Instruments
The instruments (i.e. standardised questionnaire, standardised medical diagnostic procedure, assessment of exposure) used in this survey have been used in a similar form in other studies by several authors. Among them, the authors of the present study applied them for the assessment of musculoskeletal symptoms of upper extremities and the neck in office workers [
5]. This former study sample will be used as a reference data set (see Analysis section below).
1)
Assessment of health outcome:
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Survey of exposed employees utilising a standardised questionnaire.
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Physical examination of the exposed employees, performing a standardised medical diagnostic procedure.
3)
Application of the KIM-MHO:
Standardised questionnaire
The employees' questionnaire is based on the Nordic Questionnaire [
47], parts of the Copenhagen Psychosocial Questionnaire (COPSOQ [
48]), and the FEBA questionnaire [
49]. In our study, the respective German versions of the Nordic Questionnaire [
50] and the COPSOQ [
51] are applied. The questionnaire contains sociodemographic factors (e.g. age, gender, years on the job, leisure time activities, smoking habits), musculoskeletal symptoms (e.g. prevalence, degree of disability), general working conditions (e.g. time pressure, shift work, working posture), and work-related psychosocial factors (e.g. job satisfaction, cognitive demands, social support).
Standardised medical diagnostic procedure
In a SALTSA study, a list of standard diagnoses of musculoskeletal disorders was suggested to analyse the extent to which musculoskeletal symptoms could be attributed to specific tentative diagnoses [
52]. The medical diagnostic procedure used in the present study was derived from this SALTSA study. The examination tool consists of a documentation sheet and a reference sheet. The documentation sheet is divided into three parts. Part A is a general survey to document painful or symptomatic body regions. Part B deals with specific examination techniques to be carried out if pain or symptoms in specific regions were documented in part A. According to these results, tentative diagnoses can be assigned using a list of diagnoses in part C. These are:
2.
cervico-brachial neck syndrome,
4.
medial and lateral epicondylitis,
5.
ulnar nerve compression at the elbow: cubital tunnel syndrome,
6.
radial nerve compression: radial tunnel syndrome,
7.
flexor/extensor peritendinitis/tendosynovitis of forearm/wrist region,
10.
ulnar nerve compression at the wrist: Guyon-canal-syndrom,
11.
Raynaud's phenomenon (vibration white finger) and peripheral neuropathy associated with hand-arm vibration,
12.
osteoarthritis of the distal upper extremities joints, and
13.
non-specific upper extremity musculoskeletal disorders (UEMSDs).
As compared to the SALTSA study mentioned above [
52] the list of diagnoses was modified for this survey, since usually it is differentiated between cervical neck syndrome and cervico-brachial neck syndrome in Germany. In the original SALTSA study, both were merged to "radiating neck complains".
Key Indicator Method - Manual Handling Operations (KIM-MHO)
The new draft of the KIM-MHO is the central topic of this research project. It complements the existing KIMs to assess the working conditions for physical work. In accordance with the principle of the KIMs, it contains an objective requirement and load description, and identifies potential threats to physical overload. The KIM-MHO includes job characteristics and their interaction. The key indicators to be considered in the KIM-MHO are:
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daily duration of manual work processes,
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type, duration, and frequency of executing forces,
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body posture during manual work processes,
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hand-arm posture during manual work processes,
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work organisation, and
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work conditions.
The key indicators are classified in different scales. The scales correspond to conditions in practice and range from a minimum/optimum to maximum/poor. The classification of these scales indicates potential bottlenecks for each category/indicator. By multiplying the scale value of the daily duration of activity with the sum of the other scale scores, a total value can be calculated. This calculated sum score can be used as a risk score. This score can be allocated to a risk range:
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„green": Low exposure situation, where physical overload is unlikely to occur.
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„greenish yellow": Increased exposure situation, physical overload is possible for less resilient subjects. Redesign of the workplace might be helpful for this group.
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„yellow": Highly increased exposure situation, physical overload also possible for normal subjects. Redesign of the workplace is recommended.
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„red": High exposure situation, physical overload is likely to occur. Redesign of the workplace is necessary.
Samples
The study is carried out at different workplaces with different physical exposures to heavy forces, awkward postures, and repetitive manual handling operations. Groups of approximately 40 employees at each workplace are investigated. A minimum of 200 employees are considered in total.
A previous sample of office workers (684 men and 371 women, working at visual display units [
5]) without relevant exposures from repetitive manual handling operations is used as reference group with regard to musculoskeletal symptoms.
Power calculation
In a pilot study of machine operators (2 workplaces, 56 exposed subjects) the 12-month prevalence of symptoms in the elbow, hand/wrist and foot/ankle region was higher in female machine operators than in female controls in univariate analysis (51% vs. 16%; 55% vs. 25%; 31% vs. 11%). These results were significant in multivariate analyses (elbow region: OR 4.2 [95%-CI: 1.8 - 9.4]; hand/wrist region: OR 3.5 [95%-CI: 1.6 - 7.8]; foot/ankle region: OR 3.5 [95%-CI: 1.4 - 9.0]). The prevalence of symptoms in other body regions studied did not differ. Male machine operators more frequently reported symptoms in the hand/wrist region and knee region (12-month prevalence: 51% vs. 19% and 56% vs. 27%). These results were significant in multivariate analyses (hand/wrist region OR: 4.3 [95%-CI: 2.1 - 8.6]; knee region OR: 3.0 [95%-CI: 1.5 - 6.0]). In addition, a higher risk for foot/ankle symptoms (12-month prevalence) was calculated for exposed male workers (OR: 2.8 [95%-CI: 1.2 - 6.1]).
For power calculation EpiManager-Software was used [
53]. Considering the results of this pilot study, the power of the study can be calculated as follows. Assuming only a small difference in the prevalences of symptoms between exposed and unexposed subjects of nearly 0.25 (55% - 30%, corresponding to a prevalence ratio of 1.83) the power (1-beta) of the study is calculated for men as 99% (n = 650 unexposed and n = 120 exposed men) and as 90% for women (n = 350 unexposed and n = 80 exposed women). If single workplaces with different exposures of manual handling operations are assessed, the number of exposed subjects is reduced to nearly 40 men or women per workplace. In this case and with regard to the conditions mentioned above, the power of the study is 86% (n = 40 exposed men) or 84% (n = 40 exposed women). The power calculation does not consider loss of power due to effects of confounders in the multivariate analysis.
Analysis
Analysis of research topic 1: Assessing workplaces by means of the KIM-MHO, different occupational health and safety officers should obtain similar scores.
The objectivity is determined examining the independence of results assessed by different individuals. Descriptive statistics are used to show the distribution of different workplace assessments of the involved experts (mean, median, variance, range). Inter-rater reliability for multiple raters are analysed by using standard video sequences of typical workplaces for risk assessment and by rating these videos by a group of selected experts under standardised conditions [
54].
Analysis of research topic 2: At the completion of the KIM-MHO, no significant descepancies occur between the opinions of the scientists and the operational workers involved.
At every workplace, an extensive work analysis is carried out to gather relevant data about respective manual handling operations (duration of tasks, frequency, force, posture, etc.). Based on this data, the KIM-MHO is then used by scientists and occupational health and safety officers seperately to assess the working conditions. The difference between the real exposure (as assessed by extensive work analysis) and the assessment by KIM-MHO will be used to describe the validity of the KIM-MHO. Descriptive statistics will be used to illustrate the distribution of different workplace assessments of the involved experts (mean, median, variance, range). If significant discrepancies occur, relevant parts of the KIM-MHO will be rephrased and adjusted. If rephrasing and adjusting is necessary, the modified KIM-MHO will be tested again for sufficient validity.
Analysis of research topic 3: It is assumed, that employees at workplaces with high exposures of manual handling operations show health related outcomes (musculoskeletal symptoms) more frequently than non-exposed workers, taking into consideration relevant confounders such as age, gender, constitution or disposition. Secondly it is assumed, that the KIM-MHO displays high scores at workplaces with high degrees of manual handling operations and high frequencies of musculoskeletal symptoms in exposed workers, and low scores at workplaces with low exposures of manual handling operations and low frequencies of musculoskeletal symptoms in workers.
To estimate whether prevalences of symptoms in the upper extremities and neck are excessive, the data from the employees of each workplace will be compared with a similar reference data set among employees working at visual display terminal (VDT) workstations. These reference data were generated in a cross-sectional study of 1,065 employees working at VDT [
5]. In addition, the prevalence of the tentative diagnoses will be analysed to complement the data. The exposed and unexposed cohorts are described and compared in regard to different health related outcomes (descriptive statistics in regard to prevalence of symptoms in different parts of the body and other outcomes). Multivariate regression analysis based on log-binomial models will be used for multivariate comparisons between exposed and unexposed subjects. Prevalence Ratios will be calculated as effect estimates. Relevant confounders (age, constitution, disposition, behavior, work history) are taken into consideration. Directed Acyclic Graphs will be used in confounder selection [
55]. Data will be generally stratified by gender. Higher prevalences of symptoms indicate that the KIM-MHO score should be high as well. If discrepancies occur between the prevalence of symptoms on one hand and the height of the KIM-MHO score on the other hand, the KIM-MHO will be adjusted. The association between the exposure to manual handling operations as assessed by means of the KIM-MHO and the frequency of musculoskeletal symptoms within the exposed workers will be determined (criterion validity). To assess the correlation between the KIM-MHO score and the prevalence of musculoskeletal symptoms, prevalence ratios are calculated (general linear model: log-binomial, adjusted for age, height and BMI, stratified for gender, 95% confidence intervals (95%-CI)).
Description of risks
To our knowledge, neither serious risks nor undesired effects can arise from completing the questionnaires or from the standardised physical examination by an occupational health physician. Nothing in regard to these effects has been reported in the literature. Thus, there seem to be no specific risks related to the study.
Ethical principles
The study was planned and conducted in accordance with the German medical professional code and the Helsinki Declaration of 1996 as well as the German Federal Data Protection Act. The study protocol and its amendment were approved by the Ethics Committee of the University of Witten/Herdecke (approval no. 35/2009). The study was started after the Ethics Committee gave its written and unrestricted approval.
Employees participate in the study voluntarily. They can end their participation at any time without reason and without negative consequences, e.g. for their job.
Written informed consent for participation is obtained before the survey. Employees receive written and verbal information about the main features of the study as well as about potential benefits for their health and their contribution to the common public welfare. If they accept the conditions of the study and their participation, they document their consent with their signature. A copy of this statement is intended to be kept by the employee for later reference or cancellation of participation. In the event of study discontinuation, all data will be deleted, unless the employee explicitly wishes and affirms further analysis of his/her data.