1. Department of Spinal Orthopedics, Weihai Municipal Hospital, Weihai City, P. R. China
2. Department of Joint and Sports Medicine, Shandong Provincial Third Hospital affiliated to Shandong University, Jinan City, Shandong Province, P. R. China
3. Department of Orthopaedics, Jining No.1 People’s Hospital, Jining City, P. R. China