Ming-Xiang Zou1, Jing Li1, Xiao-Bin Wang1, Guo-Hua Lv2. 1. Department of Spine Surgery, The Second Xiangya Hospital, Central South University, Changsha, China. 2. Department of Spine Surgery, The Second Xiangya Hospital, Central South University, Changsha, China. Electronic address: spinelv@163.com.