Mechanisms of Anabolic Osteoporosis Therapy

Inclusion Criteria: All postmenopausal women who are prescribed romosozumab by their treating physicians, meet the FDA-defined indication for romosozumab, and who are not at increased risk for a bone marrow aspirate or bone biopsy will be offered enrollment. The FDA approved indication for romosozumab is: "the treatment of osteoporosis in postmenopausal women at high risk for fracture, defined as a history of osteoporotic fracture, or multiple risk factors for fracture; or patients who have failed or are intolerant to other available osteoporosis therapy." Volunteers must be: 1. Female aged \> 45 years 2. Postmenopausal by either of the following criteria: 1. \> 36 since last spontaneous menses 2. \> 36 months since hysterectomy, plus serum FSH \> 40 units / liter if \< 60 years Exclusion Criteria: * renal disease (stage 4 CKD) * elevated blood PTH (intact PTH \> 77 pg/ml). * serum 25-OH vitamin D \< 20 ng/ml * 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 would preclude the subject from providing adequate informed consent or completing the protocol procedures. * known congenital or acquired bone disease other than osteoporosis. * exposure to oral bisphosphonates within the past 3 months, denosumab in the last 12 months, intravenous bisphosphonates within the past 24 months. * exposure to estrogens, SERMs, or calcitonin, oral or parenteral glucocorticoids for more than 14 days in the past 2 months. * any prior exposure to romosozumab.