1. Department of Orthopaedic Surgery, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang 310009, China
2. Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19014, USA
3. Department of Epidemiology and Biostatistics, School of Public Health, Drexel University, Philadelphia, PA 19102, USA