory movement for the trunk and proximal upper limb
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