Int. J. Environ. Res. Public Health2021, 18, 9171 10of 15 Regarding the upper extremities, the validity of questionnaires for WMSDs has not been clarified, and it is not known how an optimal questionnaire can be constructed and what information can be obtained [56]. A purely technical investigation using measurement data without clinical examination would have the advantage of resource optimization but could not be related to WMSDs either [57]. This is also supported by the relatively weak correlation between measured clinical endpoints and WMSDs in our study. Accordingly, a clinical examination based on a predetermined set of diagnostic criteria remains the gold standard for cross-sectional investigations in order to keep well-defined disorders separate from more diffuse conditions. Although clinical examination is time-consuming and hard for both the subject and the examiner, it seems to be necessary at this time to detect defined WMSDs. Although the p-value has not quite reached the conventional significance level of 0.05 in our study (p= 0.056), the correlation we found between WMSDs and the DASH score may not therefore be considered non-existent and could be of interest for the design of future studies [58]. The DASH score as a self-administered, region-specific outcome instrument for upper-extremity disability and symptoms was tested against the gold standard of WMSDs detection (i.e., the clinical examination). To our knowledge, there are no studies focusing on the correlation between WMSDs and the DASH score, whereas this is the case for some upper extremity pathologies other than WMSDs [59]. According to our analysis, the DASH score has the potential to replace the resource-intensive clinical examination as a screening tool. In case of conspicuous DASH scores, the latter could be used in a focused manner for diagnosis, with therapeutic and preventive measures derived from it. The DASH score has shown good validity, reliability, and responsiveness in relation to upper extremity disorders [60]. In comparison, the Nordic Musculoskeletal Questionnaire (NMQ), often used in cross-sectional studies, is a simple validated questionnaire that refers to complaints in nine body parts, including the hand/wrist/elbow [61]. Its content is in no way comparable to the detailed questions of the DASH, with its focus on the upper extremities, and hardly exceeds the yes/no question on subjective complaints in our study. To what extent further questionnaires are suitable for the detection of upper extremity pathologies will be the subject of future studies. For the endpoint WMSDs, the multiple analysis of our study did not show any independent predictors significant at a 0.1 level. This is partially in contrast to previous studies, in which work-related and socio-demographic characteristics have been determined as predisposing upper extremity disorders [5]. Work-related factors include static postures; excessive force and strain; vibration; repeated pushing, pulling, and lifting; overuse of particular anatomical structures or regions; poor posture or improper positioning; awkward movements; long duration of pressure; rapid work pace; short recovery periods; low decision latitude; years of service; and job satisfaction [39,62–65]. Socio-demographic characteristics predicting WMSDs include factors such as sex, age, marital status, work experience, body mass index, and physical activities [66–71]. For standardization and better comparability of future studies, the authors have selected the predictor variable set following the International Classification of Functioning, Disability, and Health (ICF). This is an internationally recognized classification of health and health-related domains [72]. The scatter plot matrix with prediction ellipses has proven to be a fast graphic analysis and a preliminary stage for a detailed statistical evaluation in our study. Multiple analyses were also used to examine the independent predictors for other clinical endpoints. Significant positive correlations between ROM and years in service, more frequent subjective complaints of the upper extremity with increasing age, higher VAS under strain with a higher BMI, and higher grip strength with the presence of a secondary occupation and/or physically demanding hobbies are particularly noteworthy. These findings are relevant for future investigations, because the relationships of independent variables to each other may disturb the identification of risk factors for WMSDs, acting as confounders. These relationships should therefore be considered when analyzing any WMSDs-related outcomes.
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