OBJECTIVE: To assess the functional results of the Vibrant Soundbridge (VBS) placed on the round window (RW) in patients with mixed hearing loss. STUDY DESIGN: Retrospective evaluation of functional hearing, with measurements performed 7 to 9 months postoperatively. SETTINGS: Two tertiary referral hospital centers. SUBJECTS: Twelve individuals with mixed severe hearing loss associated with chronic suppurative otitis media and otosclerosis. INTERVENTION: Surgical placement of the VBS mechanical effector in close contact with the RW membrane to directly drive the inner ear fluids. MAIN OUTCOME MEASUREMENT: Functional hearing gain as analyzed via pure-tone audiometry and speech audiometry with VBS off and on in quiet and in noise. RESULTS: We observed a mean gain of 37.5 dB (0.5-4 kHz) with wide individual differences. The overall gain is mainly due to the air-bone gap recovery, whereas a further 12-dB mean improvement of air-conducted threshold is evident at 2 kHz. The speech reception threshold in quiet shows a mean gain of 24 dB, whereas in noise, it requires a signal-to-noise ratio 7 to 13 dB greater than normal-hearing controls. All patients are daily users of their VBS device. CONCLUSION: A middle ear implant capable of directly driving the cochlear fluids seems to be a promising alternative for individuals with a severe to profound mixed hearing loss. However, variability in hearing recovery is great, likely reflecting variability in responsiveness of the cochlea associated with chronic pathologic findings and, possibly, variability in how the VBS effector interfaces with the RW. Modifying the shape of the VBS effector can improve the mechanical coupling to the RW to better exploit the device's amplification power
