This group will be treated with Denosumab Placebo, SC, every 4 weeks + Zoledronic acid, at a dose of 4 mg, in IV infusion not less than 15 minutes, every 4 weeks. This scheme will be administered until 745 subjects have experienced a related bone event (defined as pathological vertebral or non-vertebral fracture, radiotherapy to bones, bone surgery or compression of the spinal cord).