Musculoskeletal disorders(MSDs) are among the most common and costly health problems among working populations, and constitute a major cause of disability. Occupational health practitioners must manage, prevent, and assess the work-relatedness of this large and diverse set of disorders, which affect different body parts and have different risk factors, treatments, and prognoses. The relationships of workplace exosures to MSDS are often difficult to assess, due to the multifactorial nature of these disorders, differing findings in the medical literature on the associations between personal and work-related factors, and the difficulties in applying the results contained in the existing literature to individual patients. However, the assessment of work-related factors is often central to decisions regarding the treatment, work ability, and compensation. The multifactorial nature of MSDs has been well described: personal, psychosocial, and workplace physical exposures are all associated with higher rates of MSDs in working populations. The assessment of etiology is very complex because MSDS affecting any body part comprise a diverse set of outcomes, ranging from symptoms of discomfort to long-term work disability. The discussions devoted to work-related risk factors of MSDS often fail to consider that different risk factors may influence different stages of disease severity. For instance, risk factors assessed among workers qualified for surgery or among those with long-term disability may be different from risk factors assessed among newly symptomatic workers. While integrated models of impairment and disability describe this spectrum of severity, they do not explicitly address the differences in work-related etiological or prognostic factors among workers with different outcomes. We present a diagram of a simple conceptual modes that may clarify this issue for researchers and practitioners. This conceptual model provides a framework for designing research studies and testing hypotheses using mathematical models.