1. Gothenburg Medical Center, Vastra Frölunda, Sweden
2. Schulthess Clinic, Zurich, Switzerland
3. Orthopedic Clinic Bulovka, Praha, the Czech Republic
4. Office for Management in Medical Research, Teningen, Germany
5. Spine Unit, Schulthess Clinic, Lengghalde 2, CH-8008 Zurich, Switzerland.