Lower limb active exoskeletons, exosuits, assistive devices and specifications: a scoping review

Powered lower limb exoskeletons were introduced to improve rehabilitation by increasing the quantity and quality of the therapy that a user receives. Fundamental principles targeting neuroplasticity, the driver of recovery, are delivered with exoskeletons, yet their use is not substitute for conventional rehabilitation. To deliver effective rehabilitation, exoskeletons must align with the needs of users. When devices reportedly achieve the same thing, how can one know which approach is best? Here we review 467 lower limb devices with the goal of discovering the breadth of the specification of devices and the implications these specifications have for users. Using a scoping search strategy, we reviewed exoskeletons and assistive devices looking at device type, usability, performance and specification. Only devices that fixate to the lower limbs and actively transmit forces/torques to at least one anatomic joint were considered. Like specifications were grouped and reported, and used as the basis for discussion, drawing on relevant literature in each case. Stationary devices are unlikely to ever be used in the home. To improve the uptake of ambulating devices outside the clinic, there should be renewed focus on degrees of freedom, bi- or uni-latera application, mass, donning/doffing and the control of devices. Unilateral conditions are still being treated with bilaterial devices, and providing passive/active non-sagittal (Degrees of Freedom) DOFs need to be carefully considered with respect to environmental negotiation, task variability, and device mass. Heavier devices are unlikely to be self-donned, and donning quickly may increase the time someone is engaged in their therapy and improve dosage. Control is central to usability and incorporating user intention is critical to boosting engagement and usage outcomes. When a patient can become a passenger in rehabilitation, this delivers poor outcomes, and we need to revisit the control systems and triggers so that they take meaningful and task related input from users. The exoskeleton field is relatively young and still full of promise. Improvements in rehabilitation outcomes will be delivered through properly accommodating the needs of patients and clinics, and improving usability by providing cheaper devices that can realistically be used at home and provide meaningful and engaging methods of control.