Kinect-Based Rehabilitation Systems for Stroke Patients: A Scoping Review

Method This study was conducted according to Arksey and O'Malley's framework. To investigate the evidence on the effects of Kinect-based rehabilitation, a search was executed in five databases (Web of Science, PubMed, Cochrane Library, Scopus, and IEEE) from 2010 to 2020. Results Thirty-three articles were finally selected by the inclusion criteria. Most of the studies had been conducted in the US (22%). In terms of the application of Kinect-based rehabilitation for stroke patients, most studies had focused on the rehabilitation of upper extremities (55%), followed by balance (27%). The majority of the studies had developed customized rehabilitation programs (36%) for the rehabilitation of stroke patients. Most of these studies had noted that the simultaneous use of Kinect-based rehabilitation and other physiotherapy methods has a more noticeable effect on performance improvement in patients. Conclusion The simultaneous application of Kinect-based rehabilitation and other physiotherapy methods has a stronger effect on the performance improvement of stroke patients. Better effects can be achieved by designing Kinect-based rehabilitation programs tailored to the characteristics and abilities of stroke patients.


Introduction
Stroke is the second most prevalent cause of mortality and disability worldwide. The prevalence of stroke will increase due to the aging of the population. Moreover, stroke happens in a larger number of young populations in low-and middle-income communities [1]. It damages the sensory, motor, perception, visual, and cognitive systems, disrupts the patients' ability to conduct daily activities, and impacts their quality of life and level of independence [2,3].
Rehabilitation in stroke is a purposeful process to help the patients regain and retain their social, intelligence, mental, and physical abilities while also helping them perform their daily and social activities with some level of independence [4,5]. Rehabilitation exercises should include specific, repetitive, intensive, meaningful, and motivational tasks to improve the patients' motor performance [6]. Starting rehabilitation immediately after a stroke greatly contributes to patients' performance improvement, and effective rehabilitation depends on the patients' adherence to exercise programs and their regular performance at home and physiotherapy clinics. The process of rehabilitation in stroke patients is a long one, and patients' follow-up of this process is seriously limited due to its heavy costs, the long distance to rehabilitation centers, lack of access to such centers, patients' motor limitations, and problems associated with commuting to the health-care centers [6][7][8]. Moreover, patients' motivation for rehabilitation, which is a key factor for following the treatment and improving the outcome, is reduced because of the prolonged duration of rehabilitation [7].
The use of technology in rehabilitation is increasing rapidly. One of these technologies is video games, which is known as an effective intervention in rehabilitation. Video games are a useful solution for stroke patients who are unable to perform daily activities in the real environment and also motivate and encourage people to do rehabilitation exercises and improve motor function in stroke patients [8]. Video games are a new and useful technology that allows the user to interact with a three-dimensional environment. Studies have shown that this technology is an effective, safe, feasible solution that facilitates rehabilitation treatment [9]. In addition, video games increase motivation and increase patient satisfaction and involvement [10,11]. Studies show that video games are used for a wide range of disorders including balance, cognition, mobility, and improved motor function. Video games are a promising tool because they provide the repetitive, task-based, reward-based, and interactive situations needed to restore patient function after brain injury [12]. Kinect-based video games are a good tool for providing rehabilitation exercises in the form of games due to the features of Kinect and the limitations of stroke patients [13,14]. The application of Kinect-based rehabilitation as a low-cost and flexible method is rapidly expanding [15]. Kinect contains an RGB camera (R for red, G for green, and B for blue), a depth sensor, and a layer of microphones to record body movements and detect faces and voices [16]. Microsoft Kinect is a markless motion capture system that presents innovative and exciting methods for offering a more enjoyable treatment and promoting motivation in and adherence to the treatment [17,18]. A unique feature of Kinect is providing a method for interaction with the game without using any controllable or wearable device [19,20].
Another feature of Kinect for patients is performing rehabilitation exercises at home with no need for a physiotherapist [21]. By providing exciting and innovative rehabilitation methods, Kinect enhances adherence to treatment through adding entertaining features to the treatment, lessening costs compared to traditional rehabilitation, and making rehabilitation more accessible [17,22]. Two types of games, commercial and customized, are used in Kinectbased rehabilitation. Some studies have utilized commercial Kinect-based games for rehabilitation. Although these games had positive effects on the performance improvement of stroke patients, since they had been developed for healthy people for entertainment purposes and required a high level of speed and ability, stroke patients could not easily perform them due to their limited and diverse abilities [8,23]. On the other hand, some studies have developed games customized to the abilities of stroke patients. These games, known as serious games, were aimed for something beyond mere entertainment, and the results show that they positively affect the performance improvement of patients [24,25].
Today, serious games, especially exergames, are used by therapists as a tool for rehabilitation purposes [26,27]. Exergaming involves physical activity and is directly related to the sport in the game, not to the game or sport itself. Many studies have introduced exercise games in rehabilitation to motivate, engage, and increase patient adherence to their treatments [28,29]. Research confirms the motivational benefits of using exergames in rehabilitation regardless of their age or illness [30].
Based on the findings of systematic reviews on the clinical and technical evaluation of the Kinect sensor, the use of this rehabilitation system is acceptable due to its costeffectiveness and adequate precision in movement tracking [22,31,32]. Various studies have been conducted on the validity and accuracy of Kinect in tracking movements and the effect of Kinect on rehabilitation and motor recovery. Research on the validity and accuracy of the Kinect sensor indicates that this sensor has sufficient precision in movement tracking [20,31,33,34]. Studies on the effects of Kinect on the performance improvement of patients with neurological disorders (such as Parkinson's disease and multiple sclerosis) have also deemed this method effective [17,31,32,35].
The aim of scoping review is to determine, retrieve, and summarize the research pertinent to special issues to identify the key concepts supporting a research domain and the major sources and available evidence [36]. Scoping reviews are conducted to answer more general questions. One of their advantages is determining the feasibility and necessity of conducting a systematic review in a specific domain [36,37]. So far, no comprehensive study has been conducted on Kinect-based rehabilitation for stroke patients. Therefore, this scoping review focused on the effects of Kinect-based rehabilitation for stroke patients and its limitations and challenges. Accordingly, the following research questions were posed: (1) What is the effect of Kinect-based rehabilitation systems on the performance of stroke patients?
(2) What is the main application domain of a Kinectbased rehabilitation system for stroke patients?
(3) What are the limitations of utilizing Kinect-based rehabilitation systems for stroke patients?

Methods
The current scoping review adopted Arksey and O'Malley's methodology [36]. Based on this framework, a scoping review has five essential steps and one selective step: (1) identification of the research question; (2) recognition of pertinent researches; (3) selection of studies; (4) charting the data; and 5) summarizing and disseminating the results and (6) consultation exercise. The sixth step was omitted

Study Selection.
The electronic search was performed in the five mentioned databases. Also, hand-searching was performed in Google Scholar, and 58 articles were retrieved. The retrieved articles were then inputted to EndNote, and the duplicates were identified and removed by using the software. Subsequently, the titles and abstracts of the articles were reviewed by two authors according to the research questions and objectives. In the next step, the full text of the papers was examined by two authors concerning the inclusion and exclusion criteria. Any disagreements between the authors were resolved by discussions.
2.5. Data Extraction, Charting, and Synthesis. Data extraction was executed by using a form including the first author's name (reference), year of publication, country, the domain of rehabilitation, type of rehabilitation program (commercial vs. customized), main findings, and technical limitations of the Kinect-based rehabilitation program. The data were obtained by two authors, and disagreements were resolved upon discussions. Finally, the data extracted from the articles were inputted to Microsoft Excel for classification, synthesis, and reporting of the results.

Selection of Sources of Evidence.
Totally, 1196 articles were retrieved by searching in the databases. In the next step, by using EndNote, 184 duplicates were removed, and 954 articles remained. Subsequently, the titles and abstracts of the papers were reviewed, 856 papers were removed, and 98 remained. Then, the full text of the articles was examined, 64 articles were removed, and finally, 34 articles were included in this scoping review. Figure 1 displays the article selection process.

3.2.
Characteristics of the Sources of Evidence. The data extracted from the articles were recorded in the data extraction form ( Table 1). The majority of the studies had been conducted in the US (n = 7, 22%), followed by Spain and South Korea (n = 5, 15%). Following the invention of Kinect in 2010, the number of studies on the use of Kinect-based rehabilitation programs for stroke patients increased ( Figure 2). However, no study based on the inclusion and exclusion criteria had been conducted in 2010, 2011, and 2014. The majority of the studies had been conducted in 2018 (n = 8).

Classification of the Studies Based on the Rehabilitation
Domain. In the analysis of the domain of rehabilitation for stroke patients, most studies had focused on upper extremities (n = 22), followed by balance (n = 10), cognitive rehabilitation (n = 3), lower body (n = 2), and functional recovery (n = 2) ( Figure 3).
Furthermore, the results revealed that the use of a Kinect-based rehabilitation program increases the repetitions of the movements, improves motivation, promotes the quality of life, and enhances adherence to treatment [18, 41-44, 46, 61, 62]. Some studies had employed telerehabilitation, reporting that Kinect-based rehabilitation is a safe and effective method for providing standard    Grip muscle strength for the study group (P < 0:05).
The modified Barthel index score for the control group at the end of the treatment was significantly lower than in the study group (P < 0:05).
Kinect-based rehabilitation improves upper extremity performance.

Balance.
The results of this study showed that 26% of the articles were in the field of balance rehabilitation. In the studies studied using Box and Block Test, Barthel Index, and Berg Balance Scale, it was measured that the use of Kinect-based rehabilitation games improved patients' balance.

Cognitive Rehabilitation.
The results of this study showed that 8% of the articles were in the field of cognitive rehabilitation. The results of the studies showed that the use of Kinect-based rehabilitation games improved patients' attention, spatial awareness, and generalized cognitive functioning.

Lower Body.
The results of this study showed that 5% of the articles were in the field of lower limb rehabilitation. In these studies, the Timed Up and Go Test and Fugl-Meyer Assessment erew used to measure lower limb movements, and the results showed that it improved lower limb movement.

Technical Limitations of Kinect-Based Rehabilitation
Systems. In terms of the type of rehabilitation program used for stroke patients, the majority of the studies had designed the rehabilitation program tailored to the status and abilities of the patients (n = 13, 38%), while the other studies had utilized commercial Kinect-based programs (n = 21, 62%). Among the studies using commercial Kinect-based programs, technical limitations mostly included not challenging enough, lack of customization to the patients' abilities, complexity and difficulty of use, dependency on the therapist due to complexity, and the content of the programs being radically different from the daily activities of stroke patients [44,48,50,53,56,68]. In the studies designing games customized to the abilities of stroke patients, technical limitations included the low speed of the games, the use of inappropriate feedback, insufficient precision of movement tracking, the complexity of games and difficulty of use, inappropriate user interface, dependence on the therapist, and not customized to and compatibility with the abilities of patients ( Figure 4) [41,47,52,54,61,65].

Discussion
This scoping review investigated the effect of using Kinectbased rehabilitation systems on the performance improvement of stroke patients, the rehabilitation domain, and technical limitations. The reviewed articles were published since 2010, when Microsoft-invented Kinect was examined [10,11]. The results revealed that Kinect-based virtual rehabilitation leads to motor recovery in stroke patients. This type of rehabilitation is an effective and promising method owing to its low cost, flexibility, providing repetitive exercises, and motivation for the patients.
The most important feature of Kinect is that there is no need for any wearables during rehabilitation [20]. This feature of Kinect-based rehabilitation increases the repetitions of the movements, promotes motivation, enhances the quality of life, and increases adherence to treatment [18, 41-44, 46, 61, 62]. Moreover, due to its cost-effectiveness, flexibility, and telerehabilitation feature, the use of Kinect-based rehabilitation is a safe and effective method for providing standard rehabilitation at home [59,61,[63][64][65][66]. The results of this study show that the use of Kinect-based rehabilitation games improves motor function in the upper and lower limbs and balance and improves cognitive function in improving stroke patients. These results are in line with the results of other similar studies in the field of using Kinect-based rehabilitation in improving the motor function of the upper [69], lower limbs [70], balance [71], and cognition [72].
Most studies had also mentioned that, compared to the use of routine treatment methods alone, the simultaneous application of Kinect-based rehabilitation and other physiotherapy methods has a stronger effect on the performance improvement of stroke patients. Regarding the positive outcome of simultaneous use of Kinect-based rehabilitation and other physiotherapy methods, the results of the present research are consistent with those of other papers [73,74].
Despite all these advantages, some studies utilizing commercial Kinect-based programs reported different effects on the performance improvement of stroke patients; the reason was the limitations of these programs such as not challenging enough, not being customized to the patients' abilities, complexity, dependency on the therapist due to the complexity of the games, and the difference between the content of the games with patients' daily activities [43,44,50,56,57,68]. Although some of these programs will be beneficial in combination with other rehabilitation methods, as they have been designed for the healthy population and entertainment purposes, they require rapid and difficult movements that

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BioMed Research International may not be compatible with the abilities of stroke patients [23,75].
On the other hand, some studies had developed games customized to the abilities of stroke patients and reported positive effects on their motor recovery [42,50,53,56,61,62]. These results are in line with the findings of other researches [25,73]. To promote the effects of Kinect-based rehabilitation programs, it is necessary to pay attention to the characteristics of the patients and their abilities in the program's development process. The use of clear feedback, presenting challenges appropriate for patients' abilities [60], telemonitoring patients by the therapist [20], using rewards [69], and including the socialization feature to induce a sense of competition between patients, is essential in this process.
To promote neural plasticity in rehabilitation programs, tailor-made rehabilitation systems are promising tools for patients. Furthermore, appropriate feedback should be provided to actively engage patients in better motor recovery. One of the essential elements in rehabilitation programs is to keep the patients motivated and engaged. In this way, caregivers should provide suitable feedback to correctly execute the exercise. The caregiver should change the different parameters of exercise to make it challenging and simultaneously possible for executing.
Since the therapist cannot regularly monitor and evaluate the patient's condition in Kinect-based rehabilitation systems, using different sensors such as brain and body wearable sensors can receive more data to help better assess the patient. Captured data should be interpreted and presented by utilizing graphs to simply be understood by physicians. To enhance the efficacy of rehabilitation systems, the user interface should be designed by considering both patients' restrictions and caregivers' needs.

Limitations and Future Directions
One limitation of the current study was the diversity in the type of studies and the small samples of some studies, which pose problems in drawing definitive conclusions about the positive effects of Kinect-based rehabilitation on the motor recovery of stroke patients. Lack of access to the full text of some papers was another limitation. About the positive effect of customized Kinect-based rehabilitation programs which are tailored to the abilities of stroke patients, it is suggested more research be conducted on the design framework of such programs and their effects on the motor recovery of stroke patients. Furthermore, developing the rehabilitation systems should concentrate on a range of complex factors such as patients living environment, social environment, different challenges of daily living, and patients' skills in using various technologies. Furthermore, developing systems with a concentration on supporting personal goals and performing the rehabilitative exercise in a competitive atmosphere may increase progress over time. It will be necessary to conduct different clinical trials in large sample size, as well as different devices to determine which factors have a greater effect in achieving a better outcome. Furthermore, performing a meta-analysis study to investigate whether rehabilitation programs are beneficial in improving patients function in stroke is essential.

Conclusion
Because of some limitations such as the costs of rehabilitation, the long distance to rehabilitation centers, lack of access to such centers, patients' motor limitations, and commute problems, patients with stroke lose motivation to follow treatment. The application of Kinect-based rehabilitation is an effective solution for creating motivation and improving adherence to rehabilitation programs in stroke patients. Kinect-based rehabilitation will be more effective on the performance improvement of these patients if used as a complementary technique in combination with other rehabilitation methods. Furthermore, to promote effects on motor recovery, it is essential to pay attention to the design of rehabilitation programs customized to the abilities of stroke patients.

Additional Points
Key messages. (i) Kinect-based rehabilitation is an effective and promising solution that improves the motivation, adherence to treatment, and motor function of stroke patients. (ii) Compared to the use of routine treatment methods alone, the simultaneous application of Kinectbased rehabilitation and other physiotherapy methods has

Conflicts of Interest
The authors have no conflicts of interest relevant to this article to disclose.