1. Department of Spine Surgery, the Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, P.R. China;
2. Department of Hand and Foot Surgery, The No.252 Hospital of People’s Liberation Army of China, Baoding, Hebei 071000, P.R. China;
3. Key Laboratory of Biomechanics of Hebei Province, Shijiazhuang, Hebei, 050051, P.R. China