Bisphosphonates for Prevention of Post-Denosumab Bone Loss

The primary goal of the study is to assess the extent to which bisphosphonate therapy will prevent decreases in bone mass that may occur after cessation of denosumab in premenopausal women with idiopathic osteoporosis (IOP) enrolled in AAAN0161 (FD05114) \"Denosumab for the prevention of post-teriparatide bone loss in premenopausal women with idiopathic osteoporosis\". In addition, the investigator will observe participants for a second year off bisphosphonate therapy to assess duration of response. The hypothesis is that bisphosphonate therapy with alendronate or zoledronic acid, initiated after recovery of bone remodeling activity, will prevent significant bone loss after discontinuing denosumab.