Received: 4 June 2019
Accepted: 15 July 2019
First Online: 19 August 2019
Ethics approval and consent to participate
: The institutional review board of Xiamen university the first affiliated hospital approved the retrospective study and waived the requirement for informed consent for the use of the patients’ medical data.
: An informed consent was obtained from all patients before semi-rigid single hook wire placement.
: The authors declare that they have no competing interests.