1. Spine Group, Vall d’Hebron Institut de Recerca (VHIR), Hospital Vall d’Hebron, 08035 Barcelona, Spain
2. Orthopaedic Surgery, Hospital Josep Trueta, 17007 Girona, Spain
3. Orthopaedic Surgery, Hospital La Paz, 28046 Madrid, Spain
4. Orthopaedic Surgery, Complejo Asistencial Universitario, 24008 León, Spain
5. Physical Medicine and Rehabilitation, Hospital Vall d’Hebron, 08035 Barcelona, Spain
6. Spine Surgery Unit, Hospital Vall d’Hebron, 08035 Barcelona, Spain