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Dual-energy X-ray absorptiometric bone mineral density (DXA BMD) is a strong predictor of fracture risk in untreated patients. However, previous patient-level studies suggest that BMD changes explain little of the fracture risk reduction observed with osteoporosis treatment. We investigated the relevance of DXA BMD changes as a predictor for fracture risk reduction using data from the FREEDOM trial, which randomly assigned placebo or denosumab 60 mg every 6 months to 7808 women aged 60 to 90 years with a spine or total hip BMD T-score < -2.5 and not < -4.0. We took a standard approach to estimate the percent of treatment effect explained using percent changes in BMD at a single visit (months 12, 24, or 36). We also applied a novel approach using estimated percent changes in BMD from baseline at the time of fracture occurrence (time-dependent models). Denosumab significantly increased total hip BMD by 3.2%, 4.4%, and 5.0% at 12, 24, and 36 months, respectively. Denosumab decreased the risk of new vertebral fractures by 68% (p < 0.0001) and nonvertebral fracture by 20% (p = 0.01) over 36 months. Regardless of the method used, the change in total hip BMD explained a considerable proportion of the effect of denosumab in reducing new or worsening vertebral fracture risk (35% [95% confidence interval (CI): 20%-61%] and 51% [95% CI: 39%-66%] accounted for by percent change at month 36 and change in time-dependent BMD, respectively) and explained a considerable amount of the reduction in nonvertebral fracture risk (87% [95% CI: 35% - >100%] and 72% [95% CI: 24% - >100%], respectively). Previous patient-level studies may have underestimated the strength of the relationship between BMD change and the effect of treatment on fracture risk or this relationship may be unique to denosumab. Copyright © 2012 American Society for Bone and Mineral Research. Fil: Austin, Matthew. Amgen Incorporated; Estados Unidos Fil: Yang, Yu Ching. Amgen Incorporated; Estados Unidos Fil: Vittinghoff, Eric. University of California; Estados Unidos Fil: Adami, Silvano. Universita di Verona; Italia Fil: Boonen, Steven. Katholikie Universiteit Leuven; Bélgica Fil: Bauer, Douglas C. University of California; Estados Unidos Fil: Bianchi, Gerolamo. Azienda Sanitaria Genovese; Italia Fil: Bolognese, Michael A.. Bethesda Health Research Center; Estados Unidos Fil: Christiansen, Claus Bohn. Center For Clinical And Basic Research As; Estados Unidos Fil: Eastell, Richard. University Of Sheffield; Reino Unido Fil: Grauer, Andreas. Amgen Incorporated; Estados Unidos Fil: Hawkins, Federico. Hospital Universitario 12 de Octubre; España Fil: Kendler, David L.. University of British Columbia; Canadá Fil: Oliveri, María Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Hospital de Clínicas General San Martín; Argentina Fil: McClung, Michael R.. Oregon Osteoporosis Center; Estados Unidos Fil: Reid, Ian R.. The University of Auckland; Nueva Zelanda Fil: Siris, Ethel S.. Columbia University; Estados Unidos Fil: Zanchetta, Jose. Universidad del Salvador; Argentina Fil: Zerbini, Cristiano A.F.. Centro Paulista de Investigação Clinica; Brasil Fil: Libanati, Cesar. Amgen Incorporated; Estados Unidos Fil: Cummings, Steven R.. University of California; Estados Unidos