CHICAGO – Despite their bigger bones, postmenopausal women with osteoarthritis appear to be at a greater risk of falls and subsequent fractures, compared to their counterparts without the joint disease, according to an analysis of data from a longitudinal study of more than 50,000 women.

Among the 51,386 women in GLOW (Global Longitudinal Study of Osteoporosis in Women), 40% had osteoarthritis (OA). Women with OA experienced almost 30% more falls and had a 20% greater risk of fracture than those without OA, lead author Dr. Daniel Prieto-Alhambra said at the annual meeting of the American College of Rheumatology.

"We know that patients with osteoarthritis have bigger bones, and some have actually suggested that these bones are more resistant." However, recent papers have suggested that patients with osteoarthritis experience more falls than the general population, said Dr. Prieto-Alhambra, who is a postdoctoral research fellow at the Hospital del Mar and Municipal Institute of Medical Research in Barcelona.

Coauthor Dr. Nigel Arden noted that "we’ve seen this in other cohorts before. What was new here was that the falls would actually explain the increased risk of fracture, whereas in other cohorts, it hasn’t explained it."

Part of the disconnect between bigger bones and fractures in OA is that bone mineral density (BMD) measurements do not provide an accurate picture of BMD. "The bone density measurement is a two-dimensional measurement of a three-dimensional bone," said Dr. Arden in an interview. Individuals with OA have up to an 8% greater BMD when viewed two dimensionally. However, "when you look at volumetric density, as we’ve done in another cohort, their density is the same [as those without OA] – they just have bigger bones."

All of this can lead to a potential overestimate of BMD. "In osteoporosis, we use bone density as a predictor of fracture. People with osteoarthritis have an increased bone density and therefore should have a low risk of fracture but they have an increased risk of fracture. Therefore, we were concerned that people were being falsely reassured by their increased bone density measurements," Dr. Arden added.

In addition, "when they get osteoarthritis, they have increased rates of bone loss, which again is an independent risk factor for fracture," said Dr. Arden, who is a professor of rheumatology at the University of Oxford (England).

The study included 60,393 women aged 55 years or older. For 3 years, participants from several countries, including the United States, Canada, Australia, United Kingdom, Spain, and others, were surveyed annually. Women who were at least 55 years old and who visited a practice within the previous 2 years were eligible. The women were mailed a self-administered questionnaire at baseline; follow-up questionnaires were sent at 12-month intervals for 3 years. Participants were asked if a doctor or other health care provider had told them that they had osteoarthritis or degenerative joint disease. Information on incident falls and fractures and potential confounders were self-reported. For this analysis, women with missing baseline OA or fracture information, as well as those with celiac disease or rheumatoid arthritis, were excluded.