Questionnaires were used to obtain information from women in five occupational groups, anaesthetic nurses, surgical nurses, assistant nurses, sonographers and teachers, at baseline and at follow-up. Ten items regarding self-assessed occupational exposure and personal factors at baseline were analysed in relation to reported musculoskeletal pain at follow-up. Data were collected on pain at nine anatomical sites; i.e. the neck, shoulders, elbows, hands, upper back, lower back, hips, knees and feet. The importance of potential risk factors was analysed in relation to the number of sites of pain, as well as for pain in five of the anatomical regions, i.e. the neck, shoulders, hands, lower back and feet.
All 23 surgical departments in the healthcare regions of southern Sweden were invited to take part in the study at baseline. Invitations were also sent to all 45 departments at hospitals in Sweden where biomedical scientists perform sonography, and to 64 state-run schools from seven counties in southern Sweden. Of these, 22 surgical departments, all 45 sonography departments and 49 schools agreed to participate in the study . The baseline questionnaire was sent to all women in the occupations of interest, which totalled 2078 women at 116 different workplaces. The inclusion criterion was working at least 50% of full-time, during a period of at least three months before completing the baseline questionnaire. Of these 2078 women, 1591 participated in the study at baseline . Most of them (91%) worked full-time (≥ 30 h/week) and the mean number of years in their profession (referred to as “seniority”) was 17 (range 0.25 – 45) years.
Out of the 1591 participants at baseline, 1115 (70%) submitted responses to the follow-up questionnaire. The inclusion criterion was working at least 50% of full-time with the job-specific tasks. The participation rates among the various occupations were:
214 out of the 297 anaesthetic nurses included at baseline (72%); 209/305 surgical nurses (69%); 224/323 assistant nurses (69%); 222/291 sonographers (76%); and
246/375 teachers (66%) (Further information on drop-outs is given in Table 1.)
The questionnaires were administered at baseline (November 2008 - October 2012) and at follow-up (November 2011 - March 2015), with a mean follow-up period of 28 months (range 20 - 40 months). The questionnaires at both baseline and at follow-up were sent out to subsets that altered between the various employee categories; i.e. we started with a surgery department, thereafter a school, thereafter some sonography departments, and then another surgery department, and so on. The mean lengths of the follow-up periods were 27 months (range 20 - 40) for all the nurses, 29 months (20 - 38) for sonographers and 29 months (range 20 - 36) for teachers.
The anaesthetic nurses prepared the patients for surgery, anaesthetized the patient by intubation and checked instruments to ensure that the patient’s general status was maintained during surgery. The surgical nurses were responsible for sterility in the operating theatre and performed, for example, sterile washing of the patient. During surgery, the surgical nurses stood beside the surgeon and assisted with instruments, for example, by holding a surgical retractor to hold the incision open. Assistant nurses assisted other personnel and prepared materials and patients for surgery. For example, they opened a variety of packages containing different materials, moved trolley carts with X-ray equipment, and adjusted the operating lights. All the nurses were involved in turning, lifting and transferring the patient from the gurney to the operating table. The sonographers performed ultrasound examinations of the heart, the blood vessels, or other organs. The sonographers sat or stood at the side of the patient, held a transducer in one hand, operated a keyboard with the other hand and simultaneously observed the image on a screen. After the examination, the sonographers analysed the images at the computer. The teachers taught theoretical subjects to children aged 10 – 15 years (years 4 – 9 in the Swedish school system). Additional details concerning the work tasks and the physical workload of the occupational categories studied are given in our previous study .
The questionnaire included questions about the physical workload, psychosocial working conditions, personal and lifestyle factors, and musculoskeletal pain. Further, the participants were asked about any changes in employment or work tasks during the follow-up period, and whether these changes were associated with musculoskeletal pain. Physical workload: The mechanical exposure index (MEI ) comprised 11 items covering work postures and movements, while the physical exposure index (PHYI ) included seven items concerned with physical activity and lifting. The questions were answered on a three-point scale in both cases: 1,” little/not at all”; 2,”somewhat”; or 3,”a great deal”. The data were analysed following the classification of Balogh et al. : i.e., the sum of the points was calculated for each scale (MEI = 11 - 33; PHYI = 7 - 21), for each individual. The level of mechanical exposure was then divided into four categories: no exposure (11 - 12 points), low exposure (13 - 15 points), medium exposure (16 - 19 points) and high exposure (20 - 33 points). Physical exposure was similarly divided into no exposure (7 - 8 points), low exposure (9 - 10 points), medium exposure (11 - 13 points) and high exposure (14 - 21 points). Sensory demands, e.g. eyesight, attention, control of body movements and precision, were measured using a five-item subscale from the Copenhagen Psychosocial Questionnaire . The questions were answered on a five-point scale with the options 1: “to a very large extent”; 2: “to a large extent”; 3: “to some extent”; 4: “to a small extent” and 5: “to a very small extent”, or 1: “always”; 2: “often”; 3: “sometimes”; 4: “seldom” or 5: “never/almost never”. The mean value of the dimension was calculated for each individual.
A study-specific sum score of ergonomic factors, including MEI, PHYI and sensory demands, was then calculated. For MEI and PHYI, each participant was assigned one to four points, corresponding to the categories of mechanical and physical exposure described above (from no exposure to high exposure ). For sensory demands, where no predefined cut-offs were available, the study population was divided into quartiles, and the participants in each quartile were assigned one to four points, from the lowest quartile to the highest. In total, the sum of points ranged from 3 - 12. The number of categories was then reduced into the sum score of ergonomic factors (3 - 6 points =1; 7 - 8 points = 2; 9 - 10 points =3; and 11 - 12 points =4). The separate results for the dimensions MEI, PHYI and sensory demands are given in additional Table 1 and additional Table 2.
Satisfaction with conditions during computer work was assessed using the study-specific question: “Are you satisfied with the computer workstation arrangements?”, with the options 1: very satisfied (can work comfortably) or rather satisfied, 2: neither satisfied nor dissatisfied, 3: rather dissatisfied or very dissatisfied (uncomfortable/strenuous work).
Psychosocial working conditions: The psychosocial exposure, in terms of job demands, job control and job support from co-workers, was measured with a Swedish version of the Job Content Questionnaire (JCQ) [31-32]. Job demands were categorized in terms of nine items, e.g. working pace, hard work, excessive demands, time pressure, conflicting demands and stressful work. Job control included nine items of decision latitude (e.g. influence at work, freedom to decide how work should be done), and skill discretion (e.g. development opportunities, skill and creativity). In the dimension job support, all four items concerning support from co-workers were used. The responses to each item were given on a four-point scale, indicating the level of agreement with various statements about conditions at work. The mean value in each dimension was calculated for each individual. Higher numbers indicate higher demands, better control, and better support. A subset of the Copenhagen Psychosocial Questionnaire  was used to measure emotional demands (three items concerning e.g. emotionally difficult situations and emotional effects of work), demands on hiding emotions (two items), and leadership (eight items concerning planning of work, conflict solving, communication and concern for staff). All questions were answered on a five-point scale with the options 1: “to a very large extent”; 2: “to a large extent”; 3: “to some extent”; 4: “to a small extent” and 5: “to a very small extent”, or 1: “always”; 2: “often”; 3: “sometimes”; 4: “seldom” or 5: “never/almost never”. The mean value was calculated for each dimension for each individual.
A study-specific sum score was calculated for the psychosocial factors, based on the six dimensions: job demands, job control, job support from colleagues, emotional demands, demands of hiding emotions and leadership. For each of the dimensions job demands, emotional demands and demands of hiding emotions, the individuals in the upper quartile of the study population were assigned one point, and the remaining participants zero points. For the dimensions job control, job support and leadership, the individuals in the lowest quartile of the population were assigned one point and the remaining participants zero points. A sum score of 0-6 possible points was calculated for each individual. Due to few individuals with five or six points these two groups were combined, resulting in a possible sum score of psychosocial factors of 0-5. The separate results for the six dimensions included in the sum score are given in additional Table 1 and additional Table 2.
The occupational category for each individual was included in the analysis, in order to explain any predictive factors for pain, that were not covered by the questionnaire comprising questions about ergonomic, psychosocial and personal factors.
Personal and lifestyle factors: The participants were asked to give their age, seniority, height and weight. Their body mass index (BMI; kg/m2) was then calculated. They were also asked about personal relaxation : “How much of your leisure time (except weekends/holidays) do you usually spend for your own relaxation (without special requirements and obligations)?” (1: ≥3 hours/day; 2: 1 – 2 hours/day; and 3: <1 hour/day), domestic work : “How many hours a week do you spend working in the home that is not paid work, e.g. shopping, cooking, taking care of finances, washing, cleaning, caring for children, maintaining a car, house and garden?” (1: <10 hours/week; 2: 11 – 20 hours/week; 3: >21 hours/week), physical exercise : “Do you spend your leisure time exercising in any way? Exercise includes sports, fitness training, gymnastics, dancing, walking, cycling, etc., for at least 30 minutes per occasion” (1: twice a week or more; 2: once a week; 3: occasionally or never); and smoking habits (0: never smoked; 1: ex-smoker of at least six months’ standing; 2: smoker, but not daily; 3: daily smoker). In the analysis, the smoking categories 0-2 were merged into one category of “not daily smokers”.
Musculoskeletal pain : The participants were asked about subjective musculoskeletal complaints at nine anatomical sites: the neck, shoulders, elbows, hands, upper back, lower back, hips, knees and feet, during the preceding 12 months, according to the Standardized Nordic Questionnaire for the Analysis of musculoskeletal Symptoms . For the shoulders, elbows, hands, hips, knees and feet, pain in one or both sides of the body was regarded as one pain site. In addition, information was collected for each anatomical site on the frequency of complaints during the past year using a 5-point scale (never, seldom, sometimes, often, or very often ), as well as the intensity of complaints on an eleven-point scale, from 0 (none at all) to 10 (very, very severe ). The individual was considered to have considerable musculoskeletal pain (subsequently referred to simply as “pain”) if reporting complaints at least “seldom” with an intensity of at least 7 (very severe), or “sometimes” with an intensity of at least 3 (moderate), or “often” or “very often” with an intensity of at least 2 (slight/mild) . The condition was defined separately for each anatomical site.
The number of anatomical sites with pain was calculated for each individual (0 - 9). For assessment of multisite pain, we followed the suggested classification by Pereira de Fernandes and Burdorf : The participants were divided into five categories: 0, no pain; 1, one pain site; 2, two pain sites; 3, three pain sites and 4, ≥ four pain sites. Furthermore, five of the anatomical regions were selected for analysis of specific pain sites: the neck, shoulders, hands, lower back and feet.
All statistical analyses were performed with IBM SPSS software, version 24 (IBM Corp.). P-values ≤ 0.05 (two-tailed) were considered statistically significant. Differences between the prevalence of pain at baseline and at follow-up were evaluated with the McNemar test. Prevalence ratios (PRs) and 95% confidence intervals (CIs) for pain in the neck, shoulders, hands, lower back and feet at follow-up were first estimated in single-exposure Poisson regression models, with unit length of follow-up, for all variables collected at baseline (in total eleven factors including pain at the specific anatomical site, sum scores of ergonomic and psychosocial factors, computer work, age, BMI, personal relaxation, domestic work, physical exercise, smoking and occupational category). In the next step, PRs for pain at follow-up were estimated using Poisson regression, with unit length of follow-up, with multiple exposures (multi-exposure model), without pain at baseline. In the third step, by adjusting the multi-exposure model for pain at baseline we tried to quantify how much of the explanation from different factors concerning pain at follow-up that was not due to associations with pain that were present already at baseline. Due to the high collinearity (strong correlation) between seniority and age, seniority was omitted from the multi-exposure statistical analysis.
For multisite pain at follow-up (i.e. number of pain sites stratified into five categories: 0, 1, 2, 3 and ≥ 4 sites), associations with the eleven occupational and personal factors collected at baseline were first investigated using single-exposure ordinal regression models under the cumulative odds model with location parameters only [37 - 38]. This model estimates the average odds ratios (ORs) and 95% CIs of all possible dichotomisations of the ordinal response variable. The importance of the number of pain sites pain at baseline, for the number of pain sites at follow-up, was also estimated separately. Next, ORs for the number of pain sites at follow-up were estimated using multi-exposure ordinal regression, without the number of pain sites at baseline. Finally, the multi-exposure models were adjusted for the number of pain sites at baseline. In all regression analyses, the overall p-value reflects the strength of the empirical evidence that the pain prevalence is not constant across the contrasted groups.
As supplementary analyses we also fitted single- and multi-exposure models with the separate dimensions included in the sum-scores of ergonomic and psychosocial factors, for all pain outcomes.