Knut Hagen, MD, PhD,* Mattias Linde, MD, PhD,* Ingrid Heuch, MD, Lars Jacob Stovner, MD, PhD,* and John-Anker Zwart, MD, PhD*

Transcription

1 Pain Medicine 2011; 12: Wiley Periodicals, Inc. Original Research Articles Increasing of Chronic Musculoskeletal Complaints. A Large 11-Year Follow-Up in the General Population (HUNT 2 and 3)pme_ Knut Hagen, MD, PhD,* Mattias Linde, MD, PhD,* Ingrid Heuch, MD, Lars Jacob Stovner, MD, PhD,* and John-Anker Zwart, MD, PhD* *Department of Neuroscience, Norwegian University of Science and Technology; Norwegian National Headache Centre, St. Olavs University Hospital, Trondheim; Department of Neurology, Oslo University Hospital and University of Oslo, Norway Reprint requests to: Knut Hagen, MD, PhD, Norwegian National Headache Centre, Department of Neurology and Clinical Neurophysiology, St. Olavs. University Hospital, Trondheim 7006, Norway. Tel: ; Fax: ; knut.hagen@ntnu.no. age-adjusted prevalence of chronic MSCs was higher (P < 0.001) in HUNT 3 (47.9%, 95% CI ) compared with HUNT 2 (44.8%, 95% CI ), evident for both genders, and most prominent in the age group years. Chronic widespread MSCs were more common in HUNT 3 than in HUNT 2 among women (28.2 vs 26.0%, P < 0.001). Increased prevalence during the 11-year period was also found in supplementary analyses evaluating the influence of differences in participation rate. Conclusions. The prevalence of chronic MSCs and chronic widespread MSCs is high. The prevalence of chronic MSCs increased during the 11-year period. A nonresponse bias interfering with the comparisons over time could not completely be ruled out. Key Words. Chronic Widespread Musculoskeletal Pain; Epidemiology; ; Time Trends; General Population Abstract Objectives. To assess the prevalence of chronic musculoskeletal complaints (MSCs) in a large adult population, and to determine any changes in prevalence during an 11-year period. Methods. This study involved two large crosssectional surveys (Helseundersøkelsen i Nord- Trøndelag [HUNT] 2 and 3) of inhabitants in Nord-Trøndelag county aged 20 years performed in (N = 92,936) and (N = 94,194). Attendance rates were 70 and 42%, respectively. Respondents with chronic MSCs were identified through the screening question Have you during the last year continuously for at least 3 months had pain and/or stiffness in muscles and joints? The reliability of the screening question was evaluated in a random sample of participants (N = 563). Results. The reliability of the screening question was good (kappa value 0.63, 95% confidence interval [CI] ). In HUNT 3, 48% had chronic MSCs and 20% had chronic widespread MSCs. The Background Musculoskeletal complaint (MSC) is a common cause of sick leave and disability pension in Norway [1] and represents a major health problem in the Western societies [2]. In recognition of this, the World Health Organization endorsed the Bone and Joint decade [1]. At the start of this decade, it was contended that the prevalence of MSCs would increase in the future [3], but it is still unclear whether MSCs are becoming more common over time [4]. Inconsistent findings have been made for low back pain [4 7]. The prevalence of MSCs increased from 1993 to 2001 in Spain [8], and such an increase was also found for a cohort born during the 1940s in a recent Swedish study [9]. These two studies used very different definitions of MSCs. The Spanish study measured invalidating musculoskeletal pain caused by injury [8], whereas injury was not included in the definition of musculoskeletal pain in the latter study [9]. Thus, more studies evaluating time trends using a widely accepted definition of chronic MSCs (body pain for at least 3 months during the past year) are needed before valid conclusions can be made. 1657

2 Hagen et al. There are also very few studies on time trends of chronic widespread MSC defined as pain for at least 3 months during the past year, including occurrence of pain in three major regions and in both sides of the body [10]. An increased prevalence of widespread pain was found over a 40-year period in England [11], whereas prevalence rates were stable over a 7-year period in two other two population-based studies conducted in different regions of England [12,13]. It is not only important to know the prevalence of such complaints for the purpose of individual and societal impact, but also to detect underlying causes that can be target for intervention [14]. It has been expected that change in lifestyle may influence prevalence of MSCs over time [3]. If true, such factors should be considered when evaluating time trends of MSCs. Replications of surveys using identical methodology applied in the same geographical area are warranted. The aim of the present study was to assess the prevalence of chronic MSCs and chronic widespread MSCs in a large adult population conducted as a follow-up of a study performed 11 years earlier, and to determine any changes during this period. Methods Study Populations Nord-Trøndelag is one of 19 Norwegian counties, and is located in the middle part of the country. The population is scattered but ethnically quite homogenous and consists mainly of Caucasians. The Nord-Trøndelag Health Survey ( Helseundersøkelsen i Nord-Trøndelag, [HUNT]) is a longitudinal cohort study inviting all inhabitants 20 years old in Nord-Trøndelag County. The first HUNT study (HUNT 1, performed between 1984 and 1986) mainly focused on cardiovascular diseases, lung diseases, diabetes mellitus, and quality of life. HUNT 2 (performed between 1995 and 1997) and HUNT 3 (performed between 2006 and 2008) covered a much larger number of health-related items, including similarly phrased questions regarding chronic MSCs. Previous publications based on MSC questions in HUNT 2 have focused on, e.g., prevalence, incidence, and the relationship with socioeconomic status, body mass index (BMI), physical activity, serum lipids, comorbid conditions, and genes [15 24]. HUNT 2 In HUNT 2, an invitation letter and a first questionnaire (Q1) was mailed to all adult inhabitants about 2 weeks before the screening date. 64,780 (70%) out of 92,936 invited individuals answered Q1 and participated in a brief medical examination that included measurements of height and weight, whereas 49,483 (53%) answered all questions in a second questionnaire (Q2) to be filled in and returned from home. Q1 included the majority of MSC questions in addition to questions, e.g., about present state of health, smoking, physical exercise, and anxiety and depression measured by hospital anxiety and depression scale (HADS), whereas Q2, e.g., included question about headache. In Q1, MSCs were assessed by a screening question: Have you during the last year continuously for at least 3 months had pain and/or stiffness in muscles and joints? Those responding positively were asked to mark the localization of this pain by yes or no in one or more of to the following areas of the body: neck, shoulders, elbows, wrist/hands, upper back, low back, hips, knees, and/or ankles/feet [17]. The nine anatomical regions were copied from the Nordic Questionnaire [25] which previously has been evaluated and found to give reliable estimates for low back and upper limb and neck for symptoms during the past year [26,27]. Those responding positively to the screening question were also asked to indicate the duration of the pain, i.e., more than, or less than a year, and whether the pain had caused sick leave and/or reduced leisure time activity [17]. No question regarding whether they had pain in both sides of the body was included in HUNT 2. HUNT 3 HUNT 3 was to a large extent a replication of HUNT 2. An invitation letter including Q1 was mailed to all adult inhabitants. Among 94,194 invited adults, a total of 50,839 (54%) answered Q1 and participated in the brief medical examination, at which they were given Q2 to be filled in and returned from home. Q1 included similar questions used in HUNT 2, e.g., about present health status and smoking, and about anxiety and depression, headache, and MSCs in Q2. The Q2 included the same MSC screening question that was used in HUNT 2, and those answering yes were also asked to mark the localization of this pain in the same body areas (neck, shoulders, elbows, wrist/hands, upper back, low back, hips, knees, and/or ankles/feet). In addition, Q2 of HUNT 3 also had included pain in both sides of the body (yes or no), which was not included in HUNT 2. The screening questions in Q2 were answered by 39,771 participants (42%) (Figure 1). The response rate was higher in women (47%) than in men (37%), and highest in the age group years (55%), and lowest among those aged years (22% participated) and those 80 years old (26% participated). Participants who answered the MSC questions in Q2 (N = 39,771) were older (53.6 vs 49.4 years, P < 0.001) and more likely to be women (56 vs 49%, P < 0.001) compared with those who only answered questions in Q1 (N = 11,068). The participants had slightly more chronic pain lasting at least 6 months during the past year compared with partial participants (men: 35.4 vs 33.6%, P = 0.02; women: 42.6 vs 39.9%, P > 0.001), whereas no clear difference was found regarding self-reported poor health (men: 23.7 vs 22.6%, P = 0.10; women: 28.1 vs 29.6%, P = 0.04). 1658

3 of Chronic Musculoskeletal Complaints Number of invited adults HUNT 3 94,194 Participants HUNT 3 50,839 (54%) Nonparticipants HUNT 3 43,355 (46%) Participants answering the MSC questions 39,771 (78%) Participants not answering MSC questions 11,068 (22%) Potential participants reliability study 563 (1%) Not invited reliability study 39,208 (99%) Figure 1 Diagram of the invited population in Helseundersøkelsen i Nord-Trøndelag (HUNT) 3 according to type of participation. Participants reliability study 297 (53%) Nonparticipants reliability study 266 (47%) Reliability of the Screening Question A random sample of 563 participants in HUNT 3 was invited to a separate interview (Figure 1). Among these, 171 were not reached by at least two telephone calls. A total of 297 out of the 392 persons contacted by telephone participated in the clinical interview (53% of the total invited group). A semistructured interview performed by eight neurologists included the same questions about chronic MSCs used in Q2. The mean interval between answering the HUNT 3 questionnaire and the structured interview was 50 days (median 45 days; range, days). More details of the method have been described elsewhere [28]. Definitions of Chronic MSCs and Chronic Widespread MSCs Chronic MSCs were defined as pain and/or stiffness in muscles and joints 3 months during the past year. Chronic widespread MSCs were defined according to the 1990 American College of Rheumatology [10] as pain and/or stiffness 3 months during the past year with symptoms during the last month from all of the following regions: axial skeleton (neck, upper back, or lower back), above the waist (neck, shoulders, elbows, wrist/hands, or upper back), and below the waist (lower back, hips, knees, or ankles/feet). In HUNT 3, all individuals with chronic widespread MSCs confirmed that they had pain in both sides of the body, whereas participants were not asked to distinguish between pain in the left and right sides of the body in HUNT 2. Lifestyle Factors and Self-Reported Health Information in HUNT 2 and HUNT 3 Three questions about smoking habits were used to classify participants into three categories: current smokers, former smokers, and those who never had smoked. BMI was computed as weight/height 2. The variable was categorized into three groups: 24.9, , and 30 kg/ m 2. One question about alcohol consumption (number of times per month) was used to classify participants into three categories: 2 times/week, one to four times/ month, and less than four times/month). The questions regarding physical activity differ between HUNT 2 (weekly duration of physical activity) and HUNT 3 (frequency of physical exercise per week). In both surveys, participants were grouped into three levels of physical activity: 1) low: <1 hour or <1 occasion/week; 2) medium: 1 3 hours or one occasion/week; and 3) high: 4 hours/week or 2 occasions/week. Individuals responding positively to the question Have you suffered from headache during the last year? were defined as having headache. The question How is your present state of health? had originally four answer options that were recoded into two categories in the analyses. Very good and good were recoded as good whereas fair and poor were recoded as poor. HADS is a well-established self-rating instrument for anxiety and depression, including seven anxiety questions (HADS-A) and seven depression questions (HADS- D). In accordance with previous authors, the cutoff score for having either anxiety or depression was set at 8 [29]. 1659

4 Hagen et al. Statistical Analysis Demographic data were compared between different groups of participants and nonparticipants with independent samples t-test for continuous variables (age, BMI, and HADS score) and with the chi-square test for categorical variables. Two-tailed estimations of significance were used, and the level of significance was set at P < For the various anatomical locations of MSCs, crude prevalences in men and women were estimated separately by age decade. The overall prevalence was age adjusted, using the age distributions of all inhabitants aged 20 years in Nord-Trøndelag County in 1995 (HUNT 2) and 2006 (HUNT 3) as the standard populations. The sex ratio for each MSC category was calculated using the age-adjusted prevalence for women divided by the ageadjusted prevalence for men. In HUNT 3 we evaluated the relative influence of demographic variables, lifestyle factors, and other self-reported health information on odds ratio (OR) of chronic MSCs and chronic widespread MSCs by using logistic regression with 95% confidence interval (CI). The analyses were adjusted for either 1) only age or gender and 2) all of age, gender, all lifestyle factors, and other self-reported health information. In all analysis, participants with missing values were included. Age-adjusted prevalences were compared in the two surveys by chi-square test with the level of significance set at P < 0.01 due to multiple comparisons. By using a restructured data file, prevalences in the two surveys were also compared with logistic regression, adjusting for the following potential confounding factors: gender, age, BMI, smoking, and self-reported health information including anxiety and depression. For each analysis, participants with missing values were included. When comparing prevalences of chronic widespread MSCs in HUNT 2 and HUNT 3, we applied similar criteria for chronic widespread MSCs (i.e., not making bilateral pain mandatory in HUNT 3). The participation rate differs widely between HUNT 2 and HUNT 3 (70 vs 42%). To estimate the influence of different location of the MSC screening question (in Q1 in HUNT 2 and in Q2 in HUNT 3), we also estimated the prevalence of chronic MSCs in HUNT 2 among the group of individuals (N = 49,483, 53% of the invited population) who also answered some musculoskeletal questions in Q2. Furthermore, to estimate the influence of differences in participation rate, we also calculated the prevalence of chronic MSCs multiple times in a randomly selected group of 39,000 participants from HUNT 2 (42% of the invited population which corresponds to the 42% participation rate of HUNT 3). The mean of these figures was compared with that of HUNT 3 figures. In HUNT 3, the reliability of the screening question concerning chronic MSC and the diagnosis of chronic widespread MSCs were evaluated by comparing the answers in Q2 with those made in the semistructured interview using Cohen s kappa statistics with 95% CI. Data analysis was performed with the Predictive Analytics SoftWare (PASW) Statistics version 17.0 by SPSS Inc., an IBM Company (Chicago, IL, USA). Ethics The HUNT 2 and HUNT 3 surveys were approved by the Regional Committee for Ethics in Medical Research and the Norwegian Data Inspectorate. Results Age-adjusted prevalence of chronic MSCs in HUNT 2 and HUNT 3 according to nine different anatomical sites is listed in Table 1. in HUNT 3 The crude prevalence of chronic MSCs in HUNT 3 was 50.4% (95% CI ), whereas the overall ageadjusted prevalence was 47.9% (95% CI ) (Table 1), and highest in the age group years (Table 2). The age-adjusted prevalence in nine different anatomical sites is listed in Table 1. The age-adjusted prevalence of chronic widespread MSCs was 24.2% (95% CI ) for women and 14.5% (95% CI ) for men (overall: 20.0%, 95% CI ). As demonstrated by Table 3, the prevalence of chronic MSCs and chronic widespread MSCs was higher in women, older ages defined as 50 years, and among current smokers and those with BMI 30 kg/ m 2, HADS score 16, and poor self-reported health. Characteristics of Participants of HUNT 2 and HUNT 3 Compared with the HUNT 2 participants (N = 64,780), the participants in HUNT 3 (N = 39,771) were older and had slightly higher BMI, but had lower HADS score and were less likely to smoke, and report poor health and headache (Table 4). Comparisons of Between HUNT 2 and HUNT 3 The age-adjusted prevalence of chronic MSCs was significantly higher in HUNT 3 compared with HUNT 2 (47.9 vs 44.8%, P < 0.001) (Table 1). The increase was evident for both genders (women 52.3 vs 48.8, and men 42.4 vs 40.2, Table 1), and also when the HUNT 2 group consisted of either the 49,483 individuals (53% of all invited) who answered all questionnaires (age-adjusted prevalence of chronic MSCs: 44.8%) or the randomly selected group of 39,000 (mean age-adjusted prevalence of >100 calculations: 44.8%) corresponding to a total participation rate of 42%. The most prominent increase in prevalence of chronic MSCs during the 11-year period was found in two 1660

5 of Chronic Musculoskeletal Complaints Table 1 Age-adjusted prevalence of chronic musculoskeletal complaints (MSCs) in HUNT 2 and HUNT 3 by each gender and related to nine different anatomical sites HUNT 2 HUNT 3 N 64,780 Total 95% CI Women Men Sex Ratio N 39,771 Total 95% CI Women Men Sex Ratio Chronic MSCs 30, , * * 42.4* 1.23 Neck 16, , * * Shoulders 17, , * Upper back 6, , * * 7.4* 2.16 Lower back 15, , * * Elbows 5, , Wrist/hands 9, , Hips 11, , Knees 11, , * * 1.43 Ankles/feet 8, , Chronic widespread 15, , * * MSCs * in HUNT 3 vs HUNT 2, P < analyzed by chi-square test. Definition of chronic widespread MSCs when comparing prevalences in HUNT 2 and HUNT 3: pain and/or stiffness 3 months during the past year with symptoms during the last month from all of the following regions: axial skeletal pain (pain in the neck, upper back, or lower back), pain above the waist (neck, shoulders, elbows, wrist/hands, or upper back), and below the waist (lower back, hips, knees, or ankles/feet). Criterion not included: pain in both sides. CI = confidence interval; HUNT = Helseundersøkelsen i Nord-Trøndelag. 1661

6 Hagen et al. Table 2 of chronic musculoskeletal complaints (MSCs) in HUNT 2 and HUNT 3 related to age HUNT 2 HUNT 3 Sex Ratio Men Women Total 95% CI N 39,771 Sex Ratio Men Women Total 95% CI N 64,780 Age Groups (years) , * * 26.9* , , * , , , , , , * , , , Overall 30, , * * in HUNT 3 vs HUNT 2, P < analyzed by chi-square test. CI = confidence interval; HUNT = Helseundersøkelsen i Nord-Trøndelag. of the three youngest age groups (Figure 2). Among participants aged years, the increase was statistically significant for both genders (Table 3). In the multivariate analyses, adjusting for potential difference between HUNT 2 and HUNT 3 regarding age, four lifestyle factors (BMI, physical activity, alcohol use, and smoking), and three aspects of self-reported health information (current health status, HADS score, and headache), the overall prevalence OR of chronic MSCs was higher (1.18, 95% CI ) in HUNT 3 compared with that of HUNT 2, evident for men (1.11, 95% CI ) and women (1.23, 95% CI ). During the 11-year period, a significantly (P < 0.001) higher prevalence was found in HUNT 3 than in HUNT 2 for neck pain (29.6 vs 27.5%), upper back pain (16.0 vs 13.2), and lower back pain (27.1 vs 25.4%) in women (Table 2). Among men, a significant increase in prevalence was found for chronic knee pain only (14.0 vs 13.4%) (Table 2). By applying similar criteria for chronic widespread MSCs (i.e., not making bilateral pain mandatory), a higher overall prevalence was found in HUNT 3 than in HUNT 2 (23.6 vs 22.0%, P < 0.001), statistically significant in women only (28.2 vs 26.0%, OR 1.20, 95% CI ). Reliability of the Screening Question For the screening question regarding chronic MSC, the agreement between the interview and the questionnaire was good (kappa value 0.63, 95% CI ). The change-corrected agreement rate for chronic widespread MSCs was 0.48 (95% CI ). Discussion This is so far the largest replicate cross-sectional study using identical questions to investigate trends over time in the prevalence of chronic MSCs and chronic widespread MSCs. The main finding was that, among the HUNT 3 population, 48% had chronic MSCs and 20% had chronic widespread MSCs. Furthermore, there was a significant increase in the prevalence of chronic MSCs during the 11-year period, evident for both genders, and most prominent in the youngest age groups. Direct comparisons of results should be done with some caution due to differences in study design and methodology. Compared with other studies using similar phrasing of the screening question, the present 1-year prevalence of chronic MSCs of 48% was somewhat lower than reported in Sweden (55%) and England (50%), but somewhat higher than found in studies from The Netherlands and other parts of Norway (44%) [30 33]. The prevalence of chronic widespread pain (20%) was higher than that reported in previous studies, varying between 4 and 18% [12,13,34 38]. However, the results from these studies are not strictly comparable, e.g., because they use somewhat different screening question for diagnosing chronic widespread pain. 1662

7 of Chronic Musculoskeletal Complaints Table 3 The influence of demographic variables, lifestyle factors, and self-reported health information on odds ratio (OR) of chronic MSCs and chronic widespread MSCs in HUNT 3 Chronic MSCs Chronic Widespread MSCs Demographic Variables OR* 95% CI OR 95% CI OR* 95% CI OR 95% CI Gender (women vs men [ref.]) Age ( 50 years vs <50 years [ref.]) Lifestyle factors Smoking (daily vs never) BMI ( 30 vs <25 kg/m 2 [ref.]) Physical activity (low vs high [ref.]) Alcohol use ( 2 times a week vs <4 times month [ref.]) Self-reported health information Headache (yes vs no [ref.]) General health (poor vs good [ref.]) HADS-A and/or -D score* ( 8 vs 7 [ref.]) * Adjusted for age and gender. Adjusted for age, gender, other lifestyle factors, and other self-reported health information. Number of participants with missing values included in the analysis: smoking (N = 993), BMI (N = 132), physical activity (N = 618), alcohol use (N = 899), headache (N = 762), general health (N = 1,134), HADS score (N = 1,443). BMI = body mass index; CI = confidence interval; HADS = hospital anxiety and depression scale; HUNT = Helseundersøkelsen i Nord-Trøndelag; MSCs = musculoskeletal complaints. Several studies evaluating different types of musculoskeletal pain have reported increasing prevalence [39,40]. The prevalence of chronic pain (lasting 6 months or more) increased during a 5-year period between 2000 and 2005 in the age group years in a Danish study [41], and in Sweden the prevalence of mild or severe pain in the back, shoulders, or joints increased gradually from 1968 to 2000 in the youngest age group [9]. It may also be of relevance that an increase in musculoskeletal pain caused by injury was reported in Spain from 1993 to 2001 in the youngest age groups, particularly among women [8]. Similarly, in the present study the prevalence of chronic widespread MSCs was more common in HUNT 3 than in HUNT 2 among women. In accordance, an increased prevalence of widespread pain was found over a 40-year period in one region of England [11], whereas stable prevalence rates were found over a 7-year period in two other population-based studies conducted in different regions of this country [12,13]. Comparisons of Survey Methodologies One may ask whether higher rates of chronic MSCs in HUNT 3 could be explained by methodological factors. Table 4 Comparison between participants in HUNT 2 and HUNT 3 HUNT 2 Men (95% CI) HUNT 3 Men (95% CI) HUNT 2 Women (95% CI) HUNT 3 Women (95% CI) Total number 30,388 17,465 34,392 22,306 Age, mean years 49.8 ( ) 54.6 ( )* a 50.0 ( ) 52.8 ( )* BMI, mean (kg/m 2 ) 26.5 ( ) 27.5 ( )* a 26.3 ( ) 27.0 ( )* HADS total score, mean 7.4 ( ) 7.1 ( )* a 7.8 ( ) 7.5 ( )* Current smoking, % 28.9 ( ) 23.3 ( )* b 29.2 ( ) 26.6 ( )* Poor health, % 25.1 ( ) 23.4 ( )* b 29.7 ( ) 28.4 ( )* Headache, % 29.1 ( ) 27.8 ( ) 46.8 ( ) 42.1 ( )* * P < analyzed by; a) t-test and b) chi-square test. At least one cigarette/day. Answered poor to the question How is your present state of health? Positive response to the question Have you suffered from headache during the last year? BMI = body mass index; CI = confidence interval; HADS = hospital anxiety and depression scale; HUNT = Helseundersøkelsen i Nord-Trøndelag. 1663

8 Hagen et al. Unadjusted prevalence of chronic MSCs (%) HUNT-2 HUNT Age groups Figure 2 Unadjusted prevalence of chronic musculoskeletal complaints (MSCs) in Helseundersøkelsen i Nord-Trøndelag (HUNT) 2 and HUNT 3 by age. The strengths of this study were almost the exact replication of design and methodology, and that the study was performed in the same geographical area in a large and unselected population with a wide age range. Both surveys included self-administrated questionnaires with identical phrasing of the MSC screening question which was found to have good reliability. The agreement between the interview and the questionnaire was better for chronic MSCs than chronic widespread MSCs (kappa value 0.63 vs 0.48), most likely because individuals with chronic MSCs were identified by answers based on only one question, whereas individuals with chronic widespread MSCs were identified on the basis of multiple questions. The major drawback of the present study was that the participation rate in the HUNT studies has been decreasing gradually during the last 25 years, being 88% in , 70% in , and 54% in Because the MSC screening question was located in Q1 in HUNT 2 and in Q2 in HUNT 3, the participation rate of the MSC part actually decreased from 70% in HUNT 2 to 42% in HUNT 3. To assess possible bias due to the difference in the location of the screening question, supplementary analyses were performed using the selected HUNT 2 group who answered both Q1 and Q2 (53% of the invited population). Furthermore, we also evaluated the prevalence of chronic MSCs in HUNT 2 multiple times in a random group consisting of 42% of the invited HUNT 2 population, corresponding to the 42% participation rate of HUNT 3. These analyses also showed a consistent increasing prevalence of chronic MSCs from HUNT 2 to HUNT 3. Interestingly, participants in HUNT 3 were less likely to report poor health in HUNT 3 than in HUNT 2. One would expect the opposite if selection bias was the reason for the increased prevalence of chronic MSCs found in HUNT 3. Thus, although a nonresponse bias that interferes with the comparisons over time can not completely be ruled out, it seems less likely, also because the musculoskeletal questions were not the primary objectives of the HUNT 2 or HUNT 3. Possible Explanations of the Observed Increase in The observed increase may reflect an increase in the willingness to report MSCs for cultural or social reasons, or an increased awareness of pain syndromes. Against these explanations is the fact that no similar increase was found for other self-reported complaints like headache or general health status. If there is a true increase in prevalence of chronic MSCs and chronic widespread MSCs, the most probable explanation is that changes in society entail increased exposure to risk factors [3]. During the 11-year follow-up period, several major changes in the physical and social environment have been introduced, e.g., an increased use of computers and mobile phone, in particular in the youngest age groups [42]. In a Finnish study of adolescents aged years, girls were vulnerable to the negative consequences of intensive mobile phone usage, which was associated with perceived health complaints and musculoskeletal symptoms both directly and through deteriorated sleep and increased wakingtime tiredness [42]. However, whether increased use of computers and mobile phones can be directly linked to MSCs or indirectly due to changes in stress or physical activity among the young age groups is still unclear. In the present study, adjustments were performed regarding four 1664

9 of Chronic Musculoskeletal Complaints different types of lifestyle factors: BMI, smoking habits, alcohol use, and physical activity included. Conclusions The prevalence of chronic MSCs and chronic widespread MSCs was high. The fact that the prevalence seems to have increased during the 11-year period may indicate that exposure to environmental and other risk factors has increased. This underscores the need for further research to identify risk factors and to develop preventive strategies. List of Abbreviations BMI: body mass index; HADS: hospital anxiety and depression scale; HUNT: the Nord-Trøndelag health survey ( Helseundersøkelsen i Nord-Trøndelag ); HUNT 2: the second Nord-Trøndelag health survey; HUNT 3: the third Nord-Trøndelag health survey; MSCs: musculoskeletal complaints; Q1 and Q2: first and second questionnaire. Competing Interests The authors declare that they have no competing interest. Authors Contributions KH was responsible for the data analysis. KH, ML, IH, LJS, and JAZ participated in the study design, interpretations of data, and manuscript preparation. All authors read and approved the final manuscript. Acknowledgments The Nord-Trøndelag Health Study (the HUNT study) is a collaboration between the HUNT Research Centre, Faculty of Medicine, The Norwegian University of Science and Technology (NTNU), and the Nord-Trøndelag County Council. References 1 Statistics of sick leave in Norway in Available at: (accessed May 2011). 2 WHO Scientific Group. Burden of musculoskeletal conditions at the start of the new millennium. Technical Report Series. Genove, Switzerland: World Health Organization; 2003: Woolf AD, Pfleger B. Burden of major musculoskeletal conditions. Bull World Health Organ 2003;81: McBeth J, Jones K. Epidemiology of chronic musculoskeletal pain. Best Pract Res Clin Rheumatol 2007;21: Heistaro S, Vartiainen E, Heliövaara M, Puska P. Trends of back pain in eastern Finland, , in relation to socioeconomic status and behavioral risk factors. Am J Epidemiol 1998;148: Leino PI, Berg MA, Puska P. Is back pain increasing? Results from national surveys in Finland during 1978/ Scand J Rheumatol 1994;23: Palmer KT, Walsh K, Bendall H, Cooper C, Coggon D. Back pain in Britain: Comparison of two prevalence surveys at an interval of 10 years. BMJ 2000;320: Jiménez-Sánchez S, Jiménez-García R, Hernández- Barrera V, et al. Has the prevalence of invalidating musculoskeletal pain changed over the last 15 years ( )? A Spanish population-based survey. J Pain 2010;11: Ahacic K, Kåreholt I. of musculoskeletal pain in the general Swedish population from 1968 to 2002: Age, period, and cohort patterns. Pain 2010;151: Wolfe F, Smythe HA, Yunus MB, et al. The American College of Rheumatology 1990 Criteria for the Classification of Fibromyalgia. Report of the Multicenter Criteria Committee. Arthritis Rheum 1990;33: Harkness EF, Macfarlane GJ, Silman AJ, McBeth J. Is musculoskeletal pain more common now than 40 years ago?: Two population-based cross-sectional studies. Rheumatology (Oxford) 2005;44: Croft P, Rigby AS, Boswell R, Schollum J, Silman A. The prevalence of chronic widespread pain in the general population. J Rheumatol 1993;20: Hunt IM, Silman AJ, Benjamin S, McBeth J, Macfarlane GJ. The prevalence and associated features of chronic widespread pain in the community using the Manchester definition of chronic widespread pain. Rheumatology (Oxford) 1999;38: Aas RW, Tuntland H, Holte KA, et al. Workplace interventions for neck pain in workers. Cochrane Database Syst Rev 2011;4:CD Sulutvedt HS, Werpen HKB, Zwart JA, Hagen K. Physical activity as a predictor for chronic musculoskeletal complaints: Results from the Nord-Trøndelag Heath Study. BMC Musculoskelet Disord 2008;9: Heuch I, Hagen K, Heuch I, Nygaard Ø, Zwart JA. The impact of body mass index on the prevalence of low back pain: The HUNT study. Spine 2010;35: Svebak S, Hagen K, Zwart J-A. One-year prevalence of chronic musculoskeletal pain in an adult Norwegian county population. Relation with age and gender. The HUNT study. J Musk Pain 2006;14:

10 Hagen et al. 18 Hagen K, Svebak S, Zwart JA. Incidence of musculoskeletal complaints in a large adult Norwegian county population. The HUNT study. Spine 2006;31: Hagen K, Zwart JA, Svebak S, Bovim G, Stovner LJ. Low socio-economic status is associated with musculoskeletal symptoms among 46,901 adults in Norway. Scand J Public Health 2005;33: Heuch I, Heuch I, Hagen K, Zwart JA. Associations between serum lipid levels and chronic low back pain. Epidemiology 2010;21: Hagen K, Einarsen C, Zwart JA, Svebak S, Bovim G. The co-occurrence of headache and musculoskeletal symptoms among 51,050 adults in Norway. Eur J Neurol 2002;9: Hagen K, Bjøro T, Zwart JA, et al. Do high TSH values protect against chronic musculoskeletal complaints? The Nord-Trøndelag Health Study (HUNT). Pain 2005;113: Hoff OM, Midthjell K, Zwart JA, Hagen K. The association between diabetes mellitus, glucose, and chronic musculoskeletal complaints. Results from the Nord-Trøndelag Health. BMC Musculoskelet Disord 2008;9: Hagen K, Stovner LJ, Pettersen E, Skorpen F, Zwart JA. No association between chronic musculoskeletal complains and Val/Met polymorphism in the catechol- O-methyltransferase gene. The HUNT study. BMC Musculoskelet Disord 2006;7: Kuorinka I, Jonsson B, Kilbom A, et al. Standardised Nordic questionnaires for the analysis of musculoskeletal symptoms. Appl Ergon 1987;18: Franzblau A, Salerno DF, Armstrong TJ, Werner RA. Test-retest reliability of an upper-extremity discomfort questionnaire in an industrial population. Scand J Work Environ Health 1997;23: Palmer K, Smith G, Kellingray S, Cooper C. Repeatability and validity of an upper limb and neck discomfort questionnaire: The utility of the standardized Nordic questionnaire. Occup Med 1999;49: Hagen K, Zwart JA, Aamodt AH, et al. The validity of questionnaire-based diagnoses: The third Nord- Trøndelag health study J Headache Pain 2010;11: Bjelland I, Dahl AA, Haug TT, Neckelman D. The validity of the hospital anxiety and depression scale. An updated literature review. J Psychosom Res 2002;52: Andersson HI, Ejlertsson G, Leden I, Rosenberg C. Chronic pain in a geographically defined general population: Studies of differences in age, gender, social class, and pain localization. Clin J Pain 1993;9: Elliott AM, Smith BH, Penny KI, Smith WC, Chambers WA. The epidemiology of chronic pain in the community. Lancet 1999;354: Sirnes E, Sødal E, Nurk E, Tell GS. Epidemiology of musculoskeletal complaints in Hordaland, Norway. Tidsskr Nor Laegeforen 2003;123: Picavet HSJ, Schouten JSAG. Musculoskeletal pain in The Netherlands: s, consequences and risk groups, the DMC3-study. Pain 2003;102: Bergman S, Herrström P, Hogstrom K, et al. Chronic musculoskeletal pain, prevalence rates, and sociodemographic associations in a Swedish population study. J Rheumatol 2001;28: Andersson HI, Ejlersson G, Leden I, Rosenberg C. Characteristics of subjects with chronic pain, in relation to local and widespread pain report. Scand J Rheumatol 1996;25: Wolfe F, Ross K, Anderson J, Russell IJ, Hebert L. The prevalence and characteristics of fibromyalgia in the general population. Arthritis Rheum 1995;38: Lindell L, Bergman S, Petersson IF, Jacobsson LT, Herrstrom P. of fibromyalgia and chronic widespread pain. Scand J Prim Health Care 2000;18: McBeth J, Nicholl BI, Cordingley L, Davies KA, Macfarlane GJ. Chronic widespread pain predicts physical inactivity: Results from the prospective EPIFUND study. Eur J Pain 2010;14: [Epub ahead of print]. 39 Leboeuf-Yde C, Klougart N, Lauritzen T. How common is low back pain in the Nordic population? Data from a recent study on a middle-aged general Danish population and four surveys previously conducted in the Nordic countries. Spine 1996;21: Leijon O, Wahlström J, Mulder M. of selfreported neck-shoulder-arm pain and concurrent low back pain or psychological distress: Time-trends in a general population, Spine 2009;34: Sjøgren P, Ekholm O, Peuckmann V, Grønbaek M. Epidemiology of chronic pain in Denmark: An update. Eur J Pain 2009;13: Punamäki RL, Wallenius M, Nygård CH, Saarni L, Rimpelä A. Use of information and communication technology (ICT) and perceived health in adolescence: The role of sleeping habits and waking-time tiredness. J Adolesc 2007;30: