Funding for this research was provided by:
Finska Läkaresällskapet (-)
Otology Research Fund of Finland (20170031)
Finnish Governmental Grant (-)
Received: 11 January 2020
Accepted: 23 March 2020
First Online: 17 April 2020
Ethics approval and consent to participate
: The study was reviewed and approved by the Research Administration of the Helsinki and Uusimaa Hospital District (Y1014KORV1). Ethics committee approval was not necessary due to national legislation which does not require ethics committee approval for a retrospective registry study without patient intervention, in accordance with the Medical Research Act of Finland.
: Not applicable.
: The authors declare that they have no competing interests.