Received: 20 January 2018
Accepted: 18 April 2018
First Online: 2 May 2018
Ethics approval and consent to participate
: The study was approved by the local ethics committee (Ethik-Kommission an der Medizinischen Fakultät der Eberhard-Karls-Universität Tübingen, project number 300/2010B01).Informed consent was not required for this retrospective study.
: The authors declare that they have no competing interests.
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