2016 Volume 58 Issue 1 Pages 16-24
Objective: All occupations expose workers to varied and unique conditions. The nature of work has been recognized as influencing the health of workers. Whether predictors for chronic neck and low back pain would be occupation-specific is unknown. This study aimed to identify predictors for chronic neck and low back pain in a cohort of office workers. Methods: A prospective study was carried out among 669 healthy office workers. At baseline, risk factors were assessed using a questionnaire and standardized physical examination. A symptomatic case was defined as an individual who reported pain greater than 30 mm on a 100-mm VAS, and chronic pain was defined as experiencing ongoing neck or low back pain for greater than 3 months over the past 6 months. Two regression models were built to analyze the risk factors for developing chronic neck and low back pain. Results: Of the sample, 17 and 27% of office workers who reported a new onset of neck or low back pain developed chronicity, respectively. Predictors for chronic neck pain were high body mass index, frequent neck extension during the work day, high initial pain intensity, and high psychological job demands. The development of chronic low back pain was associated with history of low back pain and high initial pain intensity. Conclusions: The findings suggest that predictors for chronic musculoskeletal pain in a subpopulation may be a subset of predictors identified in a general population or occupation specific. Successful management to prevent chronic musculoskeletal pain may also need to consider the patient's occupation.
(J Occup Health 2016; 58: 16–24)
Neck and low back pain are significant health problems in office workers1–3). One-year prevalence estimates of neck pain in office workers range from 42–69%3–6), while those for 1-year incidence range from 27–49%7–10). Previous studies reported that between 34–51% of office workers experienced low back pain in the preceding 12 months1, 3) and that 20–23% of office workers reported new onset of low back pain during 1-year follow-up11, 12). Neck and low back pain occur episodically over a lifetime with variable recovery between episodes13). In a working population, between 60–80% of workers with neck pain reported neck pain 1 year later14), whereas between 24–61% of patients with recent onset of low back pain developed chronicity15, 16). Neck and low back pain often leads to activity limitations, sickness absence, or long-term work disability. Thus, there is a significant socioeconomic burden on patients and society17, 18).
Studies have identified several biopsychosocial factors associated with chronic neck and low back pain14, 19–21). Carroll et al. (2009) indicated in their review that older age, poor health, prior pain episodes, poor psychological health, and worrying, becoming angry, or becoming frustrated in response to neck pain were associated with poorer prognosis of outcomes in the general population with neck pain14). Henschke et al. (2008) found in their prospective cohort study that older age, compensation cases, higher pain intensity, longer duration of low back pain before consultation, more days of reduced activity because of low back pain before consultation, depression, and perceived risk of persistence were associated with longer recovery16).
All occupations expose workers to varied and unique conditions, activities, and stressors. The nature of work has been recognized as influencing workers' health17). Thus, predisposing factors for a disease in different occupations are assumed to be dissimilar and related to the characteristic exposures, demands, and conditions of specific jobs. Office work is sedentary work, mainly involving computer use, meetings, presentations, reading, and telephone calls. Office work may require sitting long periods using a computer, working in awkward positions, or performing repetitive manual tasks. Office work also unavoidably causes psychological stress. Evidence suggests that risk factors for the onset of neck and low back pain in office workers are different from those identified in a general population22, 23). It is unknown whether predictors for chronic neck and low back pain are occupation specific. Thus, the aim of this study was to identify the predictors for chronic neck and low back pain in a cohort of office workers with new onset of neck and low back pain.
A prospective cohort study with 1-year follow-up was conducted in a convenience sample of office workers recruited from nine large-scale enterprises. Individuals were included in the study if they were 18–55 years of age and working full time. Subjects were excluded if they had reported musculoskeletal symptoms in the spine in the previous 3 months with a pain intensity >30 mm on a 100-mm visual analog scale (VAS), reported pregnancy or had planned to become pregnant in the next 12 months, had a history of trauma or accidents in the spinal region, or had a history of spinal, intra-abdominal, or femoral surgery in the previous 12 months. Subjects who had been diagnosed with congenital anomaly of the spine, rheumatoid arthritis, infection of the spine and discs, ankylosing spondylitis, spondylolisthesis, spondylosis, tumor, systemic lupus erythematosus, or osteoporosis were also excluded from the study. Volunteers were screened for the study using a self-administered questionnaire.
At baseline, participants completed a self-administered questionnaire and underwent a physical examination by trained physical therapists according to a standardized protocol. Participants received a self-administered diary to record the incidence of neck and low back pain. The researcher returned to collect the diaries from participants every month over a 12-month period. The study was approved by the University Human Ethics Committee.
The self-administered questionnaire was used to gather data on individual, physical, and psychosocial factors. Individual factors included gender, age, marital status, educational level, frequency of regular exercise or sport, smoking habits, and number of driving hours a day. Physical factors included current job position, number of working hours, years of working experience, frequency of using a computer, frequency of performing various activities during work, and frequency of rest breaks. The questionnaire also asked respondents to self-rate the ergonomics of their workstations (desk, chair, and position of monitor) and work environment conditions (ambient temperature, noise level, light intensity, and air circulation). Psychosocial factors were measured by the Job Content Questionnaire (JCQ)24).
Body weight and height were measured by digital scale and a wall-mounted standiometer, respectively. Waist circumference was measured midway between the lower rib margin and the superior border of the iliac crest using a tape measure. Neck flexion range of motion was measured using a cervical range of movement device. Trunk extension flexibility was assessed by the modified-modified Schöber test25). Neck flexor endurance was assessed according to the procedure described by Harris et al. (2005)26). Erector spinae and multifidus muscle endurance was assessed by the Biering-Sörensen test27).
Before data collection, repeatability of data from the questionnaire and physical examination was assessed in 20 office workers. Each subject was tested on two occasions separated by an interim of 7 days between measurements for the questionnaire and 10 minutes for the physical examination.
The areas of the neck and lower back were defined according to the picture of the body from the standardized Nordic questionnaire28). Nonspecific neck or low back pain is neck or low back pain (with or without radiation) without any specific systematic disease being detected as the underlying cause of the complaints29). Participants answered the yes/no question “Have you experienced any neck or low back pain lasting >24 hours during the past month?” If they answered “Yes”, follow-up questions about pain intensity measured by a VAS and the presence of weakness or numbness in the upper or lower limbs were asked. Those who reported the incidence of neck and low back pain were also asked about their disability level as measured by the Neck Disability Index (NDI)30) and the Roland-Morris Disability Questionnaire (RMDQ)31), respectively.
Participants were identified as having incident neck or low back pain if they answered “Yes” to the first question, reported a pain intensity >30 mm on a 100-mm VAS, and had no weakness or numbness in the upper or lower limbs. Participants were followed until completing the 12-month follow-up or withdrawing from the study. Chronic neck or low back pain was defined as ongoing neck or low back pain for greater than 3 months over the past 6 months32), i.e., reporting incident neck or low back pain for at least 3 months in any 6 months during the 1-year follow up.
For the reliability study, the intraclass correlation coefficient was calculated for continuous data and Phi coefficient was calculated for nominal data. The ICC (3,1) was calculated for the questionnaire and physical examination outcomes.
Characteristics of subjects were described using means or proportions. Two regression models were built to analyze predictors for chronic neck and low back pain. Initially, the associations between each factor and chronic neck and low back pain were evaluated using univariate logistic regression analysis. Any factors with a p-value ≤0.2 were eligible for addition to multivariate analysis. The covariates of age, gender, initial pain intensity, and initial disability level were forced into the final adjusted model to reduce confounding. Separate multivariable logistic regression models were then performed to assess the associations between chronic neck and low back pain (LBP) and biopsychosocial factors. Adjusted ORs and 95% CIs for the final models are presented in the results section. Statistical significance was set at the 5% level. All statistical analyses were performed using the SPSS statistical software, version 17.0 (SPSS Inc, Chicago, IL, USA).
The test-retest reliability results demonstrated fair (0.53) to excellent (1.00) reliability for questionnaire outcomes and good (0.72) to excellent (1.00) reliability for physical examination outcomes.
A total of 3,446 office workers responded to the questionnaire (a response rate of 53%). Of them 2,483 were excluded because they did not meet the inclusion criteria, leaving an eligible population of 963. In total, 669 office workers agreed to participate in the physical examination (Fig. 1). Subsequently, 615 (92%) office workers were followed up for 1 year. Table 1 presents the baseline characteristics of the study population.
Flowchart of participants for the study.
Due to incomplete data from six participants, the final analysis was based on data collected from 609 participants. A total of 130 (21.3%) workers reported new onset of neck pain during the follow-up period, and 22 (16.9%) developed chronicity. The mean (SD) VAS and NDI scores for those with incident neck pain were 4.6 (1.5) mm and 6.7 (4.7), respectively.
When performing univariate analyses, factors showing a p-value ≤0.2 were body mass index, frequency of neck extension during the work day, and psychological job demands. Thus, these factors were selected for further analysis. Multivariable logistic regression analyses revealed that body mass index, frequency of neck extension during the work day, initial pain intensity, and psychological job demands were associated with chronic neck pain (Table 2).
A total of 105 (17.1%) workers reported new onset of low back pain during the follow-up period, and 28 (26.7%) developed chronicity. The mean (SD) VAS and RMDQ scores for those with incident low back pain were 4.8 (1.7) mm and 3.6 (2.8), respectively.
When performing univariate analyses, factors showing a p-value ≤0.2 were history of low back pain, body mass index, frequency of rest breaks, frequency of exercise, and psychological job demands (measured by the Job Content Questionnaire). Thus, these factors were selected for further analysis. Multivariable logistic regression analyses revealed that history of low back pain and initial pain intensity were associated with chronic low back pain (Table 3).
In this study, 17 and 27% of office workers who reported a new onset of neck and low back pain developed chronicity, respectively. Kääriä et al. (2012) reported in their prospective cohort study among middle-aged (municipal) employees in Finland that the incidence of chronic neck pain was 15% in women and 9% in men21). For low back pain, Costa et al. (2009) reported that 41.7% of patients with acute low back pain presenting to primary care in Australia developed chronicity33). Differences in incidence rates may be caused by methodological differences across studies, particularly in the definition of a symptomatic case and chronicity. Kääriä et al. (2012) simply defined symptomatic cases as those having pain in the neck and chronic cases as those having pain that persisted for more than 3 months21). Costa et al. (2009) defined symptomatic cases as those with pain lasting more than 24 hours but less than 2 weeks that was preceded by at least one pain-free month33). Participants with pain that had persisted for three months after the onset of symptoms met the criteria for chronic low back pain. In this study, a symptomatic case was defined as a case in which the subject reported pain greater than 30 mm on a 100-mm VAS, and a chronic case was defined as a case in which the subject reported ongoing neck or low back pain for greater than 3 months over the past 6 months, in accordance with the definitions by Deyo et al. (2014)32).
Although the mechanisms for the development of chronic musculoskeletal pain are not fully understood, according to the biopsychosocial model, it involves impairments of physical, psychological, and social functioning34). Information about predictors of chronic neck and low back pain is of considerable importance because chronic pain can have broad and profound effects on well-being with significant impairment of physical and psychological health35). The successful identification of such factors may suggest a role for screening patients in the early stages of pain and targeting interventions at those at high risk. Also, treatment should be targeted towards factors that have adverse effects on recovery.
We found that office workers with a high body mass index, frequent neck extension during the work day, high initial pain intensity, and high psychological job demands scores were more likely to develop chronic neck pain, whereas those with history of low back pain and high initial pain intensity were more likely to have chronic low back pain. In the general population, Kääriä et al. (2012) reported that, among women, workplace bullying, frequent sleep problems, overweight or obesity, previous acute neck pain, and chronic low back pain were predictors of chronic neck pain21). Among men, previous acute neck pain and chronic low back pain were factors predicting the development of chronic neck pain. Henschke et al. (2008)16) and Melloh et al. (2013)36) found that predictors of chronic low back pain in the general population consisted of older age, compensation cases, high pain intensity, high functional limitation due to low back pain, longer duration of low back pain before consultation, more days of reduced activity because of low back pain before consultation, feelings of depression, perceived risk of persistence, a highly resigned attitude towards a job, and low social support. The predictive value of several factors identified in previous studies in a general population, for both chronic neck and low back pain, could not be confirmed in the present study. The findings of the current study shed some light on the notion that predictors of chronic musculoskeletal pain in a subpopulation may be a subset of predictors identified in a general population or occupation specific17). Also, the findings support the notion that predictors of chronic musculoskeletal pain may be site specific. To gain further insight into predictors of the development of chronic musculoskeletal pain, future studies should consider investigation of predictors in a more specific group of the population and specific body region.
Initial pain intensity seems to be one important factor associated with chronic musculoskeletal pain because it is a predictor of both chronic neck and low back pain. In the present study, the “initial pain intensity” factor was treated as a continuous variable in the regression analysis, and the findings revealed that the higher the initial pain intensity, the higher the risk of developing chronic nonspecific neck pain. The results are consistent with previous findings37, 38). Bot et al. (2005) reported that more intense pain at baseline significantly reduced the probability of recovery at 3 months in patients with neck and shoulder pain37). Campbell et al. (2013) found that pain intensity experienced during a period of primary care consultation, and patients' perceptions about whether their back pain would persist, were significant predictors of poor outcome at 6 months and at 5 years in patients with low back pain39).
Body mass index was identified as one of the factors associated with chronic neck pain in the present study. The results are generally consistent with previous studies21, 40, 41). A number of hypotheses have been proposed to explain the link between body mass index and chronic musculoskeletal pain. Obesity is usually regarded as a pro-inflammatory state, and inflammation may be a mediator of the relationship between obesity and chronic pain41). Being overweight has been found to be associated with modified serum lipid levels and atherosclerosis, possibly affecting the nutrition of disc cells42). Also, a previous study showed that being overweight was associated with disc degeneration in the lumbar spine43).
Interestingly, frequent neck extension during the work day was identified as a predictor of chronic nonspecific neck pain. A previous study showed that the position of the computer monitor not being level with the eyes caused nonspecific neck pain in office workers44). The results of the present study further suggest that monitor height above eye level, rather than below eye level, makes the cervical spine susceptible to injury. Further study is required to enhance our understanding regarding the relationships between neck posture during work, monitor height, and the chronicity of nonspecific neck pain in office workers.
Our finding also concurs with the view that the psychosocial factor is one predictor for chronic musculoskeletal pain in office workers16, 45). In this study, several work-related psychosocial factors, including psychological job demands, decision latitude, supervisor support, coworker support, physical job demands, job security, and hazards at work, were evaluated using the Job Content Questionnaire. The findings showed that psychological job demands could differentiate office workers at a high risk of developing chronic neck pain from those at low risk. Such an association in the case of chronic low back pain just failed to reach a statistically significant level (p-value=0.05). Kääriä et al. (2012) found an association between work-related emotional exhaustion and chronic neck pain in male middle-aged employees in their prospective cohort study21). Henschke et al. (2008) also reported that feelings of depression and perceived risk of persistence were associated with longer recovery time16). Since we only examined a set of work-related psychosocial factors, it is also possible that other important psychosocial factors may be identified in future work. This issue warrants further investigation. At this stage, the precise mechanisms through which psychological factors link with chronicity of musculoskeletal disorders are not yet fully understood. However, one plausible explanation is that high psychological job demand leads to high psychological stress, which in turn adversely affects health46).
Major strengths of this study are its prospective design, allowing for the identification of the cause-effect relationships, and the inclusion of a broad range of biopsychosocial factors for their contribution to the chronicity of neck and low back pain in office workers. In addition, a large sample was successfully followed up for 1 year (92%), allowing for robust results for determining the model's goodness of fit. However, the current study has at least four main limitations. First, the use of a convenience sample restricts the external validity of this study. Thus, generalization of the results from this study to other working populations should be made with caution. Second, the nature of some work-related physical factors, i.e., frequency of performing various activities during work and frequency of rest breaks, and the diagnosis of musculoskeletal disorders were subjective, possibly leading to data inaccuracy. One noteworthy drawback of self-reported data is the risk of overestimation of exposure. Also, some workers may be more sensitive to any somatic disturbance than others. As a result, there is a risk of under- or overreporting of incidence. Future studies should consider inclusion of objective information from physical examinations to increase data accuracy. Third, in this study, subjects were included at baseline if they had reported musculoskeletal symptoms in the spine in the previous 3 months with a pain intensity ≤30 mm on a 100-mm VAS, and during the 1-year follow-up, subjects were identified as cases if they reported pain lasting more than 1 day, pain greater than 30 mm on a 100-mm VAS, and no weakness or numbness in the lower limbs. Different results may emerge with different inclusion criteria and definitions of symptomatic cases. Fourth, our sample of office workers still continued to work. Workers who continue working would have a low level of disability because it would be difficult for them to remain productive with a high level of disability. Also, office work is sedentary, which mainly involves computer use, participation in meetings, giving presentations, reading, and telephone calls. Office workers are less likely to have moderate to high disability levels because of their limited physical requirements at work. Thus, extrapolation of the results of the present study to office workers with moderate to high disability levels should be undertaken with caution.
The results of this prospective cohort study indicated that high body mass index, frequent neck extension during the work day, high initial pain intensity, and high psychological job demands scores may increase the risk of developing chronic neck pain, whereas history of low back pain and high initial pain intensity may be predictors for chronic low back pain in office workers. Such information can be used by clinicians to estimate prognosis for individual patients in primary care. Also, interventions aimed at reducing the incidence of chronic neck and low back pain should be targeted towards the modifiable predictors identified in this study.
Conflict of interests: No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.
Acknowledgment: This work was funded by the Social Security Office of Thailand (Grant No. 002/2553), the Thai Health Foundation, and the Chulalongkorn University Centenary Academic Development Project (#12).