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Intraoperative Assessment of Ossicular Fixation

Presenting Author: John Peacock

Published online by Cambridge University Press:  03 June 2016

John Peacock ,
Joris Dirckx  and
Magnus von Unge
John Peacock
Affiliation:
University of Antwerp
Joris Dirckx
Affiliation:
University of Antwerp
Magnus von Unge
Affiliation:
Dept. of Otorhinolaryngology, Akershus University Hospital and University of Oslo, Center for Clinical Research, University of Uppsala
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Abstract

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Type
Abstracts
Information
The Journal of Laryngology & Otology , Volume 130 , Supplement S3: Abstracts for the 10th International Conference on Cholesteatoma , May 2016 , pp. S116
Copyright
Copyright © JLO (1984) Limited 2016 

Learning Objectives: The middle ear ossicles can be driven with a coil and magnet and the tiny vibration amplitudes can be measured with a laser vibrometer. Some information on the degree of ossicular mobility can be extracted by measuring the velocity ratios between different measurement points.

Introduction: Pathologies such as otosclerosis and sequels of chronic otitis media may cause fixation of the middle ear ossicles, leading to hearing impairment. Knowledge of the degree of ossicular mobility is useful in order to determine the best course of surgical treatment. Routine assessment of mobility is often performed by manual palpation during surgical exploration, but this is subjective and imprecise, and a more objective method would be welcome.

Methods: A method was developed that makes use of a small magnet and coil to vibrate the ossicles in surgery after the tympanic membrane has been elevated. The method allows the ossicles to be driven at acoustic frequencies while simultaneously allowing free visual access for a laser vibrometer.

The method was evaluated with measurements on human temporal bones. Ossicular fixation was simulated by applying glass ionomer cement to the anterior mallear ligament, and to the stapes footplate. Measurements were made of the vibration response of the umbo, the incus long process, and at points on the stapes, before and after artificial fixation.

Results: The velocity ratios between different measurement points varies with the severity of the fixation. In the unfixed state the velocity ratios remain fairly consistent between temporal bones, but with increased fixation of the footplate the ratios diverge further from the unfixed.

The ratio of stapes to umbo velocity decreases when the degree of fixation increases, and may reduce by as much 40 dB in case of complete footplate fixation.

Conclusions: It is possible to drive the ossicles with a magnet and coil and measure ossicular motion with a laser vibrometer. Information on the degree of ossicular fixation could be gathered by examining the velocity ratios between different points on the ossicular chain. Since the results can be displayed immediately after the measurements, the method may even be used to assess the results of an intervention intraoperatively.