Objective To assess the importance of psychological and culturally-influenced factors as predictors of low back pain (LBP) incidence and persistence in Spanish workers.
Methods As part of the international Cultural and Psychosocial Influences in Disability (CUPID) study, 1105 Spanish nurses and office workers answered questions at baseline about LBP in the past month and past year, associated disability, occupational lifting, smoking habits, health beliefs, mental health, and distress from common somatic symptoms. At 12-month follow-up, they were asked about LBP and associated disability in the past month. Associations with LBP incidence and persistence were assessed by log binomial regression, and characterised by prevalence rate ratios (PRRs) with associated 95% CIs.
Results 971 participants (87.9%) completed follow-up. Among 579 with no LBP at baseline, 22.8% reported LBP at follow-up. After adjustment for sex, age and occupation, new LBP was predicted by poor mental health (PRR 1.5, 95% CI 1.0 to 2.2), somatising tendency (PRR 1.8, 95% CI 1.2 to 2.7) and presence of LBP for >1 month in the year before baseline (PRR 4.7, 95% CI 3.1 to 6.9). Among 392 subjects who had LBP at baseline, 59.4% reported persistence at follow-up, which was associated with presence of symptoms for >1 month in the 12 months before baseline (PRR 1.4, 95% CI 1.2 to 1.7) and more weakly with somatising tendency, and with adverse beliefs about LBP work-relatedness and prognosis.
Conclusions In Spain, as in northern European countries, psychological and culturally-influenced factors have an important role in LBP development and persistence.
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What this paper adds
Studies carried out mainly in northern Europe have linked low back pain (LBP) and associated disability with psychological risk factors such as low mood somatising tendency and adverse health beliefs.
However, health beliefs, and perhaps somatising tendency, are likely to be influenced by the cultural environment, and three previous studies have suggested that in Spain, adverse fear-avoidance beliefs have little influence on disability from back pain.
This longitudinal study of Spanish nurses and office workers found that despite possible cultural differences from other countries, poor mental health and somatising tendency predicted subsequent incidence of LBP and associated disability.
Incidence of disabling LBP was also predicted by adverse beliefs about work as a cause of back pain, and somatising tendency was also a risk factor for persistence of LBP.
In Spain as elsewhere, interventions to prevent back disorders in the workplace should not necessarily be limited to the control of physical risk factors.
Low back pain (LBP) is a major cause of incapacity for work in industrialised countries and has a substantial economic impact.1 ,2 In Spain it has been estimated that the annual cost of workers’ compensation for LBP during 1993–97 was 11 billion pesetas (approximately €67 million).3
In western countries, 60–80% of people experience LBP at some point in their lives, and the symptom is often persistent or recurrent.4 Thus, past history of LBP has been found to predict its future occurrence.5 ,6 In addition, LBP has been linked with occupational activities that stress the spine, in particular heavy lifting, bending and twisting,7 and with psychological risk factors such as low mood, somatising tendency and adverse health beliefs.8 ,9
It is possible that people with low mood, tendency to somatise, and a belief that back pain commonly arises from injury to spinal tissues and often has a poor prognosis, are prone to dwell on back pain that others would dismiss. This on its own could cause the pain to persist and become more troublesome. In addition, they may be more inclined to modify their posture or activities to protect the back and reduce their pain, with adverse consequences for its resolution. Randomised controlled trials have shown that LBP resolves faster with continued activity rather than rest,10 and in Victoria, Australia, a media campaign with the message that back pain normally resolves quickly, and encouraging people with the symptom to remain active, was followed by a reduction in back-related disability for work.11 However, much of the evidence for a role of psychological factors comes from cross-sectional surveys, making it difficult to discern cause from effect. For example, while low mood may predispose to LBP, it is also reasonable to expect that LBP would lower mood.
Furthermore, most studies to date have been conducted in northern Europe, and few data are available on the impact of psychological risk factors for LBP in southern European countries such as Spain. Two different theoretical models have been proposed.12 The ‘social pathway model’ postulates that avoidance behaviours are influenced by a combination of a macrosystem of health beliefs and health culture with a microsystem of personal health beliefs, while another (the ‘depression pathway model’) postulates that a minority of patients with LBP have coexisting low mood, not necessarily as a response to pain, and that this state can by itself lead to poor pain recovery.12 Based on these theoretical models, even in pain-free individuals, health beliefs, and possibly also tendency to somatise, could be importantly influenced by beliefs and behaviours that are prevalent in the society in which an individual lives. Moreover, personality traits and learned behaviours could be activated and enhanced in a reciprocal process with the pain experience.13 If this is true, their nature and consequences could differ substantially between countries with different cultural attitudes to illness. Three earlier studies have suggested that, unlike in northern Europe, adverse fear avoidance beliefs have little influence on disability from LBP among primary care LBP patients and elderly Spanish people.14–16
The international Cultural and Psychosocial Influences in Disability (CUPID) study was established principally to investigate the influence of culturally-determined health beliefs and expectations on the occurrence of musculoskeletal symptoms and associated disability. To explore the role of mental health, somatising tendency and health beliefs as risk factors for the incidence and persistence of back symptoms and associated disability in a Spanish working population, we analysed longitudinal data on nurses and office workers that were collected as part of the CUPID study.
Data collection was carried out between November 2007 and February 2010 at four hospitals and a university in Barcelona. Prior approval was obtained from the Parc Salut Mar Ethics Committee of Barcelona and the Health and Safety Committee of each participating centre.
From employment records, we identified all permanently employed nursing staff (excluding those from out-patient clinics and paediatric wards) and office workers aged 20–59 years who had been in their current job for at least 12 months. At each centre, a trained member of staff contacted these individuals to explain the study and invite them to take part. Those who agreed were then interviewed at their place of work by a member of the research team, who administered a computer-assisted baseline questionnaire.
Among other things, the questionnaire asked about sex, age, smoking habits, occupational lifting, health beliefs about LBP, mental health, somatising tendency, history of LBP in the past 12 months, and associated disability. Subjects were classed as exposed to occupational lifting if they reported that an average working day entailed lifting weights >25 kg by hand. Questions about health beliefs were adapted from the Fear-Avoidance Beliefs Questionnaire17 and were grouped in three domains. Participants were considered to have adverse beliefs about physical activity if they completely agreed or tended to agree both that for someone with LBP, physical activity should be avoided as it might harm the back, and also that rest was needed to get better. They were deemed to have adverse beliefs about work-relatedness if they completely agreed or tended to agree that LBP was commonly caused by people's work. And they were classed as having adverse beliefs about prognosis if they both completely agreed or tended to agree that neglecting problems such as LBP can cause permanent health problems, and also completely disagreed or tended to disagree that LBP usually gets better within 3 months. Mental health was assessed through the relevant section of the SF-36 questionnaire,18 and scores were grouped in approximate thirds of the overall distribution (good, intermediate, poor). Somatising tendency was assessed using elements of the Brief Symptom Inventory,19 and subjects were classified according to the number of common somatic symptoms from a total of five (faintness or dizziness, pains in the heart or chest, nausea or upset stomach, difficulty breathing, and hot or cold spells) that had been at least moderately distressing during the past week.
LBP was ascertained through a question which asked whether, during the past 12 months, pain had been present for a day or longer in an anatomical area between the 12th ribs and the gluteal folds, which was depicted in a diagram. Those who answered yes were asked whether the pain had been present for more than 4 weeks in total, whether it had been present in the past month, and whether during the past month it had made it difficult or impossible to cut toe nails, get dressed or do normal jobs around the house. Pain in the past month was classed as disabling if it had rendered any of these activities difficult or impossible.
Participants who consented at baseline were subsequently re-interviewed after an interval of 12 months, using a follow-up questionnaire, which again asked about LBP and associated disability in the past month.
Both the baseline and follow-up questionnaires were originally drafted in English, translated into Spanish, and then independently back-translated into English. Where the back-translation revealed misinterpretation, the translated questionnaire was modified appropriately. In addition, before the data collection began, the baseline interviews were piloted in a sample of 30 nurses to check that questions were clearly understood.
Statistical analysis was carried out with Stata V.11 software.20 Log-binomial regression was used to explore risk factors for: (i) the presence of LBP in the past month at follow-up among subjects who had been free from LBP in the past month at baseline (development of new LBP); (ii) the presence of disabling LBP in the past month at follow-up among subjects who had been free from LBP in the past month at baseline (development of new disabling LBP); (iii) the presence of LBP in the past month at follow-up among subjects who had LBP in the past month at baseline (persistence of LBP); and (iv) the presence of disabling LBP in the past month at follow-up among subjects who had disabling LBP in the past month at baseline (persistence of disabling LBP). Associations were adjusted for potential confounding variables, and summarised by prevalence rate ratios (PRRs) and associated 95% CIs.
Among 1199 potentially eligible subjects who were invited to take part in the study, 1158 (96.6%) agreed. However, 53 were subsequently excluded because they were found not to meet all of the inclusion criteria. Thus, the baseline study sample comprised 1105 participants, of whom 667 were nurses and 438 office workers. Usable follow-up information was obtained for 971 (87.9%) of these subjects (578 nurses and 393 office workers). Response rates at follow-up were slightly lower in the youngest subjects (81.7% at ages 20–29 years), but otherwise differed little in relation to the baseline risk factors of interest (table 1).
Among the 971 subjects who completed follow-up, 579 (59.6%) had been free from LBP in the past month at baseline, and of these, 132 (22.8%) reported LBP and 41 (7.1%) disabling LBP when re-interviewed after 12 months. Table 2 shows associations of new LBP and new disabling LBP with various risk factors assessed at baseline. After adjustment for sex, age and occupation, development of new LBP was more common in those participants with poor mental health (PRR 1.5, 95% CI 1.0 to 2.2, in comparison with good mental health) and multiple distressing somatic symptoms (PRR 1.8, 95% CI 1.2 to 2.7), but the strongest predictor of new LBP was earlier history of the symptom, especially if it had been present for >1 month in the 12 months before baseline (PRR in comparison with no LBP in the past 12 months 4.7, 95% CI 3.1 to 6.9). In contrast, no association was apparent with occupational lifting, although there was a higher risk in nurses as compared with office workers (PRR 1.3, 95% CI 1.0 to 1.8). When risk estimates were mutually adjusted as well as being adjusted for sex, age and occupation, they shifted somewhat towards the null, but those for past history of LBP remained highly significant.
For new disabling LBP, past history of LBP, poor mental health and somatising tendency were again significant predictors, as were adverse beliefs about the work-relatedness of LBP (PRR 3.3, 95% CI 1.2 to 9.2), and being a former smoker (PRR in comparison with never smokers 2.9, 95% CI 1.5 to 5.8) but not a current smoker (PRR 0.9). However, occupational lifting was not associated with increased risk. When risk estimates were mutually adjusted, only those for adverse beliefs about work-relatedness, former smokers and past history of LBP remained statistically significant.
The subjects who completed follow-up also included 392 who had reported pain in the past month at baseline. Of these, 233 (59.4%) still had LBP at follow-up. After adjustment for sex, age and occupation, persistence of LBP was more frequent in those with LBP for >1 month in the 12 months before baseline (PRR 1.4, 95% CI 1.2 to 1.7), and was weakly associated with somatising tendency (PRR 1.3, 95% CI 1.0 to 1.5 for those with multiple as compared with no distressing somatic symptoms) and adverse beliefs about work-relatedness (PRR 1.2, 95% CI 1.0 to 1.5) and prognosis (PRR 1.2, 95% CI 1.1 to 1.4) of LBP (table 3). Mutually adjusted risk estimates were generally slightly lower.
Among 191 subjects with disabling LBP in the past month at baseline, 77 (40.3%) still had disabling LBP in the past month at follow-up. Persistence of disabling LBP was more common in those with LBP for >1 month in the 12 months before baseline (PRR 1.6, 95% CI 1.1 to 2.4) and with poor mental health (PRR 1.7, 95% CI 1.1 to 2.7, in comparison with good mental health) (table 4). Mutual adjustment had minimal impact on these risk estimates.
In this longitudinal survey of Spanish workers, low mood and somatising tendency were significantly associated with the subsequent incidence of LBP and disabling LBP, and low mood predicted the persistence of disabling LBP. There were also indications that adverse beliefs about the work-relatedness of LBP carried an increased risk of new disabling LBP.
As far as we know, this is the first study of this type among people of working age in Spain. As well as its longitudinal design, it had the strength of being based on a substantial sample of subjects, with high response rates both at baseline and at follow-up. In particular, the items on mental health and somatising tendency were taken from validated instruments18 ,19 and have previously demonstrated predictive validity for the incidence and persistence of musculoskeletal symptoms. Similarly, the questions on fear avoidance beliefs were based on a validated questionnaire17 and have shown predictive validity in a longitudinal study. There is no reliable standard against which to assess the accuracy with which subjective symptoms such as pain are reported, but the questions about pain and disability had again been used successfully in earlier studies. Moreover, the style of our questions about symptoms was similar to that of the Nordic questionnaire,21 which has been shown to have acceptable reliability.22
Against this, our measure of occupational lifting was fairly crude (eg, there was no attempt to assess the frequency of lifting tasks), and there was only limited heterogeneity of the exposure within each of the two occupational groups studied (which had been chosen with the intention that their exposure to physical risk factors should be fairly uniform). This limitation may explain why, after adjustment for occupation, we failed to find associations of lifting with either the incidence or persistence of LBP despite strong evidence from other studies that it is an important risk factor for low back disorders.7
Because it was possible that risk factors for incidence of LBP differ from those for persistence of pain that is already present, we looked separately at associations with new LBP among those who had been free from the symptom at baseline for at least 1 month, and with the continuing presence of LBP in those who had experienced it in the month before baseline. If anything, low mood and somatising tendency tended to be more strongly associated with incidence than persistence of pain. However, the PRRs for persistence were constrained by the high overall frequency (59.4%) of this outcome (if the prevalence in those unexposed to a risk factor is x%, the maximum possible PRR in those exposed is 100/x). Also, our definition of freedom from LBP at baseline was somewhat arbitrary. Nevertheless, we found no indication that low mood and somatising tendency were predictors only of pain persistence.
Our finding that incidence and persistence of LBP were predicted by low mood and tendency to somatise accords with results from longitudinal studies in other countries.8 ,9 Furthermore, although associations with these psychological risk factors were reduced after adjustment for past history of LBP, this does not necessarily argue against their having a causal role. If they are persistent characteristics, they may also have contributed to the earlier occurrence of back symptoms.
A relation between past history of LBP and incidence of new symptoms was expected, given the findings from other studies,5 ,6 although a recent systematic review concluded that previous LBP episodes were not a useful predictor of outcome in patients with new onset of LBP.23 One explanation for the association with incident LBP might be that pain arises from structural abnormalities in the spine which persist even when the symptom resolves, and then lead to further episodes. However, demonstrable spinal pathologies such as herniated inter-vertebral disc, nerve root compression, disc degeneration and annular tear, appear to account for only a minority of cases of LBP.24 Another possible explanation is continuing exposure to important risk factors for LBP, either physical or psychological, although in our analysis, the associations with past history of LBP were little reduced by adjustment for the other risk factors analysed. It could also be that some individuals have a persistently heightened awareness of back symptoms and lower threshold for resultant disability.
It has been postulated that LBP and associated disability may also be importantly influenced by culturally determined health beliefs and expectations, and that this might explain striking temporal changes that have occurred in Britain over the past 60 years in rates of incapacity for work attributed to back disorders.25 In this study, we found some indications that the development of disabling LBP was associated with beliefs about its relation to work, and others have observed that fear-avoidance beliefs were associated both with new onset of LBP26 and also with worse prognosis in patients with established LBP.23 ,27 Three earlier studies carried out in Spanish populations suggested that the influence of fear-avoidance beliefs on LBP and associated disability was relatively small.14–16 However, these were cross-sectional and restricted to LBP patients and older subjects.
In addition to associations with psychological risk factors and past history of LBP, we also found an increased risk of new disabling pain among former smokers (table 2). However, the absence of any increased risk among current smokers suggests that this was a chance observation.
In summary, our findings indicate that despite possible cultural differences, and contrary to indications from earlier studies in older populations, among people of working age in Spain, as in northern European countries, psychological factors have an important role in the development and persistence of LBP. It follows that in Spain, as elsewhere, interventions to prevent back disorders in the workplace should not necessarily be limited to the control of physical risk factors. Job modification and ergonomic improvements may enable people with LBP to remain at work or to return to work earlier than they would otherwise have done. However, randomised controlled trials of ergonomic interventions for the prevention of LBP have tended to demonstrate an absence of benefit.28 This suggests that there is a case for a more holistic approach to prevention.
The study was conducted thanks to the participation of four hospitals (Badalona Serveis Assistencials, Consorci Sanitari Integral, Corporació Sanitària i Universitària Parc Taulí and Parc de Salut Mar) and Universitat Pompeu Fabra. The authors are very grateful to the following professionals for their contributions to participant recruitment: Xavier Orpella (Badalona Serveis Asistencials), Joan Bas (Consorci Sanitari Integral), Pilar Peña (Corporació Sanitària i Universitària Parc Taulí), Elena Brunat and Vicente San José (Parc de Salut Mar), and Fina Lorente, Anna Sala, Anna Marquez and Cristina Oliva (Universitat Pompeu Fabra). We also want to thank Montse Vergara (CiSAL) for providing the electronic version of the questionnaire.
Contributors All of the authors listed on the paper fulfil criteria for authorship and jointly participated in the study design, data analysis and drafting of the manuscript. Moreover, all authors reviewed numerous drafts of the manuscript and are in agreement with the text and findings and have all approved this final version.
Funding This project was funded by the Spanish Health Research Fund (FIS 070422).
Competing interest None.
Ethics approval Parc Salut Mar Ethics Committee of Barcelona and the Health and Safety Committee of each participating centre approved this study.
Provenance and peer review Not commissioned; externally peer reviewed.