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Abstract
Objective: To critically appraise the observational studies linking cumulative spinal loading and lower back disorders (LBD) among workers engaged in manual material handling and to explore the association between cumulative spinal loading and LBD through a meta-analysis of papers reported in the published literature.
Background: Although studies have indicated a definitive relationship between long-term exposure to manual materials handling and LBD, little is generally known about the validity of the cumulative exposure assessment methods used for predicting the risk of LBD.
Methods: A comprehensive electronic search on the subject was conducted. The articles found from the search were critically appraised from an epidemiological standpoint. The strengths and weaknesses of the studies were documented. A quantitative assessment was performed for the meta-analysis estimate using the fixed-effect and random-effects (Dersimonian and Laird method) models. The assessments were conducted in two ways: with a standard approach that does not consider study quality and with a modified method that allows weighting scores to be calculated based on the rating of the quality of each study.
Results: The electronic search resulted in identification of four epidemiological papers, three of which provided sufficient information for an assessment of epidemiological quality and two of which provided sufficient data to conduct a meta-analysis. The results showed that the methodological quality of the studies ranged from poor to marginal. Without considering the overall study quality for the exposure data, (1) there were substantial differences between the three studies that were rated for epidemiological quality as evidenced by the significant heterogeneity testing at the 10% level and (2) the difference in the mean exposure values between the study and control groups (i.e. summary mean difference) was significant at the 5% level for both the fixed-effect and random-effects models. After accounting for overall study quality, the heterogeneity was reduced but still significant at the 10% level and the summary mean difference was greater than that without the quality score. The meta-odds ratio for LBD outcomes was 1.66 (95% confidence interval using quality scores = 1.46–1.89).
Conclusions: The preliminary findings suggest that there likely is an association between cumulative spinal loading and LBD. Further, there are considerable differences among the studies in terms of exposure assessment techniques. A subsequent paper (Part II of this research) provides an in-depth analysis of cumulative spinal loading exposure methods and discusses critical issues related to their reliability and validity for estimating force distribution and practicality for field measurement.