Study design
Questionnaires were directed to women in five occupational groups [teachers (Te), anaesthetic nurses (AnN), theatre nurses (TN), assistant nurses (AsN), and sonographers (Sg)] at baseline and at follow-up.
Ten items of self-assessed occupational exposures and personal factors at baseline were analysed in relation to reported musculoskeletal pain at follow up. The experience of pain was collected for nine anatomical sites. The importance of the potential risk factors was analysed in relation to multisite pain, i.e. the number of affected pain-sites, as well as for single-site pain in the neck, the shoulders, the hands, the lower back and the feet, respectively.
Study population
At baseline, 1591 female employees from 49 public schools, 22 surgical departments and 45 sonography departments in Sweden participated in the study [19]. The inclusion criteria were work at least 50% of fulltime during a period of at least three months before fulfilling the baseline questionnaire. The participants responded to a questionnaire that included questions on ergonomic-, psychosocial-, personal- and life-style factors and musculoskeletal pain from nine anatomical sites. At baseline, we also performed clinical examinations as well as technical measurements of the physical workload among subgroups of the participants (n = 485 and n = 60, respectively) [19]. The questionnaires were administered at baseline (November 2008 - October 2012) and at follow-up (November 2011 - March 2015) with a follow-up period of mean 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, in order to make the length of the follow-up period similar. The length of the follow-up periods was for TE mean 29 (range 20–36 months) months, for the surgical staff mean 27 (range 20–40 months) months and for SG mean 29 (20–38 months) months.
Out of the 1591 participants at baseline, 1115 (70%) submitted responses to the follow-up questionnaire (246 Te, 214 AnN, 209 TN, 224 AsN and 222 Sg; Table 1). Their mean seniority at baseline were 17 (range 0.25–45) years. The participation rate among the employee categories ranged from 66% to 76%.
Table 1
Musculoskeletal pain and sum scores of ergonomic- and psychosocial factors in the total study population at baseline; among the participants at follow-up (n = 1115) and among those who dropped out of the study between baseline and follow-up (i.e., “drop-outs”; N = 476).
| | | Musculoskeletal pain at baseline | Sum score | Sum score |
| All | Multisite paina | Neck | Shoulders | Hands | Lower back | Feet | Ergonomic factors | Psychosocial factors |
| N | % | % | % | % | % | % | Mean (SD) | Mean (SD) |
| | | | | | | | | |
Included at follow-up | 1115 | 26 | 39 | 44 | 24 | 39 | 17 | 2.5 (1.0) | 1.3 (1.2) |
Teachers | 246 | 21 | 40 | 34 | 16 | 38 | 11 | 1.6 (0.8) | 1.8 (1.4) |
Anaesthetic nurses | 214 | 21 | 32 | 40 | 20 | 39 | 17 | 2.8 (1.0) | 1.2 (1.2) |
Theatre nurses | 209 | 29 | 39 | 47 | 24 | 42 | 19 | 3.3 (0.8) | 1.1 (1.1) |
Assistant nurses | 224 | 36 | 41 | 47 | 37 | 47 | 26 | 2.9 (0.9) | 1.3 (1.2) |
Sonographers | 222 | 24 | 44 | 53 | 25 | 28 | 12 | 2.3 (0.9) | 1.0 (1.1) |
| | | | | | | | | |
Drop-outs, all | 476 | 26 | 44 | 46 | 25 | 39 | 16 | 2.5 (1.1) | 1.5 (1.3) |
Non responders | 297 | 23 | 46 | 44 | 24 | 40 | 15 | 2.5 (1.1) | 1.5 (1.3) |
Retired | 59 | 39 | 37 | 44 | 34 | 36 | 24 | 2.4 (1.1) | 1.4 (1.1) |
Off duty/change of work | 78 | 28 | 47 | 52 | 20 | 39 | 16 | 2.5 (1.0) | 1.5 (1.4) |
Parental leave | 31 | 23 | 45 | 48 | 19 | 32 | 10 | 2.4 (1.1) | 1.4 (1.3) |
Other reasonb | 11 | 60 | 27 | 46 | 50 | 40 | 27 | 2.8 (1.1) | 1.4 (1.2) |
a Participants with ≥ four pain-sites |
b Not fulfilling the inclusion criteria at follow-up (n = 8) or missing in all outcome measures (n = 3). |
The distribution of musculoskeletal pain and occupational factors at baseline were generally similar among participants and drop-outs (n = 476) at follow-up, with two exceptions (Table 1): The drop-outs had, compared to the participants, a higher frequency of neck pain (44% vs. 39%), and a higher sum-score of psychosocial factors [mean 1.5 (SD 1.3) vs. mean 1.3 (SD 1.2)]. The drop-out categories are shown in Table 1.
Work tasks
The teachers (Te) educated children aged 10–15 years, in theoretical subjects in school-years 4–9 of the state school system. Among the surgical staff, the anaesthetic nurses (AnN) prepared the patient for surgery, anesthetized the patient by intubation and checked instruments to ensure that the patient’s general health was maintained during surgery. The theatre nurses (TN) was responsible for sterility in the operating theatre and performed, for example, sterile washing of the patient. During surgery, the TN stood beside the surgeon and assisted with instrumentation, for example by holding a surgical retractor to hold the incision open. Assistant nurses (AsN) assisted the other personnel and prepared materials and patients for surgery. For example, they opened a variety of packages with different materials, moved trolley carts with X-ray equipment and adjusted the operating lights. All surgical staff (AnN, TN and AsN) were involved in turning, lifting and transferring of the patients in the theatre room. The Sonographers (Sg) performed ultrasound examinations of the heart, the blood vessels, or other organs. The Sg sat or stood at the side of the patient, held a transducer in one hand, operated a keyboard with the other and simultaneously, observed a screen. After the examination, the Sg performed analysis of the images at a computer. Additional details of the work tasks and the physical workload among the occupational categories are reported in the baseline-study [19].
Questionnaire
The questionnaire included questions about the physical workload, psychosocial working conditions, personal and lifestyle factors, and musculoskeletal pain. Physical workload: The mechanical exposure index (MEI [20]) comprised 11 items of work postures and movements, and the physical exposure index (PHYI [20]) included seven items concerned with physical activity and lifting. In both scales, the items were answered on a three-point scale; 1:”hardly nothing/not at all”, 2:”somewhat” or 3:”a great deal”. For each scale, the sum of the points (MEI 11–33 possible; PHYI 7–21 possible) was calculated for each individual. The level of mechanical exposure was then defined into four categories (no exposure 11-12 points, low exposure 13-15 points, medium exposure 16-19 points and high exposure 20-33 points). The physical exposure was defined as no exposure 7-8 points, low exposure 9-10 points, medium exposure 11-13 points and high exposure 14-21 points [20]. Further, sensory demands e.g. eye sight, attention, control of body movements and precision, were measured with a five-item subscale from Copenhagen Psychosocial Questionnaire [21]. The questions were answered on a five-point-scale and the mean value in the dimension was calculated for each individual.
A study specific sum score of ergonomic factors, including MEI, PHYI and sensory demands was calculated. For MEI and PHYI each participant was given one to four points depending on the category of mechanical and physical exposure (from no exposure to high exposure), respectively. For sensory demands the study population was divided into quartiles where each participant got one to four points, from the lowest quartile to the highest. In total the sum of points ranged from 3-12 points. Then the number of categories was 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 of the dimensions MEI, PHYI and sensory demands are given in additional table 1.
The conditions during computer work were assessed by a study-specific question “Are you satisfied with the computer work-station 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) [22-23]. Job demands concerned nine items of e.g. working pace, hard work, excessive demands, time pressure, conflicting demands, and stressful work. Job control concerned 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 selected. For each item the responses used 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 indicated higher demands, better control, and better support.
A subset of the Copenhagen Psychosocial Questionnaire [21] was used to measure emotional demands (three items concerning e.g. emotionally difficult situations and emotional affection by the 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 and the mean value in each dimension was calculated for each individual.
A study-specific sum-score of psychosocial factors was crafted, 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 upper quartile of the study population was given one point, and the remaining participants zero points. For the dimensions job control, job support and leadership, respectively, the lowest quartile of the population got 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 merged together, resulting in a sum-score of psychosocial factor with 0-5 possible steps. The separate results of the six dimensions included in the sum-score are given in additional table 1.
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 about their age, seniority, height and weight [body mass index, BMI, calculated as weight in kg/height in meters2]. They were also asked about personal relaxation [24] “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 [24] “How many hours a week do you spend on work 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 [24] “Do you spend your leisure time exercising in any kind? 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 categories 0-2 were merged into one category of “not daily smokers”.
Musculoskeletal pain [19]: The participants were asked about subjective musculoskeletal complaints in nine anatomical sites: the neck, shoulders, elbows, hands, upper back, lower back, hips, knees and feet, during the preceding 12 months, according to the Nordic Questionnaire [26]. 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, for each anatomical site, information was collected about the frequency of complaints during the past year using a 5-point scale (never, seldom, sometimes, often, or very often [28]) as well as the intensity of complaints on an eleven-point-scale, from 0 (none at all) to 10 (very, very severe [27]). A subject 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) [19]. The condition was defined separately for each anatomical site.
The number of anatomical sites with pain was calculated for each individual (0-9 possible). Following the suggested classification by Pereira de Fernandes and Burdorf [17], 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. Multisite pain was defined as having pain from four or more sites of pain.
Further, five of the anatomical sites were selected for analysis of single-site pain: the neck, the shoulders, the hands, the lower back and the feet.
Statistical analyses
All statistical analyses were performed with the IBM SPSS software, version 24 (IBM Corp.). P-values ≤ 0.05 (two-tailed) were considered as statistically significant.
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 for all variables collected at baseline (in total eleven factors including pain in the actual anatomical site, sum-scores of ergonomic- and psychosocial factors, computer work, age, BMI, personal recovery, domestic work, physical exercise, smoking and occupational category). In the next step, PRs for pain at follow-up were estimated using Poisson regression 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.
Odds ratios (ORs) and 95% confidence intervals (CIs) for multisite pain at follow-up (number of pain-sites stratified into five categories, i.e. 0, 1, 2, 3 and ≥ 4 sites) were first estimated in single-exposure ordinal regression models for the eleven occupational and personal factors collected at baseline. In addition, the importance of multisite pain at baseline, for multisite pain at follow-up was estimated. Next, ORs for the multisite pain at follow-up were estimated using multi-exposure ordinal regression, without multisite pain at baseline. Finally, the multi-exposure models were adjusted for multisite pain at baseline.
Differences between prevalence of pain at baseline and at follow-up were evaluated with McNemar test.
Due to a high collinearity (strong correlation) between seniority and age, seniority was omitted from the multi-exposure statistical analysis. Seniority is reported as a single-exposure in additional table 1.
The correlation between the difference of multisite pain categories between baseline and follow-up, and the follow-up period (months) was low (Spearmans rho = 0.03).