Epidemiology of the rheumatic diseases.

Epidemiologic studies are important for both understanding and defining rheumatology practice. Controversy still exists over whether the incidence of rheumatoid arthritis is declining, and genetic studies indicate a diversity of HLA haplotypes in rheumatoid arthritis. Large longitudinal osteoarthritis studies have helped define diagnostic criteria and the role of obesity in disease progression. The negative association between osteoarthritis and osteoporosis at specific sites continues to be explored, and the value of long-term estrogen therapy in preventing bone loss has been examined. Both retrospective and prospective population studies have been used to describe the relationship between silicone gel breast implants and connective tissue disease. These and other studies have helped to define the important role of epidemiologic research in the understanding of rheumatic diseases.