Acquired brain injury (ABI) is the main cause of death and disability among young adults. In most cases, survivors can experience balance instability, resulting in functional impairments that are associated with diminished health-related quality of life. Traditional rehabilitation therapy may be tedious. This can reduce motivation and adherence to the treatment and thus provide a limited benefit to patients with balance disorders. We present eBaViR (easy Balance Virtual Rehabilitation), a system based on the Nintendo ® Wii Balance Board ® (WBB), which has been designed by clinical therapists to improve standing balance in patients with ABI through motivational and adaptative exercises. We hypothesize that eBaViR, is feasible, safe and potentially effective in enhancing standing balance.
In this contribution, we present a randomized and controlled single blinded study to assess the influence of a WBB-based virtual rehabilitation system on balance rehabilitation with ABI hemiparetic patients. This study describes the eBaViR system and evaluates its effectiveness considering 20 one-hour-sessions of virtual reality rehabilitation (n = 9) versus standard rehabilitation (n = 8). Effectiveness was evaluated by means of traditional static and dynamic balance scales.
The results suggest that eBaViR represents a safe and effective alternative to traditional treatment to improve static balance in the ABI population. These results have encouraged us to reinforce the virtual treatment with new exercises, so an evolution of the system is currently being developed.
Acquired Brain injury (ABI) is the main cause of death and disability among young adults [1 ]. ABI can cause from mild to severe impairments in cognitive, motor or psychological functions leading to difficulties in familiar, vocational and social reintegration which diminishes health-related quality of life [2 ]. Among them, ABI can cause different levels of paralysis, such as hemiplegia or hemiparesis, which dramatically affect the balance control and, consequently, the performance of activities of daily living (ADL). Traditional balance training is based on the automatic repetition of specific movements. These methods can become repetitive and aimless, and thus reduce the motivation and adherence to treatment. Balance control, as the complex constellation of impairments following ABI, demands a multidisciplinary rehabilitation approach that, with the aid of new technologies, could maximize functional recovery.
In the last few years, there has been increasing research interest in the application of virtual reality (VR) technology to rehabilitation [3 ]. In contrast with traditional rehabilitation procedures, which may be tedious, resource-intensive and costly, VR provides patients with ABI opportunities to engage in meaningful, intensive, enjoyable and purposeful tasks related to real-life interests and ADL [4 ]. The published clinical results indicate that the recovery of motor function in ABI patients with motor difficulties appears to be enhanced by using VR technology [5 -7 ]. Although most of these studies still consist of small experiments without randomized control trials [8 ], they demonstrate the feasibility of the application of VR technology in this clinical field.
In regard to standing balance, systems based on force platforms are particularly interesting, since they enable to estimate the weight distribution of the patients by means of pressure sensors [9 ,10 ]. These devices are expensive and require a dedicated area in the clinical facilities due to their size, weight and set-up. In this respect, computerized dynamic posturography can assess the ability of the automatic motor system to quickly recover from an unexpected external disturbance. Some of these systems even offer interactive and functional training exercises that fit the patients' conditions. In comparison with these platforms, the Nintendo ® WBB (a peripheral of the Nintendo ® Wii gaming system) is an inexpensive interface (less than $100USD) that has widespread availability. The WBB also has the advantage of being portable, easy and comfortable to handle thanks to its small size (0.511 m. wide by 0.316 m. long by 0.053 m. thick) and weight (3.5 kg. without batteries). Furthermore, it is a device with Bluetooth wireless connectivity that is battery operated. The WBB contains four force sensors (located in each corner) that are used to measure the user's center of balance and weight. Following the Nintendo ® gaming philosophy, users can interact naturally with the game (by means of weight transferences).
The number of studies that include Nintendo ® Wii or WBB in the rehabilitation process is increasing but still limited. Saposnik et al. evaluated the feasibility, safety and efficacy of VR rehabilitation using the Nintendo ® Wii gaming system with entertainment software to improve arm motor recovery in stroke patients [11 ]. Since the study is focused on improving arm recovery, the WBB was not used. Deutch et al. also use commercial software (Wii sports) to describe the feasibility and clinical efficacy of Nintendo ® Wii to augment the rehabilitation of an adolescent with cerebral palsy [12 ]. Loh et al. use this system as well and reported improvement in a group of patients with stroke in a non-controlled study [13 ]. Sugarman et al. report the feasibility and outcome of the WBB with a commercial program for balance training after stroke [14 ]. Although this software is not designed for balance recovery after stroke, they highlight its potential to be used in clinical settings in order to improve balance. In this sense, Clark et al. [15 ] demonstrated the convergent validity and the clinical utility of the WBB compared to a laboratory-grade force platform, which is considered the gold standard measure of balance. The results suggest that the WBB could be considered as a valid portable low-cost tool for assessing standing balance. However, the Nintendo ® Wii and WBB are entertainment systems oriented to healthy people that offer a gaming experience that differs from the therapy required by patients with ABI [16 ,17 ]. This fact has encouraged different authors to develop custom made applications oriented to diminished people using the WBB [18 -22 ]. However, they are still very conceptual designs or lack more powerful studies to evaluate their efficacy.
Therefore, we designed eBaViR, a virtual rehabilitation system for balance recovery that provides motivational task oriented exercises specifically designed for ABI people by clinical therapists. The system can fit the patients' impairment to provide a particular training session, allowing the therapists to customize the duration and difficulty of exercises to the needs of the patients in each session.
The aim of this study is to evaluate the efficacy of the eBaViR system as a rehabilitation tool for balance recovery. In this contribution, we present a randomized and controlled single blinded trial to evaluate the influence of eBaViR on balance
rehabilitation of ABI patients. We hypothesize that eBaViR is feasible, safe and potentially efficacious in enhancing standing balance.
Seventy-nine hemiparetic patients who had sustained an ABI and were attending a rehabilitation program were potential candidates for participation in this study. The inclusion criteria were: 1) age ≥16 years and <80 years; 2) chronicity > 6 months; 3) absence of cognitive impairment (Mini-Mental State Examination [23 ] cut-off >23); 4) able to follow instructions; 5) ability to walk 10 meters indoors with or without technical orthopaedic aids. The exclusion criteria were: 1) patients with severe dementia or aphasia; 2) patients whose visual or hearing impairment does not allow possibility of interaction with the system; 3) patients with hemispatial neglect; 4) patients with ataxia or any other cerebellar symptom.
After inclusion-exclusion criteria, a final consecutive sample of twenty patients remained from the total pool. This sample was divided into two groups according to the Berg Balance Scale score. Group A was made up of subjects with a high risk of falling, with Berg scores ranging from 30 to 45. Group B was made up of subjects with a low risk of falling, with a Berg score ≥46. All the subjects from both groups were randomly assigned to either a control group (traditional physiotherapy) or a trial group (eBaViR therapy). The randomization schedule was computer-generated using a basic random number generator. Two patients of the control group and one patient of the trial dropped out of the treatment due to causes unrelated to the study and system, and, consequently, their data are not included in the present contribution. The final sample consisted of 11 men and 6 women ranging from 16 to 76 years old (47.3 ± 17.8) and a mean chronicity of 570.9 ± 313.2 days. Etiology of acquired brain injury in this group of patients included severe traumatic brain injury (TBI) (n = 3), ischemic or hemorrhagic stroke (n = 11), and benign cerebral neoplasm (BCN) (n = 3). Table Table1 1 shows a summary of the characteristics of the subjects.
The hardware components of the eBaViR system consist of a conventional PC, a 42" LCD screen and a WBB. The communication between this device and the computer is established via Bluetooth protocol. This way, the exercises run on a PC and the system uses the WBB as interface.
As mentioned above, the eBaViR system does not use any commercial software. The exercises have been programmed using an authoring system for interactive 2D and 3D applications and designed with the help of clinical specialists in balance rehabilitation. The system has been developed with three main goals in mind: obtaining a valid and adaptive system for the balance rehabilitation of the patients, achieving a system that reinforces the motivation of the patients during the rehabilitative process and providing the therapists with objective data of the evolution of the patients.
The first goal is achieved thanks to the interface used in the system: the patient interacts with the games, specifically designed by specialists, through weight transferences in sitting and standing position, which is an essential process in standing balance rehabilitation [24 ,25 ]. The system calibrates the maximum excursion of the patients and adapts the range of motion of the exercises to fit their impairment. In addition, the therapist can configure the difficulty of the session with other parameters (number of items, speed, etc.). This way, the therapist can easily customize the training of each patient.
The second goal is achieved by designing the system with a playful scheme. For the patient, the system is basically a set of three games, which make the rehabilitative sessions more amenable. By means of its configuration, the system also tries to avoid frustrating gaming experiences in which the patients are not able to fulfill some tasks due to their motor or cognitive impairments.
The last goal is achieved registering the relevant outcomes of each exercise (scores, time, etc.) and the maximum excursion of the patients.
In each session, the patient plays the three games of the system (Simon. Balloon Breaker and Air Hockey ). A brief explanation of the purpose of each one of these games can be found in Table S1, Additional file 1. Although their visual aspect can be similar to commercial games, the games have been designed to optimize the visual and audio feedback and to simplify other stimuli to allow patients with cognitive impairments to follow the exercises and to focus on the motor task.
The workflow is the same for the three games (see Figure Figure1 1 ).
Flow of the game. The flow of the game can be divided into: 1) Setup; 2) Calibration; 3) Gameplay; 4) Break; 5) Scores.
First, each game begins with an initial setup screen (Figure (Figure1, 1. screen 1). This initial screen allows the therapist to parameterize the game to suit the needs of each patient. There are two sets of parameters: a set that configures the rehabilitation session (such as the duration of the session and the number of breaks per session), and a set that configures the game level (such as the size or the speed of the game elements).
Once the rehabilitation session and the game have been configured and the virtual movements have been adjusted to the patient's excursion, the rehabilitation session can start. The eBaViR system allows the patient to play in standing or in sitting position to improve balance control in both conditions. In standing position the patients are required to maintain their soles on the WBB. In sitting position, the patients sit directly on the WBB. In the study presented in this paper, the patients play with the system in standing position (Figure (Figure1, 1. screen 3), with programmed pauses that are configured by the specialist in the setup screen (Figure (Figure1, 1. screen 4). During this session, the system gives the patient auditory feedback with a positive reinforcement when the patient accomplishes his/her goal throughout the sessions and a different reinforcement when the patient performs an incorrect action. The patient's score is continuously displayed and points are accumulated to calculate the final score. At the end of the rehabilitation session, the system shows the patient's percentage of hits and errors made during the game (Figure (Figure1, 1. screen 5). Game results and sounds serve as motivational elements. Figure Figure2 2 shows patients of the trial group in the course of a virtual rehabilitation session.