Non-surgical intervention: The intervention is based on a treatment model described by Brox et al (Spine 2003;28:1913-1921) and consists of a cognitive approach and supervised physical exercise. The treatment is interdisciplinary and is directed by a team of physiotherapists and specialists in physical medicine and rehabilitation. The intervention is organized as an outpatient treatment in groups of 6 - 8 patients during a period of 12 - 15 treatment days. In agreement with the patient, individual goals for the rehabilitation process are established.