A quarter century perspective on low back pain : a longitudinal study

Abstract

The focus of this thesis is analyses of associations between occupational and non-occupational conditions on the one hand, and low back pain on the other. Methodological aspects of assessment of information about psychosocial working conditions, as well as of consequences of attrition in longitudinal studies, have also been examined. The study group consisted of a group of individuals, drawn from the general Swedish population and examined in 1969 (783 participants), who were followed up in 1993 (484 participants) and in 1997 (420 participants). When data concerning psychosocial and physical conditions and low back pain (LBP) from the base-line examination in 1969 were analyzed, work-related factors had a long-term effect mainly in interaction with leisure-time factors. A method for retrospective collection of information about psychosocial work conditions was developed and evaluated. Inter-rater reliability and the agreement between self-reported and inferred exposure to various demanding psychosocial conditions at work were analyzed. It was possible to retrospectively and reliably assess information about psychosocial work conditions for a long period of years, when an individual time ruler was used in a structured interview, in which earlier conditions were compared to the present. Information about the physical and psychosocial working conditions and low back pain during 1970-1993 was collected retrospectively, and analyzed with a nested case-control design. Forty-six percent of the participants became cases of LBP during the 24 years. Factors at work were seen to be risk indicators for LBP among both genders. Low influence over work conditions among women and poor social relations at work among men, in combination with other factors, seem to be of high relevance for the occurrence of low back pain. When depression was added to physical and psychosocial factors at work and during leisure time as potential predictors for incident (ILBP) and chronic low back pain (CLBP) among women and men, a number of physical, and several non-occupational, factors were associated with ILBP and CLBP among men, and a number of occupational psychosocial factors with ILBP and CLBP among women. Depression in 1993 was not a predictor for ILPB or CLBP in women, but was associated with CLBP among men. The consequences of attrition in a longitudinal study of musculoskeletal disorders and occupational risk factors were examined. Some differences, mainly consisting of a somewhat lower educational level and lower income level among the dropouts, were found in the analyses of difference between participants and dropouts, and these resulted in increased or decreased ratio estimates of 0. 1-0.2, with the exception of overtime work among men, where the decrease was 0.4-0.5. Further studies, where information about occupational and non-occupational conditions, physiological stress markers, and about organizational and societal phenomena are included in the same analysis are needed to deepen the understanding of some of the findings in the present thesis. Gender, as well as ethnicity, socioeconomic status and level of education are important analytic concepts in these studies.