Baseline Measurement of Bone Mass Predicts Fracture in White Women

Abstract

STUDY OBJECTIVE: To determine if a single bone mass measurement of the radius is predictive of future fractures at any site. DESIGN: Observational study of a cohort of free-living subjects and a cohort of retirement-home residents with an average follow-up of 6.7 years and 5.5 years, respectively (range, 1 to 15 years for both cohorts). SETTING: General community and a retirement home. SUBJECTS: Volunteer sample of white women (386 free-living and 135 living in a retirement home) who were free of disease and were not receiving medication known to affect bone metabolism. In terms of physical condition subjects ranged from the totally independent to the wheelchair-bound. MEASUREMENTS AND MAIN RESULTS: A radial bone mass measurement was done at the initial visit. Subsequent non-spine fractures were reported by the subjects at follow-up visits, which were less than a year apart in most cases, and verified with medical records. Cox regression was used to model time to first fracture as a function of age and bone mass. These analyses showed that for every 0.1 g/cm decrement in bone mass, the relative risk of fracture was 2.2 (CI, 1.7 to 2.8) for the free-living and 1.5 (CI, 1.2 to 1.9) for the retirement-home residents. Baseline age did not predict the risk of fracture in either cohort, and controlling for baseline age did not reduce the relative-risk estimates of bone mass. Similar analyses also showed that bone mass was a statistically significant predictor for first hip fractures (n = 30) among the nursing-home residents (relative risk, 1.9; CI, 1.4 to 2.7) and first forearm fractures (n = 10) among the free living (relative risk, 3.6; CI, 1.9 to 6.8). For both cohorts, the 8-year probability of any nonspine fracture was about 80% for subjects with initial bone mass less than 0.6 g/cm and was less than 10% for subjects with initial bone mass greater than 0.8 g/cm. Similarly, those in the retirement home with bone mass below 0.6 g/cm had a 6-year probability of hip fracture of 43%, compared with a 17% risk for those with greater bone mass. CONCLUSION: A single bone mass measurement of the radius is predictive of future nonspine fractures at all sites, and at both the forearm and the hip. Baseline age was not a significant predictor of fracture within either cohort. Relative-risk estimates were not dissimilar across fracture sites.