Osteoarthritis interferes with FRAX measurements of fracture risk
MedWire News: The probability of fracture could be underestimated in patients with unilateral hip osteoarthritis when measured using FRAX, according to research.
Osteoarthritis and osteoporosis are generally considered to be mutually exclusive but a previous study found that 25% of women with advanced osteoarthritis had occult osteoporosis. Another study of patients scheduled for hip replacement due to advanced unilateral osteoarthritis found that bone mineral density (BMD) was significantly higher for the osteoarthritic hip compared with the contralateral hip.
The latest study, published in the Journal of Clinical Densitometry, analyzed the impact of this BMD discordance on assessments of osteoporosis and fracture risk made using the FRAX calculator.
FRAX is a tool developed by the World Health Organization to calculate 10-year probability of experiencing total (spine, hip, forearm and humerus) and hip fracture based on measurements of BMD at the femoral neck, combined with data on risk factors such as age and weight.
Meryl LeBoff and colleagues, at Brigham and Women's Hospital in Boston, USA, enrolled 22 women and 13 men aged 41 years and over who were scheduled for a hip replacement because of unilateral hip osteoarthritis. BMD was calculated at the femoral neck, trochanter, and total hip at both hips using dual-energy X-ray absorptiometry.
The findings show significant differences in the femoral neck BMD T-scores, total fracture probabilities, and hip fracture probabilities, for the osteoarthritic and the contralateral hips.
The median values of the femoral neck BMD T-score were -0.6 for the osteoarthritic hip and -1.2 for the contralateral hip. This meant that 6-11% of the patients' fracture probabilities were underestimated by the FRAX calculator when data from the osteoarthritic hip were used.
"On the basis of the contralateral (non-OA [non-osteoarthritic]) hip, four additional subjects (11%) were identified who would receive recommendations for OP [osteoporosis] treatment on the basis of total fracture probability alone," says LeBoff.
"Thus, the use of [femoral neck] BMD T-score data from a hip with known or occult OA in the FRAX calculator may alter estimation of fracture probabilities and important OP treatment decisions."
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By Chloe McIvor