Investigating the orthotic effect of a passive gravity-compensated exoskeletal device on upper-limb function in...

Multiple Sclerosis (MS) is a neurodegenerative disorder causing lower and upper-limb (UL) impairments and significantly affecting independence. Current assistive technologies for UL rehabilitation in People with MS (PwMS) rely on actuated robotic systems, which present high costs and complexity. Passive gravity-compensated exoskeletons represent a promising alternative; however, their functional benefits remain underexplored. This study aimed to redesign and evaluate the orthotic effect of a passive gravity-compensated exoskeleton device in supporting upper-limb function in PwMS.

This pilot cross-sectional study presents two phases: (I) redesigning an existing passive exoskeleton to improve usability and adaptability; (II) evaluating the orthotic effect and usability of the redesigned exoskeleton in a cohort of PwMS. Functional performance was assessed using the Action Research Arm Test (ARAT) and a modified Box and Block Test (mBBT) under Exoskeleton Supported and Exoskeleton Unsupported conditions. Kinematic parameters were extracted from three instrumented ARAT items, and usability was assessed with the System Usability Scale (SUS).

Phase I led to an iterative refinement of the exoskeleton, incorporating feedback from three PwMS and two therapists. In Phase II, thirteen PwMS (age: 59 [55-69] years; 10 males; EDSS: 7.5 [6.5-8.0] points) with different UL disabilities were recruited. Four participants with severe impairments increased the UL movement (orthotic effect) by 35.8% [29.0%-41.9%] and 24.1% [14.9%-33.3%] in the vertical and anteroposterior direction, with 8 [6.5-9.25] points improvements in the overall ARAT. Conversely, three individuals with mild UL disability needed 2.63 [2.17-3.45] seconds more to complete the instrumented ARAT items increasing the Jerk Index by 0.53[0.51-0.68]. The overall ARAT decreased by 7 [6-8] points and they transported 10[9-18] blocks less in the mBBT. The remaining participants with an FSS > 5.5 points, transported 9.5 [8-11.25] blocks more in the mBBT. The median SUS score was 70[62.5-70].

Collaboration between therapists and engineers was key in refining the exoskeleton during phase I. Phase II results supported its positive orthotic effect for PwMS, particularly for those with moderate to severe UL impairments and fatigue. However, for individuals with mild deficits, the device may alter movement dynamics, affecting execution quality. Future improvements should focus on reducing bulk for clinical use. Additionally, studies on larger populations are needed to validate these findings.