1. Department of Endoscopic Diagnosis, Daqing Oilfield General Hospital, Daqing, China
2. Department of Orthopaedic, Daqing Oilfield General Hospital, Daqing, China
3. Department of Obstetrics, Daqing Oilfield General Hospital, Daqing, China
4. Department of Orthopaedic, Chengde Medical University Affiliated Hospital, Chengde, China