Sheng Shi1, Xin-Feng Li1, Zu-De Liu2. 1. Department of Orthopaedic Surgery, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, P. R. China. 2. Department of Orthopaedic Surgery, Renji Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, P. R. China. Electronic address: rjliuzd@163.com.