The aim of this study is to determine whether denosumab (an FDA-approved osteoporosis therapy), in combination with teriparatide (an FDA-approved osteoporosis therapy), will increase bone mineral density more than either one alone in postmenopausal osteoporotic women.

Inclusion Criteria:

Must satisfy A and B and C and D below:

• (A) Women aged > 55
• (B) Postmenopausal
• (C) Osteoporotic with high risk of fracture

Exclusion Criteria:

• Confirmed serum alkaline phosphatase above upper normal limit with no explanation
• Liver disease (AST or ALT > 2 x upper normal limit).
• Renal disease (serum creatinine > 2.0 mg/dl).
• Hypercalcemia (Ca >10.5 mg/dL)
• Elevated blood PTH (intact PTH > 65 pg/ml)
• Serum 25-OH vitamin D < 20 ng/ml
• HCT < 32%.
• History of malignancy (except basal cell carcinoma) or radiation therapy.
• Significant cardiopulmonary disease including unstable coronary artery disease, stage D ACC/AHA heart failure or any other condition that the investigator deems may preclude the subject from participating safely or completing the protocol procedures.
• Major psychiatric disease that in the opinion of the investigator would preclude the subject from providing adequate informed consent or completing the protocol procedures.
• Excessive alcohol use or substance abuse that in the opinion of the investigator would preclude the subject from providing adequate informed consent or completing the protocol procedures.
• Known congenital or acquired bone disease other than osteoporosis (including osteomalacia, hyperparathyroidism, Paget's disease)
• Current use or use in the past 6 months of oral bisphosphonate
• Current use or use within the past 3 months of estrogens, selective estrogen receptor modulators, or calcitonin.
• Use of oral or parenteral glucocorticoids for more than 14 days within the past 6 months.
• Any current or previous use of strontium or any parenteral bisphosphonate.
• Known sensitivity to mammalian cell-derived drug products.
• Known sensitivity to teriparatide or any of its excipients.