1. Department of Orthopedic Surgery West China Hospital West China Medical School Sichuan University Chengdu Sichuan 610000 P. R. China
2. Department of Medical Epidemiology and Biostatistics Karolinska Institutet Stockholm 171 77 Sweden
3. Clinical Epidemiology and Biostatistics School of Medical Sciences Örebro University Örebro 701 85 Sweden
4. Department of Urology Faculty of Medicine and Health Örebro University Örebro 701 85 Sweden
5. Department of Epidemiology Harvard T.H. Chan School of Public Health Boston Massachusetts 02115 SA
6. Institute of Environmental Medicine Karolinska Institutet Stockholm 171 77 Sweden