[Review] Principles of Efficiency and Safety Assessment in Using Exoskeletons for Patients with Lower Limb Paralyses – Full Text

In rehabilitation of patients who have lost their ability to move independently due to the paralysis of lower limbs, using exoskeletons is a perspective direction. In recent years a great number of robotic devices improving walking of people with lower paraparesis have been developed. However, their comparison is hindered since there are no standardized approaches to the assessment of their efficiency and safety. In this review, general principles of evaluating external robotic devices have been presented, and methods of determining safety and convenience of exoskeleton usage have been analyzed. Assessment of qualitative and quantitative parameters of exoskeleton-assisted walking has also been considered. The characteristic of the questionnaires, standard tests and biochemical investigations, which are used in approbation of exoskeletal devices in people with paraplegia has been presented. Possible ways of evaluating energy expenditure when moving in exoskeletons are shown. The need of elaborating a unified evaluation strategy of walking in exoskeletons has been substantiated.

 

Introduction. Bioengineering devices, enhancing functional capabilities of patients with pathology of the musculoskeletal apparatus, include, among others, exoskeletons, which are special constructions that are put on a man in the form of an external frame, reproduce the biomechanics of his movements, improve muscular power, and reduce metabolic expenditure for walking [1–7]. In rehabilitation medicine, the development of exoskeletons for patients who have lost the ability to ambulate due to paralyzation of the lower limbs, is the most grounded and perspective [8–15]. A sufficient number of models of robotic orthoses and exoskeletons enabling patients with lower paraplegia and paraparesis to stand up and sit down, walk along an even surface and ascend stairs [16–27]. Creation and improvement of such systems require assessment of their efficiency and safety. Nevertheless there are not so many publications on this topic. The majority of these works touch upon more simple robotic devices compared to skeletons [28–31] often using different metrical sets [32–34]. Assessing the efficiency of a new robotic device with functional electrostimulation for patients with lower limb paraparesis, Goldfarb et al. analyzed an average walking speed, heart rate (HR), arterial pressure (AP), gas exchange, variability of the angles in the pelvic and knee joints [30, 35]. An average walking speed and HR normalized relative to the walking speed served as criteria of evaluation of orthoses for people with paraplegia in the works of Nene, Harvey, Winchester et al. [36–39]. Ohta et al. assessed a robotic orthosis designed for patients with vertebral-cerebrospinal trauma (VCST) using walking speed, step length, amplitude of vertical and lateral displacement of the head in walking [16]. In some cases, in addition to the walking speed, the authors took into consideration the maximal distance the patient could travel without rest using the device [40–42], or the kinematics of motions in the knee or pelvic joints [43]. Kobetic et al. studied the efficiency of a robotic orthosis intended for restoration of the capacity of persons with paraparesis to standing, walking and ascending stairs by analyzing the kinematics of motions in the knee joint [9]. A short analysis of biomechanical parameters was presented also in the work of Jung et al.: the investigators performed a comparative analysis of gaits of patients with spinal cord traumas using robotic devices and without their assistance [44]. In order to evaluate the efficiency of using exoskeletons for rehabilitation of stroke patients Fan et al. analyzed indices of surface electromyogram [45]. Quantitative characteristic of the efficiency of an active lower limb exoskeleton in the work of Neuhaus et al. was given on the basis of walking speed, and an extent of efforts expended on the exoskeleton control was evaluated by registration of the HR, respiration rate, color of the skin; the authors assessed also the stability of standing (ability of the patient to catch a ball), and cognitive efforts (ability to maintain a visual contact) [22]. Apart from walking, of patient’s capacity to sit down and stand up in the exoskeleton was estimated in some cases; for this purpose angles in the pelvic and knee joints [46], as well as pressure of the arms on the wheel-chair handles during these maneuvers were used [20, 21].

On the whole, it should be noted that a generally accepted methodology of exoskeleton assessment has not been worked out so far [47–50]. But the analysis of the literature showed, that a great deal of investigations are devoted to the elaboration of the general principles of approbation of novel robotic device, exoskeletons for lower limbs in particular. Approbation of exoskeletons usually includes testing of the walk in the exoskeleton and determination of such indices as energy expenditure, safety, convenience and simplicity of using the external device [24, 51]. These approaches to approbation are valid for all types of lower limb exoskeletons, making it possible to compare different variants of exoskeleton devices [52, 53].[…]

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