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Risk Factors for the Onset of Nonspecific Low Back Pain in Office Workers: A Systematic Review of Prospective Cohort Studies
LITERATURE REVIEW RISK FACTORS FOR THE ONSET OF NONSPECIFIC LOW BACK PAIN IN OFFICE WORKERS: A SYSTEMATIC REVIEW OF PROSPECTIVE COHORT STUDIES Prawit Janwantanakul, PhD, a Ekalak Sitthipornvorakul, BSc (Hon), b and Arpalak Paksaichol, MSc b
ABSTRACT Objective: The purpose of this study was to systematically review prospective cohort studies to identify risk factors for the onset of low back pain (LBP) in office workers. Methods: Online searches were conducted on PubMed, CINAHL Plus with full text, ScienceDirect, PEDro, ProQuest, and Scopus databases from 1980 to November 2011 using the following keywords: low back pain paired with risk or prognostic factors and office or computer or visual display unit (VDU) or visual display terminal (VDT). The methodological quality of each study was assessed using a 21-item checklist, which was divided into 2 parts: the internal validity (11 items) and descriptive quality (10 items) of studies. Strength of evidence for risk factors associated with the development of nonspecific LBP was assessed by defining 5 levels of evidence based on the number of studies and the quality score of studies. Results: Eighteen full-text articles were identified, and 15 were excluded. A total of 3 articles were judged to meet the selection criteria and were included in the methodological quality assessment. Risk factors were divided into 3 groups: individual, work-related physical, and work-related psychosocial risk factors. There was strong evidence that history of LBP is a predictor of the onset of LBP. Limited evidence was found that the combination of postural risk factors and job strain is associated with the onset of LBP. Conclusion: After review of 3 high-quality prospective studies on the association between risk factors and the onset of nonspecific LBP in office workers, few risk factors were found to predict the onset of LBP in office workers. (J Manipulative Physiol Ther 2012;35:568-577) Key Indexing Terms: Musculoskeletal Diseases; Risk Factors; Low Back Pain; Computers; Review
ow back pain (LBP) is a significant health problem in office workers with a 1-year prevalence rate of between 34% and 51% 1,2 and a 1-year incidence rate of 23%. 3 A significant portion of patients with LBP has developed chronicity. 4,5 As a result, LBP causes consider-
L a
Associate Professor, Department of Physical Therapy, Faculty of Allied Health Sciences, Chulalongkorn University, Bangkok, Thailand. b PhD Candidate, Department of Physical Therapy, Faculty of Allied Health Sciences, Chulalongkorn University, Bangkok, Thailand. Submit requests for reprints to: Prawit Janwantanakul, PhD, Associate Professor, Department of Physical Therapy, Faculty of Allied Health Sciences, Chulalongkorn University, 154 Rama I Road, Pathumwan, Bangkok, Thailand 10330 (e-mail: [email protected]). Paper submitted February 20, 2012; in revised form June 28, 2012; accepted July 4, 2012. 0161-4754/$36.00 Copyright © 2012 by National University of Health Sciences. http://dx.doi.org/10.1016/j.jmpt.2012.07.008
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able personal suffering due to pain, disability, and impaired quality of work and life in general, which can result in a significant socioeconomic burden on both patients and society. In the United States, the total cost of LBP in 2006 exceeded 100 billion US dollars, 6 whereas in the Netherlands, the total cost of LBP in 2007 was estimated at 3.5 billion euro. 7 The cost of LBP to society is likely to increase, given that many developing nations have been industrializing their economy, thus increasing the number of workers in the office environment at the global level. The etiology of LBP is assumed to be of multifactorial origin and often includes individual, physical, and psychosocial factors that may contribute to the development and persistence of low back disorders. 8 Each occupation exposes workers to varied and unique conditions, activities, and stressors. The nature of work varies greatly across employment sectors and has been recognized as influencing the health of workers. 9 Thus, predisposing factors for musculoskeletal symptoms in different occupations are assumed to be dissimilar and related to those characteristic exposures, demands, and conditions of the specific job. 10
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Office work is sedentary work in nature, which commonly involves prolonged sitting, computer use, participation in meetings, giving presentations, reading documents and materials, and frequent use of the telephone and other electronic devices. 11 Physiologic deconditioning 12 and/or accumulation of musculoskeletal overload 13 may increase the office worker's susceptibility to LBP. Prolonged sitting or sustained lumbar flexion, which has been found to reduce the ability of the spine to resist force acting upon it, 14 may predispose the lumbar spine to injury during loading. Office work also unavoidably causes mental stress, which may play an intermediate role in causing LBP. 15 Studies have identified several individual factors associated with LBP in office workers, including older age, female sex, high body mass index, smoking, and previous symptoms. 3,16,17 Regarding work-related risk factors, more senior position, sitting for long hours, poor workstation ergonomics, and awkward working postures have been linked to increased risk of LBP. 16-19 Some psychosocial problems, such as job satisfaction, repetitive work, job strain, and anger during last 30 days, have also been found to contribute to an increased occurrence of LBP. 17,19 However, a number of these studies were cross-sectional in design, 16-18 which only allowed for the association between exposures and outcome to be examined. It is therefore not possible to establish the causal relationship between exposures and outcome. Research to identify the causal factors of a disease requires longitudinal research design, which permits the tracking of study participants' activities, health status, and exposures over time. 20 The aim of this article is to systematically review prospective cohort studies to gain insights into the status of literature investigating risk factors for the onset of LBP in office workers as well as to assess the strength of evidence. Such information would be of value for policy makers and health care providers to determine effective prevention measures to decrease the incidence and burden of LBP in the workplace.
METHODS Data Sources and Search Strategy Online searches were conducted on PubMed, CINAHL Plus with full text, ScienceDirect, PEDro, ProQuest, and Scopus databases from 1980 to November 2011 using the following keywords: low back pain paired with risk or prognostic factors and office or computer or visual display unit (VDU) or visual display terminal (VDT). Articles were initially screened based on title and abstract; full-text copies were then retrieved of articles that met all inclusion criteria. Subsequently, full-text copies were read to make a final decision regarding inclusion or exclusion. The search and full inclusion process were performed by 1 reviewer (ES). After inclusion of the articles based on the selection criteria, references were searched for additional articles.
Janwantanakul et al Risk Factors for Low Back Pain
Selection of Studies A reviewer (ES) selected relevant articles from the articles retrieved using the search strategy. The selection criteria were the following: 1. The study population was office workers or those working with computers or visual display units or visual display terminals. 2. Study samples were free from LBP at baseline assessment. Studies in a population with specific underlying pathology, such as tumors, fractures, infection, inflammatory disorders, and osteoporosis, were excluded. 3. The study design was a prospective cohort study with a follow-up period of 1 year or more. Experimental studies were excluded. 4. The onset of LBP was assessed separately from other musculoskeletal symptoms. 5. Nonspecific LBP, that is, LBP (with or without radiation) without any specific systematic disease being detected as the underlying cause of the complaints, was assessed in the study. 6. The article was a full, peer-reviewed report published in English. Letters, abstracts, books, conference proceedings, and posters were excluded.
Quality Assessment of Studies The articles that met the selection criteria were independently evaluated by 2 reviewers (ES and AP) to determine methodological quality. The methodological quality of each study was assessed by using a 21-item checklist for quality appraisal modified from van der Windt et al 21 and Ariëns et al 22 (Table 1). The checklist was divided into 2 parts: the internal validity (11 items) and descriptive quality (10 items) of studies. Each item was scored as positive (1), negative (0), or unclear (if insufficient information was available for a specific item) (0). The scoring for each item of the 2 reviewers was compared. Disagreements between the reviewers on individual items were identified and discussed in an attempt to achieve consensus. The interrater agreement of this quality assessment was derived by calculating the percentage agreement as well as Cohen κ for categorical items, both before and after the consensus discussion. If agreement could not be reached, a third reviewer (PJ) was consulted to achieve a final judgment. Studies scoring a minimum of 6 of 11 (N50%) for internal validity with a total score of 11 of 21 (N50%) or greater were deemed “high quality.” 21-25
Data Extraction Data extraction was performed by the first reviewer (ES). For each article, the first author and year of publication, study population, sample size, drop-out rate,
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Table 1. Methodological quality criteria Item
Score
Internal validity criteria Study population 1. Positive if the participation rate is ≥80% or if participation rate is 60%-80% and nonresponse is not selective (data presented) 2. Positive if the response at main moment of follow-up is ≥80% or if the nonresponse is not selective (data presented) Exposure assessments, physical load at work (if not included in the design, not applicable) 3. Method for measuring physical load at work: direct measurement and observation (+), interview, or questionnaire only (−) 4. Positive if N1 dimension of physical load is assessed: duration, frequency, or amplitude 5. Positive if N1 aspect of psychosocial factors is assessed: work demands, job control, social support Outcome assessments 6. Positive if data were collected for ≥1 y 7. Method for assessing LBP: physical examination blinded to exposure status (+), self-reported: specific questions relating to LBP or use of manikin (+), single question (−) Analysis and data presentation 8. Positive if the appropriate statistical model is used (univariate or multivariate model) 9. Positive if measures of association are presented (OR/RR), including 95% CIs and numbers in the analysis (totals) 10. Positive if the analysis is controlled for confounding or effect modification is studied 11. Positive if the number of cases in the multivariate analysis is at least 10 times the number of independent variables in the analysis (final model) Descriptive quality criteria Study objective 12. Positive if a specific, clearly stated objective is described Study population 13. Positive if the main features of the study population are described (sampling frame and distribution of the population by age and sex) Exposure assessments, physical load at work (if not included in the design, not applicable) 14. Positive if data are collected and presented about physical load at work 15. Positive if the data on physical load at work were collected using standardized methods of acceptable quality a Exposure assessments, psychosocial factors at work (if not included in the design, not applicable) 16. Positive if data are collected and presented about psychosocial factors at work 17. Positive if the data on psychosocial factors at work were collected using standardized methods of acceptable quality a Exposure assessments, other 18. Positive if data are collected and presented about physical or psychosocial exposure during leisure time 19. Positive if data are collected and presented about history of LBP Outcome assessments 20. Positive if data were collected at least every 3 mo 21. Positive if the data on outcome were collected using standardized methods of acceptable quality a
+/−/? +/−/? +/−/? +/−/? +/−/? +/−/ +/−/
+/−/ +/−/ +/−/ +/−/
+/−/ +/−/
+/−/ +/−/ +/−/ +/−/ +/−/ +/−/ +/−/ +/−/
+, positive; −, negative; ?, unclear. a This item was scored positive if one of the following criteria was met: (i) for direct measurements, intraclass correlation coefficient greater than 0.60 or κ greater than 0.40; (ii) for observational methods, intraclass correlation coefficient greater than 0.60 or κ greater than 0.40 for the interobserver or intraobserver reliability; and (iii) for self-reported data, intraclass correlation coefficient greater than 0.60 or κ greater than 0.40 for the interobserver or intraobserver reliability.
outcome measured (pain and disability), duration of followup, risk factors, the strength of the association between risk factors, and the onset of LBP in terms of odds ratio (OR), hazard ratio (HR), or rate ratio (RR) with 95% confidence interval (CI) were extracted.
• Limited evidence: findings of one high-quality study or consistent findings in one or more low-quality studies. • Conflicting evidence: inconsistent findings irrespective of study quality. • No evidence: no studies found.
Data Analysis The strength of evidence for risk factors associated with the development of nonspecific LBP was assessed by defining 5 levels of evidence based on the number of studies and the quality score of studies 26: • Strong evidence: consistent findings from 2 or more high-quality cohorts. • Moderate evidence: consistent findings from at least one high-quality study and one or more low-quality cohorts.
A risk factor association was considered positive only if it was statistically significant and was derived from multivariate results. A risk factor association was considered negative only if it was statistically insignificant and was derived from multivariate results. Statistical significance was concluded if the reported P value was less than .05 or if the 95% CIs around an RR or similar statistic (such as OR or HR) did not cross 1.
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Janwantanakul et al Risk Factors for Low Back Pain
Computerized search of databases by one reviewer (n=7,112)
Excluded
7,094 abstracts did not meet the selection criteria based on screening of abstracts and titles
18 full-text articles retrieved for closer inspection by one reviewer
Excluded
References search for additional articles 0 articles
15 articles did not meet the selection criteria based on full-text articles 12 articles were not conducted on office workers 1 article assessed low back pain but not separately from other symptoms 1 article assessed specific low back pain 1 article included symptomatic subjects at baseline assessment
3 articles were included for methodological quality assessment
Fig 1. Flow diagram of the data screening process.
Sensitivity Analysis
Methodological Quality Assessment
Sensitivity analysis was conducted to assess whether a priori cutoff point of greater than 50% for study quality might have influenced the level of evidence and, potentially, the results of the review. Thus, the effect of the cutoff point used in the methodological quality assessment for qualification as a high-quality study on the synthesized results was assessed by shifting the cutoff point from greater than 50% to greater than 60% or shifting the cutoff point from greater than 50% to greater than 70%.
The scoring of 2 reviewers of the included studies before discussion had an agreement rate of 78% (49/63). The overall interrater agreement was κ = 0.54 with an SE of measurement of 0.11. After discussion, the 2 reviewers had an agreement rate of 98% (62/63). Then, the overall interrater agreement was κ = 0.96 with an SE of measurement of 0.03. This represents very good agreement between the 2 reviewers. 28 Disagreements were often related to reading errors or interpretation of the quality criteria list. These disagreements were resolved during a consensus meeting. However, disagreements persisted on 1 item (item 9) in the study from Verbeek and van der Beek. 27 A third reviewer (PJ) made the final decision in this case. The results of the methodological quality appraisal are presented in Table 2. The scores for the methodological quality of the studies ranged from 12 to 14 points (57%67%). The median score was 14 points (67%). All 3 studies were scored as high-quality studies. 3,19,27 The items in the criteria list rated as negative in most studies were participation rate (item 1, 0%), assessment of physical load at work (item 3, 0%), quality of assessment
RESULTS Selection of Studies The initial search of the computerized databases yielded 7112 citations (Fig 1). After the screening of abstracts and titles, 18 full-text articles were read in full. Fifteen articles were excluded because they did not meet the selection criteria. A total of 3 articles were judged to meet the selection criteria and were included in the methodological quality assessment. 3,19,27
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14/21 (67) 14/21 (67) 12/21 (57)
method for physical load at work (item 15, 0%), assessment of exposure during leisure time (item 18, 0%), and frequency of data collection during follow-up period (item 20, 0%).
6/10 6/10 6/10
Study Characteristics
− − + 33 − − − 0
− − − 0
+ + − 67
All included studies were conducted on office workers or computer users (Table 3). The sample sizes varied greatly from 271 to 3475. The drop-out rate during follow-up ranged from 7% to 30%. Lapointe et al 19 defined incident cases as those experiencing LBP, ache, or discomfort during the study period, whereas Verbeek and van der Beek 27 defined incident cases as those experiencing pain or stiffness in the back during the study period. Juul-Kristensen et al 3 defined incident cases as those reporting increased frequency of days with LBP during the study period, from less than 8 days in the baseline questionnaire to greater than 7 days in the follow-up questionnaire. The follow-up period was between 0.6 and 5.6 years.
+ + + 100
Summary of Risk Factors
+, positive; −, negative; ?, unclear; DQ, descriptive quality; IV, internal validity.
+ − − 33 − − ? 0 Juul-Kristensen et al3 Lapointe et al19 Verbeek and van der Beek27 Positive (%)
− + − 33
− − − 0
+ + + 100
+ + + 100
+ + + 100
+ + + 100
+ + − 100
+ + + 100
+ + + 100
8/11 8/11 6/11
+ + + 100
+ + + 100
− − 0
+ + + 100
+ + + 100
19 17 16 15 14 13 12 4 1 Study reference
2
3
5
6
7
8
9
10
11
IV score
DQ criteria IV criteria
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18
20
21
DQ score
Total score (%)
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Table 2. Methodological quality score of three studies (studies are ranked according to their total scores and, in case of equal ranking, in alphabetical order of the first author's surname)
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Risk factors were divided into 3 groups: individual, work-related physical, and work-related psychosocial risk factors (Table 4). All factors (21/22) but history of LBP were investigated by only 1 study. There was strong evidence that history of LBP is a predictor of the onset of LBP. Limited evidence was found that the combination of postural risk factors and job strain (for females only) is associated with the onset of LBP. There was limited evidence that age, general health complaints, daily computer use, adjustability of chair or desk, availability of arm rest, screen height relative to eye level, frequency of standing during work, disturbance of glares or reflection, influence on the timing of work pauses, necessity to work fast, frequency of feeling discomfort while sitting, frequency of feeling discomfort with climatic condition, cognitive and sensory demand, influence at work, developmental possibilities, social support, job demands, depression, and the combination of low/high postural risk factors and high/ low job strain (for males only) have no predictive value for the onset of LBP.
Sensitivity Analysis Changing the cutoff point from greater than 50% to greater than 60%, 2 conclusions would be altered including: • The level of evidence for history of LBP would change from strong to moderate. • The level of evidence for age, general health complaints, frequency of feeling discomfort while sitting, frequency of feeling discomfort with climatic condition, job demands, and depression would change from limited “no” to no evidence.
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Table 3. Summary of study characteristics Study population, sample size, and drop-out at follow-up
Study Juul-Kristensen et al
Lapointe et al19
Verbeek and van der Beek27
3
Office workers in Denmark n = 3475 Drop-out 23%
Outcome measurement (follow-up period)
Risk factors
Strength of association
Frequency or intensity of LBP (17-23 mo; mean, 21 mo)
Multivariate logistic regression model adjusted for sex and age (with 95% CI) Previous symptoms OR, 2.4 (1.70-3.39) (for frequency of LBP) White-collar workers at the 6-mo incidence proportion Multiple logistic regression model 3 large public service of lower back adjusted for age, stressful life organizations in Québec symptoms event at baseline and follow-up, City, Canada (0.6-5.6 y; mean, 3.2 y) number of children, education n = 2431 level, and musculoskeletal symptoms to other body Drop-out 7% regions at baseline (with 95% CI) Low postural risk factors OR, 2.53 (1.09-5.85) and high job strain (for females only) High postural risk factors OR, 2.51 (1.23-5.09) and low job strain (for females only) High postural risk factors OR, 5.51 (2.33-13.03) and high job strain (for females only) Office workers at the social Back pain during the Multiple logistic regression service department of the city past year model (with 90% CI) of Amsterdam (12 months) Prior back pain ≤4 on VAS OR, 3.0 (1.5-6.0) n = 271 Prior back pain N 4 on VAS OR, 10.3 (4.1-25.5) Drop-out 30%
With a cutoff point of greater than 70%, there would have been no study obtaining high-quality status.
DISCUSSION The present review is the first to summarize the results of prospective cohort studies on individual, work-related physical, and work-related psychosocial factors for the development of nonspecific LBP. In undertaking this review, we were surprised to discover that there have been very few prospective cohort studies on risk factors for the onset of nonspecific LBP in office workers that were qualified according to the selection criteria. We found heterogeneity among studies as to aspects such as case definition, risk factors, and follow-up duration. Thus, the analysis of the results was limited to a qualitative summary. Of 22 investigated factors, the results indicated strong evidence for history of LBP and limited evidence for the combination of postural risk factors and job strain (for females only) as predictors for new-onset LBP in office workers. Most factors previously investigated have no predictive value for future LBP, such as age, daily computer use, workstation ergonomics, social support, and job demands.
Methodological Considerations The items in the criteria checklist rated as negative in all 3 studies were participation rate, assessment method of physical load at work and its quality, assessment of
exposure during leisure time, and frequency of data collection during follow-up period. No included studies had a participation rate of 80% or higher. 3,19,27 In general, studies with low levels of participation may be more vulnerable to self-selection bias than those with high participation. 29 Therefore, a low participation rate in a population survey may threaten the internal validity of studies. 30 Common methods for the assessment of physical exposures at work include subjective judgment, systematic observation, and direct measurement. 31,32 All studies used a self-reported questionnaire to assess physical load at work. 3,19,27 Many of the subjective methods, particularly those nonstandardized methods of acceptable quality, had problems with test-retest reliability, which may have led to a poor validity of exposures. 33,34 All included studies did not report the test-retest reliability of their measurement tools. Using a reliable systematic observation or objective measurement, instead of subjective judgment, to evaluate physical load at work is recommended to improve the quality of data. This is also true for the onset of LBP, which was diagnosed based upon self-report only in all studies. Some workers may be more sensitive to any somatic disturbance than others. As a result, there is the risk of an overreport of the incidence. The inclusion of information from a physical examination should be considered as increasing the accuracy of diagnosis. All included studies did not measure physical exposures during leisure time. Apart from work time, exposures
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Table 4. Overall level of evidence for risk factors and their association for the onset of LBP in office workers
Group Individual
Risk factor
History of LBP Age General health complaints Work-related Daily computer physical use Adjustability of chair Adjustability of desk Availability of arm rest Screen height relative to eye level Frequency of standing during work Disturbance of glares or reflection Influence on the timing of work pauses Necessity to work fast Frequency of feeling discomfort while sitting Frequency of feeling discomfort with climatic condition Work-related Cognitive demand psychosocial Sensory demand Influence at work Developmental possibilities Social support Job demands Depression Combination of postural risk factors and high job strain Females Males
Cohorts assessed + findings
+ high + low quality quality (references) (references) − findings
− high − low quality quality Level of (references) (references) evidence
2 1 1
2/2 (100%) 2 (3, 27) – – – –
– – –
– – 1/1 (100%) 1 (27) 1/1 (100%) 1 (27)
– –
Strong Limited no. Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (27)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (27)
–
Limited no.
1 1 1 1
– – – –
– – – –
– – – –
1/1 (100%) 1/1 (100%) 1/1 (100%) 1/1 (100%)
– – – –
Limited no. Limited no. Limited no. Limited no.
1 1 1
– – –
– – –
– – –
1/1 (100%) 1 (3) 1/1 (100%) 1 (27) 1/1 (100%) 1 (27)
– – –
Limited no. Limited no Limited no.
1 1
1/1 (100%) 1 (19) – –
– –
– – 1/1 (100%) 1 (19)
– –
Limited Limited no.
1 (3) 1 (3) 1 (3) 1 (3)
Positive findings (+ findings) were considered significant associations (P b .05 or the 95% CIs around RRs, ORs, or HRs did not cross 1) from the multivariate results. Negative findings (− findings) were considered not significant associations.
during leisure time should be assessed and included as part of the cumulative dose that an individual is exposed to. Previous studies demonstrated the association between physical activity during leisure time and LBP. 35,36 Measuring exposure during both work and leisure time may be more representative of an individual's exposure. The frequency of data collection of LBP incidence during the follow-up period for the included studies varied
considerably, ranging from 0.6 to 5.6 years. All studies collected data only twice: at the beginning and the end of study. A longer recall period regarding the incidence of LBP during follow-up period may increase recall bias. 37 This bias may be pronounced in studies in which detailed information, such as the duration of experiencing pain and/ or pain intensity, was required. Regular data collection during the follow-up period is recommended.
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Evidence of Risk Factors for the Onset of LBP in Office Workers In this review, the onset of LBP was considered to be the onset of any reported low back symptoms, regardless of severity of symptoms, duration of symptoms, and level of disability. This pragmatic choice was made because of the fact that this review focused on a specific group of the population and only a small number of studies qualified for inclusion in the review. Of the 3 studies, 2 followed up for 1 year or more, 3,27 and the remaining study followed up between 0.6 and 5.6 years, with an average of 3.2 years. 19 The predictive value of any exposures depends on the duration of follow-up as well as the disease of interest. A long duration of follow-up is generally considered a strength in prospective cohort studies, as it usually results in a larger number of cases and thereby increases the power of the statistical analysis. 38 Thus, a long duration of follow-up is likely to enhance the internal validity of the study. In the literature, there are 2 systematic review studies on risk factors for the onset of LBP. However, both studies focused on psychologic factors. 39,40 In the general population, Hoogendoorn et al 39 systematically reviewed cohort and case-control studies for psychosocial factors at work and in private life that predicted the occurrence of back pain and found strong evidence for low social support in the workplace and low job satisfaction. In the working population, Linton 40 in their systematic review of prospective cohort studies found moderate to strong evidence for job satisfaction, monotonous tasks, work relations, demands, stress, perceived ability to work, work pace, control, emotional effort at work, and the belief that work is dangerous. The predictive value of most factors identified in previous reviews could not be confirmed in the present review, which only showed strong evidence for history of LBP and limited evidence for the combination of postural risk factors and job strain as predictors of the onset of LBP among office workers. One possible explanation for the observed variation in the results among studies may be due to the limited number of studies in a population of office workers. However, the findings suggest that risk factors for the onset of LBP in a subpopulation may be a subset of risk factors identified in a general population or occupation specific. 9 To gain further insight into risk factors for the development of LBP, future studies should consider the investigation of risk factors in a more specific group of the population. Although history of LBP is a nonmodifiable risk factor, this information is useful for clinicians when planning preventive measures for LBP among office workers. By identifying those at risk (ie, office workers with history of LBP), this would mean the enhancement of resource allocation to those most in need and most likely to benefit from it. Otherwise, a large number of people would receive intervention, which is likely to compromise its
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effectiveness. 41,42 The combination of 2 risk factors (ie, poor working postures and high job strain) appears to predispose female office workers to new-onset LBP. Thus, the prevention of LBP among female workers should at least include identifying the causes of poor working postures and high job strain and then developing strategies to rectify them.
Sensitivity Analysis By changing the cutoff point from greater than 50% to greater than 60%, some conclusions about risk factors with strong and limited evidence, namely, history of LBP, age, general health complaints, frequency of feeling discomfort while sitting, frequency of feeling discomfort with climatic condition, job demands, and depression, would alter. Because all included studies had total scores of less than 70%, shifting the cutoff point from greater than 50% to greater than 70% would have led to no study qualifying as a high-quality study. This variation in the level of evidence reflects the fact that there have been very few good-quality studies investigating risk factors for the development of LBP in office workers. Most of the factors included in the review have been supported by evidence from 1 highquality study only. Thus, this review was limited in its ability to draw conclusions about the predictive nature of these factors, and the conclusions may change or additional risk factors will be identified when new studies become available in the future. The findings point out an urgent need for further study in this area before any firm conclusions can be drawn.
Strengths and Limitations The major strength of this study is that the literature was systematically searched, articles were evaluated for their methodological quality by 2 independent reviewers, and information was extracted and synthesized based on the number of studies and the quality score of studies. In addition, the inclusion of only prospective cohort studies allows for the establishment of the causal relationship between exposures and outcome. However, the limitations of the present review should be taken into consideration when interpreting its results. First, the search strategy was limited to full reported publications in English. The possibility of publication and selection bias cannot be ruled out, which may have affected the results of this review. Second, the researchers summarized the results from studies with substantial heterogeneity in study characteristics. This may explain the observed variation in the results among studies. Future research is required to indicate whether differences in these aspects affect the association between risk factors and the onset of LBP. Last, as no universally accepted quality assessment tool for prospective cohort studies exists, the quality assessment tool used in the present review was based on the assembly of criteria lists in the previous reviews. 21,22 In addition, the
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quality assessment tool was arguably divided into 2 parts: the internal validity (11 items) and descriptive quality (10 items) of studies. However, it is believed that the items included in the quality assessment tool assessed the important components to validate these types of studies.
CONCLUSION Three high-quality prospective studies on the association between risk factors and the onset of nonspecific LBP in office workers were reviewed and analyzed. Very few risk factors were found to predict the onset of LBP in office workers, which included history of LBP and the combination of postural risk factors and job strain. Because all but 1 factor have been investigated by only 1 study and there are several methodological limitations among included studies, this review was limited in its ability to draw conclusions about the factors leading to LBP in office workers and the conclusions may change when new studies become available in the future. The health of office workers deserves consideration, and more research is needed on this topic.
Practical Applications • Strong evidence was found for history of LBP to be a predictor of the onset of LBP in office workers. • Most factors previously investigated have no predictive value for future LBP, such as age, daily computer use, workstation ergonomics, social support, and job demands. • There have been very few prospective cohort studies on risk factors for the onset of nonspecific LBP in office workers, and thus, more highquality studies in this area are needed.
FUNDING SOURCES AND POTENTIAL CONFLICTS OF INTEREST This work was funded by Chulalongkorn University Centenary Academic Development Project (no .12). No conflicts of interest were reported for this study.
REFERENCES 1. Ayanniyi O, Ukpai BO, Adeniyi AF. Differences in prevalence of self-reported musculoskeletal symptoms among computer and non-computer users in a Nigerian population: a cross-sectional study. BMC Musculoskelet Disord 2010;11:177. 2. Janwantanakul P, Pensri P, Jiamjarasrangsri V, Singsongsook T. Prevalence of self-reported musculoskeletal symptoms among office workers. Occup Med (Lond) 2008;58: 436-8.
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3. Juul-Kristensen B, Søgaard K, Strøyer J, Jensen C. Computer users' risk factors for developing shoulder, elbow and back symptoms. Scand J Work Environ Health 2004;30:390-8. 4. Costa CM, Maher CG, McAuley JH, et al. Prognosis for patients with chronic low back pain: inception cohort study. BMJ 2009;339:b3829. 5. Henschke N, Maher CG, Refshauge KM, et al. Prognosis in patients with recent onset low back pain in Australian primary care: inception cohort study. BMJ 2008;337:a171. 6. Katz JN. Lumbar disc disorders and low-back pain: socioeconomic factors and consequences. J Bone Joint Surg Am 2006;88:21-4. 7. Lambeek LC, van Tulder MW, Swinkels IC, et al. The trend in total cost of back pain in The Netherlands in the period 2002 to 2007. Spine 2011;36:1050-8. 8. Manchikanti L. Epidemiology of low back pain. Pain Physician 2000;3:167-92. 9. Côté P, van der Velde G, Cassidy JD, et al. The burden and determinants of neck pain in workers. Results of the bone and joint decade 2000–2010 task force on neck pain and its associated disorders. J Manipulative Physiol Ther 2009;32: S70-86. 10. Sihawong R, Janwantanakul P, Sitthipornvorakul E, Pensri P. Exercise therapy for office workers with nonspecific neck pain: a systematic review. J Manipulative Physiol Ther 2011; 34:62-71. 11. IJmker S, Blatter BM, van der Beek AJ, van Mechelen W, Bongers PM. Prospective research on musculoskeletal disorders in office workers (PROMO): study protocol. BMC Musculoskelet Disord 2006;7:55. 12. Mikkelsson LO, Nupponen H, Kaprio J, et al. Adolescent flexibility, endurance strength, and physical activity as predictors of adult tension neck, low back pain, and knee injury: a 25 year follow up study. Br J Sports Med 2006;40: 107-13. 13. Hedman TP, Fernie GR. Mechanical response of the lumbar spine to seated postural loads. Spine 1997;22:734-43. 14. Adams MA. Mechanical testing of the spine—an appraisal of methodology, results and conclusions. Spine 1995;20:2151-6. 15. Gomzi M, Bobic J, Radosevic-Vidacek B, et al. Sick building syndrome: psychological, somatic, and environmental determinants. Arch Environ Occup Health 2007;62:147-55. 16. Omokhodion FO, Sanya AO. Risk factors for low back pain among office workers in Ibadan, Southwest Nigeria. Occup Med (Lond) 2003;53:287-9. 17. Spyropoulos P, Papathanasiou G, Georgoudis G, et al. Prevalence of low back pain in Greek public office workers. Pain Physician 2007;10:651-9. 18. Janwantanakul P, Pensri P, Jiamjarasrangsri V, Sinsongsook T. Associations between prevalence of self-reported musculoskeletal symptoms of the spine and biopsychosocial factors among office workers. J Occup Health 2009;51:114-22. 19. Lapointe J, Dionne CE, Brisson C, Montreuil S. Interaction between postural risk factors and job strain on self-reported musculoskeletal symptoms among users of video display units: a three-year prospective study. Scand J Work Environ Health 2009;35:134-44. 20. Caroll LJ, Hogg-Johnson S, Côté P, et al. Course and prognostic factors for neck pain in workers. Results of the bone and joint decade 2000–2010 task force on neck pain and its associated disorders. J Manipulative Physiol Ther 2009;32: S108-16. 21. van der Windt DAWM, Thomas E, Pope DP, et al. Occupational risk factors for shoulder pain: a systematic review. Occup Environ Med 2000;57:433-42.
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22. Ariëns GA, van Mechelen W, Bongers PM, Bouter LM, van der Wal G. Physical risk factors for neck pain. Scand J Work Environ Health 2000;26:7-19. 23. Hoogendoorn WE, van Poppel MN, Bongers PM, Koes BW, Bouter LM. Physical load during work and leisure time as risk factors for back pain [review]. Scand J Work Environ Health 1999;25:387-403. 24. Hooftman WE, van Poppel MN, van der Beek AJ, Bongers PM, van Mechelen W. Gender differences in the relations between work-related physical and psychosocial risk factors and musculoskeletal complaints. Scand J Work Environ Health 2004;30:261-78. 25. IJmker S, Huysmans MA, Blatter BM, et al. Should office workers spend fewer hours at their computer? A systematic review of the literature. Occup Environ Med 2007;64:211-22. 26. McLean SM, May S, Klaber-Moffett J, Sharp DM, Gardiner E. Risk factors for the onset of non-specific neck pain: a systematic review. J Epidemiol Community Health 2010;64: 565-72. 27. Verbeek JHAM, van der Beek AJ. Psychosocial factors at work and back pain: a prospective study in office workers. Int J Occup Med Environ Health 1999;12:29-39. 28. Altman DG. Practical Statistics for Medical Research. London England: Chapman and Hall; 1991. 29. Chen J, Wacholder S, Morton LM. Quantifying selection bias in epidemiologic studies. Am J Epidemiol 2005;161(Suppl): S145. 30. Morton LM, Cahill J, Hartge P. Reporting participation in epidemiologic studies: a survey of practice. Am J Epidemiol 2006;163:197-203. 31. van der Beek AJ, Frings-Dresen MHW. Assessment of mechanical exposure in ergonomic epidemiology. Occup Environ Med 1998;55:291-9. 32. Burdorf A, van der Beek AJ. Exposure assessment strategies for work-related risk factors for musculoskeletal
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disorders. Scand J Work Environ Health 1999;25(Suppl 4): 25-30. Heinrich J, Blatter BM, Bongers PM. A comparison of methods for the assessment of postural load and duration of computer use. Occup Environ Med 2004;61:1027-31. IJmker S, Leijssen JNM, Blatter BM, et al. Test–retest reliability and validity of self-reported duration of computer use at work. Scand J Work Environ Health 2008;34:113-9. Bjorck-van Dijken C, Fjellman-Wiklund A, Hildingsson C. Low back pain, lifestyle factors and physical activity: a population-base study. J Rehabil Med 2008;40:864-9. Brown WJ, Mishra G, Lee C, Bauman A. Leisure time physical activity in Australian women: relationship with well being and symptoms. Res Q Exerc Sport 2000;71:206-16. Björkstén MG, Boquist B, Talbäck M, Edling C. The validity of reported musculoskeletal problems. A study of questionnaire answers in relation to diagnosed disorders and perception of pain. Appl Ergon 1999;30:325-30. Nielsen NR, Thygesen LC, Johansen D, Jensen G, Grønbaek M. The influence of duration of follow-up on the association between alcohol and cause-specific mortality in a prospective cohort study. Ann Epidemiol 2005;15:44-55. Hoogendoorn WE, van Poppel MNM, Bongers PM, Koes BW, Bouter LM. Systematic review of psychosocial factors at work and private life as risk factors for back pain. Spine 2000; 25:2114-25. Linton SJ. Occupational psychosocial factors increase the risk for back pain: a systematic review. J Occup Rehabil 2001;11: 53-66. Linton SJ, Halldén K. Can we screen for problematic back pain? A screening questionnaire for predicting outcome in acute and subacute back pain. Clin J Pain 1998;14:209-15. Moons KGM, Royston P, Vergouwe Y, Grobbee DE, Altman DG. Prognosis and prognostic research: what, why, and how? BMJ 2009;338:1317-20.
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ABSTRACT Objective: The purpose of this study was to systematically review prospective cohort studies to identify risk factors for the onset of low back pain (LBP) in office workers. Methods: Online searches were conducted on PubMed, CINAHL Plus with full text, ScienceDirect, PEDro, ProQuest, and Scopus databases from 1980 to November 2011 using the following keywords: low back pain paired with risk or prognostic factors and office or computer or visual display unit (VDU) or visual display terminal (VDT). The methodological quality of each study was assessed using a 21-item checklist, which was divided into 2 parts: the internal validity (11 items) and descriptive quality (10 items) of studies. Strength of evidence for risk factors associated with the development of nonspecific LBP was assessed by defining 5 levels of evidence based on the number of studies and the quality score of studies. Results: Eighteen full-text articles were identified, and 15 were excluded. A total of 3 articles were judged to meet the selection criteria and were included in the methodological quality assessment. Risk factors were divided into 3 groups: individual, work-related physical, and work-related psychosocial risk factors. There was strong evidence that history of LBP is a predictor of the onset of LBP. Limited evidence was found that the combination of postural risk factors and job strain is associated with the onset of LBP. Conclusion: After review of 3 high-quality prospective studies on the association between risk factors and the onset of nonspecific LBP in office workers, few risk factors were found to predict the onset of LBP in office workers. (J Manipulative Physiol Ther 2012;35:568-577) Key Indexing Terms: Musculoskeletal Diseases; Risk Factors; Low Back Pain; Computers; Review
ow back pain (LBP) is a significant health problem in office workers with a 1-year prevalence rate of between 34% and 51% 1,2 and a 1-year incidence rate of 23%. 3 A significant portion of patients with LBP has developed chronicity. 4,5 As a result, LBP causes consider-
L a
Associate Professor, Department of Physical Therapy, Faculty of Allied Health Sciences, Chulalongkorn University, Bangkok, Thailand. b PhD Candidate, Department of Physical Therapy, Faculty of Allied Health Sciences, Chulalongkorn University, Bangkok, Thailand. Submit requests for reprints to: Prawit Janwantanakul, PhD, Associate Professor, Department of Physical Therapy, Faculty of Allied Health Sciences, Chulalongkorn University, 154 Rama I Road, Pathumwan, Bangkok, Thailand 10330 (e-mail: [email protected]). Paper submitted February 20, 2012; in revised form June 28, 2012; accepted July 4, 2012. 0161-4754/$36.00 Copyright © 2012 by National University of Health Sciences. http://dx.doi.org/10.1016/j.jmpt.2012.07.008
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able personal suffering due to pain, disability, and impaired quality of work and life in general, which can result in a significant socioeconomic burden on both patients and society. In the United States, the total cost of LBP in 2006 exceeded 100 billion US dollars, 6 whereas in the Netherlands, the total cost of LBP in 2007 was estimated at 3.5 billion euro. 7 The cost of LBP to society is likely to increase, given that many developing nations have been industrializing their economy, thus increasing the number of workers in the office environment at the global level. The etiology of LBP is assumed to be of multifactorial origin and often includes individual, physical, and psychosocial factors that may contribute to the development and persistence of low back disorders. 8 Each occupation exposes workers to varied and unique conditions, activities, and stressors. The nature of work varies greatly across employment sectors and has been recognized as influencing the health of workers. 9 Thus, predisposing factors for musculoskeletal symptoms in different occupations are assumed to be dissimilar and related to those characteristic exposures, demands, and conditions of the specific job. 10
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Office work is sedentary work in nature, which commonly involves prolonged sitting, computer use, participation in meetings, giving presentations, reading documents and materials, and frequent use of the telephone and other electronic devices. 11 Physiologic deconditioning 12 and/or accumulation of musculoskeletal overload 13 may increase the office worker's susceptibility to LBP. Prolonged sitting or sustained lumbar flexion, which has been found to reduce the ability of the spine to resist force acting upon it, 14 may predispose the lumbar spine to injury during loading. Office work also unavoidably causes mental stress, which may play an intermediate role in causing LBP. 15 Studies have identified several individual factors associated with LBP in office workers, including older age, female sex, high body mass index, smoking, and previous symptoms. 3,16,17 Regarding work-related risk factors, more senior position, sitting for long hours, poor workstation ergonomics, and awkward working postures have been linked to increased risk of LBP. 16-19 Some psychosocial problems, such as job satisfaction, repetitive work, job strain, and anger during last 30 days, have also been found to contribute to an increased occurrence of LBP. 17,19 However, a number of these studies were cross-sectional in design, 16-18 which only allowed for the association between exposures and outcome to be examined. It is therefore not possible to establish the causal relationship between exposures and outcome. Research to identify the causal factors of a disease requires longitudinal research design, which permits the tracking of study participants' activities, health status, and exposures over time. 20 The aim of this article is to systematically review prospective cohort studies to gain insights into the status of literature investigating risk factors for the onset of LBP in office workers as well as to assess the strength of evidence. Such information would be of value for policy makers and health care providers to determine effective prevention measures to decrease the incidence and burden of LBP in the workplace.
METHODS Data Sources and Search Strategy Online searches were conducted on PubMed, CINAHL Plus with full text, ScienceDirect, PEDro, ProQuest, and Scopus databases from 1980 to November 2011 using the following keywords: low back pain paired with risk or prognostic factors and office or computer or visual display unit (VDU) or visual display terminal (VDT). Articles were initially screened based on title and abstract; full-text copies were then retrieved of articles that met all inclusion criteria. Subsequently, full-text copies were read to make a final decision regarding inclusion or exclusion. The search and full inclusion process were performed by 1 reviewer (ES). After inclusion of the articles based on the selection criteria, references were searched for additional articles.
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Selection of Studies A reviewer (ES) selected relevant articles from the articles retrieved using the search strategy. The selection criteria were the following: 1. The study population was office workers or those working with computers or visual display units or visual display terminals. 2. Study samples were free from LBP at baseline assessment. Studies in a population with specific underlying pathology, such as tumors, fractures, infection, inflammatory disorders, and osteoporosis, were excluded. 3. The study design was a prospective cohort study with a follow-up period of 1 year or more. Experimental studies were excluded. 4. The onset of LBP was assessed separately from other musculoskeletal symptoms. 5. Nonspecific LBP, that is, LBP (with or without radiation) without any specific systematic disease being detected as the underlying cause of the complaints, was assessed in the study. 6. The article was a full, peer-reviewed report published in English. Letters, abstracts, books, conference proceedings, and posters were excluded.
Quality Assessment of Studies The articles that met the selection criteria were independently evaluated by 2 reviewers (ES and AP) to determine methodological quality. The methodological quality of each study was assessed by using a 21-item checklist for quality appraisal modified from van der Windt et al 21 and Ariëns et al 22 (Table 1). The checklist was divided into 2 parts: the internal validity (11 items) and descriptive quality (10 items) of studies. Each item was scored as positive (1), negative (0), or unclear (if insufficient information was available for a specific item) (0). The scoring for each item of the 2 reviewers was compared. Disagreements between the reviewers on individual items were identified and discussed in an attempt to achieve consensus. The interrater agreement of this quality assessment was derived by calculating the percentage agreement as well as Cohen κ for categorical items, both before and after the consensus discussion. If agreement could not be reached, a third reviewer (PJ) was consulted to achieve a final judgment. Studies scoring a minimum of 6 of 11 (N50%) for internal validity with a total score of 11 of 21 (N50%) or greater were deemed “high quality.” 21-25
Data Extraction Data extraction was performed by the first reviewer (ES). For each article, the first author and year of publication, study population, sample size, drop-out rate,
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Table 1. Methodological quality criteria Item
Score
Internal validity criteria Study population 1. Positive if the participation rate is ≥80% or if participation rate is 60%-80% and nonresponse is not selective (data presented) 2. Positive if the response at main moment of follow-up is ≥80% or if the nonresponse is not selective (data presented) Exposure assessments, physical load at work (if not included in the design, not applicable) 3. Method for measuring physical load at work: direct measurement and observation (+), interview, or questionnaire only (−) 4. Positive if N1 dimension of physical load is assessed: duration, frequency, or amplitude 5. Positive if N1 aspect of psychosocial factors is assessed: work demands, job control, social support Outcome assessments 6. Positive if data were collected for ≥1 y 7. Method for assessing LBP: physical examination blinded to exposure status (+), self-reported: specific questions relating to LBP or use of manikin (+), single question (−) Analysis and data presentation 8. Positive if the appropriate statistical model is used (univariate or multivariate model) 9. Positive if measures of association are presented (OR/RR), including 95% CIs and numbers in the analysis (totals) 10. Positive if the analysis is controlled for confounding or effect modification is studied 11. Positive if the number of cases in the multivariate analysis is at least 10 times the number of independent variables in the analysis (final model) Descriptive quality criteria Study objective 12. Positive if a specific, clearly stated objective is described Study population 13. Positive if the main features of the study population are described (sampling frame and distribution of the population by age and sex) Exposure assessments, physical load at work (if not included in the design, not applicable) 14. Positive if data are collected and presented about physical load at work 15. Positive if the data on physical load at work were collected using standardized methods of acceptable quality a Exposure assessments, psychosocial factors at work (if not included in the design, not applicable) 16. Positive if data are collected and presented about psychosocial factors at work 17. Positive if the data on psychosocial factors at work were collected using standardized methods of acceptable quality a Exposure assessments, other 18. Positive if data are collected and presented about physical or psychosocial exposure during leisure time 19. Positive if data are collected and presented about history of LBP Outcome assessments 20. Positive if data were collected at least every 3 mo 21. Positive if the data on outcome were collected using standardized methods of acceptable quality a
+/−/? +/−/? +/−/? +/−/? +/−/? +/−/ +/−/
+/−/ +/−/ +/−/ +/−/
+/−/ +/−/
+/−/ +/−/ +/−/ +/−/ +/−/ +/−/ +/−/ +/−/
+, positive; −, negative; ?, unclear. a This item was scored positive if one of the following criteria was met: (i) for direct measurements, intraclass correlation coefficient greater than 0.60 or κ greater than 0.40; (ii) for observational methods, intraclass correlation coefficient greater than 0.60 or κ greater than 0.40 for the interobserver or intraobserver reliability; and (iii) for self-reported data, intraclass correlation coefficient greater than 0.60 or κ greater than 0.40 for the interobserver or intraobserver reliability.
outcome measured (pain and disability), duration of followup, risk factors, the strength of the association between risk factors, and the onset of LBP in terms of odds ratio (OR), hazard ratio (HR), or rate ratio (RR) with 95% confidence interval (CI) were extracted.
• Limited evidence: findings of one high-quality study or consistent findings in one or more low-quality studies. • Conflicting evidence: inconsistent findings irrespective of study quality. • No evidence: no studies found.
Data Analysis The strength of evidence for risk factors associated with the development of nonspecific LBP was assessed by defining 5 levels of evidence based on the number of studies and the quality score of studies 26: • Strong evidence: consistent findings from 2 or more high-quality cohorts. • Moderate evidence: consistent findings from at least one high-quality study and one or more low-quality cohorts.
A risk factor association was considered positive only if it was statistically significant and was derived from multivariate results. A risk factor association was considered negative only if it was statistically insignificant and was derived from multivariate results. Statistical significance was concluded if the reported P value was less than .05 or if the 95% CIs around an RR or similar statistic (such as OR or HR) did not cross 1.
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Computerized search of databases by one reviewer (n=7,112)
Excluded
7,094 abstracts did not meet the selection criteria based on screening of abstracts and titles
18 full-text articles retrieved for closer inspection by one reviewer
Excluded
References search for additional articles 0 articles
15 articles did not meet the selection criteria based on full-text articles 12 articles were not conducted on office workers 1 article assessed low back pain but not separately from other symptoms 1 article assessed specific low back pain 1 article included symptomatic subjects at baseline assessment
3 articles were included for methodological quality assessment
Fig 1. Flow diagram of the data screening process.
Sensitivity Analysis
Methodological Quality Assessment
Sensitivity analysis was conducted to assess whether a priori cutoff point of greater than 50% for study quality might have influenced the level of evidence and, potentially, the results of the review. Thus, the effect of the cutoff point used in the methodological quality assessment for qualification as a high-quality study on the synthesized results was assessed by shifting the cutoff point from greater than 50% to greater than 60% or shifting the cutoff point from greater than 50% to greater than 70%.
The scoring of 2 reviewers of the included studies before discussion had an agreement rate of 78% (49/63). The overall interrater agreement was κ = 0.54 with an SE of measurement of 0.11. After discussion, the 2 reviewers had an agreement rate of 98% (62/63). Then, the overall interrater agreement was κ = 0.96 with an SE of measurement of 0.03. This represents very good agreement between the 2 reviewers. 28 Disagreements were often related to reading errors or interpretation of the quality criteria list. These disagreements were resolved during a consensus meeting. However, disagreements persisted on 1 item (item 9) in the study from Verbeek and van der Beek. 27 A third reviewer (PJ) made the final decision in this case. The results of the methodological quality appraisal are presented in Table 2. The scores for the methodological quality of the studies ranged from 12 to 14 points (57%67%). The median score was 14 points (67%). All 3 studies were scored as high-quality studies. 3,19,27 The items in the criteria list rated as negative in most studies were participation rate (item 1, 0%), assessment of physical load at work (item 3, 0%), quality of assessment
RESULTS Selection of Studies The initial search of the computerized databases yielded 7112 citations (Fig 1). After the screening of abstracts and titles, 18 full-text articles were read in full. Fifteen articles were excluded because they did not meet the selection criteria. A total of 3 articles were judged to meet the selection criteria and were included in the methodological quality assessment. 3,19,27
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14/21 (67) 14/21 (67) 12/21 (57)
method for physical load at work (item 15, 0%), assessment of exposure during leisure time (item 18, 0%), and frequency of data collection during follow-up period (item 20, 0%).
6/10 6/10 6/10
Study Characteristics
− − + 33 − − − 0
− − − 0
+ + − 67
All included studies were conducted on office workers or computer users (Table 3). The sample sizes varied greatly from 271 to 3475. The drop-out rate during follow-up ranged from 7% to 30%. Lapointe et al 19 defined incident cases as those experiencing LBP, ache, or discomfort during the study period, whereas Verbeek and van der Beek 27 defined incident cases as those experiencing pain or stiffness in the back during the study period. Juul-Kristensen et al 3 defined incident cases as those reporting increased frequency of days with LBP during the study period, from less than 8 days in the baseline questionnaire to greater than 7 days in the follow-up questionnaire. The follow-up period was between 0.6 and 5.6 years.
+ + + 100
Summary of Risk Factors
+, positive; −, negative; ?, unclear; DQ, descriptive quality; IV, internal validity.
+ − − 33 − − ? 0 Juul-Kristensen et al3 Lapointe et al19 Verbeek and van der Beek27 Positive (%)
− + − 33
− − − 0
+ + + 100
+ + + 100
+ + + 100
+ + + 100
+ + − 100
+ + + 100
+ + + 100
8/11 8/11 6/11
+ + + 100
+ + + 100
− − 0
+ + + 100
+ + + 100
19 17 16 15 14 13 12 4 1 Study reference
2
3
5
6
7
8
9
10
11
IV score
DQ criteria IV criteria
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18
20
21
DQ score
Total score (%)
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Table 2. Methodological quality score of three studies (studies are ranked according to their total scores and, in case of equal ranking, in alphabetical order of the first author's surname)
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Risk factors were divided into 3 groups: individual, work-related physical, and work-related psychosocial risk factors (Table 4). All factors (21/22) but history of LBP were investigated by only 1 study. There was strong evidence that history of LBP is a predictor of the onset of LBP. Limited evidence was found that the combination of postural risk factors and job strain (for females only) is associated with the onset of LBP. There was limited evidence that age, general health complaints, daily computer use, adjustability of chair or desk, availability of arm rest, screen height relative to eye level, frequency of standing during work, disturbance of glares or reflection, influence on the timing of work pauses, necessity to work fast, frequency of feeling discomfort while sitting, frequency of feeling discomfort with climatic condition, cognitive and sensory demand, influence at work, developmental possibilities, social support, job demands, depression, and the combination of low/high postural risk factors and high/ low job strain (for males only) have no predictive value for the onset of LBP.
Sensitivity Analysis Changing the cutoff point from greater than 50% to greater than 60%, 2 conclusions would be altered including: • The level of evidence for history of LBP would change from strong to moderate. • The level of evidence for age, general health complaints, frequency of feeling discomfort while sitting, frequency of feeling discomfort with climatic condition, job demands, and depression would change from limited “no” to no evidence.
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Table 3. Summary of study characteristics Study population, sample size, and drop-out at follow-up
Study Juul-Kristensen et al
Lapointe et al19
Verbeek and van der Beek27
3
Office workers in Denmark n = 3475 Drop-out 23%
Outcome measurement (follow-up period)
Risk factors
Strength of association
Frequency or intensity of LBP (17-23 mo; mean, 21 mo)
Multivariate logistic regression model adjusted for sex and age (with 95% CI) Previous symptoms OR, 2.4 (1.70-3.39) (for frequency of LBP) White-collar workers at the 6-mo incidence proportion Multiple logistic regression model 3 large public service of lower back adjusted for age, stressful life organizations in Québec symptoms event at baseline and follow-up, City, Canada (0.6-5.6 y; mean, 3.2 y) number of children, education n = 2431 level, and musculoskeletal symptoms to other body Drop-out 7% regions at baseline (with 95% CI) Low postural risk factors OR, 2.53 (1.09-5.85) and high job strain (for females only) High postural risk factors OR, 2.51 (1.23-5.09) and low job strain (for females only) High postural risk factors OR, 5.51 (2.33-13.03) and high job strain (for females only) Office workers at the social Back pain during the Multiple logistic regression service department of the city past year model (with 90% CI) of Amsterdam (12 months) Prior back pain ≤4 on VAS OR, 3.0 (1.5-6.0) n = 271 Prior back pain N 4 on VAS OR, 10.3 (4.1-25.5) Drop-out 30%
With a cutoff point of greater than 70%, there would have been no study obtaining high-quality status.
DISCUSSION The present review is the first to summarize the results of prospective cohort studies on individual, work-related physical, and work-related psychosocial factors for the development of nonspecific LBP. In undertaking this review, we were surprised to discover that there have been very few prospective cohort studies on risk factors for the onset of nonspecific LBP in office workers that were qualified according to the selection criteria. We found heterogeneity among studies as to aspects such as case definition, risk factors, and follow-up duration. Thus, the analysis of the results was limited to a qualitative summary. Of 22 investigated factors, the results indicated strong evidence for history of LBP and limited evidence for the combination of postural risk factors and job strain (for females only) as predictors for new-onset LBP in office workers. Most factors previously investigated have no predictive value for future LBP, such as age, daily computer use, workstation ergonomics, social support, and job demands.
Methodological Considerations The items in the criteria checklist rated as negative in all 3 studies were participation rate, assessment method of physical load at work and its quality, assessment of
exposure during leisure time, and frequency of data collection during follow-up period. No included studies had a participation rate of 80% or higher. 3,19,27 In general, studies with low levels of participation may be more vulnerable to self-selection bias than those with high participation. 29 Therefore, a low participation rate in a population survey may threaten the internal validity of studies. 30 Common methods for the assessment of physical exposures at work include subjective judgment, systematic observation, and direct measurement. 31,32 All studies used a self-reported questionnaire to assess physical load at work. 3,19,27 Many of the subjective methods, particularly those nonstandardized methods of acceptable quality, had problems with test-retest reliability, which may have led to a poor validity of exposures. 33,34 All included studies did not report the test-retest reliability of their measurement tools. Using a reliable systematic observation or objective measurement, instead of subjective judgment, to evaluate physical load at work is recommended to improve the quality of data. This is also true for the onset of LBP, which was diagnosed based upon self-report only in all studies. Some workers may be more sensitive to any somatic disturbance than others. As a result, there is the risk of an overreport of the incidence. The inclusion of information from a physical examination should be considered as increasing the accuracy of diagnosis. All included studies did not measure physical exposures during leisure time. Apart from work time, exposures
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Table 4. Overall level of evidence for risk factors and their association for the onset of LBP in office workers
Group Individual
Risk factor
History of LBP Age General health complaints Work-related Daily computer physical use Adjustability of chair Adjustability of desk Availability of arm rest Screen height relative to eye level Frequency of standing during work Disturbance of glares or reflection Influence on the timing of work pauses Necessity to work fast Frequency of feeling discomfort while sitting Frequency of feeling discomfort with climatic condition Work-related Cognitive demand psychosocial Sensory demand Influence at work Developmental possibilities Social support Job demands Depression Combination of postural risk factors and high job strain Females Males
Cohorts assessed + findings
+ high + low quality quality (references) (references) − findings
− high − low quality quality Level of (references) (references) evidence
2 1 1
2/2 (100%) 2 (3, 27) – – – –
– – –
– – 1/1 (100%) 1 (27) 1/1 (100%) 1 (27)
– –
Strong Limited no. Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (3)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (27)
–
Limited no.
1
–
–
–
1/1 (100%) 1 (27)
–
Limited no.
1 1 1 1
– – – –
– – – –
– – – –
1/1 (100%) 1/1 (100%) 1/1 (100%) 1/1 (100%)
– – – –
Limited no. Limited no. Limited no. Limited no.
1 1 1
– – –
– – –
– – –
1/1 (100%) 1 (3) 1/1 (100%) 1 (27) 1/1 (100%) 1 (27)
– – –
Limited no. Limited no Limited no.
1 1
1/1 (100%) 1 (19) – –
– –
– – 1/1 (100%) 1 (19)
– –
Limited Limited no.
1 (3) 1 (3) 1 (3) 1 (3)
Positive findings (+ findings) were considered significant associations (P b .05 or the 95% CIs around RRs, ORs, or HRs did not cross 1) from the multivariate results. Negative findings (− findings) were considered not significant associations.
during leisure time should be assessed and included as part of the cumulative dose that an individual is exposed to. Previous studies demonstrated the association between physical activity during leisure time and LBP. 35,36 Measuring exposure during both work and leisure time may be more representative of an individual's exposure. The frequency of data collection of LBP incidence during the follow-up period for the included studies varied
considerably, ranging from 0.6 to 5.6 years. All studies collected data only twice: at the beginning and the end of study. A longer recall period regarding the incidence of LBP during follow-up period may increase recall bias. 37 This bias may be pronounced in studies in which detailed information, such as the duration of experiencing pain and/ or pain intensity, was required. Regular data collection during the follow-up period is recommended.
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Evidence of Risk Factors for the Onset of LBP in Office Workers In this review, the onset of LBP was considered to be the onset of any reported low back symptoms, regardless of severity of symptoms, duration of symptoms, and level of disability. This pragmatic choice was made because of the fact that this review focused on a specific group of the population and only a small number of studies qualified for inclusion in the review. Of the 3 studies, 2 followed up for 1 year or more, 3,27 and the remaining study followed up between 0.6 and 5.6 years, with an average of 3.2 years. 19 The predictive value of any exposures depends on the duration of follow-up as well as the disease of interest. A long duration of follow-up is generally considered a strength in prospective cohort studies, as it usually results in a larger number of cases and thereby increases the power of the statistical analysis. 38 Thus, a long duration of follow-up is likely to enhance the internal validity of the study. In the literature, there are 2 systematic review studies on risk factors for the onset of LBP. However, both studies focused on psychologic factors. 39,40 In the general population, Hoogendoorn et al 39 systematically reviewed cohort and case-control studies for psychosocial factors at work and in private life that predicted the occurrence of back pain and found strong evidence for low social support in the workplace and low job satisfaction. In the working population, Linton 40 in their systematic review of prospective cohort studies found moderate to strong evidence for job satisfaction, monotonous tasks, work relations, demands, stress, perceived ability to work, work pace, control, emotional effort at work, and the belief that work is dangerous. The predictive value of most factors identified in previous reviews could not be confirmed in the present review, which only showed strong evidence for history of LBP and limited evidence for the combination of postural risk factors and job strain as predictors of the onset of LBP among office workers. One possible explanation for the observed variation in the results among studies may be due to the limited number of studies in a population of office workers. However, the findings suggest that risk factors for the onset of LBP in a subpopulation may be a subset of risk factors identified in a general population or occupation specific. 9 To gain further insight into risk factors for the development of LBP, future studies should consider the investigation of risk factors in a more specific group of the population. Although history of LBP is a nonmodifiable risk factor, this information is useful for clinicians when planning preventive measures for LBP among office workers. By identifying those at risk (ie, office workers with history of LBP), this would mean the enhancement of resource allocation to those most in need and most likely to benefit from it. Otherwise, a large number of people would receive intervention, which is likely to compromise its
Janwantanakul et al Risk Factors for Low Back Pain
effectiveness. 41,42 The combination of 2 risk factors (ie, poor working postures and high job strain) appears to predispose female office workers to new-onset LBP. Thus, the prevention of LBP among female workers should at least include identifying the causes of poor working postures and high job strain and then developing strategies to rectify them.
Sensitivity Analysis By changing the cutoff point from greater than 50% to greater than 60%, some conclusions about risk factors with strong and limited evidence, namely, history of LBP, age, general health complaints, frequency of feeling discomfort while sitting, frequency of feeling discomfort with climatic condition, job demands, and depression, would alter. Because all included studies had total scores of less than 70%, shifting the cutoff point from greater than 50% to greater than 70% would have led to no study qualifying as a high-quality study. This variation in the level of evidence reflects the fact that there have been very few good-quality studies investigating risk factors for the development of LBP in office workers. Most of the factors included in the review have been supported by evidence from 1 highquality study only. Thus, this review was limited in its ability to draw conclusions about the predictive nature of these factors, and the conclusions may change or additional risk factors will be identified when new studies become available in the future. The findings point out an urgent need for further study in this area before any firm conclusions can be drawn.
Strengths and Limitations The major strength of this study is that the literature was systematically searched, articles were evaluated for their methodological quality by 2 independent reviewers, and information was extracted and synthesized based on the number of studies and the quality score of studies. In addition, the inclusion of only prospective cohort studies allows for the establishment of the causal relationship between exposures and outcome. However, the limitations of the present review should be taken into consideration when interpreting its results. First, the search strategy was limited to full reported publications in English. The possibility of publication and selection bias cannot be ruled out, which may have affected the results of this review. Second, the researchers summarized the results from studies with substantial heterogeneity in study characteristics. This may explain the observed variation in the results among studies. Future research is required to indicate whether differences in these aspects affect the association between risk factors and the onset of LBP. Last, as no universally accepted quality assessment tool for prospective cohort studies exists, the quality assessment tool used in the present review was based on the assembly of criteria lists in the previous reviews. 21,22 In addition, the
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quality assessment tool was arguably divided into 2 parts: the internal validity (11 items) and descriptive quality (10 items) of studies. However, it is believed that the items included in the quality assessment tool assessed the important components to validate these types of studies.
CONCLUSION Three high-quality prospective studies on the association between risk factors and the onset of nonspecific LBP in office workers were reviewed and analyzed. Very few risk factors were found to predict the onset of LBP in office workers, which included history of LBP and the combination of postural risk factors and job strain. Because all but 1 factor have been investigated by only 1 study and there are several methodological limitations among included studies, this review was limited in its ability to draw conclusions about the factors leading to LBP in office workers and the conclusions may change when new studies become available in the future. The health of office workers deserves consideration, and more research is needed on this topic.
Practical Applications • Strong evidence was found for history of LBP to be a predictor of the onset of LBP in office workers. • Most factors previously investigated have no predictive value for future LBP, such as age, daily computer use, workstation ergonomics, social support, and job demands. • There have been very few prospective cohort studies on risk factors for the onset of nonspecific LBP in office workers, and thus, more highquality studies in this area are needed.
FUNDING SOURCES AND POTENTIAL CONFLICTS OF INTEREST This work was funded by Chulalongkorn University Centenary Academic Development Project (no .12). No conflicts of interest were reported for this study.
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