Musculoskeletal disorders (MSDs) affect a large proportion of the working population and their quality of life and contribute to increasing healthcare costs, lost work days and higher social insurance expenditures in most welfare states. One of the most worrying aspects of this "epidemic" is the high number of patients in working age that become permanently disabled and dependent of social insurance benefits because of MSD [1
]. A growing literature has identified prognostic factors or causes of chronicity among patients with short-term disability caused by back pain [8
] and other MSDs [11
] in order to improve treatment and secondary prevention.
Indicators relevant to the epidemiology of MSD are scarce [1
]. However, studies of sickness absence (SA) and permanent work-disability might outline the functional consequences of MSDs when cause-specific information is present [16
]. Within universal social insurance systems, like in Sweden and Norway, population-based studies are feasible, since most women have paid work [7
Gender differences are a key feature of the MSD epidemiology. A female excess in SA is found in countries with different social insurance systems and different levels of sickness absenteeism [7
], even though some studies differ [21
]. This corresponds to findings from epidemiological surveys of MSDs, in the general population [22
] or in occupational samples [24
] which have consistently found a higher prevalence among women [26
]. A gender and site specific analysis of data from the Dutch cross sectional DMC3 study [22
] showed a "slightly different" pattern in women and men with regard to the association of musculoskeletal pain with age, education, use of health care, disability and work-leave variables [27
]. Behavioural factors and hazardous workplaces lead to more fractures and other injuries among men. Several studies on predictors of chronicity in MSD have shown that women with MSDs might have an increased risk of chronicity [13
]. However, this has not been a subject for in-depth assessment.
Recently, investigators from different countries have discussed the need for gender specific studies of work related MSDs, without specifically mentioning the aspect of chronicity [28
]. A main issue here is how statistical analyses should be performed, with adjustment or stratification for gender. Data from two large epidemiological studies from the US [29
] and Canada [30
] were analyzed both with adjustment for gender and separately for women and men in order to identify the full range of associations. Thus, in this study we decided to assess the gender difference with both approaches.
MSDs dominate social insurance expenditure in the Nordic countries, with respect to both short-term and permanent work disability. In the period 1994-2003, 150,374 women and 129,612 men obtained disability pension (DP) in Norway. Forty-one percent of these women and 28% of the men were certified with a MSD [31
] whereas the incidence of DP caused by non-MSD was nearly similar. Thus, the higher prevalence of MSD among women has led to a "gender-gap" in the use of social insurance.
MSD might have different meanings and consequences for women and men and there are several explanations of the gender difference in MSD, with varying degrees of evidence [32
] which may also have relevance with respect to chronicity: The exposure-theory claims that women generally have poorer working conditions, whereas the vulnerability theory claims that women are more strongly affected by pathogenic factors. Biological factors might explain the increased vulnerability and a higher prevalence of MSDs like osteoporosis, rheumatoid arthritis and fibromyalgia in women [33
]. Mental/physical co-morbidity [35
] and the interplay between pain and depression contribute to the functional consequences of MSDs, since depression is more common in women [36
] and may affect pain differently [37
] There are also differences in health beliefs and help seeking [27
]. Gender differences in self rated health has been shown to vary in countries with different welfare state models, with the largest female/male difference in the Nordic countries [40
]. The double-burden theory implies that the combined exposure to stressors in the family and at work might lead to musculoskeletal problems and SA [41
] which might have different consequences depending on the extent of gender inequality [43
]. Finally, socioeconomic variables play an important role in musculoskeletal morbidity [17
] and different positions in society and workplace hierarchies might therefore also contribute to gender differences. Low socioeconomic status, education and income are both exposures and might lead to increased vulnerability. Adjusting for socioeconomic variables might reduce the gender differences significantly [17
]. When also including workplace factors, the gender difference might "disappear" completely [21
The aims of this national prospective cohort study were: To assess the chronicity/transition into permanent DP after sickness absence with a MSD and to investigate possible gender differences. If a gender difference is present, to investigate possible socioeconomic and medical (biological) explanations.