Posture and gait outcomes following otolith-targeted vestibular implantation in adults with bilateral vestibulopathy

Introduction: Bilateral vestibulopathy (BVP) is a chronic condition characterized by bilateral loss or severe reduction of vestibular function (Strupp et al., 2017). Patients with BVP have absent or markedly reduced input from both vestibular organs, resulting in persistent imbalance, disequilibrium, and oscillopsia. Oscillopsia refers to the perception that the visual environment is bouncing or unstable during head movement and results from failure of the vestibulo-ocular reflex. BVP has an estimated prevalence of approximately 28 per 100,000 adults in the United States (Ward et al., 2013), which extrapolates to roughly 1–2 million patients worldwide.Individuals with BVP commonly struggle to walk in the dark or on uneven ground and often require canes or walkers. Daily activities usually considered trivial become painstakingly difficult in severe BVP: walking, taking a shower, driving a car, or putting on clothes in the morning, etc. (Guinand et al., 2012). Symptoms worsen in dim light conditions or in uneven terrain. Consequently, patients are at increased risk of falling and have a poor quality of life (Jorissen et al., 2025; Van Rompaey et al., 2025) which does not improve over time (Loos et al., 2025).Vestibular rehabilitation therapy (VRT) is currently the standard of care for BVP. Although VRT may improve symptoms in patients with mild or partial vestibular loss, many individuals with BVP experience only modest functional gains (Herdman et al., 2015). Given the lack of effective restorative treatments and inspired by the success of cochlear implants for sensorineural hearing loss, several research groups have investigated vestibular implants as a means of restoring vestibular input (Soto et al., 2023). The BionicVEST consortium is the only group to date that is developing a vestibular implant specifically targeting the otolith region of the inner ear. This region is fundamental for balance because it continuously senses gravity and linear acceleration, providing the brain with a stable reference for spatial orientation and postural control.Methods: The BionicVEST vestibular implant is based on a modified cochlear implant platform designed to deliver continuous electrical pulse trains to the inferior vestibular nerve. The BionicVEST feasibility trials were conducted from September 2018 onwards, with the goal of exploring the effect of this vestibular implant across three participating centers in Belgium and Spain. The first-generation BionicVEST investigational device was implanted in 11 patients and had an intracochlear electrode array for restoring hearing in addition to an electrode for vestibular stimulation.The second-generation BionicVEST vestibular implant is currently being evaluated in the ongoing BionicVEST2 study, a prospective, multicentric, staged feasibility clinical trial (https://clinicaltrials.gov/study/NCT06805175). The system is designed to preserve hearing in the implanted ear and has a dedicated vestibular electrode array. It operates with an external processor and programming software. At the time of this interim analysis, 11 of 18 planned adult participants have been implanted.The primary endpoint of the BionicVEST2 clinical trial is improvement from baseline to six months post-activation in functional gait performance, assessed using the Dynamic Gait Index (DGI) and Functional Gait Assessment (FGA). Secondary efficacy endpoints include improvement in objective postural control, assessed using the global score of the Sensory Organization Test (SOT) and Limits of Stability (LOS), as well as clinically significant improvements in the Dizziness Handicap Inventory (DHI) and Falls Efficacy Scale–International (FES-I).Other secondary endpoints are the impact of implantation on hearing thresholds assessed by clinically significant worsening of hearing thresholds from baseline in the implanted ear, and the quality-of-life changes up to six months post-activation using the EQ-5D-5L questionnaire. In addition, the protocol includes exploratory objectives to investigate residual effects of stimulation on balance symptoms and to assess cost-benefit and cost-utility outcomes.Results: The 11 patients implanted with the first-generation BionicVEST vestibular implant (mean age of 55 ± 15 years), showed significant enhancements in balance, particularly in gait assessments like the DGI, supporting the potential of vestibular implants to improve functional mobility. These functional improvements were accompanied by a clinically meaningful enhancement in quality of life, as measured by the DHI. Furthermore, the SOT score improved significantly (Ramos-de-Miguel et al., 2025).However, responses across participants are heterogeneous, both in the initial BionicVEST trial and in the interim findings of the ongoing BionicVEST2 study (currently 12 patients implanted, with a mean age of 64 ± 10 years). While several participants exhibited clear improvements in functional gait performance, these gains were not always consistent with corresponding improvements in vestibular-dependent posturography measures. This dissociation highlights the complexity of balance restoration and suggests that the mechanism of action of the vestibular implant - particularly its impact on multisensory integration and central compensation - remains incompletely understood and warrants further investigation.Conclusions: In conclusion, the BionicVEST vestibular implant, designed to electrically stimulate the inferior vestibular nerve, demonstrates promising potential to restore balance function in patients with BVP. As the field of vestibular implantation advances, many challenges will arise. Much as with the cochlear implant journey, these challenges require significant research efforts to maximise outcomes for patients.Acknowledgements: The BionicVEST projects received funding from the European Union under the H2020 project grant 801127 and EIC Transition grant 101112779.