Development of hand-guided measurement device of stapes mobility using the micromachining technique

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The ossicular chain, consisting of the malleus, incus and stapes, plays an important role in auditory mechanics. If some part of the ossicles becomes fixed, hearing loss occurs. In order to improve the level of hearing, the fixated part is replaced with a prosthesis. This surgery is called "tympanoplasty." It is important to evaluate the stapes mobility during the tympanoplasty, because it affects the prognosis of improvement of the hearing level. However, objective measurement of stapes mobility has not yet to be achieved.In this study, an apparatus which is clinically useful for measuring the stapes mobility based on the method of Wada et al. (2000) was developed by assembling a small-sized force sensor and a high-precision actuator, and its clinical applicability was evaluated by measuring stapes mobility in the guinea pig. The following conclusions can be drawn.1. Miniaturization of the apparatus was realized by the use of a small-sized capacitive force sensor and a hydraulic micromanipulator with a flexible coil rod and wires. Owing to this technology, the stapes mobility is measurable during surgery without impairing the sensitivity and repeatability.2. The equivalent stiffness of the normal stapes in guinea pigs was 17±3 N/m (N = 5).3. The difference between the stiffness of the normal stapes and that of the artificially fixed stapes which corresponds to the symptom of otosclerosis was clearly distinguished. Therefore, the new apparatus developed in this study would be helpful for diagnosing stapes fixation.