Rheumatoid arthritis (RA) and osteoarthritis (OA) are two of the most common chronic musculoskeletal disorders worldwide. A survey conducted by the American Academy of Orthopaedic Surgeons reported that 7.3 million orthopaedic procedures were performed in US hospitals in 1995. Of these, OA and back pain were the most commonly treated problems. Musculoskeletal disorders as a whole account for $215 billion each year in health care costs and loss of economic productivity.
Less common than OA, RA affects 1% of the population world- wide. Although the long-term prognosis for RA likely will improve with new pharmacologic therapies, the disease remains a difficult problem. Average life expectancy of afected patients is reduced by 3 to 18 years, and 80% of patients are disabled after 20 years. On average, the annual cost of each case of RA in the United States is approximately $6,000. Although contemporary drugs are effective, our ability to diagnose RA with a high degree of sensitivity and specificity remains limited. The development of a diagnostic assay—the identification of a biomarker for RA—would enable the delivery of new effective therapies earlier in the disease stage, possibly before signs of joint destruction manifest. Despite the many advances in our understanding of the pathophysiology of both RA and OA, identifying the etiology of these disorders continues to be elusive.