Epidemiology of the rheumatic diseases.

Understanding, description, and classification of musculoskeletal pain syndromes have been further substantiated, but linking them to physical and psychological variables remains problematic. Core tools to measure disability in a population context forms a stable, well validated set of instruments, which increasingly has been translated, tested, and applied in sociocultural settings and in outcome research. Evidence for a declining incidence of rheumatoid arthritis seems established, and paleopathologic evidence indirectly provides some support for a possible causative environmental agent. Within an epidemiologic framework, immunogenetic studies continue to suggest an increasing number of subsets of rheumatoid arthritis, systemic lupus erythematosus, and ankylosing spondylitis variants. Studies in which the overuse hypothesis was tested as a cause in the etiology of osteoarthritis have provided conflicting results. Increasing evidence shows a secular trend in loss of bone mineral density, resulting in an increased fracture incidence. However, validated methods to safely prevent osteoporosis and fracture are also being established. Finally, although they are now well recognized and scientifically productive, large long-term epidemiologic studies should be critically examined.