1. Department of Orthopedics; The First Hospital of China Medical University; 155 North Nanjing Street Shenyang 110001 Liaoning China
2. Department of Orthopaedics, Xijing Hospital; Fourth Military Medical University; 127 Changle Western Road Xi'an 710032 China
3. Department of Orthopaedics; Air Force General Hospital, PLA; Beijing China
4. Institute of Medical Information; Chinese Academy of Medical Sciences; Beijing China