1. Graduate School of Health Management, Keio University, Fujisawa 252-0883, Japan
2. Department of Orthopedic Surgery, Tokai University School of Medicine, Isehara 259-1193, Japan
3. Department of Clinical Epidemiology, National Hospital Organization Tokyo Medical Center, Meguro 152-8902, Japan
4. Department of Orthopedic Surgery, National Hospital Organization Tokyo Medical Center, Meguro 152-8902, Japan