643 postmenopausal women with osteoporosis who had used oral bisphosphonate for a minimum of 2 years were randomized to either subcutaneous injections of denosumab 60mg - one at baseline and another at 6 months - or intravenous injection of zoledronic acid 5mg. The purpose of this study was to evaluate if denosumab offered noninferior or superior efficacy and safety to zoledronic acid for increasing bone mineral density in this patient population. The increase in the lumbar spine, total hip, femoral neck, and distal one-third radius bone mineral density were superior in the denosumab group compared to the zoledronic acid group. The incidence of atypical femoral fracture and osteoporosis-related fracture was not significantly different between groups.