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Workplace
A prospective cohort study on severe pain as a risk factor for long-term sickness absence in blue- and white-collar workers
  1. Lars Louis Andersen1,
  2. Ole Steen Mortensen1,2,
  3. Jørgen Vinsløv Hansen1,
  4. Hermann Burr1
  1. 1National Research Centre for the Working Environment, Copenhagen, Denmark
  2. 2Department of Occupational and Environmental Medicine, Bispebjerg University Hospital, DK 2400 Copenhagen, NV
  1. Correspondence to Dr Lars Louis Andersen, National Research Centre for the Working Environment, Lersø Parkalle 105, Copenhagen 2100, Denmark; lla{at}nrcwe.dk

Abstract

Objective To estimate the impact of pain in different body regions on future long-term sickness absence (LTSA) among blue- and white-collar workers.

Method Prospective cohort study in a representative sample of 5603 employees (the Danish Work Environment Cohort Study) interviewed in 2000, and followed in 2001–2002 in a national sickness absence register. Cox regression analysis was performed to assess the risk estimates of mutually adjusted severe pain in the neck/shoulder, low back, hand/wrist and knees for onset of LTSA, defined as receiving sickness absence compensation for at least 3 consecutive weeks. Age, gender, body mass index, smoking and diagnosed disease were controlled for.

Results In 2000 the prevalence among blue- and white-collar workers, respectively, of severe pain was 33% and 29% (neck/shoulder), 33% and 25% (low back), 16% and 11% (hand/wrists), and 16% and 12% (knees). During 2001–2002, the prevalence of LTSA among blue- and white-collar workers was 18% and 12%, respectively. Hand/wrist pain (HR 1.49, 95% CI 1.23 to 1.81) and low back pain (HR 1.30, 95% CI 1.11 to 1.53) were significant risk factors among the total cohort. Neck/shoulder pain was a significant risk factor among white-collar workers only (HR 1.35, 95% CI 1.21 to 1.85). Knee pain was not a significant risk factor.

Conclusion While hand/wrist pain and low back pain are general risk factors for LTSA, neck/shoulder pain is a specific risk factor among white-collar workers. This study suggests the potential for preventing future LTSA through interventions to manage or reduce musculoskeletal pain.

  • Epidemiology
  • musculoskeletal
  • sickness absence

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What this paper adds

  • There is a need to investigate the impact of pain in different body regions on long-term sickness absence among different socioeconomic groups, to thereby more efficiently target prevention strategies.

  • Our study shows that low back pain and hand/wrist pain are general risk factors for future sickness absence, and that neck/shoulder pain is a specific risk factor among white-collar workers.

  • Our study suggests the potential for preventing future long-term sickness absence through interventions to manage or reduce musculoskeletal pain.

Introduction

Sickness absence constitutes a global socioeconomic burden, with almost 200 million lost working days per year in Britain alone.1 Consequently, strategies to reduce sickness absence are one of the top political priorities in the European Union.2 Long-term sickness absence (LTSA) accounts for up to 75% of total absence costs although constituting only a third of all lost working days.1 In spite of national ambitions to reduce the burden, sickness absence has remained stable over recent decades, however with some increase during the economic boom period just after 2000.3

Worldwide, a third or more of all registered occupational diseases are musculoskeletal disorders. While low back pain and neck/shoulder pain are known risk factors for sickness absence,4–8 only a few large prospective studies have reported on the impact of pain in other regions of the body.5 6 Moreover, blue-collar compared with white-collar workers have an increased risk of sickness absence due to musculoskeletal disorders.5 Overall, there is a need to investigate the impact of pain in different body regions on future LTSA among blue- and white-collar workers, to thereby more efficiently target national prevention strategies.

This study estimates the impact of pain in different body regions on future LTSA among blue- and white-collar workers.

Methods

Population

A random sample of 5603 employees in Denmark were interviewed by telephone in 2000 (the Danish Work Environment Cohort Study, DWECS),9 and followed in 2001–2002 in a national sickness absence register. The panel started out with a random sample drawn in 1990 from the central population register, consisting of 9653 people aged 18–59 years on 1 October 1990. The DWECS is an open cohort study which included young people and immigrants in 1995 and 2000. The combined 2000 sample consisted of 11 437 people living in Denmark, of whom 8583 participated (∼75%). Of these, 5603 were aged 18–64 years and employed currently or within the 2 months prior to the interview. After omitting individuals sick in the week before baseline, the data set consisted of 5510 workers. Of these, 414 had missing information on the questions below. Therefore, the analyses were based on 5096 employees (mean (SD) age 40 (11) years, body mass index (BMI) 24.5 (3.7) kg/m2, smokers 37%, women 49%).

Variables

The respondents were classified into two socioeconomic groups according to employment grade, job title and education.10 White-collar workers included managers, academics, people with 3–4 years of vocational education and other salaried workers. Blue-collar workers comprised skilled, semiskilled or unskilled workers. There were 1759 blue- and 3337 white-collar workers.

Weekly data on sickness absence were obtained from a national register of social transfer payment (DREAM), and linked to DWECS via the unique personal identification number which is given to all Danish citizens at birth. Due to statistical power considerations and the fact that Danish citizens are registered with DREAM when having at least 3 consecutive weeks of sickness absence, we defined LTSA as having registered sickness absence for at least 3 consecutive weeks in the 2-year follow-up period.

Musculoskeletal pain

Intensity of pain in the neck, right and left shoulder, right and left hand/wrist, low back and knees was assessed using a modified version of the PRIM questionnaire11 based on a 10-point pain score.12 The following question was posed by the interviewer: “On a scale of 0 to 9 with 0 being no discomfort at all and 9 being the worst possible pain, state your average degree of discomfort in your [body region] in the last 3 months”. Severe pain was defined as reporting at least 4 on the scale.11 12

Statistical analyses

The Cox proportional hazard model was used for modelling the probability of LTSA in the period 2001–2002, with severe pain in the neck/shoulder, hand/wrists, low back and knees as mutually adjusted independent explanatory variables. Interaction effects between regions were also tested. Control variables were gender, age, smoking status (‘never or former’ and ‘current’), BMI and diagnosed disease (self-report). Age and BMI were included in the analysis with linear effects on LTSA.

The data on LTSA correspond to survival times which in most cases are censored as the cohort is only followed for 2 years from 1 January 2001 until 31 December 2002. When individuals had an onset of LTSA in the period 2001–2002, the survival times were non-censored and referred to as event times.

Apart from main effects, interactions of socioeconomic position with each of the four pains were also modelled. Interactions were omitted from the analysis if they were non-significant.

The estimation method was maximum likelihood and the PHREG procedure of the statistical computer program SAS 9.2 was used.

Results

The prevalence of severe pain in the neck/shoulder, low back, knees and hand/wrists was 33%, 33%, 16% and 16%, respectively, in blue-collar workers, and 29%, 25%, 12% and 11% in white-collar workers. During the 2001–2002 follow-up, 18% and 12% of the blue- and white-collar workers, respectively, developed LTSA. Table 1 shows that severe hand/wrist pain and severe low back pain were significant risk factors for onset of LTSA in the total cohort. A significant interaction between socioeconomic position and severe neck/shoulder pain was found (p=0.02). Neck/shoulder pain predicted LTSA in white-collar workers only. As there was no significant interaction between body regions, HRs when having pain in more than one region were calculated as the product of the respective regions.

Table 1

Mutually adjusted HRs (95% CIs) for long-term sickness absence (n=5096)

Discussion

Several prospective cohort studies report that low back pain and neck/shoulder pain are risk factors for sickness absence among different job groups.4–8 Our study confirms these findings for low back pain, but shows a significant interaction between neck/shoulder pain and socioeconomic position. While the prevalence of severe neck/shoulder pain was similarly high among blue- (33%) and white-collar workers (29%), this type of pain was a risk factor for LTSA in white-collar workers only. Two thirds of our random sample of Danish employees consisted of white-collar workers, which underlines the socioeconomic impact of neck/shoulder pain. In contrast to the present findings, other studies have reported neck and/or shoulder pain to be a risk factor for self-reported sickness absence among manual labour employees.4 5 The different results between studies may be explained by different predictors, different outcomes, register versus self-report, adjustment for confounders and specific job groups.

Although hand/wrist pain was less prevalent than neck/shoulder and low back pain, the risk for sustaining LTSA when having hand/wrist pain was higher. As employees depend on their hand/wrists for manual labour as well as information processing, these findings make sense. Although knee pain adjusted for diagnosed disease was not a risk factor for LTSA in our representative sample of blue- and white-collar workers, others reported knee pain to be a risk factor for self-reported LTSA5 and disability.6 Thus, specific occupations and different countries may show different results.

Widespread pain markedly increased risk of LTSA. Although controlled for diagnosed disease, severe pain in several regions of the body could be a symptom of undiagnosed progressing disease.

In conclusion, the present study from a representative sample of 5603 Danish employees shows that hand/wrist pain and low back pain are general risk factors for future LTSA, and that neck/shoulder pain is a risk factor specifically among white-collar workers. Knee pain was not a significant risk factor. The potential for preventing LTSA through interventions to manage or reduce musculoskeletal pain symptoms is enormous.

References

Footnotes

  • Competing interests None.

  • Ethics approval The study has been notified to and registered by Datatilsynet (the Danish Data Protection Agency). According to Danish law, questionnaire and register based studies do not need approval by ethics and scientific committees, nor informed consent.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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