22. Based on the results from existing randomized studies comparing fusion surgery with conservative treatment in patients suffering from CLBP it has not been evident that surgery is advisable. However, in previous studies the symptoms of the patients selected has been described simply as "chronic low back pain". The patients in the investigators study were selected based on a more specific symptom analysis. Furthermore, in previous studies the level to fuse has been chosen based on radiological findings whereas a mechanical provocation tests is used in the present study. Two of the previous studies stated the importance of cognitive-behavioral therapy in CLBP patients, resulting in equally good results as following fusion surgery. To study the specific effect of surgery, therefore, both groups in the investigators study received quite the same treatment with cognitive-behavioral therapy and physiotherapy, the difference between the two groups being that one group also received surgery.