1. Faculty of Naval Medicine, Second Military Medical University, Shanghai 200433, P.R. China
2. Department of Orthopaedics, Spinal Section, Changzheng Hospital, Second Military Medical University, Shanghai 200003, P.R. China
3. Cadet Brigade, Second Military Medical University, Shanghai 200433, P.R. China
4. Department of Orthopaedics, The 455 Hospital of Chinese People's Liberation Army, Shanghai 200052, P.R. China