## Results
### Safety and Usability of Robotic Devices  
In the field of robot-assisted rehabilitation, the safety of the robotic device must be ensured. In particular, this represents a very crucial aspect because the patients interact physically with the robots and, generally, they are not able to retract their arm when a critical situation occurs. For this reason, hard safety measures in terms of hardware and software adjustments must be taken. For example, at software level, many devices (_Armeo Spring_[44], _AMADEO_[53], _Noviint Falcon_[56], _ChARMin_[51]) reported the implementation of algorithms to limit the range of motion, the force exerted and/or the speed generated on the arm of the patients. Regarding the _InMotion2_[45], the backdrivability of the device has been cited as safety feature. It is worth mentioning that, even if not explicitly reported on the selected papers, the robotic devices used in the rehabilitation domain, need to implement basic safety features as requested by international regulations. In order to be more precise, we decided to consider three categories: (1) commercial robots; (2) prototypes used in clinical studies; (3) prototypes not already used in clinical studies. The devices belonging to the first category are identified in the \"Market available\" column of Table 1. In order to obtain the medical certification and then the authorization to be commercial, these devices must address all the safety features requested by law. In this same way, considering the prototypes used in the clinical studies, they should have implemented the same safety features of the commercial ones in order to be authorized by the Institutional Review Committee (IRB) for the use with human subjects. However, for the third category, the safety mechanisms should be reported in the papers. Indeed, the _IOTA_ device presents an emergency stop button that immediately arrests the motors if pressed [55], while, the _PASCAL_ has brakes that block movements in the horizontal axes and a magnetic release that disconnects the robot from the power in case of emergency [60].  
Another remarkable aspect is the concept of the usability of a robotic device for rehabilitation. Firstly, the robot should ensure a high level of comfort for the user. In this regard, in general, it has been shown [62] that an end-effector robot is more flexible than an exoskeleton in fitting different sizes of body parts, reducing setup time and increasing ease of use for new patients. Moreover, there is some minimal information on the usability of some of the selected devices: the _IOTA_ is drawn  
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to be lightweight and fit children aged 7 to 12 years old [55] while the _ChARMin_ has two different modules to best fit and cover the range of patients aged 5 to 18 years old [63]. Another aspect is related to the operator point of view: the robot should be properly designed to be easily applied on patients, reducing the cognitive load of the operator itself. The operator should supervise the therapy, monitor the patient's safety, set the protocol and adjust its parameters according to the child's level of impairment.  
Finally, we want to emphasize what is missing in most of the selected studies: the safety and usability perceived by the operator and the patient. Indeed, we found only three studies [45; 63; 64] in which researchers asked, through a questionnaire, the acceptance and tolerance of the device (_InMotion2_, _ChARMin_) to therapists and end-users (e.g., children or their parents).