VANCOUVER, BC—Osteoarthritis (OA) is expected to become more common with the inevitable demographic shift of an increasing global population over age 60. Surprising data from Canadian researchers suggest that, at least for women, age is only part of the problem.

Jacek A. Kopec, PhD, and colleagues report one of the few OA incidence studies ever conducted, which showed an increase in OA cases among women that exceeded the effects attributable to aging. They suspect that obesity accounts for the additional increase in OA incidence.¹

"[A]n increasing trend in age-standardized rates seems consistent with the effect of obesity. Obesity is a strong risk factor for hip and hand OA. The prevalence of obesity has been on the rise in [British Columbia] and elsewhere in both men and women. In addition, the effect of obesity on knee OA may be stronger in women and knee OA is more common in women," Dr. Kopec said.

The researchers used data on medical visits and hospital admissions for the 4 million patients covered by the Medical Services Plan of British Columbia for fiscal years 1991-1997 through 2003-2004 to describe changes in OA incidence rates.

They found that over the two periods compared in the study that

• Crude OA incidence rates, defined as at least one visit or hospitalization with a diagnostic code for OA increased from 10.5 to 12.2 per 1000 women
• Age-standardized rates did not change in men but increased from 14.7 to 16.7 per 1000 women

Similar incidence trends were observed when OA was defined using more stringent criteria (at least two visits or one hospitalization with a code for OA). The researchers point out only about half of the increase in crude OA incidence among women could be accounted for by population aging. They also note that, although other risk factors such as genetics, hormonal factors, congenital anomalies, vitamins and minerals, joint alignment, muscle strength, and neuromuscular control might play a role in causing OA, they are less established as risk factors than aging and obesity.

"Whatever the cause of the observed trends, OA is diagnosed more and more often by physicians, especially in women. The diagnosis of OA has serious consequences for the patient and the healthcare system. More studies are needed to assess plausible scenarios for future OA prevalence based on demographic trends and changes in the major risk factors," Dr. Kopec concluded.

Reference

1. Kopec JA, Rahman MM, Sayre EC, et al. Trends in physician-diagnosed osteoarthritis incidence in an administrative database in British Columbia, Canada, 1996-1997 through 2003-2004. Arthritis Rheum. 2008;59:929-934.