Effectiveness of Bone Conduction Stimulation Applied Directly to the Otic Capsule Measured at Promontory: Assessment in Cadavers

Abstract

Introduction: The aims of this study included: (a) to develop a method of direct acoustic bone conduction (BC) stimulation applied directly to the otic capsule, (b) to investigate the effect of different stimulation sites on the promontory displacement amplitude, and (c) to find the best stimulation site (among 2 located directly on the otic capsule and 1 standard site approved for clinical use) that provides the greatest transmission of vibratory energy. Methods: Measurements were performed on 9 cadaveric whole human heads. A commercial scanning laser Doppler vibrometer was used. The promontory displacement was recorded in response to BC stimulation delivered by an implant at 3 sites: BC1 on the squamous part of the temporal bone, BC2 on the ampulla of the lateral semicircular canal, and BC3 between the semicircular canals. The displacement of the promontory was analyzed in detail. Results: The results show that BC1 caused an overall smaller promontory displacement than both sites BC2 and 3. BC3 stimulation is more efficient than that at BC2. Conclusions: BC is an effective method of acoustic stimulus delivery into the inner ear, with the effectiveness increasing when approaching closer to the cochlea. Placing the implant directly on the labyrinth and thus applying vibrations directly to the otic capsule is possible and very effective as proved in this study. The results are encouraging and represent the potential of new stimulation sites that could be introduced in the field of BC hearing rehabilitation as the possible future locations for implantable BC hearing devices.

Detailed Analysis of the Space between the Semicircular Canals for the Purpose of Direct Bone Conduction Stimulation of the Inner Ear

“…The results of the mentioned studies [Kwacz et al, 2019;Lachowska et al, 2019;Niemczyk et al, 2020] present a potential of new stimulation sites that could be introduced in the field of BC hearing rehabilitation. However, both new BC stimulations sites involved drilling the bone near the SC, which might be questionable in terms of the safety of this procedure.…”

“…The distance plays an important role, and the shorter the distance is the more efficient the stimulation is [Stenfelt et al, 2000;Stenfelt and Goode, 2005;Eeg-Olofsson et al, 2008, 2013Kwacz et al, 2019;Lachowska et al, 2019;Niemczyk et al, 2020]. Kwacz et al [2019], Niemczyk et al [2020], and Lachowska et al [2019] demonstrated that BC vibrations applied directly to the otic capsule seem to be more efficient than if applied outside the petrous part of the temporal bone. The authors sought to investigate the potential benefits of the proposed alternative stimulation sites, comparing them to the standard BC implants with stimulation applied to the squamosal portion of the temporal bone.…”

“…The first one is in the direct proximity of the ampulla of the lateral SC and the second one is between the superior and lateral SC, which is, to be more precise, the area located more medially, slightly above the lateral SC in the space between the crura of the superior SC. Overall, the second location has been proven to be the most efficient in terms of the transmission of vibratory energy both in cadavers [Kwacz et al, 2019;Niemczyk et al, 2020] and in patients [Lachowska et al, 2019].…”

“…However, until recently, all of these locations described in the literature were situated outside of the real otic capsule with no direct contact with its bone. In recent studies by Kwacz et al [2019] and Niemczyk et al [2020] performed in cadavers and one by Lachowska et al [2019] performed in living humans, 2 new sites for the BC titanium implant were proposed to directly stimulate the cochlea from the closest possible distance, which was the bone forming the ampulla of the lateral semicircular canal (SC) and the bone between the superior and lateral SC. The 2 locations can be approached by the otosurgeon, which was shown in these studies.…”

Directional sensitivity of bone conduction stimulation on the otic capsule in a finite element model of the human temporal bone

“…Experiments on dry human temporal bones and skulls showed that acceleration components of the OC vibrations measured during BC stimulation depended on the distance from the stimulation site to the inner ear 12 and the implant location 13 . Studies on cadaveric human heads 14 and patients 15 showed that the results for stimulation on the OC site were several times as good as for implantation on the temporal bone squamous.…”