1. Department of Orthopaedics, Lanzhou University Second Hospital, Lanzhou, Gansu 730000, P. R. China
2. Department of Spine Surgery, Honghui Hospital, Xi'an Jiao tong University, Shaanxi 710000, P. R. China
3. Department of Gastrointestinal Surgery, Lanzhou University Second Hospital, Lanzhou, Gansu 730000, P. R. China