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Study of the Feasible Size of a Bone Conduction Implant Transducer in the Temporal Bone

Reinfeldt, Sabine*; Östli, Per*; Håkansson, Bo*; Taghavi, Hamidreza*; Eeg-Olofsson, Måns; Stalfors, Joacim

doi: 10.1097/MAO.0000000000000682
Prosthetic Devices

Hypothesis The aim was to assess the temporal bone volume to determine the suitable size and position of a bone conduction implant (BCI) transducer.

Background A BCI transducer needs to be sufficiently small to fit in the mastoid portion of the temporal bone for a majority of patients. The anatomical geometry limits both the dimension of an implanted transducer and its positions in the temporal bone to provide a safe and simple surgery.

Methods Computed tomography (CT) scans of temporal bones from 22 subjects were virtually reconstructed. With an algorithm in MATLAB, the maximum transducer diameter as function of the maximum transducer depth in the temporal bone, and the most suitable position were calculated in all subjects.

Results An implanted transducer diameter of 16 mm inserted at a depth of 4 mm statistically fitted 95% of the subjects. If changing the transducer diameter to 12 mm, a depth of 6 mm would fit in 95% of the subjects. The most suitable position was found to be around 20 mm behind the ear canal.

Conclusion The present BCI transducer casing, used in ongoing clinical trials, was designed from the results in this study, demonstrating that the present BCI transducer casing (largest diameter [diagonal]: 15.5 mm, height: 6.4 mm) will statistically fit more than 95% of the subjects. Hence, the present BCI transducer is concluded to be sufficiently small to fit most normal-sized temporal bones and should be placed approximately 20 mm behind the ear canal.

*Department of Signals and Systems, Chalmers University of Technology, Gothenburg, Sweden; and †Ear, Nose, and Throat Department, Sahlgrenska University Hospital, Gothenburg, Sweden

Address correspondence and reprint requests to Sabine Reinfeldt, Ph.D., Department of Signals and Systems, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden. E-mail:

All authors disclose no conflict of interest, except Bo Håkansson, who holds several patents related to the BCI device.

This study was supported by Vinnova (Sweden’s Innovation Agency).

Copyright © 2015 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company