Introduction Chronic low back pain (CLBP) is a highly prevalent health condition, and the leading cause of years lived with disability. The high prevalence causes a substantial impact on patients, communities and health-care systems. There is a continuing challenge to offer evidence-based rehabilitation for patients with CLBP. There is a lack of studies on adequate follow-up approaches to maintain successful treatment. No earlier study has assessed if the positive treatment effects of a multidisciplinary rehabilitation intervention can be maintained with an intervention alternating between inpatient interventions and home-based activities.

Aim To assess if a novel multidisciplinary rehabilitation intervention is more effective in maintaining successful treatment after 6 months, than a usual multidisciplinary rehabilitation intervention in patients with CLBP.

The novel intervention is a 14-week program alternating between in total three weeks of inpatient intervention and home-based activities. This alternation allows the participants time and opportunity to adapt and transfer inpatient learning to activities and participation in their own environment in interaction with everyday life situations and surroundings. Usual care is a four-week inpatient intervention. It is hypothesized that the intervention will be superior to usual care.

Method The study will be conducted at The Danish Rheumatism Associations' rehabilitation centre Sano Aarhus. 160 participants with CLBP will be randomly allocated to one of two groups. The novel intervention consists of: 1) a pre-admission day, 2) two weeks of home-based activities, 3) two-week inpatient period, 4) four weeks of home-based activities, 5) 1st two-days inpatient follow-up, 6) six weeks of home-based activities and 7) 2nd two-days inpatient follow-up. Usual care consists of a four-week inpatient intervention.

The two groups will be compared according to disability, pain, pain self-efficacy, quality of life, depression and exercise capacity.

Relevance The present study has emerged out of the fields where patients, clinicians and researchers intersect and is consequently highly clinically relevant. If positive treatment effects can be maintained or even improved in the long term, the results may serve as inspiration for the design of multidisciplinary rehabilitation interventions in clinical practice; this will be valuable for future patients with CLBP.

Introduction Chronic low back pain (CLBP) is a highly prevalent health condition, and the leading cause of years lived with disability both globally and in Denmark. In the majority of patients with CLBP, no underlying pathology or cause can be identified and CLBP is acknowledged to be multifactorial.

CLBP is defined by symptoms lasting for a period longer than three months. The high prevalence of CLBP causes a substantial impact on patients and their families, communities and health-care systems, as well as a financial burden. Besides pain and disability people with CLBP often experience psychosocial consequences with signs of anxiety and depression and effects on social, leisure, and work life. Recognition of the physical, psychological and social consequences of CLBP led to the development of the widely accepted biopsychosocial model in the understanding and managing of CLBP.

The World Health Organization's (WHO) International Classification of Functioning, Disability and Health (ICF) provides a framework for applying the biopsychosocial model into clinical practice, especially into rehabilitation. By emphasizing, that disability is a dynamic interaction between the dimensions of body function, activity, participation, and environmental and personal factors, ICF helps treating the patients rather than only their low back pain by addressing all the biopsychosocial dimensions of their disability.

Disability itself arises through complex and multi-factorial mechanisms and therefore, rehabilitation processes are defined as complex health interventions undertaken in a complex environment. Rehabilitation is rather a process than a treatment or specific action, and a multidisciplinary team most effectively manages the complex problems seen in rehabilitation. Rehabilitation has many potential active ingredients, and combining the different components in a whole is more than the sum of its parts.

There is a continuing challenge to offer evidence-based rehabilitation for patients with CLBP. A systematic review by Kamper identified and assessed risk of bias in 12 randomized controlled trials (RCT's) comparing two multidisciplinary rehabilitation interventions. In March 2016 we performed an updated literature search in PubMed identical to that of the review and identified one additional RCT comparing two multidisciplinary interventions. Risk of bias in the additional study was assessed using Cochrane risk of bias tool (The Cochrane Collaboration ) identical to the review.

Nine of the 13 studies had disability and pain as primary or secondary outcome. The multidisciplinary interventions being compared varied across the nine studies in content and/or time frame. As the studies were very heterogenic, a pooled comparison and description was not possible. Overall the nine studies showed that multidisciplinary rehabilitation had a positive effect on disability and pain in the short and medium term, but there were discrepancy in the studies whether the effect can be maintained in the long term. A literature search identified two studies on follow-up care. One study tested the effect of multidisciplinary rehabilitation with subsequent booster sessions conducted by telephone within 12 months after discharge, and found only slight advantages, but no statistical significance of the booster sessions. The other study compared a 3-month exercise follow-up program and routine follow-up on patients with CLBP who had completed a 3-week outpatient multidisciplinary rehabilitation program. Favourable outcomes after one year were observed in both groups, but only patients attending the exercise follow-up program improved in disability.

There is a lack of studies on adequate follow-up approaches to maintain successful treatment. No earlier study has assessed if the positive treatment effects of a multidisciplinary rehabilitation intervention can be maintained with an intervention alternating between inpatient interventions and home-based activities.

Aim To assess if a novel multidisciplinary rehabilitation intervention is more effective in maintaining successful treatment after 6 months, than a usual multidisciplinary rehabilitation intervention in patients with chronic low back pain.

The novel intervention is a 14-week program alternating between in total three weeks of inpatient intervention and home-based activities. This alternation will allow the participants time and opportunity to adapt and transfer inpatient learning to activities and participation in their own environment in interaction with everyday life situations and surroundings. Furthermore, the novel intervention will consist of a higher degree of patient involvement than the usual intervention. Usual care is a four-week inpatient intervention.

Objectives (i) To compare changes in the two multidisciplinary rehabilitation groups on disability, pain, pain self-efficacy, quality of life, anxiety/depression and exercise capacity.

(ii) To examine the association between changes in disability versus changes in pain, pain self-efficacy, quality of life, anxiety/depression and exercise capacity.

Hypotheses (i) The intervention group will experience a five points larger improvement in Oswestry Disability Index compared to usual care. Furthermore, the intervention group will experience a larger improvement in pain, pain self-efficacy, quality of life, anxiety/depression and exercise capacity compared to usual care.

(ii) There is negative association between changes in disability and quality of life, pain self-efficacy and exercise capacity, respectively. There is a positive association between disability and pain and anxiety/depression, respectively. The strongest association will be between disability and pain self-efficacy.

Materials and methods Study setting All participants will be recruited from, treated and tested at Sano Aarhus, Denmark. A rheumatologist will perform the selection of participants based on the clinical problem of referral.

Randomization An independent administrative assistant will perform a randomly allocated computer-generated randomization of participants into either intervention or control group. Stratified randomization on the basis of Oswestry Disability Index score below and above 40 will be used in order to achieve approximate balance of disability in the two groups. 1:1 allocation in blocks of 6 will be used. Due to waiting time, randomization will take place in average 5-6 months before study start.

Blinding As both interventions will be performed in the same physical setting at the same time, blinding of participants and intervening clinicians will not be possible due to knowledge of content and duration of the intervention the participants are allocated to. Intervening clinicians involved in the treatment of both groups will assess physical status of the participants. In order to raise equal expectations, participants will be blinded to the study hypothesis by telling them the RCT is intended to compare two equal multidisciplinary rehabilitation interventions both meeting current scientific standards and appropriate to improve health status.

The researchers involved in the statistical analyses will be blinded to treatment groups.

Sample size Oswestry Disability Index was used for sample size calculation. Based on data from the literature and a pilot study on 25 patients with CLBP from Sano, mean change is estimated to 10 in the intervention group and 5 in the control group, and the standard deviation on the changes is estimated to 10. Using 80% power and a significance level of 0.05, 64 participants will be required in each group. A dropout rate of 20% is estimated, for what reason it will be planned to recruit a total of 160 participants.

Interventions The content of both interventions will be described in details in a study protocol as recommended for complex interventions.

Both groups will be managed by the same multidisciplinary staff in the same physical setting at the same time. Participants in the two groups will inevitably meet each other, and thus both they and the multidisciplinary staff will have the opportunity to compare and discuss the different rehabilitation interventions. Despite the possible overflow between the two rehabilitation interventions, the present parallel design has been preferred rather than a staggered design where waiting time and external circumstances would have been different between the two groups.

Data collection Demographics and PROMs will be collected before the randomization (baseline), and due to 5-6 months of waiting time again at the beginning of the inpatient rehabilitation intervention (intervention start). Exercise capacity test performed by a trained physiotherapist using a standardized protocol, and clinical and neurological findings collected by an experienced rheumatologist using a standardized examination protocol, will be collected at the first inpatient contact.

Follow-up data will be collected at the end of the inpatient rehabilitation intervention, at each follow-up (intervention group) and at 6 and 12 months. Participants dropping out will be asked to fill in the PROMs at 6 months.

Participants enter data directly in a database via a link. In order to minimize missing data a reminder will be send via email after one week. If participants are unable to fill out the electronic versions, an independent administrative assistant will enter data from a paper copy of the questionnaires.

Perspective The present study has emerged out of the fields where patients, clinicians and researchers intersect and is consequently highly clinically relevant. If positive treatment effects can be maintained or even improved in the long term, the results may serve as inspiration for the design of multidisciplinary rehabilitation interventions in clinical practice; this will be valuable for future patients with CLBP.

Inclusion Criteria:

• low back pain for more than 12 months with or without sciatica and/or with or without generalized pain identified by ICD-10 codes
• Oswestry Disability score > 20.

Exclusion Criteria:

• a rated physical status of > 3 according to the American Society of Anesthesiologists Physical Status Classification System
• axial spondyloarthritis
• spinal fracture within the last 3 months
• severe osteoporosis
• active cancer
• active psychiatric pathology assessed by general practitioner before referral
• pregnancy
• low Danish language skills.