## 1 Introduction
The clinical perspective offers a different approach toward these devices. In most cases, in fact, the clinician (or the end-user themselves in fewer cases) needs to select the most proper exoskeleton for a patient within a set of suitable candidates. Nevertheless, the choice is driven by the clinical picture of the end-user and their functional and structural impairments especially. Accordingly, the requirements assessed by the clinician may not necessarily overlap with the technical features typically adopted to describe the performance of an exoskeleton in a design context. For instance, the clinician might look for solutions to counteract the strength reduction in grasping, whereas the designer will describe the force generated by the motors. Given these core differences in the approach to exoskeletons, a mismatch between technical requirements and clinical needs inevitably occurs. In this context, the mapping of technical features and clinical specifications is necessary to enable a proper understanding of these two worlds, although according to the authors' knowledge, no investigations in this sense seem to be present in current literature. Research in the healthcare field is currently grounded on the principles and guidelines advocated by the Evidence-Based Medicine (EBM) approach with the aim of improving the quality of medical studies and, consequently, the reliability and confidence of clinical decision-making. According to EBM, formulating a proper and well-framed research question represents the initial and crucial step to conducting valid and valuable research. In this view, EBM recommends that a research question is formulated by using a specialized framework known as PICO [13]. PICO is an acronym that stands for Population/Problem, Intervention, Comparison, and Outcome. In this work, we decided to adopt the PICO framework to organize the information retrieved from the analyzed studies in view of technical-clinical feature mapping. In particular, we primarily focused our attention on the problem intended to be the specific structural/functional impairment belonging to a given health condition. Within this context, the current paper aims to provide a roadmap (i) for both design and selection of exoskeletons for hand rehabilitation, (ii) to discriminate among the peculiarities of soft, rigid, and hybrid devices, and (iii) with an impairment-oriented rationale. To reach this goal, the mapping of technical features and clinical specifications expected for the exoskeleton is outlined. For this analysis, a PICO-inspired approach is applied to identify the clinical requirements from the impairment analysis; this approach is also integrated into the proposed exoskeleton design process, which enables the identification of the technical requirements of a device. The development process of the work began with an in-depth analysis of the state-of-the-art technology related to rigid, soft, and hybrid devices. An initial selection of articles was based on a search of the Scopus database, proceeding with subsequent searches for each device family using specific keywords. Based on the analysis of the papers found in this initial phase and the step-by-step definition of the roadmap with impairment-oriented rationale for device design and selection, further searches were conducted, aiming at an in-depth analysis dealing with specific aspects, for instance, control, wearability, or applications in specific clinical scenarios. This process resulted in an analysis of more than 100 papers. In this context, a clarification of the definitions of rigid, hybrid, and soft exoskeletons that we adopted for device classification is necessary. There is no well-established classification among rigid, soft, and hybrid exoskeletons. Various authors have proposed and explained their own classifications in review papers. [PERSON] et al. [14] distinguished between two classes of exoskeleton based on their structures: rigid when they are made with rigid structural elements (metal or plastic) and soft when they are made from textiles.