## 4 Discussion
Muscle debility, tissue damage, and knee pain after TKA surgery can reduce the proprioceptive inputs needed to maintain balance ([PERSON], 2022). Non-immersive virtual reality devices are good for recovering balance because they provide proprioceptive, vestibular, and visual information to perform virtual and active exercises. This modality of VRBR is safer than immersive VRBR because it is unnecessary to use headset mounted-displays, which can induce adverse effects related to visual and vestibular information, such as dizziness, visual vertigo, or visual temporospatial disorientation, that can reduce the efficacy of VRBR [78]. Thus, non-immersive VRBR has shown to be an effective and safe therapy to increase the balance in these patients and others with musculoskeletal or neurological disorders. We have assessed the increase in knee flexion ROM and quadriceps strength related to improvement in knee function. These two variables, never assessed in previous reviews, improved after applying VRBR. More specifically, in increasing knee flexion ROM, VRBR is more effective when it is applied in combination with CT, and for quadriceps strength, we only can assess the effect of VRBR in comparison to CT because no study provided data from the VRBR plus CT subgroup, showing that VRBR is more effective than CT. In improving knee flexion ROM, immersive VRBR is more effective than non-immersive VRBR, although the level of evidence was low. Distraction induced by VRBR may be responsible for the capability to perform virtual and active exercises without paying attention to knee pain, which favors improving knee ROM and strength, showing better functional independence, in contrast to CT. Finally, the other three variables (gait speed, functional independence, and aerobic capacity) were assessed. No statistically significant differences were found between VRBR and CT for these variables. However, it is important to consider that only two studies were included in the meta-analysis of each one. We cannot include the case-control study of [PERSON] and colleagues (2022) for not being an RCT, but in this study, VRBR was not superior to CT in improving gait speed [79]. These three variables are not being assessed in the recent RCT, so it is important to include them in future RCTs to clarify if VRBR can affect them. In addition to the effect on the previous variables, VRBR is interesting to include in the TKA recovery protocols because it could reduce the recovery time. For example, [PERSON] and colleagues showed that the time spent to obtain 90\({}^{\circ}\) of knee flexion with VRBR plus CT was 13.48 days, while that with only CT was 15.24 days [66]. Reducing the recovery time can minimize the economic costs associated with rehabilitation and the return to work. [PERSON] and colleagues, in 2019, showed that approximately 65% of participants who use VRBR return to work before 3 months from surgery TKA, compared with only 46% of patients under CT [62]. Opposite to CT, which sometimes focuses on analytic passive or active joint movements or repetitive strength exercises that cause low motivation for the patients, VRBT may be more suitable for working on functional activities of daily living in a playful and motivating way through video games or the recreation of virtual scenarios. This increases the adherence of patients to the therapy and could explain the positive effect of VRBR. Another benefit of VRBR is that it can be used at the patients' homes through telerehabilitation programs supervised by a physiotherapist [80], increasing patient rehabilitation frequency and shortening recovery times [81]. A recent study showed that approximately 21% of patients with recent TKA are dissatisfied with the therapy when it does not resolve knee pain and function. Dissatisfied patients incurred a mean cost of $21,156.18, and when the therapy is effective, and knee pain is reduced, increasing their satisfaction, the mean cost is downgraded to $13,453.84 [82].