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The objective of the study was to provide an inventory of predictive instruments and their constituting parameters associated with return to work in patients with subacute (2–10 weeks pain duration) and chronic (10–24 weeks pain duration) non-specific low back pain (NSLBP). Data sources included systematic review in Medline, Embase, Cinahl, Central, PEDro, Psyndex, PsychInfo/PsycLit, and Sociofile up to September 2008, in reference lists of systematic reviews on risk factors, and of included studies. For the systematic review, two reviewers independently assessed study eligibility and quality, and extracted data. Disagreements were resolved by consensus. Risk factors were inventorised and grouped into a somatic and psychosocial domain. 23 studies reporting on subacute and 16 studies reporting on chronic patients were included. The studies on subacute patients reported on a total of 56 biomedical factors out of which 35 (63%) were modifiable and 61 psychosocial factors out of which 51 (84%) were modifiable. The corresponding values in studies on chronic patients were 44 biomedical [27 (62%) modifiable] and 61 [40 (66%) modifiable] respectively. Our data suggest that the interdisciplinary approach in patients at risk to develop persistent NSLBP is justified in both, the subacute and chronic disease stages. Psychosocial interventions might be more effective in subacute stages since a higher proportion of modifiable risk factors were identified in that group.
Low-back pain is one of the most important reasons for GP visits in developed countries. In the UK, for example, low-back pain accounts for about 7 million GP visits annually . Whereas the majority of low back pain patients recover without a specific intervention within a few weeks, only about 20% of the affected will remain on sick leave and about half of them will stay on prolonged sick leave or sustained restriction in function . This small proportion of patients with persistent symptoms account for about 80% of the total costs of NSLBP .
From a clinical perspective it remains challenging to tailor the most appropriate therapies considering both, clinical outcome and costs. Guidelines suggest that patients at risk for delayed recovery should be identified early and receive a multifaceted therapy considering biological, psychological and social factors [3, 4]. These programmes aim to improve functional restoration and promote return to work. Various studies showed advantage of a biopsychosocial approach compared to an isolated biomedical approach [5, 6]. However, to our knowledge there has been no study investigating to what extent the biopsychosocial approach is superior to a psychosocial approach in patients with chronic NSLBP non-specific low back pain. Arguably, the biopsychosocial approach is only justified if biomedical risk factors still play a major role in patients with delayed recovery. We therefore performed two systematic reviews, one focusing on risk factors of patients with subacute NSLBP, and one focusing on risk factors of patients with chronic NSLBP. We aimed at categorising risk factors into a biomedical and a psychosocial domain and aimed at comparing the proportions in the subacute and chronic stage. The final aim was then to draw a conclusion regarding the usefulness of biomedical interventions in patients with chronic unspecific low back pain.
We searched Medline (PubMed Version), Embase (Ovid interface), PsychINFO/PsychLIT, Cinahl, Central, PEDro, Psyndex, Sociofile from inception to October 2008. The full search algorithm is available on request.
In addition, we checked the reference lists of the included publications, relevant systematic reviews, relevant articles on the topic, guidelines, expert reports, and the ‘related articles’ query in Medline. We imposed no language restrictions. Health care professionals with sufficient knowledge of the given language assessed articles in other languages than English, e.g. German, French, Spanish or Italian.
An epidemiologist and an information specialist defined the search strategy applying previously published rigorous methods . Two reviewers screened the titles, keywords, and abstracts of all retrieved records. The agreement between reviewers for study selection was good (kappa = 0.73). We looked for prospective cohort studies reporting on biomedical and psychosocial factors related to return to work in patients suffering from subacute (2–10 weeks pain duration) or chronic (10–24 weeks pain duration) NSLBP. In the case of multiple publications on the same study population, all publications were retrieved to gather the most possible information. Two independent evaluators classified each factor as modifiable or not modifiable. In the event of disagreement consensus was reached between evaluators.
One reviewer extracted the salient features from each study using a data extraction form that was pre-tested using one of the included studies. A second reviewer double-checked the extraction form for discrepancies. From each study data regarding setting (e.g., year, country of origin), gender, mean age and number of participants were documented (Table 1).
Through our search we retrieved 5,784 records from which 479 records appeared to be potentially relevant for subacute patients and 554 records for chronic patients. Full text assessment resulted in exclusion of 452 articles reporting on subacute patients and 545 articles reporting on chronic patients. Finally, we included 23 studies assessing 59–1,885 subacute patients [9–31] and 16 studies assessing 76–945 chronic patients [32–42]. For details on study selection please see Fig. 1.
Publication years ranged from 1988 to 2008. The mean age of subacute patients ranged from 30 to 48 years, and for the chronic patients from 39 to 49 years. The proportion of male patients ranged from 33 to 88% in the subacute populations (except one study, where only men were included) and from 32 to 76% in the chronic populations. The proportion of men over all studies was 67% for the subacute group and 60% for chronic group. The studies were conducted in eight different countries including Canada, Denmark, Germany, Israel, Netherlands, Norway, Sweden, and USA. For details see Table 1.
Table 2 shows the distribution of risk factors for return to work for the subacute and chronic group, which were stratified for the two biomedical (modifiable and not modifiable) and psychosocial domains (modifiable and not modifiable).
Studies on subacute patients reported 117 significant (P < 0.05) predictors in the model, out of which 56 were biomedical (35 modifiable, 21 non-modifiable) and 61 psychosocial (51 modifiable, 10 non-modifiable). Studies on chronic patients reported 105 significant (P < 0.05) predictors in the model, out of which 44 were biomedical (27 modifiable, 17 non-modifiable) and 61 psychosocial (40 modifiable, 21 non-modifiable).
To our knowledge this is the first meta-epidemiologic study comparing risk factors for return to work in two populations of patients with a different duration of NSLBP. We found that the pattern of risk factor does not change markedly with increasing duration of symptoms. We observed a higher rate of modifiable psychosocial factors at earlier stages compared to later stages. Our findings are in accordance with findings by Waddell et al. . They showed that at the subacute stage psychosocial factors play a eminent role in development of chronic NSLBP. Our data suggest that psychosocial interventions might be more effective at an early disease stage since we found a higher proportion of modifiable factors in the subacute group compared to the chronic group. Finally our data support current LBP guidelines recommending a multidisciplinary approach of physicians, physiotherapists and psychologists irrespective of the duration of symptoms.
One strength of this study is the application of a robust systematic review methodology. We made strenuous efforts to minimize the risk of selection bias. Another strength is that relevant reports were searched systematically without language restriction. The definition and clinical implementation of non-specific LBP remains a problem. Some of the studies reviewed included patients with nerve root irritation. We decided to include these studies, as the suggested management of this diagnosis is the same as for NSLBP unless there are severe and progressive neurological deficits. There is a lack of consistency concerning the predictors included in the selection process for the models and the predictors retained in the final models.
The predictive values and their generalizability are moderate in the studies included. This is not surprising, bearing in mind that many factors influence these values in LBP patients: unstable course of LBP, large differences of risk profile in different settings, interventions, changing risk profile over time, large amount of factors influencing return to work, some are rare, but if present they are strong predictors. We assume that the inconsistencies between predictors of the included studies are due to the inclusion of patients with different risk profiles, different interventions, and different instruments that were used to identify a predictor. However, we were unable to perform statistical analyses confirming this suspicion.
In a recent publication by Hayden and co-workers about the quality of systematic reviews in the field of prognostic low back pain research the authors identified various methodological flaws on both, the study and review level . While we think that we ruled out most of the shortcomings observed in the Hayden review in our study, we agree with their observation that prognostic studies, particularly in the field of low-back pain research need further methodological improvement. We propose the inclusion of existing standardized instruments completed with additional risk factors related to the biopsychosocial model (e.g. patients attitudes and beliefs, e.g. about recovery and future work capability, and work situation (measured work load and self-perceived work situation), family context, social relationships at work place, local economy, etc.), assessed at a common and clinically relevant time point (e.g. between 4 and 12 weeks pain duration) in a sufficiently large population. The process of validation should follow expert recommendations [45–49]. Another important issue relates to the reporting of primary studies. We propose that future authors of observational studies in the field of low back pain consult the recently published STROBE (STrengthening the Reporting of OBservational studies in Epidemiology)  reporting guidelines. The experience of earlier initiatives to improve reporting such as the Consort, STARD and QUOROM statements  showed promising improvements.
Our data suggest that the interdisciplinary approach in patients at risk to develop chronic NSLBP is justified in both, the subacute and chronic stage. Psychosocial interventions might be more effective in subacute stages since a higher proportion of modifiable risk factors were identified in that group.
C. A. M. Heitz and R. Hilfiker equally contributed to this work.