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Abstract

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

Objective

To quantify the relative contribution of work-related physical and psychosocial factors, individual factors, and health-related factors to the development of more severe musculoskeletal pain in the neck and upper limbs and the back and lower limbs.

Methods

In this cohort study of 5,604 workers from industrial and service companies, we collected information on work-related physical and psychosocial exposures and on individual and health-related factors. Questionnaires were completed at baseline by 4,006 participants (71.5%) and after 24 months by 3,276 (82%). At followup, participants with no or minor pain were included in Cox regression analyses to determine which factors predicted more severe regional pain.

Results

Of the 4,006 baseline respondents, only 7.7% were free of regional pain. A total of 1,513 participants were free of severe pain at baseline and completed the 24-month followup. Highly repetitive work predicted arm pain, heavy lifting and prolonged standing predicted low back pain, and heavy pushing or pulling predicted lower limb pain. Low job satisfaction predicted neck/shoulder pain and lower limb pain, whereas other psychosocial work place factors were only of marginal importance. High levels of fear avoidance were associated with arm pain and lower limb pain. A high body mass index was highly associated with lower limb pain.

Conclusion

Very few workers are totally free of pain in musculoskeletal regions, and we question the concept of incidence of musculoskeletal pain. The transition from no or minor pain to more severe pain was influenced by physical and psychosocial work place factors together with individual and health-related factors.

Regional musculoskeletal pain is common in working populations and in the general population (1–4). Within the last 30 years, much effort has been put into research to identify risk factors for primary prevention, first by focusing on physical hazards in the work place (e.g., heavy lifting, awkward postures, repetitive movements) and second by also introducing psychosocial work place factors (e.g., job demands, job control, social support, and job satisfaction). Many risk factors have been identified in various studies, but no great success has been seen in intervention studies (5, 6). It looks as if regional musculoskeletal pain problems are here to stay, and are perhaps a ubiquitous part of modern working life (7, 8).

It has recently been proposed in a European guideline on back pain that the general nature and course of commonly experienced low back pain means that there is limited scope for preventing its incidence, and that prevention should be focused on reduction of the impact and consequences of back pain (ref.9 and www.backpaineurope.org). This message could possibly be extended to other regional pain, such as arm pain, neck/shoulder pain, and lower limb pain.

The aim of the present study was to examine the effect of work-related factors and individual and health-related factors on the onset of more severe musculoskeletal pain at 24 months of followup among participants with no or minor pain at baseline in 4 regions (the neck/shoulders; the elbow, forearm, and hand; the low back; the hip, knee, and foot) as well as in any of the 4 regions.

SUBJECTS AND METHODS

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

Study design.

This was a prospective cohort study of a general working population in western Denmark. At baseline and at 24 months, subjects completed a questionnaire, which ascertained regional pain status, work-related physical and psychosocial factors, and health-related factors.

Study subjects.

The study population consisted of workers from 39 different work places, of which 19 were in the service sector and 20 were in different kinds of industry. Work places were recruited through the 3 local occupational health services with the aim of composing a study population of approximately equal proportions of workers from the service sector and workers from industrial companies. The purpose was to include a general working population with the intention of subsequently performing a randomized controlled study of the effect of information and ergonomic interventions versus no intervention. This subsequent part of the study will be reported separately.

Baseline information.

A self-administered questionnaire was mailed to all the workers on the basis of information received from the companies. The questionnaire included information across the following domains: physical risk factors in the work place, psychosocial factors at work, health-related factors, and other individual factors. The occupations of the participants were based on information received from the work places and were classified according to International Standard Classification of Occupations (ISCO-88), developed by the International Labour Organisation.

Physical risk factors.

The participants were asked about several manual handling activities, posture, and repetitive movements. These included lifting with the hands, lifting weight at or above shoulder height, pulling or pushing weights, squatting, standing, and repetitive movements with the hands. Participants were asked to estimate the weights they had lifted, how many lifts per hour, and the duration of each task. Postures and repetitive movements were assessed by questions about the amount of time spent in these postures and performing these repetitive movements in a typical work hour during the last day of work. These questions have been validated by comparing the responses according to a direct observation technique and have been used in studies of different outcomes (10–12).

The physical exposure variables were categorized as follows. For lifting with the hands, lifting at or above shoulder level, and pushing or pulling, we combined the questions on weight with the number of activities per hour to form a cumulative exposure measure, where the referent group consisted of participants who did not perform these activities. The remaining participants were dichotomized according to the distribution level to obtain contrasts between groups. Repetitive movements were divided into a reference group performing repetitive work (repetitive movements of the hand or arm) for <10 minutes per hour, a medium repetition group performing such work for 10–44 minutes per hour, and a high repetition group performing such work for >45 minutes per hour. Posture variables were dichotomized into sitting for >30 minutes per hour or not, standing for >30 minutes per hour or not, and squatting for >5 minutes per hour or not.

Psychosocial risk factors.

Psychosocial risk factors were assessed using a standardized questionnaire developed by the Danish National Institute of Occupational Health (13, 14). The questionnaire included 10 items about job demands (4 on work load, 3 on sensory demands, and 3 on cognitive demands), 7 items about job control (4 on decision latitude and 3 on freedom at work), and 9 items about social support (4 on social support from supervisors and 5 on social support from colleagues). The questionnaire items had 5 alternative responses for each question (always, often, sometimes, seldom, and never/almost never); these responses were dichotomized and given a raw score of 1 or 0. Four scales were constructed as raw score summations for job demands, job control, and social support from supervisors or colleagues. High scale values indicated a high level of job demands, a low level of job control, and low levels of social support. We also included single-item questions on quality of leadership (“All in all, are you satisfied with the way your workplace is managed?”; responses on a 6-point Likert scale ranged from “Hardly at all” to “To a very great extent”) and job satisfaction (“How satisfied are you with your work, all in all?”; responses on a 6-point Likert scale ranged from “Very dissatisfied” to “Very satisfied”).

Individual and health-related risk factors.

Education level was categorized as 1 of 3 groups: low (7–9 years of school education), medium (10 years), and high (college education and higher). Leisure time physical activity was categorized as low (almost none or light activity for <2 hours/week or light activity for 2–4 hours/week) and high (light activity >4 hours/week or 2–4 hours of hard physical activity or hard physical activity for >4 hours/week). On the basis of self reports of height and weight, the body mass index (BMI) was categorized as low or normal (index <25), overweight (index 25–29), or severely overweight (index ≥30).

Fear avoidance was assessed by the Fear-Avoidance Beliefs Questionnaire (FABQ) (15). On the basis of factor analysis, 2 scales were used, one for fear avoidance of work (Cronbach's α = 0.86) and the other for fear avoidance of physical activity (Cronbach's α = 0.84). Cut points for low, medium, and high levels of fear avoidance were made according to quartiles.

Health anxiety was assessed by the 7-item version of the Whiteley Index (16). The responses were dichotomized as a little bit and quite a bit, and were summed to produce a scale with 3 categories (Cronbach's α = 0.83). From questions about persistent diseases lasting more than 6 months (diabetes, depression, migraine, hypertension, chronic bronchitis, rheumatic diseases, and other somatic diseases), a variable was created for having a disease or not.

Pain status assessment.

Regional pain status was assessed for each of the 4 regions by asking, “How much have you been bothered by pain during the past 12 months?” There were 7 categories of answers, which are shown here with their percentages of distribution at baseline: not at all (7.7%), very little (16.7%), little (22.3%), some (20.0%), quite a lot (17.5%), much (9.8%), and very much (6.1%) (17, 18). More severe pain was operationalized as some pain to very much pain, and none or minor pain was operationalized as not at all, very little, and little pain.

Followup assessment.

All subjects who answered the baseline questionnaire received a questionnaire at 24 months in followup. Up to 2 reminders were mailed to the participants. Pain status and other health status, including fear-avoidance beliefs, were assessed in the same way as at baseline. The participants were also asked about job status at followup, if they had changed jobs, and if so, whether this change was related to musculoskeletal pain.

Absence because of sickness.

Episodes of absences because of sickness for >2 weeks were collected from the DREAM register in the Danish Ministry of Labor, where all sickness absences for >2 weeks are centrally collected. The DREAM database includes information on all public transfer payments administered by Danish ministries and municipalities and Statistics Denmark for all Danish citizens on a weekly basis since 1991. The data for our cohort were merged with the DREAM register data in order to analyze sickness absences among respondents and nonrespondents.

Statistical analysis.

The analysis of risk factors for more severe pain at 24 months of followup was conducted with Cox proportional hazards analysis, yielding hazard ratios (HRs) with 95% confidence intervals (95% CIs). The analysis was conducted among those who had no or minor pain at baseline, which were those indicating that they had been bothered not at all, very little, and little according to the 7-point Likert scale used for pain assessment. Pain status at 24 months was dichotomized at the same level as at baseline, as more severe pain (from some to very much pain) versus no or minor pain.

The analysis was performed for each of the 4 regions as well as for any of the 4 regions. First, partially adjusted HRs were obtained for each potential risk factor, adjusting for age, sex, occupational group, and intervention group for the body region in question. Second, a multivariate model within each domain was constructed, and factors with a P value of less than 0.10 were included in the final multivariate model. When there were high correlations between variables, the one with the highest point estimate in the partially adjusted model was used. We tested for interaction between all risk factors if they were considered to be plausible (e.g., interaction between job demands, job control, and social support), but no interaction term contributed to the final model (e.g., with a P value of less than 0.10).

All analyses were performed with the Stata statistical package (version 9.0; Stata, College Station, TX).

RESULTS

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

A flow chart showing the distribution of the participants, from the 5,604 eligible participants to the 4,006 who answered the baseline questionnaire, and to the 3,276 who answered the followup questionnaire at 24 months, is shown in Figure 1. The 1,513 participants who were free of severe pain at baseline and completed the followup were the main group used for further analysis in this study. As shown in Figure 1, there was no selection based on the intervention group or on pain from baseline to the 24-month followup assessment.

thumbnail image

Figure 1. Distribution of the study participants with onset of severe pain over the 2-year followup. Participants were asked to complete a questionnaire at baseline and at 24 months (followup 1). Intervention group 1 represents controls, group 2 received information, and group 3 received information and a work place visit.

Download figure to PowerPoint

Table 1 shows the distribution of participants and the prevalence rates of severe pain in the 4 assessment regions at baseline and at 24 months. At baseline, the prevalence rates of regional pain varied among the different occupational groups, where skilled workers in industrial work places had the lowest rate of neck/shoulder pain (22%), and were at the lowest end on the other 3 outcomes, whereas cleaning and kitchen workers had high levels of neck/shoulder pain (49%), arm pain (28%), low back pain (29%), and lower leg pain (27%). Nurse assistants had the highest level of low back pain (31%). The 4 regional pain outcomes were highly correlated with each other: r = 0.45 for the correlation between neck/shoulder pain and arm pain; r = 0.42 for neck/shoulder pain and low back pain; and r = 0.38 for low back pain and lower leg pain.

Table 1. Study participation and prevalence rates of severe musculoskeletal pain in the 4 assessment regions at baseline and at the 24-month followup*
Study groupNo. of eligible subjectsBaseline24-month followup
Response rateNeck/shoulder painElbow, forearm, hand painLow back painHip, knee, foot painResponse rateNeck/shoulder painElbow, forearm, hand painLow back painHip, knee, foot pain
  • *

    Except where indicated otherwise, values are percentages.

Production           
 Administrative work67672321216128222111513
 Skilled workers1417522171712791681917
 Unskilled workers1,87467382225227632212724
Service           
 Administrative58280431726148331162619
 Nurses8257629112214842392113
 Nurse assistants1,04271442131238734203026
 Cleaning and kitchen30367492829278337233323
 Technical staff16178321323178635243035
Total5,60472371825188230172521

At followup, the response rates ranged from 76% among unskilled industrial workers to 87% among nurse assistants (Table 1). The transition of no or minor pain to some or more severe pain showed that more severe pain in the neck/shoulder region occurred in 16% (skilled industrial workers) to 37% (cleaning and kitchen workers) of subjects at 24 months of followup. Arm pain was lowest among skilled industrial workers (8%), and highest among unskilled industrial workers (21%), cleaning and kitchen workers (23%), and technical staff in the service sector (24%). Low back pain ranged from 15% among administrative workers in industry to 33% among cleaning and kitchen workers and 30% among nurse assistants. Lower limb pain was highest among cleaning and technical staff in the service sector (35%) and among the nurse assistants (26%). The differences between occupational groups were significant (at the 0.05 level) for all 4 assessment regions.

Partially adjusted associations.

Table 2 shows the associations between physical risk factors and the onset of more severe regional pain, adjusted for sex, age, occupational group, and intervention group. Highly repetitive work was significantly associated with neck/shoulder pain (HR 1.5 [95% CI 1.0–2.1]), arm pain (HR 1.9 [95% CI 1.2–3.1]), low back pain (HR 1.7 [95% CI 1.2–2.6]), and any pain (HR 1.4 [95% CI 1.1–1.8]). Lifting and pushing/pulling was associated in an exposure-response pattern with all 5 outcomes, with 30–60% elevated risk in those with medium exposure and 50–100% elevated risk in those with the highest exposure. Lifting ≥50 kg per hour at or above shoulder level was associated with neck/shoulder pain (HR 2.1 [95% CI 1.3–3.5]), arm pain (HR 2.2 [95% CI 1.1–4.3]), lower limb pain (HR 2.0 [95% CI 1.1–3.5]), and any regional pain (HR 1.6 [95% CI 1.1–2.3]). Sitting for >30 minutes per hour was not associated with any of the outcomes, whereas standing for >30 minutes per hour was associated with all outcomes (risk estimates elevated from 1.7 to 2.1). Squatting for >5 minutes per hour was associated with lower leg pain (HR 1.6 [95% CI 1.1–2.3]) and neck/shoulder pain (HR 1.6 [95% CI 1.1–2.2]) and was marginally associated with low back pain and any regional pain.

Table 2. Work-related physical risk factors and new onset of severe regional musculoskeletal pain, partially adjusted*
Physical risk factorNo. of subjectsHazard ratio (95% confidence interval)
Neck/shoulder painElbow, forearm, hand painLow back painHip, knee, foot painAny regional pain
  • *

    Adjusted for sex, age, occupational group, and intervention group.

Repetitive work      
 0–9 minutes per hour8931.01.01.01.01.0
 10–44 minutes per hour2561.0 (0.7–1.5)1.2 (0.7–2.1)1.3 (0.8–1.9)1.4 (0.9–2.1)1.1 (0.8–1.4)
 45–60 minutes per hour2601.5 (1.0–2.1)1.9 (1.2–3.1)1.7 (1.2–2.6)1.1 (0.7–1.8)1.4 (1.1–1.8)
Lifting, cumulative      
 Never6841.01.01.01.01.0
 1–99 kg per hour4791.4 (0.9–1.9)1.3 (0.8–2.1)1.4 (0.9–2.0)1.6 (1.1–2.3)1.3 (1.0–1.7)
 ≥100 kg per hour2901.9 (1.3–2.7)1.6 (0.9–2.7)1.9 (1.3–2.8)1.8 (1.2–2.8)1.6 (1.2–2.0)
Pushing, cumulative      
 Never8241.01.01.01.01.0
 1–354 kg per hour3271.3 (0.9–1.9)1.6 (0.9–2.7)1.9 (1.3–2.8)1.6 (1.1–2.5)1.5 (1.1–1.9)
 ≥355 kg per hour3051.5 (1.0–2.2)1.8 (1.1–3.1)1.7 (1.1–2.5)2.0 (1.4–3.0)1.5 (1.1–1.9)
Lifting at or above shoulder level      
 Never1,3071.01.01.01.01.0
 1–49 kg per hour901.2 (0.7–2.2)0.9 (0.4–2.2)1.2 (0.6–2.2)1.4 (0.8–2.7)1.3 (0.9–1.9)
 ≥50 kg per hour782.1 (1.3–3.5)2.2 (1.1–4.3)1.0 (0.5–2.0)2.0 (1.1–3.5)1.6 (1.1–2.3)
Sitting >30 minutes per hour      
 No1,0841.01.01.01.01.0
 Yes2860.7 (0.5–1.1)1.0 (0.6–1.7)0.9 (0.6–1.4)1.0 (0.6–1.5)0.9 (0.7–1.3)
Standing >30 minutes per hour      
 No1,3841.01.01.01.01.0
 Yes1141.8 (1.2–2.9)2.0 (1.1–3.7)2.1 (1.3–3.3)1.7 (1.0–2.9)1.7 (1.1–2.3)
Squatting >5 minutes per hour      
 No1,0821.01.01.01.01.0
 Yes2831.6 (1.1–2.2)1.2 (0.7–2.0)1.5 (1.0–2.1)1.6 (1.1–2.3)1.3 (1.0–1.7)

Of the psychosocial risk factors (Table 3), high job demands were not associated with worsening of pain. Low job control was significantly associated with low back pain (HR 1.7 [95% CI 1.2–2.3]) and lower limb pain (HR 1.6 [95% CI 1.1–2.2]). Social support from supervisors was marginally associated with lower limb pain (HR 1.4 [95% CI 1.0–2.0]), and social support from colleagues was associated with lower limb pain (HR 1.9 [95% CI 1.3–2.7]), and any regional pain (HR 1.3 [95% CI 1.1–1.7]). Management quality was only marginally associated with the outcomes. Low job satisfaction was significantly associated with neck/shoulder pain, lower limb pain, and any regional pain, with risk estimates from 1.6 for any regional pain to 2.2 for lower limb pain.

Table 3. Work-related psychosocial risk factors and new onset of severe regional musculoskeletal pain, partially adjusted*
Psychosocial risk factorNo. of subjectsHazard ratio (95% confidence interval)
Neck/shoulder painElbow, forearm, hand painLow back painHip, knee, foot painAny regional pain
  • *

    Adjusted for sex, age, occupational group, and intervention group.

Job demands      
 Low9401.01.01.01.01.0
 High5650.9 (0.7–1.3)0.8 (0.5–1.2)1.2 (0.9–1.7)0.9 (0.7–1.4)0.9 (0.7–1.1)
Job control      
 High1,0301.01.01.01.01.0
 Low4751.3 (0.9–1.8)1.5 (0.9–2.2)1.7 (1.2–2.3)1.6 (1.1–2.2)1.2 (1.0–1.5)
Social support from supervisors      
 High1,0301.01.01.01.01.0
 Low4721.2 (0.8–1.6)1.3 (0.8–1.9)1.1 (0.8–1.6)1.4 (1.0–2.0)1.2 (0.9–1.5)
Social support from colleagues      
 High1,2341.01.01.01.01.0
 Low2701.3 (0.9–1.8)1.5 (0.9–2.4)1.1 (0.8–1.6)1.9 (1.3–2.7)1.3 (1.1–1.7)
Management quality      
 High1,0501.01.01.01.01.0
 Low4361.2 (0.9–1.6)1.3 (0.9–2.0)1.3 (0.9–1.9)1.3 (0.9–1.8)1.2 (1.0–1.5)
Job satisfaction      
 High1,4221.01.01.01.01.0
 Low781.9 (1.1–3.2)1.3 (0.5–2.9)1.2 (0.6–2.2)2.2 (1.3–3.8)1.6 (1.1–2.3)

Many of the individual and health-related factors conferred an increased risk of worsening pain, including low education level for neck/shoulder pain (HR 1.8 [95% CI 1.1–3.0]) and BMI ≥30 for neck/shoulder pain, low back pain, and lower leg pain (HR 2.8 [95% CI 1.7–4.5]) (Table 4). Fear avoidance for work was not associated with pain worsening, whereas fear avoidance for physical activity showed minor positive associations with all outcomes, except for any regional pain. Health anxiety was only marginally associated with neck/shoulder pain. Other chronic diseases at baseline were significantly associated with pain worsening for all regions, most pronounced for arm pain (HR 1.6 [95% CI 1.0–2.4]) and lower leg pain (HR 1.7 [95% CI 1.2–2.4]).

Table 4. Demographic and health-related risk factors and new onset of severe regional musculoskeletal pain, partially adjusted*
Risk factorNo. of subjectsHazard ratio (95% confidence interval)
Neck/shoulder painElbow, forearm, hand painLow back painHip, knee, foot painAny regional pain
  • *

    Adjusted for sex, age, occupational group, and intervention group.

Education level      
 High3531.01.01.01.01.0
 Medium6681.2 (0.8–1.9)2.0 (1.1–3.9)0.9 (0.6–1.4)1.3 (0.8–2.2)1.1 (0.9–1.5)
 Low4541.8 (1.1–3.0)1.9 (0.9–4.0)1.1 (0.7–1.8)1.4 (0.8–2.5)1.2 (0.9–1.7)
Smoking      
 No1,1201.01.01.01.01.0
 Yes3821.3 (0.9–1.7)1.3 (0.8–2.0)1.0 (0.7–1.4)1.1 (1.0–1.1)1.1 (0.9–1.4)
Leisure time physical activity      
 Low8201.01.01.01.01.0
 High6720.8 (0.6–1.1)0.7 (0.4–1.0)1.0 (0.7–1.3)1.2 (0.9–1.7)0.9 (0.7–1.1)
Body mass index      
 <258961.01.01.01.01.0
 25–294801.1 (0.8–1.5)0.9 (0.5–1.4)1.2 (0.8–1.7)1.5 (1.0–2.1)1.1 (0.9–1.4)
 ≥301161.8 (1.1–2.8)1.5 (0.8–2.8)1.8 (1.1–2.9)2.8 (1.7–4.5)1.5 (1.1–2.2)
Fear avoidance, work      
 Low3821.01.01.01.01.0
 Medium6110.8 (0.5–1.1)0.9 (0.5–1.4)1.0 (0.7–1.4)1.3 (0.9–2.0)0.9 (0.7–1.2)
 High3630.9 (0.6–1.3)1.1 (0.6–1.8)0.9 (0.6–1.5)0.8 (0.5–1.3)0.9 (0.6–1.2)
Fear avoidance, physical activity      
 Low3821.01.01.01.01.0
 Medium6641.1 (0.7–1.6)1.9 (1.1–3.4)1.0 (0.7–1.5)1.3 (0.9–2.1)1.1 (0.9–1.5)
 High3191.2 (0.8–1.8)1.3 (0.7–2.7)1.2 (0.7–1.8)1.4 (0.9–2.4)1.0 (0.8–1.4)
Whiteley Index for health anxiety      
 Low1,2861.01.01.01.01.0
 Medium1491.3 (0.8–2.1)1.3 (0.7–2.4)1.4 (0.9–2.2)1.1 (0.7–1.9)1.1 (0.8–1.6)
 High661.3 (0.7–2.6)1.0 (0.4–2.7)0.9 (0.4–2.0)1.1 (0.5–2.3)1.1 (0.6–1.7)
Other chronic disease      
 No1,1901.01.01.01.01.0
 Yes3151.4 (1.0–1.9)1.6 (1.0–2.4)1.1 (0.7–1.6)1.7 (1.2–2.4)1.3 (1.0–1.6)

Final model.

In the final multivariate model (Table 5), subjects with high levels of repetitive work had an increased risk of arm pain (HR 1.7 [95% CI 1.0–2.9]). Lifting ≥100 kg per hour predicted worsening of low back pain (HR 1.5 [95% CI 1.0–2.3]). Lifting ≥50 kg at or above shoulder level remained significant for neck/shoulder pain (HR 1.9 [95% CI 1.1–3.3]) and pushing/pulling for lower limb pain (HR 1.6 [95% CI 1.0–2.5]). Standing for >30 minutes per hour was associated with low back pain (HR 1.9 [95% CI 1.2–3.0]) and any regional pain (HR 1.6 [95% CI 1.2–2.3]).

Table 5. Final model of risk factors for more severe regional pain, multivariate associations*
Risk factorHazard ratio (95% confidence interval)
Neck/shoulder painElbow, forearm, hand painLow back painHip, knee, foot painAny regional pain
  • *

    Adjusted for sex, age, occupational group, intervention group, and all other factors in each column.

Repetitive work     
 0–9 minutes per hour 1.0   
 10–44 minutes per hour 1.1 (0.6–2.0)   
 45–60 minutes per hour 1.7 (1.0–2.9)   
Lifting, cumulative     
 Never  1.0  
 1–99 kg per hour  1.2 (0.8–1.8)  
 ≥100 kg per hour  1.5 (1.0–2.3)  
Lifting at or above shoulder level     
 Never1.0    
 1–49 kg per hour1.1 (0.6–2.0)    
 ≥50 kg per hour1.9 (1.1–3.3)    
Pushing, cumulative     
 Never   1.0 
 1–354 kg per hour   1.4 (0.9–2.3) 
 ≥355 kg per hour   1.6 (1.0–2.5) 
Squatting >5 minutes per hour     
 No1.0  1.0 
 Yes1.4 (1.0–2.0)  1.2 (0.8–1.8) 
Standing >30 minutes per hour     
 No  1.0 1.0
 Yes  1.9 (1.2–3.0) 1.6 (1.2–2.3)
Job control     
 High  1.0  
 Low  1.5 (1.1–2.2)  
Social support from colleagues     
 High   1.0 
 Low   1.6 (1.0–2.4) 
Job satisfaction     
 High1.0  1.0 
 Low2.1 (1.2–3.6)  1.6 (0.9–3.0) 
Body mass index     
 <25   1.01.0
 25–29   1.4 (0.9–2.1)1.1 (0.8–1.4)
 ≥30   2.3 (1.3–3.9)1.4 (1.0–2.0)
Fear avoidance, physical activity     
 Low 1.0 1.0 
 Medium 1.9 (1.1–3.5) 1.6 (0.9–2.6) 
 High 1.3 (0.6–2.7) 1.8 (1.1–3.2) 
Education level     
 High1.01.0   
 Medium1.2 (0.7–1.8)1.9 (0.9–3.7)   
 Low1.6 (0.9–2.7)1.8 (0.8–3.9)   
Other chronic disease     
 No1.01.0 1.0 
 Yes1.3 (0.9–1.9)1.9 (1.2–3.1) 1.7 (1.1–2.5) 

The effects of the psychosocial risk factors at work were modest, aside from the association of low job satisfaction with increased risk of neck/shoulder pain (HR 2.1 [95% CI 1.2–3.6]). BMI ≥30 increased the risk of lower leg pain (HR 2.3 [95% CI 1.3–3.9]) and, to a lesser extent, the risk of any regional pain (HR 1.4 [95% CI 1.0–2.0]). Fear avoidance for physical activity was a risk factor for arm pain and for lower limb pain. Sex was not significantly associated with any of the 5 outcomes for pain worsening (data not shown). Other chronic diseases were significant for arm pain (HR 1.9 [95% CI 1.2–3.1]) and for lower limb pain (HR 1.7 [95% CI 1.1–2.5]). In the final model, there was only a tendency for the education level to have an impact on neck/shoulder and arm pain.

Respondents versus nonrespondents.

Table 6 shows the distribution of mean age, sex (% female), and sickness-related absences for >2 weeks during the 2 years preceding the study for all eligible study participants, grouped according to nonrespondents at baseline, dropouts from baseline to 24 months, those who participated in both assessments (baseline and followup), and the total population. Both the nonrespondents and the dropouts seemed to be younger, included more males, and had more episodes of sick leave before the study was initiated. A comparison between the 730 who dropped out and the 3,276 who were followed up at 24 months showed no differences in pain or other health-related outcomes at baseline, but significantly more of the dropouts lived alone (22.5% versus 12.5%), and there were more smokers among dropouts (42.1% versus 29.1%). There were no significant differences for the variables that were included in the final multivariate model.

Table 6. Demographic characteristics and prevalence of sickness-related absence for >2 weeks during the 2 years preceding the study
VariableNonrespondents (n = 1,598)Dropouts (n = 730)Followup (n = 3,276)Total (n = 5,604)
Age, mean ± SD years41.1 ± 10.939.6 ± 10.444.9 ± 9.943.9 ± 10.5
No. (%) female893 (55.9)397 (54.4)2,087 (63.7)3,377 (60.3)
No. (%) with sickness-related absence  for >2 weeks    
 During 2000252 (15.8)119 (16.3)368 (11.2)739 (13.2)
 During 2001257 (16.1)102 (14.0)359 (11.0)718 (12.8)

DISCUSSION

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

In this study, we examined the effect of work-related physical and psychosocial factors in combination with individual and health-related factors in relation to more severe regional pain in a prospective cohort of 4,006 industrial and service workers. The study benefits from investigating risk factors from several domains together and from investigating different regional pain symptoms in the same population, rather than analyzing different specific outcomes in separate studies. The main findings were that physical work place factors, psychosocial factors, and factors related to health and beliefs about health were all associated with more severe regional pain. Physical factors at work predicted pain worsening in specific regions, rather than just any regional pain. Highly repetitive work predicted arm pain, heavy lifting predicted low back pain, and pushing/pulling heavy weights predicted lower limb pain. These effects favor a specific effect of physical factors on pain worsening. Low job satisfaction was associated with all outcomes, but in the final model was significantly associated only with neck/shoulder pain and lower limb pain, whereas low job control was associated with low back pain, and low social support from colleagues was associated with lower limb pain. These associations indicate nonspecific effects of psychosocial factors at work.

Fear avoidance of physical activity, but not work, was of some importance for lower limb pain and arm pain, but it is possible that fear avoidance is of minor importance in this rather healthy working population than in a population in the later stages of more severe and disabling pain. Other chronic disease should be acknowledged in the secondary prevention of musculoskeletal pain.

Nonrespondents and dropouts in this study were characterized as younger males who smoked, lived alone, and had more lengthy periods of sick leave during the 2 years before the study. The same findings have been noted in other studies (19, 20), and this group's unwillingness to participate is well known. The dropouts were no different in terms of pain status or exposures at baseline, so we do not think that this selection would severely interfere with our risk estimates.

In this study, we chose to include all participants from baseline with no or only minor pain, instead of restricting the study to a followup of pain-free participants, which has been the method of choice in other studies (12, 21). We did that deliberately. When it comes to musculoskeletal pain incidence, it seems difficult to us to define a pain-free population. In our population, only 7.7% had not been bothered by pain in 1 of the 4 regions within the previous year. The occurrence of regional pain is normally distributed in the population. Furthermore, pain in one region is strongly correlated with pain in other regions and is strongly correlated with pain status in subsequent years. We would postulate that there is no such thing as a pain-free population, and even if there were, the characteristics of such a small group would be so special that it would hamper its use as a reference group in epidemiologic studies.

The exposures in the current study were measured 2 years prior to the measurement of pain status. Changes in exposure may well have occurred during the followup period, and we have no later measures. But we know that 80% of the participants in the followup cohort still had the same job and 10% had another similar job, so we have no reason to think that the exposures were radically changed. This study was a part of an intervention study with 3 arms, and all the analyses were adjusted for the intervention group, which did not contribute significantly to any of the models (data not shown).

The most serious drawback to exposure assessments in this study is that the physical exposures were derived from self reports. Even though the temporal relationship between measures fulfills an acceptable standard procedure, the self reports could easily be flawed by the subjects' pain status, given the discussion above concerning the very few pain-free individuals in such a population. Furthermore, common beliefs in different occupational groups about the occupational hazards experienced by their group could also influence self reports of exposure. In Denmark, nurse assistants have received a great deal of attention with regard to their musculoskeletal pain problems in recent years, and in our study, they scored highest on pushing and pulling and next highest on lifting, which could not be confirmed by observation in 2 nursing homes for 2 hours on typical working days (data not shown). We do not know in what other way the results of this study could be distorted because of self reports. It is possible that any such distortion could affect the results both positively and negatively. But, from the results, it nevertheless seems plausible that repetitive movements could be a risk factor for arm pain, which also has been found by others (22, 23). Lifting is a well-known risk factor for worsening of low back pain, and squatting as a risk factor for lower leg pain also seems possible, since squatting has been found to be a risk factor for knee arthritis (24).

Pain status was ascertained only at 2 time points, and even if we know that pain status at baseline was strongly associated with pain status at followup, we do not know the exact time frame for pain worsening in the study. Fluctuations in pain status have been confirmed in a previous study (25).

Beliefs about pain and health predicted pain status at followup, but this association was small after adjustment for other factors. Several studies have indicated the importance of health beliefs with regard to back pain, but the association is of the same magnitude as for other regional musculoskeletal pain. A part of the burden of regional musculoskeletal pain could well fit under the umbrella of medically unexplained symptoms (26), and in this study, the regional pain from all 4 regions was also correlated with mental health and vitality (according to the Short Form 36 health survey) (data not shown), which would further confirm that some pain symptoms belong to this large pool of functional symptoms. We do not know anything about the pathology behind the regional pain symptoms in our cohort, but from other studies of general working populations, we have found very few specific disorders among the study participants with pain complaints (19, 20). In a recent study of arm pain, evidence was found for a higher importance of physical exposures for more specific disorders, which calls for better descriptions of case definitions in epidemiologic studies based not only on self reports, but also on clinical examination findings (23). Because of the low prevalence and incidence of specific disorders, very large studies have to be conducted or, next best, one has to rely on well-conducted case reference studies.

We found some effects of work-related psychosocial factors. A review of psychosocial risk factors and low back pain in prospective studies found no effect (27). A more recent 6-month longitudinal study found that high job strain (the combination of high job demands and low job control) was associated with the occurrence of low back pain and neck/upper extremity symptoms as well as with the taking of sick leave because of musculoskeletal pain (21). In that study, pain was defined as any pain within the last 12 months, and participants with pain at baseline were excluded from the analyses. In our study, we found no effect of job strain, but low job control alone was associated to a minor degree with low back pain. In order to resolve these discrepancies of the importance of psychosocial factors at work, there is a need to develop more person-independent measures of the psychosocial work environment (28).

In summary, we have demonstrated that the reporting of more severe regional musculoskeletal pain is multifactorial, as has been demonstrated in other studies. We have questioned the notion of incidence of regional musculoskeletal pain, and we agree that interventions should address efforts to reduce the consequences of regional pain (9, 29). In addition, the concerted action of all stakeholders in the work place is necessary to provide work places that support workers with regional pain complaints so that they can keep up with their jobs and to make work places comfortable and accommodating so that workers with regional pain can cope with their regional pain complaints, which seems to be a ubiquitous part of modern working life (30). Doctors and other health care professionals should refrain from upgrading unexplained pain complaints to somatic or psychiatric diseases, should provide reassurance about the good prognosis of most musculoskeletal pain, and should support the necessary changes in the work place (31).

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES

Dr. Andersen had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study design. Andersen, Frost.

Acquisition of data. Andersen, Haahr, Frost.

Analysis and interpretation of data. Andersen, Haahr, Frost.

Manuscript preparation. Andersen, Haahr, Frost.

Statistical analysis. Andersen.

REFERENCES

  1. Top of page
  2. Abstract
  3. SUBJECTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. AUTHOR CONTRIBUTIONS
  7. REFERENCES
  • 1
    HagbergM, SilversteinBA, WellsRP, SmithR, CarayonP, HendrickH, et al, editors. Work-related musculoskeletal disorders (WMSD): a handbook for prevention. London: Taylor & Francis; 1995.
  • 2
    Panel on Musculoskeletal Disorders and the Workplace, Commission on Behavioral and Social Sciences and Education, National Research Council, Institute of Medicine. Musculoskeletal disorders and the workplace: low back and upper extremities. Washington: National Academy Press; 2001.
  • 3
    SilmanAJ, HochbergMC, editors. Epidemiology of the rheumatic diseases. 2nd ed. New York: Oxford University Press; 2001.
  • 4
    Nachemson AL, Jonsson E. Neck and back pain: the scientific evidence of causes, diagnosis and treatment. Philadelphia: Lippincott Williams & Wilkins; 2000.
  • 5
    Linton SJ, van Tulder MW. Preventive interventions for back and neck pain problems: what is the evidence? Spine 2001; 26: 77887.
  • 6
    Van Poppel MN, Hooftman WE, Koes BW. An update of a systematic review of controlled clinical trials on the primary prevention of back pain at the workplace. Occup Med (Lond) 2004; 54: 34552.
  • 7
    Macfarlane GJ, McBeth J, Garrow A, Silman AJ. Life is as much a pain as it ever was [letter]. BMJ 2000; 321: 897.
  • 8
    Hadler NM, Carey TS. Low back pain: an intermittent and remittent predicament of life. Ann Rheum Dis 1998; 57: 12.
  • 9
    Burton AK, Balague F, Cardon G, Eriksen HR, Henrotin Y, Lahad A, et al. How to prevent low back pain. Best Pract Res Clin Rheumatol 2005; 19: 54155.
  • 10
    Pope DP, Silman AJ, Cherry NM, Pritchard C, Macfarlane GJ. Validity of a self-completed questionnaire measuring the physical demands of work. Scand J Work Environ Health 1998; 24: 37685.
  • 11
    Pope DP, Silman AJ, Cherry NM, Pritchard C, Macfarlane GJ. Association of occupational physical demands and psychosocial working environment with disabling shoulder pain. Ann Rheum Dis 2001; 60: 8528.
  • 12
    Harkness EF, Macfarlane GJ, Nahit E, Silman AJ, McBeth J. Mechanical injury and psychosocial factors in the work place predict the onset of widespread body pain: a two-year prospective study among cohorts of newly employed workers. Arthritis Rheum 2004; 50: 165564.
  • 13
    Kristensen TS, Borg V, Hannerz H. Socioeconomic status and psychosocial work environment: results from a Danish national study. Scand J Public Health Suppl 2002; 59: 418.
  • 14
    Kristensen TS, Hannerz H, Hogh A, Borg V. The Copenhagen Psychosocial Questionnaire: a tool for the assessment and improvement of the psychosocial work environment. Scand J Work Environ Health 2005; 31: 43849.
  • 15
    Waddell G, Newton M, Henderson I, Somerville D, Main CJ. A Fear-Avoidance Beliefs Questionnaire (FABQ) and the role of fear-avoidance beliefs in chronic low back pain and disability. Pain 1993; 52: 15768.
  • 16
    Fink P, Ewald H, Jensen J, Sorensen L, Engberg M, Holm M, et al. Screening for somatization and hypochondriasis in primary care and neurological in-patients: a seven-item scale for hypochondriasis and somatization. J Psychosom Res 1999; 46: 26173.
  • 17
    Lassen CF, Mikkelsen S, Kryger AI, Brandt LP, Overgaard E, Thomsen JF, et al. Elbow and wrist/hand symptoms among 6,943 computer operators: a 1-year follow-up study (the NUDATA study). Am J Ind Med 2004; 46: 52133.
  • 18
    Lassen CF, Mikkelsen S, Kryger AI, Andersen JH. Risk factors for persistent elbow, forearm and hand pain among computer workers. Scand J Work Environ Health 2005; 31: 12231.
  • 19
    Andersen JH, Kaergaard A, Frost P, Thomsen JF, Bonde JP, Fallentin N, et al. Physical, psychosocial, and individual risk factors for neck/shoulder pain with pressure tenderness in the muscles among workers performing monotonous, repetitive work. Spine 2002; 27: 6607.
  • 20
    Andersen JH, Kaergaard A, Mikkelsen S, Jensen UF, Frost P, Bonde JP, et al. Risk factors in the onset of neck/shoulder pain in a prospective study of workers in industrial and service companies. Occup Environ Med 2003; 60: 64954.
  • 21
    Ijzelenberg W, Burdorf A. Risk factors for musculoskeletal symptoms and ensuing health care use and sick leave. Spine 2005; 30: 15506.
  • 22
    Macfarlane GJ, Hunt IM, Silman AJ. Role of mechanical and psychosocial factors in the onset of forearm pain: prospective population based study. BMJ 2000; 321: 6769.
  • 23
    Ryall C, Coggon D, Peveler R, Reading I, Palmer KT. A case-control study of risk factors for arm pain presenting to primary care services. Occup Med (Lond) 2006; 56: 13743.
  • 24
    Coggon D, Croft P, Kellingray S, Barrett D, McLaren M, Cooper C. Occupational physical activities and osteoarthritis of the knee. Arthritis Rheum 2000; 43: 14439.
  • 25
    Papageorgiou AC, Croft PR, Thomas E, Ferry S, Jayson MI, Silman AJ. Influence of previous pain experience on the episode incidence of low back pain: results from the South Manchester Back Pain Study. Pain 1996; 66: 1815.
  • 26
    Wessely S, Nimnuan C, Sharpe M. Functional somatic syndromes: one or many? Lancet 1999; 354: 9369.
  • 27
    Hartvigsen J, Lings S, Leboeuf-Yde C, Bakketeig L. Psychosocial factors at work in relation to low back pain and consequences of low back pain: a systematic, critical review of prospective cohort studies. Occup Environ Med 2004; 61: e2.
  • 28
    Walker-Bone K, Cooper C. Hard work never hurt anyone: or did it? A review of occupational associations with soft tissue musculoskeletal disorders of the neck and upper limb. Ann Rheum Dis 2005; 64: 13916.
  • 29
    Burton AK, Balague F, Cardon G, Eriksen HR, Henrotin Y, Lahad A, et al. Chapter 2. European guidelines for prevention in low back pain: November 2004. Eur Spine J 2006; 15 Suppl 2: S13668.
  • 30
    Hadler NM. Back pain in the workplace: what you lift or how you lift matters far less than whether you lift or when. Spine 1997; 22: 93540.
  • 31
    Waddell G, Burton AK. Occupational health guidelines for the management of low back pain at work: evidence review. Occup Med (Lond) 2001; 51: 12435.