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Abstract
Objectives
To determine (1) levels on fibrous tissue and bony growth around the ceramic receiver–stimulator of cochlear implants in situ and (2) if these ceramic receiver–stimulators can withstand a tractive force of 5 N without displacing.
Methods
During revision surgery, we measured the extent of the fibrous tissue and bone growth around the receiver–stimulators in 13 subjects. After completely exposing the receiver–stimulator, we measured the tractive force it could withstand without displacing. The tractive force was gradually increased until either displacement or a force of approximately 5.5 N was reached.
Results
In 6 out of 10 subjects the receiver–stimulator did not displace when up to 5 N of tractive force was applied. Three subjects could not be evaluated. Statistical analysis was not possible due to the small sample size; however, we found no correlation between the degree of bone growth around the receiver–stimulator and (1) the length of time the implants remained in situ before revision or (2) the tractive force a receiver–stimulator could withstand without displacing.
Discussion
As bone growth around the receiver–stimulator is often limited, even years after implantation, it might therefore only play a minor role in preventing displacement. In contrast, fibrous tissue encapsulation of the implant bed of the receiver–stimulator may be the key stabilizing factor. In any case, when completely exposed, the 6 out of 10 receiver–stimulators could still withstand a tractive force of 5 N (calculated force generated by magnetic resonance imaging (MRI) with 1.5 T) without displacing.
Conclusions
During MRI, it is strongly recommended to secure ceramic receiver–stimulators with an external pressure bandage in order to minimize risk and possible user discomfort.
Acknowledgements
The authors would like to thank Martin Eisendle (MED-EL) for his valuable comments during data analysis and Michael Todd (MED-EL) for proofreading the manuscript. We are grateful to Prof. Dr. med. Joachim Mueller, who ex- and implanted subject #3.
The study was partially funded by MED-EL (Innsbruck, Austria) although the authors themselves did not receive any financial support.