In order to maximize the early anabolic effect with teriparatide (TPTD), and to avoid the development of tachyphylaxis to the continued daily administration of TPTD beyond 6 months, cyclic therapy might be optimal. Since Denosumab (Prolia) is a potent antiresorptive agent with a rapid off-effect, it might be the optimal agent to help maximize bone gains with cyclic TPTD/antiresorptive therapy. Our primary hypothesis is that the increment in bone density of the spine by DXA will be greater in women randomized to receive the cyclic sequential regimen (three separate 6 month cycles of daily subcutaneous TPTD, each followed by one subcutaneous injection of Denosumab) compared with daily sequential therapy (18 months of daily subcutaneous TPTD followed by Denosumab therapy for 18 months).