During the past 25-30 years, surgery with total disc replacement (TDR) has become an option for a selection of patients with chronic low back pain (LBP) traditionally treated conservatively or operated on with spinal fusion. Randomized trials comparing TDR with fusion have found the clinical outcome of TDR at least equivalent to that of fusion, and the only study comparing TDR to non-surgical treatment (The Norwegian TDR study) concludes that TDR is significantly more effective than multidisciplinary rehabilitation (REHAB) after 2 years. However, the long-term effects of TDR in terms of clinical results, costs, reoperation- and revision rate, degenerative changes and prognostic factors have not been investigated in high quality prospective trials. This is very much required since TDR surgery is offered a great number of patients world wide, and is associated with high complexity and risk of serious complications and difficult revision. Hence, the overall aim of the present study is to evaluate the long term (eight years follow-up) effect of The Norwegian TDR study where TDR surgery were compared to modern multidisciplinary rehabilitation in patients with chronic low back pain and localized degenerative disc changes.

Two-year results of the Norwegian TDR study were published in BMJ in May 2011 (Hellum et al). The current protocol is 8-year follow-up of patients included in the Norwegian TDR study.

Hypothesis of the 8-year follow-up:

Main hypothesis (H0): There are no differences in change between TDR and REHAB for pain and disability measured by Oswestry Disability Index (main outcome), back pain, quality of life, psychological variables, work status, patients satisfaction, drug use, urinary incontinence, and back surgeries after 8 years.

Secondary Hypothesis:

1. There are no differences in incidence and degree of disc degeneration at adjacent level or facet joint degeneration at index level between groups (radiological analysis).
2. There is no association between baseline characteristics, pelvic anatomy / sagittal balance (defined by lumbar lordosis, pelvic tilt, pelvic incidence angle and sacral slope), and clinical outcome after TDR.
3. There is no difference in cost effectiveness between surgery and REHAB 8 years after inclusion to the study.

Statistical analysis:

The investigators will use the same analysis as for 2-years results: two-way ANOVA, mixed model, regression analysis. p<0.05 will be considered statistically significant

Additional analysis (not conducted at 2 years):

1. cross-overs will receive last value before cross-over/fusion surgery
2. survival analysis
3. pelvic anatomy / sagittal balance (defined by lumbar lordosis, pelvic tilt, pelvic incidence angle and sacral slope) will be included in the predictor analysis
4. Both CT scans and MRI are taken for the evaluation of index level facet arthropathy

Inclusion Criteria:

• aged 25-55 years
• had low back pain as the main symptom for at least 1 year
• structured physiotherapy or chiropractic treatment for at least 6 months without sufficient effect
• Oswestry Disability Index (ODI) of at least 30
• degenerative intervertebral disc changes in L4/L5 and/or L5/S1.Degeneration had to be restricted to the two lower levels. The following degenerative changes were evaluated: at least 40% reduction of disc height, Modic changes type I and/or II, high-intensity zone in the disc, and morphological changes classified as changes in signal intensity in the disc of grade 3 or 4. The disc was classified as degenerative if the first criteria alone or at least two changes were found on magnetic resonance imaging. The discs were independently classified by two observers (orthopaedic surgeon /radiologist). When in disagreement, the images were classified by a third observer and the outcome decided by simple majority.

Exclusion Criteria:

• Generalized chronic pain syndrome (widespread myofascial pain)
• Degeneration established in more than two levels. To be classified as a normal disc, the disc height must not be reduced more than 40% and all other criteria of degenerative disc disease aforementioned must be absent. The classification of a normal disc is performed by two independent observers. If disagreement, the pictures will be classified by a third observer and the outcome decided by simple majority.
• Symptoms of spinal stenosis
• Disc protrusion or recess stenosis with nerve root affection
• Spondylolysis
• Isthmic spondylolisthesis
• Arthritis
• Former fracture of L1 - S1
• Ongoing psychiatric or somatic disease that excludes either one or both treatment alternatives
• Does not understand Norwegian language, spoken or in writing
• Drug abuse
• Osteoporosis
• Congenital or acquired deformity

Patients were examined by an orthopaedic surgeon and a specialist in physical medicine and rehabilitation together, which had to agree on inclusion.