Virtual reality-based interventions for the rehabilitation of vestibular and balance impairments post-concussion: a scoping review | Journal of NeuroEngineering and Rehabilitation | Full Text

Through the evaluation of scientific literature, this scoping review found that VR is an effective therapeutic tool for vestibular and balance impairments post-concussion across all investigated categories—balance, gait, and functional. However, it remains unclear if VR is more favourable than traditional vestibular rehabilitation. A recent study with level two evidence by Sessoms and colleagues [4], compared VR vestibular rehabilitation with traditional vestibular rehabilitation. Of the four outcome measures used by Sessoms (ABC, DHI, SOT, FGA), only one reported a greater improvement with VR compared to traditional rehabilitation (SOT). Of these outcome measures, ABC and DHI are subjective measures, and the FGA is a more functional test. The SOT, however, is a highly validated measure using computerised posturography (CDP), which is sensitive to postural sway (i.e., via quantification of displacement of centre of gravity), making it the gold standard outcome measure for instrumented balance assessment [4, 52,53,54]. A study conducted by Meldrum [24], also deemed traditional vestibular rehabilitation to be no more beneficial for 100% of outcome measures reported, although the VR group reported more enjoyment, less tiredness and less difficulty with balance exercises. Likewise, Lei, Sunzi, and Dai, [25] support the notion that VR vestibular rehabilitation cannot achieve the same effect as traditional vestibular rehabilitation, but at least can be used as an alternative therapy. Despite these references, the findings in this scoping reviews are not undervalued, nor does it deflect from the quality of these studies. Instead, this serves as information to clinicians, showing that both traditional and VR vestibular therapy can provide patients with benefits depending on the availability, yet more definitive research is needed to ascertain the benefits of both therapy types.

There are multiple rationales to explain the positive findings of VR technology in the field of rehabilitation. Due to the range of VR modalities and capabilities, interventions can be individualised to enhance the experience dependent on presenting signs and symptoms by offering a real time multidimensional and multisensory environment [54]. Clinicians can stringently control and modify a patient’s perceived environment as well as manipulate the visual, somatosensory, and vestibular information to target specific patient deficits, with the ability to regress and progress training in real time [54]. In order to enhance neuroplasticity, therapeutic delivery should be patient-specific and allow for dynamic feedback delivered continuously during treatment that can be augmented to replicate real-life environments [55]. Cheung [56] supports this concept by stating that VR designs allow for in-depth analysis of the patient’s activity and ability, where specified real-time feedback can be provided to promote the desired neuroplastic changes. Furthermore, VR offers more abundant augmented feedback, greater opportunities for consistent task repetition, and optimal control over different practice challenge levels [57]. The consistent task repetition offered by VR therapies results in adaptations remaining long after a patient’s exposure to the virtual environment, particularly in vestibular therapy for post-concussion patients. [58]

The findings of this scoping review support improved balance outcomes with the use of VR as a rehabilitation tool for patients with vestibular impairments post-concussion. Of the four outcome measures identified with moderate quality of evidence, three of these outcomes were categorised under balance – two subjective measures (ABC and DHI) and one objective measure (BBS). Despite this review having no good quality of evidence (modified GRADE), the findings suggest that of the current literature identified, VR is an effective rehabilitation tool for improving balance outcomes post-concussion [59,60,61,62].

Multiple studies have investigated the use of VR therapy in treating balance impairments across a wide range of disorders. A study conducted by Phu and colleagues [59], assessed balance in community-dwelling older adults at high falls risk using a fully immersive VR system. Their results found VR to be effective in improving static and dynamic balance and reducing fear of falling and fall rates over a 9-month period [59]. Furthermore, another study examined the use of VR to treat balance impairment in patients with Parkinson’s Disease (PD) [25]. The study used the BBS as an outcome measure and found that rehabilitation training based on VR technology is more effective than conventional training in improving PD patients’ balance function [1, 25].A third study is also in favour of VR treatment for balance impairments, suggesting that VR combined with conventional therapy compared to conventional therapy alone is effective in improving balance in individuals post-stroke, again using the BBS as an outcome measure [60]. All three studies support the findings in this review, that VR is a useful treatment option for treating balance impairments post-concussion.

Balance requires integration of multiple information sources (visual, vestibular, and somatosensory), adapting and reacting to both the body and the surrounding environments [61]. These behaviours are influenced by both intention-based and stimulus-based actions (feedforward and feedback) indicative of ascending as well as descending control processes [61]. Furthermore, concussion impairs central integration of balance information and reduces the ability to multi-task. Additionally, the cognitive impacts associated with concussion cause issues adapting and reaction to different environments, specifically affecting stimulus-based actions [62]. VR has been shown to positively effect balance impairments post-concussion, providing opportunities to manipulate visual information relating to oneself and the environmental characteristics [63, 64]. This is further demonstrated by the findings in this review.

The primary rationale for using VR for vestibular and balance rehabilitation is that realistic visual environments may enhance adaptation by causing retinal slip, which a recent study by Mao et al. [64] suggest is the key to adjusting the vestibular system. The retinal slip is the movement of a visual image across the retina, a powerful signal that can be induced by horizontal or vertical head movements while maintaining visual fixation on a target. Retinal slip can also be induced by position error signals, imagined motion of the target, and strobe lighting, all of which are possible utilising VR technology [67].

Studies show that concussion causes dysfunction of the vestibulo-ocular reflex (VOR) [64,65,66]. The VOR can be adapted in VR simulations with an increase in VOR gain, and VR can be used to increase the rate of adaptation by specifically adapting scenes to a person’s capability, thereby facilitating their recovery [64]. Furthermore, it has been noted that VR scenes promote rehabilitation more effectively than optokinetic-based therapies, since VR offers the ability to finely control the virtual scene [64]. Overall, the use of VR is still a relatively new concept, and though the relationship between VR and balance rehabilitation appears promising, more research is required to better understand it.

Three separate systematic reviews [25, 68, 69] have proven the effectiveness of VR in improving gait for patients with Parkinson’s disease and post-stroke patients.

The findings from this review suggest similar outcomes for patients experiencing vestibular and balance impairments post-concussion when using VR compared to conventional rehabilitation methods.VR is a useful tool in the therapy of gait training, given VR technology can change locomotion and feedback features such as speed, trajectory, and obstacle circumvention behaviours [63]. Not only is VR useful for gait outcomes in patients with vestibular and balance impairments, three separate systematic reviews [25, 68, 69] have proven the effectiveness of VR in improving gait for patients with Parkinson’s disease and post-stroke patients. Gait is reliant on concurrently integrating multiple information sources (visual, vestibular, and somatosensory), and motor commands, to adapt to contextual demands, which VR can provide and manipulate [70].

Furthermore, de Amorim and colleagues [71] highlight that VR offers opportunities for rehabilitation of weight transfer between limbs, unipedal support, triple flexion, and load acceptance during initial support, all of which are affected post-concussion. [72] However, VR is unable to provide clinicians and patients with other important aspects of gait, such as dissociation of waists, impulsion, and continuous anterior displacement of the centre of mass [71].Therefore, more research is needed to investigate the effectiveness of VR modalities to improve gait abnormalities seen in those with a concussion. [71]

Level of immersion (non-, semi- or fully immersive) can influence the effectiveness of rehabilitation for improving patients’ gait function. Recent literature [73] suggests that more immersive VR systems may bring additional benefits compared to training with less immersive VR systems due to the ability to generate a stronger feeling of ‘being physically present’. However, our findings show otherwise. Of the gait outcome measures, only one measure was used within multiple studies [4, 45, 47, 48, 51], the Functional Gait Assessment. Within these studies, the greatest improvement in FGA score was seen in the non-immersive and semi-immersive studies [45, 47]. A postulation for why, may be the restriction placed on a patients’ environment when in an immersive VR headset, making it difficult to perform gait and functional activities, compared to balance activities performed on the spot [74]. Furthermore, perhaps the cognitive load is too high with full immersion, or the feeling of ‘being physically present’ may cause symptoms of visual motion sensitivity and headaches making treatment less tolerable [73]. This highlights the need for further research to solidify which level of VR immersion might best improve gait ability post-concussion. Nevertheless, VR has the opportunity to provide cognitive challenges while walking through a virtual environment, allowing better integration of all senses within a safe environment, and perhaps central reweighting of balance information, which can be a component necessary for motion and visual motion sensitivity [47]. Furthermore, it has the potential to speed up the process of improving spatial disorientation back to a level of high functional performance [47].

This scoping review shows some moderate evidence supporting improvement in the functional gait assessment (FGA) of > 25%. However, this percentage could be higher if VR were able to provide the opportunity to cover all aspects of gait, including abnormal acute single-task simple gait, poor subacute balance control during dual-task gait, and subacute gait abnormalities during specific complex gait tasks [71, 72]. This could be possible if gait rehabilitation combined VR with other technologies such as a traditional treadmill or omnidirectional treadmill [75]. A study [76] conducted on the healthy population investigated the effect of VR during both fixed speed and self-paced treadmill walking. At fixed speed walking, the use of VR on a treadmill led to slightly improved gait pattern, while at self-paced walking, patients altered their gait technique to maximise stability. However, the effects found were too small to be clinically relevant. A further study [77] investigated the effects of treadmill training with VR on gait in children with cerebral palsy. Results showed that gait velocity and walking endurance improved to greater extents in the VR treadmill training group compared to treadmill training group. These findings promote the combination of VR with other training methods to maximise gait rehabilitation. The evidence is currently limited, and non-specific to post-concussion patients, however, based on the low quality of evidence found in this review, further research into best practice for VR for gait outcomes is necessary.

Current literature [78, 79] has demonstrated that VR is an effective tool to support and improve activities of daily living (ADLs) and functional ability of older adults in comparison to traditional rehabilitation. The findings from this scoping review suggest that these effects are also present in patients with vestibular and balance impairments post-concussion.

The findings for the functional outcomes saw improvements of > 50%, suggesting VR is useful in targeting specific day-to-day tasks. However, these findings were all very low to low quality, highlighting the urge for further research to ascertain effectiveness of VR for functional outcome measures. The low quality could be due to the fact that functional outcome measures can be harder to standardise. Despite the low-quality evidence, these findings still demonstrate improvement in functional measures using VR as a rehabilitation tool. This is possibly due to VR technologies being able to address functional rehabilitation goals given it can simulate real world environments, allowing for specific impairments to be trained within a functional context [20, 46]. Within a virtual environment, practiced tasks can replicate real-world conditions and the choice of scenes can be based on functional needs of the patient, thus applicability and transferability to daily living is more likely [20]. This is an advantage to clinicians, given the opportunity for rehabilitation flexibility in adapting the exercises specifically to patients’ needs, while the patient remains in a safe environment. Of the limited research available discussing the functional benefits of VR, the overarching argument is that VR-based interventions relying on functional tasks offers the potential for more effective rehabilitation given the training is conducted in more naturalistic settings than traditional interventions [79].

Gaps in the literature

After reviewing the current literature, the authors have identified gaps and therefore the potential for future research. Despite having a wide array of search terms, the authors only managed to find ten suitable studies, all within the past nine years. It was noticeable that current research tends to focus on the assessment role of VR for vestibular and balance impairments post-concussion [26,27,28,29,30], despite there being opportunities to extend the same principles for the training of skills required for successful improvements for patients following a concussion [80]. Therefore, to further make conclusions about the use of VR in rehabilitation, and provide clinicians with robust evidence on its benefits, more prospective research is required.

The current research lacks detail on the most appropriate way of applying VR intervention and intensity suitability in a program according to the severity of concussion experienced by patients [64]. Future research would benefit from exploring the mechanism of the integrated central and peripheral nervous system, visual, vestibular and proprioceptive sensation, and more detailed clinical techniques for the use of VR in rehabilitation [64]. Establishing a quantitative standard of VR intervention is highly warranted and will improve the operational feasibility of VR. Likewise, clinicians would benefit from research surrounding the feasibility of VR in a home-based setting and if a home-based intervention has the same validity and clinical relevance as in clinical settings.