Long-term risk of incident vertebral fractures

Context: Vertebral fractures are the most common osteoporotic fracture. Women with low bone mineral density (BMD) and prevalent vertebral fractures have a greater risk of incident vertebral fractures over the short-term, but their absolute risk of vertebral fracture over the long-term is uncertain. Objective: To examine the absolute risk of incident vertebral fracture by BMD and prevalent vertebral fracture status over 15 years. Design, Setting, and Participants A total of 9704 white women were recruited at 4 US clinical centers and enrolled in the Study of Osteoporotic Fractures, a longitudinal cohort study. Of these, 2680 attended a clinic visit an average of 14.9 years after baseline; mean age of 68.8 years at entry and 83.8 years at follow-up. Mean Outcome Measure: Incident vertebral fractures identified from lateral spinal radiographs defined as a decrease of at least 20% and 4mmat any vertebral level. Prevalent vertebral fractures were identified on the baseline radiographs using vertebral morphometry. Bone mineral density was measured at the total hip and lumbar spine using dual-energy x-ray absorptiometry. Results: Of the 2680 women, 487 (18.2%) had an incident vertebral fracture including 163 of the 394 (41.4%) with a prevalent vertebral fracture at baseline and 324 of the 2286 (14.2%) without a prevalent vertebral fracture at baseline (odds ratio, 4.21; 95% confidence interval, 3.33-5.34). Low BMD was associated with an increased risk of incident vertebral fracture (odds ratio per 1 SD decrease in total hip BMD, 1.78 [95% confidence interval, 1.58-2.00]). The absolute risk of vertebral fracture ranged from 56% among women with total hip BMD T score of -2.5 or less and a prevalent vertebral fracture to 9% in women with normal BMD and no prevalent vertebral fracture. Conclusions: Low BMD and prevalent vertebral fractures are independently related to new vertebral fractures over 15 years of follow-up. Women with a prevalent vertebral fracture have a substantially increased absolute risk of an incident fracture, especially if they have osteoporosis diagnosed by BMD.