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 4 mm at 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.