1. Department of Orthopedic Surgery, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
2. Weifang Maternal and Child Health Hospital, Weifang, Shandong 261000, P.R. China
3. The Second Clinical Medical College of Lanzhou University, Lanzhou, Gansu 730030, P.R. China
4. Neurosurgery Research Laboratory, West China Hospital, Sichuan Univerisity, Chengdu, Sichuan 610041, P.R. China