Maintaining bone mineral density (BMD) after discontinuing denosumab (Prolia) is a major clinical challenge, as rapid bone loss commonly occurs when treatment is stopped, especially after more than three years of use. Standard sequential therapy with bisphosphonates such as zoledronic acid (Aclasta) often fails to fully prevent BMD decline, and most bone loss occurs within the first year, making effective suppression of the rebound effect essential. This study investigates whether a de-escalation strategy-using half-dose denosumab (30 mg every six months) combined with sequential zoledronic acid-can better preserve lumbar spine BMD after long-term denosumab therapy. Eligible participants include postmenopausal women and men ≥50 years old with osteoporosis or osteopenia-related fractures who have received ≥3 years of denosumab. The open-label trial applies stratified randomization based on denosumab duration (\<4 years vs. ≥4 years), assigning 22 participants to each group. Control group: standard therapy with one zoledronic acid infusion at the end of denosumab's effect and a second infusion one year later. Intervention group: half-dose denosumab plus zoledronic acid at study entry, a second half-dose denosumab injection at six months, and a second zoledronic acid infusion at twelve months. The study aims to determine whether this combined tapering-plus-bisphosphonate approach more effectively prevents lumbar spine BMD loss compared with conventional sequential therapy.