1. Department of Sport and Sport-Pedagogic, Pedagogic-University, Freiburg, Germany
2. Grasshoppers Football Club, Zurich, Switzerland
3. Gothenburg Medical Center, Vastra Frolunda, Sweden
4. ffice for Management in Medical Research, Tenningen, Germany
5. Schulthess Clinic, Zurich, Switzerland
6. Orthopedic Clinic Bulovka, Praha, the Czech Republic
7. Address correspondence and reprint requests to Jiri Dvorak, MD, Spine Unit, Schulthess Clinic, Lengghalde 2, CH-8008 Zurich, Switzerland.