Fracture prediction in rheumatoid arthritis: validation of FRAX with bone mineral density for incident major osteoporotic fractures.

OBJECTIVES: FRAX® uses clinical risk factors, with or without bone mineral density (BMD), to calculate 10-year fracture risk. Rheumatoid arthritis (RA) is a risk factor for osteoporotic fracture and a FRAX input variable. FRAX predates the current era of RA treatment. We examined how well FRAX predicts fracture in contemporary RA patients. METHODS: Administrative data from patients receiving BMD testing were linked to the Manitoba Population Health Research Data Repository. Observed cumulative 10-year Major Osteoporotic Fracture (MOF) probability was compared with FRAX-predicted 10-year MOF probability with BMD for assessing calibration. MOF risk stratification was assessed using Cox regression. RESULTS: RA patients (N = 2,099, 208 with incident MOF) and non-RA patients (N = 2,099, with 165 incident MOF) were identified. For RA patients, FRAX predicted 10-year risk was 13.2% and observed 10-year MOF risk was 13.2% (95% CI 11.6% to 15.1%). The slope of the calibration plot was 0.67 (95% CI 0.53-0. 81) in those with RA vs 0.98 (95% CI 0.61-1.34) in non-RA patients. Risk was overestimated in RA patients with high FRAX scores (>20%), but FRAX was well-calibrated in other groups. FRAX stratified risk in those with and without RA (hazard ratios 1.52, 95% 1.25-1.72 vs 2.00, 95% 1.73-2.31), with slightly better performance in the latter (p-interaction = 0.004). CONCLUSIONS: FRAX predicts fracture risk in contemporary RA patients but may slightly overestimate risk in those already at high predicted risk. Thus, the current FRAX tool continues to be appropriate for fracture risk assessment in RA patients.