A Population Study on Differences in the Determinants of a Specific Shoulder Disorder versus Nonspecific Shoulder Pain without Clinical Findings

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1 American Journal of Epidemiology Copyright ª 2005 by the Johns Hopkins Bloomberg School of Public Health All rights reserved Vol. 161, No. 9 Printed in U.S.A. DOI: /aje/kwi112 A Population Study on Differences in the Determinants of a Specific Shoulder Disorder versus Nonspecific Shoulder Pain without Clinical Findings Helena Miranda 1, Eira Viikari-Juntura 1, Sami Heistaro 2, Markku Heliövaara 2, and Hilkka Riihimäki 3 1 Department of Physiology, Finnish Institute of Occupational Health, Helsinki, Finland. 2 Department of Health and Functional Capacity, Finnish National Public Health Institute, Helsinki, Finland. 3 Department of Epidemiology and Biostatistics, Finnish Institute of Occupational Health, Helsinki, Finland. Received for publication June 18, 2004; accepted for publication January 8, Musculoskeletal pain frequently occurs without particular clinical findings. Pain per se may be determined by factors other than those indicating a clinical disorder. The authors examined the prevalence and determinants of clinically diagnosed chronic rotator cuff tendinitis and self-reported nonspecific shoulder pain. The Health 2000 survey, carried out in in Finland, included a nationally representative sample of 8,028 persons aged 30 years or more. In the present study, analyses were restricted to subjects aged years who had held a job during the preceding 12 months. The prevalences of chronic rotator cuff tendinitis and nonspecific shoulder pain were 2.0% (78 of 3,909 subjects) and 12% (410 of 3,525 subjects), respectively. Nonspecific pain was related to burnout (adjusted odds ratio (OR) ¼ 1.7, 95% confidence interval (CI): 1.4, 2.2), depression (among women, the adjusted OR was 1.8 (95% CI: 1.1, 2.9) for mild depression and 3.0 (95% CI: 1.6, 5.6) for severe depression), and inability to express one s feelings (alexithymia) (adjusted OR ¼ 1.6, 95% CI: 1.1, 2.5). However, these factors were not associated with chronic rotator cuff tendinitis, determinants of which were work-related cumulative loading on the shoulder, age, and insulin-dependent diabetes mellitus (adjusted OR ¼ 8.8, 95% CI: 1.9, 40.3). The determinants of specific musculoskeletal disorders differ from those of subjective complaints without clinical findings. Such complaints may be indicators of adverse psychological and psychosocial factors rather than the presence of an underlying pathologic condition. musculoskeletal physiologic phenomena; pathological conditions, signs and symptoms; shoulder pain; tendinitis Epidemiologic studies on common musculoskeletal disorders, such as shoulder and upper extremity disorders, have mainly concerned occupational populations (1, 2). However, results from studies of these selected populations may lack comparability and generalizability. The occurrence of musculoskeletal diseases as well as the relative contribution of various risk factors for the development of these disorders should be assessed in the general population. There is still a great need for population-based studies on these disorders in general, but particularly on specific disorders with welldefined objective diagnostic criteria. During the past several years, substantial effort has been put into developing criteria that would allow the compilation of more comparable data on musculoskeletal conditions (3, 4). However, a specific diagnosis can only be made in a minority of persons with musculoskeletal symptoms (5, 6). Nonspecific pain the presence of pain without physical signs or recognizable pathology is a common complaint, but little is known of its etiology (6, 7). It has been suggested that nonspecific musculoskeletal pain may be a precursor of a more severe disease. Musculoskeletal conditions, such as degenerative disorders, may have several stages causing a wide variety of symptoms (e.g., from mild pain to pain causing disability); consequently, risk factors may act differently during these different stages. Alternatively, nonspecific pain could be considered an independent entity with its own risk factors. In general, there is still a substantial gap in knowledge regarding the possible etiologic disparity between different types of musculoskeletal disorders. If the risk factors vary considerably, or if the exposure-response relation for a certain risk factor diverges in different conditions, separate strategies are also required for prevention. Our aim in this study was to assess the prevalence of a specific shoulder disorder and nonspecific shoulder Correspondence to Dr. Helena Miranda, Department of Physiology, Finnish Institute of Occupational Health, Topeliuksenkatu 41 a A, FIN Helsinki, Finland ( helena.miranda@jippii.fi). 847

2 848 Miranda et al. complaints in a general population and to compare the roles of several determinants, including biomechanical and psychosocial factors, in these conditions. MATERIALS AND METHODS Study population and design The Health 2000 survey was carried out in Finland from fall 2000 to spring 2001 (8). The survey consisted of several questionnaires, an extensive interview, laboratory and functional capacity tests, and a clinical examination. A nationally representative two-stage stratified cluster sample was drawn by stratifying Finland into 20 strata consisting of the 15 biggest cities and five university hospital districts. The 15 cities and 65 of the 234 municipalities or groups of municipalities with joint primary care (within the five university hospital districts), which were drawn by systematic sampling, formed 80 clusters. A total of 8,028 persons aged 30 years or older were sampled from these clusters. Of the working-age (30 64 years) subjects (n ¼ 5,871), 88 percent (n ¼ 5,152) participated in the interview and 83 percent (n ¼ 4,886) attended the health examination (8). In the present study, analyses were restricted to subjects aged years who had held a job during the preceding 12 months (n ¼ 4,071). Persons with a history of rheumatoid arthritis (n ¼ 46) or severe shoulder injury due to trauma (n ¼ 30) were excluded from the study. Information on shoulder pain was obtained from 93 percent of the subjects, and 94 percent were clinically examined. Outcomes The two outcomes defined for this study were a specific shoulder disorder, namely clinically diagnosed chronic rotator cuff tendinitis, and nonspecific shoulder pain. Chronic rotator cuff tendinitis. Chronic rotator cuff tendinitis was diagnosed by a specially trained physician using a consensus case definition (3). The criteria were history of pain in the rotator cuff region lasting for at least 3 months, pain during the month preceding the examination, and pain in the rotator cuff region upon one or more resisted active movements (abduction of the arm (supraspinatus), external rotation of the arm (infraspinatus, teres minor), and internal rotation of the arm (subscapularis)) or painful arc of shoulder abduction. The study population for this outcome consisted of 3,740 subjects (unweighted number of observations). The mean age was 44.4 years (standard deviation, 8.6), and 52 percent were men. Nonspecific shoulder pain. Shoulder pain was based on two questions: Have you experienced shoulder pain during the preceding 30 days? and If so, have you experienced shoulder pain during the preceding 7 days? For assessment of nonspecific shoulder pain, persons who had clinical findings in the palpation or provocation tests of the shoulder or had a clinical shoulder diagnosis made by the field physician were excluded from this analysis. Subjects with prevalent cases of nonspecific shoulder pain were defined as those who had experienced shoulder pain during the preceding 7 days, whereas the reference group consisted of persons who had not had shoulder pain during the preceding 7 days. The study population for this outcome consisted of 3,378 subjects (unweighted number of observations). The mean age was 44.1 years (standard deviation, 8.6), and 51 percent were men. Determinants The determinants were divided into four groups: individual factors, work-related physical loading, work-related psychosocial and organizational factors, and individual psychological factors. They were assessed by means of the interview and questionnaires. Individual factors consisted of age, body mass index (weight (kg)/height (m) 2 ), smoking, leisure-time physical exercise, length (years) of education, family status, and diabetes mellitus. The information on diabetes was obtained from both the questionnaire and clinical diagnoses made by the field physicians. The diagnostic criteria were based on current clinical practice. Diabetes in this study was classified to distinguish between type 1 and type 2 diabetes. Work-related physical loading was assessed during the interview. The respondents were asked whether they had been exposed (yes/no) to different work load factors in their current job and in their five most long-lasting past jobs. They were also asked about the duration (in years) of employment in current and previous jobs. A cumulative sum index for the number of years of exposure to each work load factor was calculated, and the data were classified into five categories (none and 1 3, 4 13, 14 23, or >23 years of exposure). For many of the exposures, the median cumulative index value was 13 years, and the cutoff value for the highest quartile was 23 years. Only 29 subjects had held more than five previous jobs, meaning that the cumulative index covered the whole occupational history for more than 99 percent of the subjects. The work load factors were: driving a motor vehicle, frequent lifting, heavy lifting, working with a hand above shoulder level, work requiring high hand force, work requiring repetitive motion of the hand or wrist, work requiring intensive keying (e.g., typing, computer work), and working with a vibrating tool. Work-related psychosocial and organizational factors were assessed with questionnaires and included job satisfaction, job strain and social support (Karasek et al. s Job Content Questionnaire), uncertainty of employment prospects, the threat of being bullied or mentally abused, the social climate at work, knowledge and skills required at work, and burnout (Maslach Burnout Inventory General Survey) (9 11). Of the individual psychological factors, depression (Beck Depression Inventory), inability or difficulty in describing or being aware of one s emotions or moods, also known as alexithymia (20-item Toronto Alexithymia Scale), and sense of coherence (Sense of Coherence Scale, short version) were measured (12, 13). Statistical methods The population weighting was used in the data analyses to correct the age, sex, living district, and language distributions

3 Determining Shoulder Disorder vs. Nonspecific Shoulder Pain 849 TABLE 1. Prevalence of chronic rotator cuff tendinitis in a Finnish general population aged years in Age (years) group (no.) Total (n ¼ 3,909*) Men (n ¼ 1,993*) Women (n ¼ 1,916*) No. % 95% CIy group (no.) No. % 95% CI group (no.) No. % 95% CI , , , , , , , , , , , , , , , , , 2.8 1, , 2.5 * Weighted number of observations. y CI, confidence interval. of the sample to correspond to those of the Finnish population. In addition, the possible dependencies between individuals in the same cluster were taken into account in the analyses. Both gender-combined and gender-specific analyses were performed using logistic regression modeling. The results are expressed as odds ratios with 95 percent confidence intervals. The modeling was a three-level process consisting of univariable models (first level), group models (second level), and multivariable models (third level). All of the models included age and sex as possible confounders. First, variables in the univariable models that had p values less than 0.2 in Wald s test were chosen for further analyses. Second, variables in the same group were placed into a multivariable model. From each group model, variables with p values less than 0.2 were selected for the third level, the final multivariable modeling. The least significant variables were eliminated from the model one at a time until the final multivariable model contained only statistically significant variables (p 0.05) (in addition to age and sex). There was no evidence of residual confounding by those individual factors eliminated from the final model. Correlation between all variables was checked in order to prevent the effects of collinearity in the modeling. Correlation coefficients were less than 0.5 for all variables except for three physical work-load factors: frequent lifting, heavy lifting, and work requiring high hand force. These variables were not placed into the same model; instead, only the variable with the strongest or most robust estimate in the univariable model was chosen for further analyses. The correlation between work-related physical and psychosocial factors was always lower than 0.2. Statistical analyses were performed with the statistical software packages SAS (version 8.2; SAS Institute, Inc., Cary, North Carolina) and SUDAAN (version 8.0.2; RTI International, Research Triangle Park, North Carolina). RESULTS Prevalence of chronic rotator cuff tendinitis Seventy-eight subjects were diagnosed with chronic rotator cuff tendinitis (table 1). The prevalence did not differ markedly between men and women, but it increased steadily with age in both genders. However, there were no cases in the oldest age group of women. Determinants of chronic rotator cuff tendinitis Length of education in the women and diabetes in the men were the individual factors related to the outcome in the univariable analyses (see Web table 1, available on the Journal s website at Both factors were also statistically significant determinants in the multivariable models (table 2). Body mass index, smoking, leisure-time physical exercise, and family status were not associated with chronic rotator cuff tendinitis. All work-related physical factors except intensive keying work were associated with the outcome in the univariable analyses. However, only working with a hand above shoulder level in both genders and heavy lifting in the women retained their statistical significance in the final multivariable models. In the men, even relatively short-term exposure (1 3 years) to working with a hand above shoulder level increased the risk of chronic rotator cuff tendinitis more than threefold, whereas in the women, the risk started to increase after a longer exposure time. Heavy lifting for 4 13 years showed an increased risk in the women. Of the work-related psychosocial and organizational factors, the psychological demands of work, burnout, and the threat of being bullied showed univariable associations with the outcome, but none of these factors remained in the final multivariable models. None of the individual psychological factors were associated with the outcome in the univariable analyses. Prevalence of nonspecific shoulder pain A total of 410 subjects reported shoulder pain (table 3). The women reported pain more often than did the men. In the women, prevalence was highest in the age group years and slightly declined thereafter. In the men, peak prevalence was seen among those aged years. Determinants of nonspecific shoulder pain Of the individual factors, length of education in the men was associated with nonspecific shoulder pain in the

4 850 Miranda et al. TABLE 2. Multivariable models for determinants of chronic rotator cuff tendinitis in a Finnish general population aged years in Total Men Women Determinant No. of exposed* (n ¼ 3,885) ORy 95% CIy No. of exposed* (n ¼ 1,978) OR 95% CI No. of exposed* (n ¼ 1,907) Age (years) , , , , , , , , , 17.6 Gender Male 1, Female 1, , 1.6 Length (years) of education , , 1.4 Diabetes mellitus None 3, No medical treatment/pill treatment/pill þ insulin treatment , , 7.1 Insulin treatment only , , 62.7 of working with a hand above shoulder level (1 hour/day) None 2, , , , , , , , , , , , 12.4 > , , , 7.9 of heavy lifting (lifting >20 kg, >10 times/day) None 1, , , , 5.4 > , 8.6 * Subjects with no missing values for the determinants in the multivariable model. y OR, odds ratio; CI, confidence interval. OR 95% CI univariable model (Web table 2). Body mass index, diabetes, smoking, leisure-time physical exercise, and family status did not show univariable associations with the outcome. All work-related physical factors except working with a vibrating tool were associated with the outcome in the gender-combined and gender-specific univariable analyses. In the final multivariable models, significantly increased odds ratios were found for occupational driving in the men, whereas determinants for the women were working in tasks requiring high hand force and intensive keying (table 4). Several work-related psychosocial and organizational factors, as well as individual psychological factors, were associated with nonspecific shoulder pain in the univariable analyses. In the final multivariable models, the strongest associations (p < 0.001) were found for burnout and pain in both genders combined, as well as in the men, and for

5 Determining Shoulder Disorder vs. Nonspecific Shoulder Pain 851 TABLE 3. Prevalence of nonspecific shoulder pain in a Finnish general population aged years in Age (years) group (no.) Total (n ¼ 3,525*) Men (n ¼ 1,798*) Women (n ¼ 1,727*) No. % 95% CIy group (no.) No. % 95% CI group (no.) No. % 95% CI , , , , , , , , , , , , , , , , , , , , 15.3 * Weighted number of observations. Subjects with clinical findings in the palpation or provocation tests of the shoulder or a clinical shoulder diagnosis made by the field physician were excluded from the analysis. y CI, confidence interval. depression and pain in the women. In addition, alexithymia was statistically significantly associated with nonspecific shoulder pain in the multivariable analysis in both genders combined. Intensity of pain The intensity of pain during the preceding week varied slightly between the cases with different outcomes (table 5). Persons with chronic rotator cuff tendinitis had somewhat higher values of intensity, as measured with a numerical scale ranging from 1 to 10 (10 being defined as the worst possible pain), compared with persons with nonspecific shoulder pain. However, among women, the difference was small (only one unit in the mean value). More than half of the women with nonspecific pain reported their pain intensity to be 5 or higher, and 15 percent reported it as being between 8 and 10. DISCUSSION In this study, every eighth employed Finn had shoulder pain without clinical findings. Such pain was found to be six times as common as a specific shoulder disorder. Moreover, women perceived nonspecific pain without any clinical findings to be almost as intense as pain caused by a chronic disorder. It is often assumed that nonspecific pain arises from lower pain tolerance among subjects with altered pain perception. However, this hypothesis was not supported by a recent population study, which showed that subjects with nonspecific arm pain had pain tolerance equal to that of persons without pain and actually had higher pain tolerance than persons with specific upper limb disorders (14). There was a distinct discrepancy in determinants between the outcomes. The results support our primary hypothesis that specific clinical musculoskeletal disorders and nonspecific symptoms may be different entities with differing etiology. In general, it seems likely that biologic, metabolic, and biomechanical factors contribute more to the development of structural and pathologic changes, which in turn cause clinical findings. Nonspecific symptoms without clinical findings seem instead to be related to other types of determinants, such as psychological factors and personality traits. Insulin-dependent diabetes increased the risk of chronic rotator cuff tendinitis almost 13-fold in the men. Although there were few chronic rotator cuff tendinitis patients with insulin-dependent diabetes, the association was statistically highly significant. To our knowledge, this is the first study in a general population to demonstrate an association between rotator cuff tendinitis and diabetes. Many previous clinical studies have shown the prevalence of shoulder disorders such as adhesive capsulitis and calcific periarthritis to be higher among diabetics than among nondiabetics (15, 16). In the population-based Mini-Finland Study (a study corresponding to the Health 2000 survey that was conducted 20 years earlier), diabetes was related to shoulder impairment (17). An exact pathomechanical link between diabetes and shoulder disorders is unknown. However, a condition similar to that found in the hands of diabetics (i.e., increased glycosylation, decreased collagen degradation, and microvascular complications leading to tendon sheath thickening) may also affect shoulder tendons, causing mechanical irritation and inflammation in the rotator cuff area (18). Current epidemiologic evidence suggests that sustained elevated postures of the arm at work are major risk factors for shoulder disorders (1, 2). Our population-based results also showed that cumulative exposure to working with a hand above shoulder level had the strongest and most constant association with chronic rotator cuff tendinitis. The biologic mechanism is highly plausible; it has been shown that the intramuscular pressure in the rotator cuff muscles increases continuously with increasing degrees of upper arm elevation, causing blood flow impairment and reduced recovery from local muscle fatigue, even during moderate arm elevation only (19). In addition, elevated arm postures may mechanically irritate the tendon structures between the humeral head and the undersurface of the acromion. These mechanisms may lead to inflammation and eventually to accelerated degeneration. Depression was the strongest determinant of nonspecific shoulder pain in the women, increasing the risk to threefold for those with severe depression compared with those without symptoms of depression. Contradicting the common

6 852 Miranda et al. TABLE 4. Multivariable models for determinants of nonspecific shoulder pain in a Finnish general population aged years in Determinant No. of exposed* (n ¼ 2,937) Total Men Women ORy 95% CIy No. of exposed* (n ¼ 1,635) OR 95% CI No. of exposed* (n ¼ 1,451) Age (years) , , , , , , , , , , , 4.7 Gender Male 1, Female 1, , 2.0 of driving a motor vehicle (4 hours/day, >3 months/year) None 2, , , , , , , , 2.4 > , , 2.6 of work requiring high hand force (1 hour/day) None 1, , , , 2.5 > , 4.1 of work requiring intensive keying (4 hours/day) None , , , 2.0 > , 3.2 Burnout None 2, , Mild or severe , , 3.2 Depression None 1, Mild , 2.9 Severe , 5.6 Alexithymia No 2, Yes , 2.5 OR 95% CI * Subjects with no missing values for the determinants in the multivariable model. y OR, odds ratio; CI, confidence interval.

7 Determining Shoulder Disorder vs. Nonspecific Shoulder Pain 853 TABLE 5. Intensity of shoulder pain during the preceding week in a Finnish general population aged years in Pain intensity* Chronic rotator cuff tendinitis Total Men Women Nonspecific shoulder pain Chronic rotator cuff tendinitis Nonspecific shoulder pain Chronic rotator cuff tendinitis Nonspecific shoulder pain Mean score 5.6 (2.4)y 4.3 (2.3) 5.5 (2.5) 3.8 (2.1) 5.7 (2.3) 4.7 (2.4) Median score * Measured with a numerical scale ranging from 1 to 10 (10 being defined as the worst possible pain). y Numbers in parentheses, standard deviation. assumption that psychological factors, such as depression, are rather the consequence than the cause of pain, the authors of a recent review did not find evidence that musculoskeletal symptoms would lead to subsequent depression (20). On the contrary, several prospective studies have shown that depressive symptoms predict future musculoskeletal symptoms, such as low back pain (21), shoulder pain (22), neck pain (23, 24), and forearm pain (25). In addition, symptoms of burnout and alexithymia were found more often among subjects with nonspecific pain than among those without pain. Both burnout and alexithymia have rarely been studied in relation to musculoskeletal morbidity. We found no studies on the possible contributing role of burnout in the development of musculoskeletal disorders, but in one study, burnout was associated with a longer duration of disability caused by musculoskeletal pain (26). Alexithymia is often described as a constant trait characterized by difficulty in distinguishing between feelings and physical states and in identifying and describing one s feelings (having no words for feelings ). Difficulty in expressing feelings can occur in the form of unpleasant bodily sensations or pain. Alexithymia has been connected with various somatic and psychosomatic symptoms, including chronic pain (27, 28). However, there is little evidence that alexithymia causes or contributes to chronic organic or somatic changes (29). Additionally, in our study alexithymia was associated with nonspecific shoulder pain but not with the clinical disorder. The Finnish Health 2000 data are exceptional in many ways. The original sample represents the whole population of persons aged 30 years or older in Finland. Therefore, the results can be well generalized to the Finnish adult population. The participation rate was very good; of the working-age subjects, percent participated. Most of the items in the questionnaires, the interview, the testing, and the examination protocols were selected on the basis of standardized, generally accepted recommendations or nationally established practice. The health examination was designed to generate specific clinical diagnoses with welldefined criteria, such as rotator cuff tendinitis. To increase the validity and repeatability of the diagnostic testing, we used only the best-documented tests. The physicians were specially trained using a video-feedback technique. In addition to the comprehensive data on musculoskeletal disorders, detailed information on other diseases was collected. Regarding work-related items, valuable information on the distribution of physical exposures in the general population was obtained. The classification of physical exposures was based on current knowledge of the potentially harmful qualitative and quantitative features of physical work. There were some limitations in our study. Cross-sectional studies are prone to a form of selection bias called the healthy worker effect. Such selection occurs when persons with musculoskeletal symptoms do not seek or are not hired for jobs involving physically demanding tasks, or when workers who develop symptoms during physical work change to lower-exposure work (or leave the labor market entirely) and those with better health status and physical fitness remain at work. The healthy worker effect may have caused underestimation in the risk estimates. It may also have affected our results regarding physical loading, as indicated by the drops in the odds ratios for chronic rotator cuff tendinitis in the categories with the longest cumulative exposure. The effects seemed to differ for women and men. Among women, the risk of chronic tendinitis decreased considerably after 13 years of physically heavy work (i.e., lifting and the use of high hand force) (Web table 1). For the men, the risk started to decrease later, after 23 years of exposure to heavy work. This may imply that women are more susceptible to physically heavy work and therefore selection out of heavy-work occupations occurs earlier for women than for men. Note that the healthy worker effect is not the only explanation for the decrease in the effects in the categories with the longest cumulative exposure. In addition, correlation with age may have decreased the effects of long-term exposure when these factors were adjusted for each other. Recall error better recall or overestimation of past exposure among persons with current musculoskeletal symptoms may bias risk estimates in cross-sectional studies. Especially, persons with more severe symptoms may be more prone to overestimation of physical loading in their work (29). In general, when physical work load is assessed with self-administered questionnaires, the subjective estimate of the work load may be somewhat inaccurate, but direct measurements (e.g., observation) are not feasible in such an extensive population survey as the Health 2000 study.

8 854 Miranda et al. For assessment of nonspecific shoulder pain, subjects with clinical findings or a shoulder diagnosis were excluded from the study population. The exclusion may have been incomplete to some extent, since no radiologic imaging was used. However, regarding the nature of the determinants, degeneration presumably plays a minor role in nonspecific shoulder pain. In conclusion, every eighth employed person in Finland experiences shoulder pain without clinical findings. In this study, subjects with such nonspecific pain reported symptoms of burnout, depression, and alexithymia significantly more often than did those without pain. Psychological and psychosocial factors, however, were not associated with the specific clinical disorder evaluated (chronic rotator cuff tendinitis), determinants of which were merely mechanical and biologic: cumulative static loading on the shoulder, age, and diabetes. 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