Minimally invasive laser vibrometry (MIVIB) with a floating mass transducer - A new method for objective evaluation of the middle ear demonstrated on stapes fixation.

Ossicular fixation through otosclerosis, chronic otitis media and other pathologies, especially tympanosclerosis, are treated by surgery if hearing aids fail as an alternative. However, the best hearing outcome is often based on knowledge of the degree and location of the fixation. Objective methods to quantify the degree and position of the fixation are largely lacking. Laser vibrometry is a known method to detect ossicular fixation but clinical applicability remains limited. A new method, minimally invasive laser vibrometry (MIVIB), is presented to quantify ossicle mobility using laser vibrometry measurement through the ear canal after elevating the tympanic membrane, thus making the method feasible in minimally invasive explorative surgery. A floating mass transducer provides a clinically relevant transducer to drive ossicular vibration. This device was attached to the manubrium and drove vibrations at the same angle as the longitudinal axis of the stapes and was therefore used to assess ossicular chain mobility in a fresh-frozen temporal bone model with and without stapes fixation. The ratio between the umbo and incus long process was shown to be useful in assessing stapes fixation. The incus-to-umbo velocity ratio decreased by 15 dB when comparing the unfixated situation to stapes fixation up to 2.5 kHz. Such quantification of ossicular fixation using the incus-to-umbo velocity ratio would allow quick and objective analysis of ossicular chain fixations which will assist the surgeon in surgical planning and optimize hearing outcomes.

Intraoperative assessment of ossicular fixation.

Determining the degree of ossicular fixation is a difficult task, with the final assessment often being made with manual palpation during exploratory tympanotomy. A more objective method to evaluate ossicular fixation would be valuable. In this paper we describe a new method which makes use of a magnet and coil to measure ossicular motion through the ear canal with an elevated tympanic membrane. We report measurements of the vibration response at the umbo, the tip of the incus long process and the lateral posterior crus of the stapes before and after artificially fixing the stapes footplate and anterior mallear ligament with luting cement. Results were obtained on temporal bones, but the practicality of the method allows easy clinical implementation. Velocity ratios between different measurement points along the ossicular chain may provide a quantitative indication of the degree of stapes fixation. Isolated anterior mallear ligament fixation was not distinguishable from the unfixed condition.

Towards quantitative diagnosis of ossicular fixation: Measurement of stapes fixations using magnetically driven ossicles in human temporal bones.

CONCLUSION: Information on the degree of stapes fixation can be found by measuring the ratio of stapes to umbo and stapes to incus velocity. OBJECTIVES: To evaluate a method of quantifying ossicular fixation in an ear with elevated tympanic membrane. METHOD: Measurements were made on four fresh-frozen human temporal bones. After elevating the tympanic membrane, a small magnet was attached to the manubrium and an electromagnetic excitation coil was used to vibrate the ossicles. The vibration response of the umbo, the tip of the incus long process, and the posterior crus of the stapes were measured before and after partially fixing the footplate with luting cement. RESULTS: The velocities at the different measurement points were unequally affected by the fixation. The difference in the velocity ratio between different points provides an indication of the degree of footplate fixation.